Hydrogen Liquefaction Machine

Abstract

A method for liquefying hydrogen is provided. Hydrogen is liquefied through a process utilizing refrigeration from hydrogen at one, two, or three different pressures, as well as a nitrogen refrigeration cycle. As the hydrogen is cooled and liquefied, one or more catalytic stages are used to convert the ortho-hydrogen to para-hydrogen. The subcooled liquid hydrogen supplies the final stage of the ortho-hydrogen to para-hydrogen conversion to reduce or eliminate vaporization of hydrogen during the exothermic ortho-hydrogen to para-hydrogen conversion.

Description

[Background technology]

[0001] Hydrogen liquefiers have been around for a long time, with significant developments supporting the space program in the second half of the 20th century. However, the largest existing hydrogen liquefiers have a capacity of approximately 30 tonnes per day, and in the future, larger liquefiers will likely be needed to support a hydrogen economy. Several research papers, such as Essler et al.'s ("Report on technology overview and barriers to energy- and cost-efficient large-scale hydrogen liquefiers", Fuel Cells and Hydrogen Joint Undertaking, 2012), have been published to explore more cost-effective hydrogen liquefier designs to reduce power consumption and capital costs.

[0002] Typically, a hydrogen liquefaction process may include the steps of warm refrigeration, feed purification, low-temperature refrigeration, ortho-para conversion, pressure reduction, and storage. There are many methods in the prior art for configuring each of these steps. Warm refrigeration typically uses liquid nitrogen or a refrigeration cycle with a working fluid such as nitrogen or a mixed refrigerant. There are several variations of the low-temperature refrigeration cycle that are independent of the rest of the liquefier process.

[0003] In some configurations, the hydrogen feed is kept completely separate from the closed-loop cryogenic refrigeration system, which may be a hydrogen cycle (using normal hydrogen or parahydrogen) or may use some other component such as helium or neon or a mixture. The cooled hydrogen feed is subcooled before storage so that there is very little flash vapor, and boil-off from storage is typically recompressed (e.g., in an ejector) and recondensed by the cryogenic refrigeration cycle.

[0004] In other configurations, a portion of the normal hydrogen feed is used in the refrigeration cycle and recycled back into the feed to provide low temperature refrigeration in an open loop.

[0005] In yet another configuration, the parahydrogen is recycled independently of the feed and used in a low temperature refrigeration cycle, with make-up for the refrigeration cycle being provided from flash gas at the cold end of the process and a portion of the condensed recycle providing a portion of the liquid product.

[0006] Within the refrigeration cycle, different numbers of expanders may be arranged in series or parallel, or a combination of both, and refrigeration may or may not be present in series between the expanders. Despite the limited expansion ratio with hydrogen, turboexpanders are preferred for their reliability and low maintenance, but expansion engines may also be used. The ortho-para conversion of the feed (and recycle) may be carried out continuously in heat exchangers or in a series of adiabatic conversion reactors operating at different temperatures.

[0007] The necessity of ortho-para conversion in liquid hydrogen production is explained by Gursu et al. ("An Optimization Study of Liquid Hydrogen Boil-Off Losses," Int. J. Hydrogen Energy, 17:3 227-236, 1992). Hydrogen occurs as one of two different isomers: an ortho species with the same proton nuclear spin and a para species with the opposite nuclear spin. At higher temperatures, the equilibrium mixture is 75% ortho-hydrogen (also known as normal hydrogen), but as the temperature approaches 0 K, the equilibrium mixture approaches 100% para-hydrogen. The conversion of ortho-hydrogen to para-hydrogen is exothermic; therefore, liquid hydrogen with 75% ortho-hydrogen is gradually converted to para-hydrogen, and the heat generated boils off nearly 70% of the liquid hydrogen. To reduce this risk, liquid hydrogen is typically given a product specification of a minimum percentage of para-hydrogen to reduce boil-off.

[0008] Ohira ("A Summary of Liquid Hydrogen and Cryogenic Technologies in Japan's WE-NET Project", AIP Conference Proceedings, 710:27, 2004) describes a process suitable for large-scale hydrogen liquefaction, including a hydrogen closed-loop cryogenic refrigeration system. Newton (US3380809) describes a process for recirculating parahydrogen to provide cryogenic refrigeration.

[0009] A need exists for a large-scale hydrogen liquefier having a low-temperature refrigeration cycle that addresses and / or ameliorates at least some of the above-mentioned shortcomings of existing hydrogen liquefaction systems. Summary of the Invention

[0010] In at least some implementations, the present disclosure relates to improvements in low temperature refrigeration cycles, preferably for use particularly applicable to large scale hydrogen liquefaction machines.

[0011] In small-scale liquefiers, it is advantageous to have a relatively low pressure in the hydrogen recycle loop to keep the volumetric flow rate higher and improve machine (compressor and expander) efficiency, despite the higher pressure drop in the heat exchangers. As the scale increases, increasing the pressure in the hydrogen recycle loop and decreasing the volumetric flow rate is beneficial to process efficiency. At large scales, available compressor capacity is exceeded. For low-pressure hydrogen recycle loops as currently practiced, the higher volumetric flow rate into the compressor results in more compressors than in the embodiments shown in this disclosure.

[0012] The critical point of hydrogen is about 13 bar and 33 K, and for large liquefiers it is desirable to set the expander discharge pressure to approach this 13 bar pressure while remaining below the critical pressure. However, increasing the pressure increases the saturation temperature of the gas leaving the coldest expander, and therefore increases the minimum temperature that can be achieved by expander cooling.

[0013] Cooling below the discharge temperature of the cold expander must be by vaporizing some of the liquid hydrogen at lower pressures (typically near atmospheric pressure). As the main recycle return pressure (and therefore temperature) increases, this process becomes less efficient as more hydrogen must be boiled at low pressure and compressed into the recycle compressor suction. Also, the size and cost of the low-pressure hydrogen compressor increases as its flow rate increases.

[0014] Furthermore, at least some implementations of the present disclosure provide a means to improve the efficiency and reduce the cost of hydrogen liquefaction processes with higher pressure recycle return by introducing an intermediate pressure return between the low-pressure hydrogen product and the intermediate pressure of the final expander exhaust. The low-pressure compressor is then split into two sections and the suction volumetric flow rate is reduced. The intermediate pressure return stream may be flash gas from the pressure reduction of the liquid hydrogen, or vaporized liquid hydrogen, or a combination of both. Significant power savings can be achieved by utilizing hydrogen at three pressures compared to one or two.

[0015] Aspect 1: A method for liquefying hydrogen, the method comprising: cooling a hydrogen feed comprising ortho- and para-hydrogen by indirect heat exchange to form a cold hydrogen stream; expanding at least a portion of the cold hydrogen stream to produce a partially vaporized intermediate-pressure hydrogen stream; separating the partially vaporized intermediate-pressure hydrogen stream to produce an intermediate-pressure hydrogen vapor stream and an intermediate-pressure hydrogen liquid stream; expanding at least a portion of the intermediate-pressure hydrogen liquid stream to produce a partially vaporized low-pressure hydrogen stream; warming the partially vaporized low-pressure hydrogen stream, or a stream derived from the partially vaporized low-pressure hydrogen stream, by indirect heat exchange to produce a warmed low-pressure hydrogen stream; 1. A method for producing a hydrogen feed comprising: warming a hydrogen vapor stream by indirect heat exchange to produce a warmed intermediate-pressure hydrogen stream; compressing and combining the warmed low-pressure hydrogen stream, the warmed intermediate-pressure hydrogen stream, and the warmed medium-pressure hydrogen stream to produce a recycle stream; cooling the recycle stream by indirect heat exchange to produce a cooled recycle stream; expanding at least a portion of the cooled recycle stream to produce a first low-pressure medium-pressure hydrogen stream; and warming the first low-pressure medium-pressure hydrogen stream by indirect heat exchange to produce the warmed medium-pressure hydrogen stream, wherein the intermediate-pressure hydrogen vapor stream at least partially provides a cooling duty for cooling the hydrogen feed by indirect heat exchange. Embodiment 2: The method of embodiment 1, further comprising catalytically converting at least a portion of the orthohydrogen to parahydrogen in a cryogenic hydrogen stream. Aspect 3: The method of aspect 2, wherein the pressure of the cryogenic hydrogen stream is above the critical pressure and the temperature of the cryogenic hydrogen stream is below the critical temperature. Aspect 4: The method of any of Aspects 1-3, further comprising warming at least a portion of the intermediate pressure hydrogen liquid stream by indirect heat exchange to produce a second warmed intermediate pressure hydrogen stream; and compressing and combining the second warmed intermediate pressure hydrogen stream with the warmed low pressure hydrogen stream, the warmed intermediate pressure hydrogen stream, and the warmed medium pressure hydrogen stream to produce a recycle stream. Aspect 5: The method of any one of Aspects 1-4, further comprising splitting a portion of the intermediate-pressure hydrogen vapor stream and / or the warmed intermediate-pressure hydrogen stream to produce a purge gas stream, wherein the hydrogen feed and the purge gas stream comprise one or more light gases selected from the group consisting of helium and neon, and wherein the purge gas stream is enriched with respect to the light gas relative to the hydrogen feed. Embodiment 6: The method of any one of embodiments 1-5, further comprising catalytically converting at least a portion of the orthohydrogen in the cooled recycle stream to parahydrogen. Embodiment 7: The method of any one of embodiments 1-6, further comprising separating, while cooling, the hydrogen feed to form a cold hydrogen stream enriched in hydrogen relative to the hydrogen feed and a waste stream depleted in hydrogen relative to the hydrogen feed. Aspect 8: The method of any of Aspects 1-7, further comprising expanding at least a portion of the cooled hydrogen stream to produce a second medium-pressure hydrogen stream; and warming and combining the second medium-pressure hydrogen stream and the first cold medium-pressure hydrogen stream by indirect heat exchange to produce a warmed medium-pressure hydrogen stream. Embodiment 9: The method of any one of embodiments 1-8, further comprising expanding at least a portion of the cooled recycle stream to produce a cold recycle stream; and combining the cold recycle stream with a cold hydrogen stream. Embodiment 10: The method of any one of embodiments 1-9, wherein the recycle stream comprises greater than 90% by volume of parahydrogen. Aspect 11: The method of any of Aspects 1-10, further comprising: compressing at least a portion of the nitrogen stream by one or more compression stages to produce a compressed nitrogen stream; cooling the compressed nitrogen stream by indirect heat exchange to produce a cooled, compressed nitrogen stream; expanding at least a portion of the cooled, compressed nitrogen stream to produce a partially condensed nitrogen stream; separating the partially condensed nitrogen stream to produce a nitrogen vapor stream and a nitrogen liquid stream; and warming and combining at least a portion of the nitrogen vapor stream and the nitrogen liquid stream by indirect heat exchange to produce a nitrogen return stream, wherein the nitrogen stream comprises the nitrogen return stream, and wherein the nitrogen vapor stream and at least a portion of the nitrogen liquid stream provide, at least in part, a cooling duty for cooling the hydrogen feed by indirect heat exchange. Embodiment 12: The method of embodiment 11, further comprising splitting at least a portion of the nitrogen liquid stream to produce a liquid nitrogen product. Aspect 13: The method of Aspect 11 or Aspect 12, further comprising: cooling and splitting a portion of the compressed nitrogen stream by indirect heat exchange to produce a cold nitrogen expander feed; expanding the cold nitrogen expander feed to produce a first cold medium-pressure nitrogen stream; warming the first cold medium-pressure nitrogen stream by indirect heat exchange to produce the first medium-pressure nitrogen stream; and providing a medium-pressure nitrogen recycle stream to an intermediate stage of the one or more compression stages, wherein the medium-pressure nitrogen recycle stream comprises the first medium-pressure nitrogen stream. Aspect 14: The method of Aspect 13, further comprising: extracting a portion of the nitrogen stream from an intermediate stage of the one or more compression stages to produce a warm nitrogen expander feed; expanding the warm nitrogen expander feed to produce a second low-temperature medium-pressure nitrogen stream; and warming the second low-temperature medium-pressure nitrogen stream by indirect heat exchange to produce a second medium-pressure nitrogen recycle stream, wherein the medium-pressure nitrogen recycle stream comprises the second medium-pressure nitrogen recycle stream. Aspect 15: The method of Aspect 14, further comprising: expanding at least a portion of the cooled compressed nitrogen stream to produce a third low-temperature medium-pressure nitrogen stream; and warming the third low-temperature medium-pressure nitrogen stream by indirect heat exchange to produce a third medium-pressure nitrogen recycle stream, wherein the medium-pressure nitrogen recycle stream comprises the third medium-pressure nitrogen recycle stream. Aspect 16: The method of any one of Aspects 1-15, further comprising: separating the partially vaporized low-pressure hydrogen stream to produce a low-pressure hydrogen vapor stream and a low-pressure hydrogen liquid stream; splitting at least a portion of the low-pressure hydrogen liquid stream to form a low-pressure hydrogen return stream; and warming the low-pressure hydrogen return stream by indirect heat exchange and combining it with the low-pressure hydrogen vapor stream to produce a warmed low-pressure hydrogen stream. Embodiment 17: The method of any one of embodiments 1 to 16, further comprising catalytically converting at least a portion of the ortho hydrogen in the hydrogen feed to para hydrogen. Aspect 18: A method for converting ortho-hydrogen to para-hydrogen in a hydrogen feed, the method comprising: cooling a hydrogen feed comprising ortho-hydrogen and para-hydrogen by indirect heat exchange to form a low-temperature hydrogen stream, wherein the pressure of the low-temperature hydrogen stream is above the critical pressure and the temperature of the low-temperature hydrogen stream is below the critical temperature; and catalytically converting at least a portion of the ortho-hydrogen in the low-temperature hydrogen stream to para-hydrogen to produce a low-temperature para-hydrogen-enriched hydrogen stream, wherein the pressure of the low-temperature para-hydrogen-enriched hydrogen stream is above the critical pressure and the temperature of the low-temperature para-hydrogen-enriched hydrogen stream is below the critical temperature. [Brief explanation of the drawings]

[0016] The present disclosure will now be described in conjunction with the accompanying drawings, in which like numerals refer to like elements, and in which:

[0017] [Figure 1A] 1 is a flowsheet depicting the warm end of a hydrogen liquefaction process according to an exemplary embodiment of the present disclosure. [Figure 1B] 1 is a flowsheet depicting the cold end of a hydrogen liquefaction process according to an exemplary embodiment of the present disclosure. [Figure 1C] 1C is a flowsheet depicting a modification of the embodiment of FIG. 1B in which the low-pressure partially vaporized hydrogen is not separated before reheating, according to an additional exemplary embodiment of the present disclosure. [Figure 1D] 1C is a flowsheet depicting a modification of the embodiment of FIG. 1B in which the intermediate-pressure stream is split after the cold hydrogen stream is reduced in pressure, according to an additional exemplary embodiment of the present disclosure. [Figure 1E] 1C is a flowsheet depicting a variation of the embodiment of FIG. 1B in which the intermediate-pressure liquid is subcooled against the vaporizing low-pressure liquid prior to storage, according to an additional exemplary embodiment of the present disclosure. [Figure 1F] FIG. 1C is a flowsheet depicting a variation of the embodiment of FIG. 1E in which the cooled recycled hydrogen passes through a separate ortho-para conversion reactor before mixing with the converted feed hydrogen, according to an additional exemplary embodiment of the present disclosure. [Figure 2A] 1B is a flowsheet depicting a modification of the embodiment of FIG. 1A in which the intermediate pressure loop is omitted, according to an additional exemplary embodiment of the present disclosure. [Figure 2B] 1C is a flowsheet depicting a modification of the embodiment of FIG. 1B in which the intermediate pressure loop is omitted, according to an additional exemplary embodiment of the present disclosure. [Figure 2C] 1C is a flowsheet depicting a modification of the embodiment of FIG. 1B in which the intermediate and medium pressure loops are omitted, according to an additional exemplary embodiment of the present disclosure. [Figure 3] 1 is a table showing flow parameters from Example 1. [Figure 4] 1 is a table showing flow parameters from Example 2. [Figure 5] 10 is a table showing flow parameters from Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0018] The following detailed description provides only preferred exemplary embodiments and is not intended to limit the scope, applicability, or configuration of the present invention. Rather, the following detailed description of preferred exemplary embodiments will provide those skilled in the art with an effective description for implementing preferred exemplary embodiments of the present invention. Various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the present invention, as set forth in the appended claims.

[0019] As used herein, the articles "a" or "an" when applied to any feature in the embodiments of the invention described and claimed herein mean one or more. The use of "a" and "an" does not limit the meaning to a single feature unless such a limitation is specifically stated. The article "the" preceding a singular or plural noun or noun phrase refers to the particular named feature or to particular named features and may have singular or plural connotations depending on the context in which it is used.

[0020] The term "and / or" placed between a first entity and a second entity includes any of the following meanings: (1) the first entity only, (2) the second entity only, or (3) the first entity and the second entity. The term "and / or" placed between the last two entities in a list of three or more entities means at least one of the entities in the list, including any specific combination of the entities in the list. For example, "A, B, and / or C" has the same meaning as "A, and / or B, and / or C," and includes the following combinations of A, B, and C: (1) A only, (2) B only, (3) C only, (4) A and B but not C, (5) A and C but not B, (6) B and C but not A, and (7) A, B, and C.

[0021] The term "plurality" means "two or more."

[0022] The adjective "any" means any quantity of one, some, or all indiscriminately.

[0023] The phrase "at least a portion" means "part or all." "At least a portion of a stream" has the same composition, with the same concentration of each species, as the stream from which it originates.

[0024] As used herein, "first," "second," "third," etc. are used to distinguish between multiple steps and / or features and do not indicate total number or relative location in time and / or space unless expressly stated as such.

[0025] The terms "depleted" or "lean" mean that the stream has a lower mole percent concentration of the indicated component than the original stream from which it was formed. "Depleted" and "lean" do not mean that the stream is completely devoid of the indicated component.

[0026] The terms "rich" or "enriched" mean having a greater mole percent concentration of the indicated component than the stream from which it was formed.

[0027] The term "indirect heat exchange" refers to a process in which sensible and / or latent heat is transferred between two or more fluids without the fluids in question physically contacting one another. Heat may be transferred via any number of suitable means, including through the walls of the heat exchanger or through the use of an intermediate heat transfer fluid. The term "hot stream" refers to any stream that exits a heat exchanger at a lower temperature than it entered. Conversely, a "cold stream" is one that exits a heat exchanger at a higher temperature than it entered.

[0028] Figure 1A shows the warm end of the hydrogen liquefaction process. Gaseous hydrogen feed 100, at a pressure between 15 and 100 bar or between 20 and 30 bar and ambient temperature, is cooled to approximately 80 K in warm heat exchanger 1 to produce cooled hydrogen stream 101. All pressures listed are absolute. In the embodiment shown in Figure 1A, the cooling duty in warm heat exchanger 1 is provided by a warm nitrogen refrigeration system, although any suitable cooling fluid could be used, including introduced liquid nitrogen, liquid natural gas, or mixed refrigerants.

[0029] The low pressure make-up nitrogen 160 is mixed with the nitrogen return stream 179 from the warm heat exchanger 1 to form a nitrogen stream 161 at a pressure of between 0.7 and 2 bar, or between 0.7 and 1.5 bar, which is compressed in the low pressure nitrogen compressor 29 to a pressure of between 4 and 16 bar, or between 6 and 12 bar, and then cooled in the first aftercooler 30 to form an intermediate pressure nitrogen stream 163. The intermediate pressure nitrogen stream 163 is compressed in the intermediate pressure nitrogen compressor 31 to a pressure of between 20 and 45 bar, or between 25 and 35 bar, and then cooled in the second aftercooler 32 to form an intermediate nitrogen stream 166. At least a portion of the intermediate nitrogen stream 166 is then compressed in one or more nitrogen companders to a pressure of between 45 and 100 bar, or between 50 and 70 bar, to form a compressed nitrogen stream 171. 1A uses first and second nitrogen companders 33 and 35, followed by third and fourth aftercoolers 34 and 36, respectively. At least a portion of compressed nitrogen stream 171 is then cooled in warm heat exchanger 1 to form cooled compressed nitrogen stream 172. At least a portion of cooled compressed nitrogen stream 172 is reduced in pressure across valve 40 to approximately 1.1 bar to form partially condensed nitrogen stream 174, which is then separated in separator 41 to produce nitrogen vapor stream 178 and nitrogen liquid stream 175. At least a portion of nitrogen liquid stream 175 may be split to form liquid nitrogen product 176. The remaining portions of nitrogen liquid 177 and nitrogen vapor stream 178 are warmed in warm heat exchanger 1 to provide the refrigeration duty for cooling gaseous hydrogen feed 100. Nitrogen liquid 177 may be vaporized in warm heat exchanger 1 and combined with nitrogen vapor stream 178 before, within, or after warm heat exchanger 1 to form nitrogen return stream 179 .

[0030] A portion of the compressed nitrogen stream 171 may be split and cooled in warm heat exchanger 1 to produce cold nitrogen expander feed 183. Cold nitrogen expander feed 183 is reduced in pressure in cold nitrogen expander 38 to match the pressure of medium-pressure nitrogen stream 163 to form a first cold medium-pressure nitrogen stream 184.

[0031] A portion of stream 166 may be split and cooled in warm heat exchanger 1 to form warm nitrogen expander feed 186. Warm nitrogen expander feed 186 is reduced in pressure in warm nitrogen expander 37 to match the pressure of medium-pressure nitrogen stream 163 to form a second cold medium-pressure nitrogen stream 187.

[0032] Cold nitrogen expander 38 and warm nitrogen expander 37 can be used to act as turbines that can be used to generate power and / or to mechanically drive compressors in the process. In Figure 1A, cold nitrogen expander 38 drives nitrogen compander 35 and warm nitrogen expander 37 drives nitrogen compander 33.

[0033] A portion of the cooled compressed nitrogen stream 172 may be split off and reduced in pressure across valve 39 to match the pressure of medium pressure nitrogen stream 163 to form a third cooled medium pressure nitrogen stream 181.

[0034] The first cold medium-pressure nitrogen stream 184, the second cold medium-pressure nitrogen stream 187, and the third cold medium-pressure nitrogen stream 181 may be warmed in warm heat exchanger 1 and may be combined before, in, or after warm heat exchanger 1 to form medium-pressure nitrogen recycle stream 182. Medium-pressure nitrogen recycle stream 182 may then be combined with medium-pressure nitrogen stream 163 before medium-pressure nitrogen compressor 31.

[0035] Each nitrogen compressor, each containing one or more stages, may be a separate machine or may be combined into a multi-stage machine. For example, nitrogen companders 33 and 35 may be combined into a single machine if only one of warm nitrogen expander 37 and cold nitrogen expander 38 is used.

[0036] Optionally, residual levels of impurities such as methane, oxygen, and nitrogen may be removed from the cooled hydrogen stream 101 to prevent freezing at liquid hydrogen temperatures. Impurities are typically removed by temperature swing adsorption as shown in Figure 1A, with adsorber 2a and 2b operating such that one adsorber removes impurities while the other adsorber is regenerated.

[0037] The purified cooled hydrogen stream 102 may then be fed to an adiabatic ortho-para conversion reactor 3 where the ortho-hydrogen is exothermically converted to para-hydrogen. The hydrogen stream 103 is then re-cooled back to about 80 K in warm heat exchanger 1, after which the cooled hydrogen stream 104 enters the cold end of the hydrogen liquefaction machine.

[0038] FIG. 1B shows an embodiment of the cold end of a hydrogen liquefier, in which cooled hydrogen stream 104 is first cooled to approximately 25 K in low-temperature heat exchanger 4. During the process, cooled hydrogen stream 104 may undergo one or more stages of ortho-para conversion. According to the exemplary embodiment depicted in FIG. 1B, there are three initial stages of ortho-para conversion in three reactors: ortho-para conversion reactor 5, ortho-para conversion reactor 6, and ortho-para conversion reactor 7. Each successive ortho-para conversion reactor operates at a lower temperature, shifting the equilibrium toward para-hydrogen and increasing the amount of conversion possible. The product of each ortho-para conversion reaction is returned to low-temperature heat exchanger 4, which is closer to the warm end than the feed was withdrawn, due to the exothermic reaction reheating the hydrogen stream. Cold hydrogen stream 111 exits low-temperature heat exchanger 4 at approximately 25 K and enters low-temperature ortho-para conversion reactor 8. The low-temperature hydrogen stream 111 is a subcooled liquid having a temperature below the critical temperature and a pressure above the critical pressure. Operating at a higher pressure allows the low-temperature ortho-para conversion reactor 8 to operate at a higher temperature without the risk of vapor formation that could damage the catalyst. In the prior art, the final ortho-para conversion reactor is typically operated at a lower temperature, near the boiling point of hydrogen, which exhibits higher conversion to para-hydrogen. However, this approach typically produces a liquid hydrogen product with a higher para-hydrogen fraction than the product specification requires. In accordance with at least some embodiments of the present disclosure, the disclosed systems and processes allow the temperature, and therefore the para-hydrogen fraction, to be controlled closer to the product specification, minimizing unwanted exothermic reactions and thereby reducing overall process power demands compared to existing hydrogen liquefaction plants.

[0039] The para-hydrogen-enriched cryogenic hydrogen stream 112 exits the cryogenic ortho-para conversion reactor 8 and may be split into two or more portions. According to the exemplary embodiment depicted in FIG. 1B , the two portions are a first cryogenic hydrogen fraction 114 and a second cryogenic hydrogen fraction 139. The first cooled hydrogen fraction 114 is reduced in pressure to between 2 and 8 bar to form a partially vaporized intermediate-pressure hydrogen stream 115, which is then separated into an intermediate-pressure hydrogen stream 133 and an intermediate-pressure hydrogen stream 116 in an intermediate-pressure separator 11. The intermediate-pressure separator 11 may be any vessel or column capable of effecting phase separation. The intermediate-pressure hydrogen vapor stream 133 is heated in a cryogenic heat exchanger 4. At least a portion of the intermediate-pressure hydrogen liquid stream 132 may be reheated in the cryogenic heat exchanger 4, either in a separate heat exchanger path or after being mixed with the intermediate-pressure hydrogen vapor stream 133, to produce a partially reheated intermediate-pressure hydrogen stream 134.

[0040] At least a portion of intermediate-pressure hydrogen liquid stream 116 may be reduced in pressure to between 0.7 and 2 bar, or between 0.7 and 1.5 bar, to form a partially vaporized low-pressure hydrogen stream 124, which may then be separated in low-pressure separator 16 into low-pressure hydrogen vapor stream 126 and low-pressure hydrogen liquid stream 119. Low-pressure separator 16 may be any vessel or column capable of effecting phase separation. Low-pressure hydrogen liquid stream 119 enters storage tank 14 via flow control valve 13, from which liquid hydrogen product 121 may be withdrawn. Boil-off vapor 122 from storage tank 14 may be combined with low-pressure hydrogen vapor stream 126. A portion of low-pressure hydrogen liquid stream 119 may be split to form low-pressure liquid hydrogen return stream 125, which is heated in cryogenic heat exchanger 4 with low-pressure hydrogen vapor stream 126. The low pressure hydrogen return stream 125 may be used to subcool the low temperature hydrogen stream 111, if desired, in a separate heat exchanger path or after being mixed with the low pressure hydrogen vapor stream 127 in the low temperature heat exchanger 4 to produce a partially reheated low pressure hydrogen stream 128.

[0041] Partially reheated low-pressure hydrogen stream 128 and partially reheated intermediate-pressure hydrogen stream 134 enter the warm end of the hydrogen liquefier depicted in FIG. 1A and are heated in warm heat exchanger 1 to form warmed low-pressure hydrogen stream 129 and warmed intermediate-pressure hydrogen stream 135, respectively. Warmed low-pressure hydrogen stream 129 may be compressed in low-pressure compressor 17 to form stream 130, which may then be cooled in inter-stage cooler 18 to form stream 131. Warmed intermediate-pressure hydrogen stream 135 may then be combined with stream 131 and compressed in intermediate-pressure compressor 19 to form stream 137, which may then be cooled in inter-stage cooler 20 to form stream 138. Stream 138 may be compressed in intermediate-pressure compressor 21 to form stream 144, which may then be cooled in aftercooler 22 to form recycle stream 145 at a pressure between 25 and 100 bar or between 30 and 65 bar. Low pressure compressor 17, intermediate pressure compressor 19, and intermediate pressure compressor 21 may be separate machines each having one or more stages, or may be combined into a single multi-stage machine. Recycle stream 145 is then cooled in warm heat exchanger 1 to form cooled recycle stream 146, which is then purified in guard adsorber bed 23 to form stream 147, which is then returned to the cold end of the hydrogen liquefier.

[0042] If the feed contains small amounts of light gases, such as helium and neon, that are difficult to remove via adsorption, then, at least in some example implementations, the process may require a purge stream (not shown). The purge stream may be provided by splitting off a portion of the intermediate-pressure hydrogen vapor stream 133 and / or the warmed intermediate-pressure hydrogen stream 135. The purge stream may be supplied from the overhead of the intermediate-pressure separator 11 such that it is enriched in light gases relative to the gaseous hydrogen feed 100.

[0043] In the embodiment depicted in Figure 1B, at least a portion of stream 147 may be split to form stream 148 and expanded over one or more expansion stages. Figure 1B shows an embodiment using three expansion stages in warm expander 24, intermediate temperature expander 25, and cold expander 26. Stream 148 may be cooled in cold heat exchanger 4 after warm expander 24 and intermediate temperature expander 25, and may be heated in cold heat exchanger 4 after cold expander 26. One or more stages of the expander may be used to act as a turbine, which may be used to generate power and / or to mechanically drive a compressor in the process. After one or more stage expansions, the first cold medium-pressure hydrogen stream 153, at a pressure between 4 and 16 bar or between 6 and 12 bar, is warmed in cold heat exchanger 4 to form partially reheated medium-pressure hydrogen stream 141, which, as shown in the embodiment depicted in Figure 1A, is returned to the warm end of the hydrogen liquefier, where it is warmed in warm heat exchanger 1 to form warmed medium-pressure hydrogen stream 142. The warmed medium-pressure hydrogen stream 142 is then compressed in medium-pressure compressor 21.

[0044] 1B, at least a portion of stream 147 is split and cooled in cryogenic heat exchanger 4 to form stream 154. Stream 154 may then be reduced in pressure across valve 27 to form cryogenic recycle stream 155, which may be combined with cryogenic hydrogen stream 111. In at least some embodiments, cryogenic recycle stream 155 may be combined with para-hydrogen-enriched cryogenic hydrogen stream 112 at the warm end of the hydrogen liquefier, e.g., in low-pressure compressor 17, intermediate-pressure compressor 19, and intermediate-pressure compressor 21, where there is no concern about conversion of para-hydrogen to ortho-hydrogen.

[0045] Warm heat exchanger 1 and cold heat exchanger 4 may be combined into a single heat exchanger or may be further subdivided into smaller heat exchangers as dictated by lower capital costs in the former case or ease of operation in the latter.

[0046] The hydrogen refrigeration circuit operates as an open loop, operating with a hydrogen working fluid that is greater than 85% parahydrogen, or greater than 90% parahydrogen, or greater than 95% parahydrogen. Operating the hydrogen refrigeration circuit with nearly pure parahydrogen has the advantage that nearly pure parahydrogen boil-off vapor 122 from the storage tank 14 and / or tanker being filled can be returned and recompressed into the low-pressure compressor 17. The present disclosure may also be applied to other low-temperature hydrogen refrigeration systems, such as those with a closed refrigerant or open-loop systems in which regular hydrogen is recirculated and expanded.

[0047] The second cold hydrogen fraction 139 is reduced in pressure across valve 10 to between 4 and 16 bar, or between 6 and 12 bar, to form a second cold medium-pressure hydrogen stream 140. The second cold medium-pressure hydrogen stream 140 is warmed first in cold heat exchanger 4 and then in warm heat exchanger 1, either in a separate path from the first cold medium-pressure hydrogen stream 153, or after being combined with the first cold medium-pressure hydrogen stream 153 before, after or within cold heat exchanger 4 and / or warm heat exchanger 1. If kept separate from the first cold medium-pressure hydrogen stream 153, the warmed second medium-pressure hydrogen stream 140 may also be compressed in medium-pressure compressor 21.

[0048] 1C shows an alternative embodiment to FIG. 1B in which at least a portion of medium-pressure hydrogen liquid stream 116 is split to form stream 117. At least a portion of stream 117 is reduced to a pressure between 0.7 bar and 2 bar or between 0.7 bar and 1.5 bar to form a partially vaporized low-pressure hydrogen stream 124, which is then warmed in cryogenic heat exchanger 4. At least a portion of stream 117 is split to form low-pressure hydrogen liquid stream 119, which is then reduced in pressure and sent to storage tank 14 from which liquid hydrogen product 121 can be withdrawn. Stream 117 may also be subcooled in cryogenic heat exchanger 4 (not shown) before being reduced in pressure. This configuration may have more pressure available to transfer the liquid to storage and avoids the installation of a low-pressure separator, but the amount of boil-off vapor 122 from storage may be increased by increased flash vapor from the feed.

[0049] Figure 1D shows an alternative embodiment to Figure 1B in which the para-hydrogen-enriched cold hydrogen stream 112 is first depressurized to about 10 bar before being split into two or more fractions. In the embodiment depicted in Figure 1D, the para-hydrogen-enriched cold hydrogen stream 112 is depressurized and then split into a first cold medium-pressure hydrogen stream 191 and a second cold medium-pressure hydrogen stream 140. This configuration provides an alternative control valve configuration to the embodiment depicted in Figure 1B.

[0050] FIG. 1E illustrates an alternative embodiment to FIG. 1B in which intermediate-pressure liquid hydrogen stream 117 is split into first intermediate-pressure liquid fraction 223 and second intermediate-pressure liquid fraction 218. First intermediate-pressure liquid fraction 223 is reduced in pressure across valve 15 to between 0.7 bar and 2 bar or between 0.7 bar and 1.5 bar, as in the embodiment depicted in FIG. 1B. Second intermediate-pressure liquid fraction 218 is cooled in subcooler 212 within low-pressure separator 16 against boiling low-pressure liquid hydrogen to form subcooled liquid hydrogen product 119a, which is reduced in pressure across valve 13 and delivered to storage tank 14. Subcooled liquid hydrogen product 119a is at a higher pressure than liquid hydrogen storage tank 14 in the embodiment depicted in FIG. 1B, which may facilitate transfer to storage tanks located at higher elevations and / or longer distances for the remainder of the process.

[0051] Figure 1F shows an alternative embodiment to Figure 1E in which the cold recycle stream 155 is reacted in a second cold ortho-para conversion reactor 328 to form a cold recycle stream 356 enriched in para-hydrogen. The cold recycle stream enriched in para-hydrogen is reduced in pressure across valve 329 and combined with the partially vaporized intermediate-pressure hydrogen stream 115. This configuration has the advantage that the pressures of the gaseous hydrogen feed 100 and the recycle stream 145 can be more easily varied independently.

[0052] The intermediate-pressure hydrogen loop present in the embodiments shown in Figures 1A-1F may be omitted to simplify the process. The warm end of the hydrogen liquefaction process without the intermediate-pressure hydrogen loop is shown in an additional embodiment depicted in Figure 2A. The nitrogen refrigeration loop, hydrogen cooling, and purification steps may be similar to the embodiment depicted in Figure 1A. Partially reheated low-pressure hydrogen stream 128 may be heated in warm heat exchanger 1 to produce warmed low-pressure hydrogen stream 129, which may then be compressed in low-pressure compressor 17 to form stream 130, which may then be cooled in inter-stage cooler 18 to form stream 131. Stream 131 may then be compressed in intermediate-pressure compressor 19 to form stream 137, which may then be cooled in inter-stage cooler 20 to form stream 138. Partially reheated intermediate-pressure hydrogen stream 141 may be heated in warm heat exchanger 1 to produce warmed intermediate-pressure hydrogen stream 142, which may then be combined with stream 138 to produce stream 143. Stream 143 is compressed in intermediate-pressure compressor 21 to form stream 144, which may then be cooled in aftercooler 22 to form recycle stream 145 at a pressure between 25 and 100 bar or between 30 and 65 bar. Low-pressure compressor 17, intermediate-pressure compressor 19, and intermediate-pressure compressor 21 may be separate machines or combined into a single multi-stage machine. The exemplary embodiment shown in FIG. 2A depicts intermediate-pressure compressors 17 and 19 as separate machines. Recycle stream 145 is then cooled in warm heat exchanger 1 to form cooled recycle stream 146, which is then purified in guard adsorber bed 23 to form stream 147, which is then returned to the cold end of the hydrogen liquefier.

[0053] The embodiment depicted in Figure 2B shows the cold end of a hydrogen liquefaction process having a low-pressure loop and an intermediate-pressure loop. This process differs from the embodiment depicted in Figure 1B in that the first cryogenic hydrogen fraction 114 is reduced in pressure to between 0.7 bar and 2 bar, or between 0.7 bar and 1.5 bar, to form a partially vaporized low-pressure hydrogen stream 124. The partially vaporized low-pressure hydrogen stream 124 may be separated in low-pressure separator 16 into a low-pressure hydrogen vapor stream 126 and a low-pressure hydrogen liquid stream 119, as in the embodiment depicted in Figure 2B, or may be split into a liquid product portion and a portion that is sent directly back to cryogenic heat exchanger 4, as in the embodiment depicted in Figure 1C.

[0054] The embodiment depicted in Figure 2C shows the cold end of the hydrogen liquefaction process with only a low-pressure loop. The para-hydrogen-enriched cryogenic hydrogen stream 112 is not split; rather, the entire stream is reduced in pressure to between 0.7 and 2 bar or between 0.7 and 1.5 bar to form a partially vaporized low-pressure hydrogen stream 124. The partially vaporized low-pressure hydrogen stream 124 may be separated in low-pressure separator 16 into a low-pressure hydrogen vapor stream 126 and a low-pressure hydrogen liquid stream 119, as in the embodiment shown in Figure 2C, or may be split into a liquid product portion and a portion that is sent directly back to cryogenic heat exchanger 4, as in the embodiment shown in Figure 1C.

[0055] Other embodiments of the present disclosure (not shown) may include a hydrogen liquefier in which any of the following may be boiled in a thermosiphon arrangement with an associated separator rather than in a once-through configuration, as shown in the embodiment shown in FIG. 1B: second low-temperature medium-pressure hydrogen stream 140, intermediate-pressure hydrogen liquid stream 132, and / or low-pressure liquid hydrogen return stream 125.

[0056] Example 1 A computer simulation of an embodiment of the process depicted in Figures 1A and 1B was performed using Aspen Plus™, a commercial process simulation software package available from Aspen Technology, Inc. The feed stream was pure hydrogen at 305 K and 31 bar, with ambient equilibrium concentrations of 75% orthohydrogen and 25% parahydrogen. Key flow parameters such as composition, pressure, temperature, and flow rate, along with total power consumption, are shown in the table in Figure 3.

[0057] Subcooling the cold hydrogen stream 111 at high pressure allows the para-hydrogen enriched cold hydrogen stream 112 to remain in the liquid phase after the exothermic reaction of ortho-hydrogen to para-hydrogen is complete. Subsequent flashing in stages allows more vapor to be recycled at higher pressures, lowering power demands and reducing the physical size of the low-pressure compressor 17.

[0058] Example 2 The benefits of the intermediate-pressure loop can best be illustrated by comparing it to an embodiment of the present disclosure lacking the loop. Computer simulations of the process of Figures 2A and 2B were performed using Aspen Plus™. The feed stream was pure hydrogen at 305 K and 31 bar, with ambient equilibrium concentrations of 75% orthohydrogen and 25% parahydrogen. Key flow parameters such as composition, pressure, temperature, and flow rate, along with total power consumption, are shown in the table in Figure 4. A comparison with Example 1 shows that removal of the intermediate-pressure loop results in a 2.5% increase in power consumption.

[0059] Example 3 The simplest cycle, with only the low-pressure loop, was also modeled. Computer simulations of the embodiment depicted in Figures 2A and 2C were performed using Aspen Plus™. The feed stream was pure hydrogen at 305 K and 31 bar, with ambient equilibrium concentrations of 75% orthohydrogen and 25% parahydrogen. Key flow parameters, such as composition, pressure, temperature, and flow rate, along with total power consumption, are shown in the table in Figure 5. A comparison with Example 1 shows that removal of the intermediate and medium-pressure loops results in a 4.7% increase in power consumption.

[0060] While the principles of the present disclosure have been described above in connection with the preferred embodiment, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention. The present disclosure also encompasses the following: [Aspect 1] 1. A method for liquefying hydrogen, comprising: cooling a hydrogen feed comprising ortho- and para-hydrogen by indirect heat exchange to form a low-temperature hydrogen stream; expanding at least a portion of the cryogenic hydrogen stream to produce a partially vaporized intermediate pressure hydrogen stream; separating the partially vaporized intermediate-pressure hydrogen stream to produce an intermediate-pressure hydrogen vapor stream and an intermediate-pressure hydrogen liquid stream; expanding at least a portion of the intermediate-pressure hydrogen liquid stream to produce a partially vaporized low-pressure hydrogen stream; warming the partially vaporized low-pressure hydrogen stream, or a stream derived from the partially vaporized low-pressure hydrogen stream, by indirect heat exchange to produce a warmed low-pressure hydrogen stream; warming the intermediate pressure hydrogen vapor stream by indirect heat exchange to produce a warmed intermediate pressure hydrogen stream; compressing and combining the warmed low-pressure hydrogen stream, the warmed intermediate-pressure hydrogen stream, and the warmed medium-pressure hydrogen stream to generate a recycle stream; cooling the recycle stream by indirect heat exchange to produce a cooled recycle stream; expanding at least a portion of the cooled recycle stream to produce a first low temperature medium pressure hydrogen stream; warming the first cold medium-pressure hydrogen stream by indirect heat exchange to produce the warmed medium-pressure hydrogen stream; wherein said intermediate-pressure hydrogen vapor stream at least partially provides a cooling duty for cooling said hydrogen feed by indirect heat exchange. [Aspect 2] further comprising catalytically converting at least a portion of the ortho-hydrogen to para-hydrogen in the low temperature hydrogen stream; 2. The method of claim 1, wherein the pressure of the cryogenic hydrogen stream is above the critical pressure and the temperature of the cryogenic hydrogen stream is below the critical temperature. [Aspect 3] warming at least a portion of the intermediate pressure hydrogen liquid stream by indirect heat exchange to produce a second warmed intermediate pressure hydrogen stream; 2. The method of claim 1, further comprising compressing the second warmed intermediate-pressure hydrogen stream and combining it with the warmed low-pressure hydrogen stream, the warmed intermediate-pressure hydrogen stream, and the warmed medium-pressure hydrogen stream to generate the recycle stream. [Aspect 4] further comprising splitting a portion of the intermediate-pressure hydrogen vapor stream and / or the warmed intermediate-pressure hydrogen stream to generate a purge gas stream; the hydrogen feed and the purge gas stream comprise one or more light gases selected from the group consisting of helium and neon; 2. The method of claim 1, wherein the purge gas stream is enriched in light gases relative to the hydrogen feed. [Aspect 5] catalytically converting at least a portion of the ortho-hydrogen in the hydrogen feed to para-hydrogen; 2. The method of claim 1, further comprising catalytically converting at least a portion of the orthohydrogen in the cooled recycle stream to parahydrogen. [Aspect 6] 2. The method of claim 1, further comprising separating the hydrogen feed while cooling to form a cold hydrogen stream enriched in hydrogen relative to the hydrogen feed and a waste stream depleted in hydrogen relative to the hydrogen feed. [Aspect 7] expanding at least a portion of the low temperature hydrogen stream to produce a second medium pressure hydrogen stream; 2. The method of claim 1, further comprising warming the second medium-pressure hydrogen stream and the first cold medium-pressure hydrogen stream by indirect heat exchange and combining them to produce the warmed medium-pressure hydrogen stream. [Aspect 8] expanding at least a portion of the cooled recycle stream to produce a cold recycle stream; 2. The method of claim 1, further comprising combining the cold recycle stream with the cold hydrogen stream. [Aspect 9] 2. The method of claim 1, wherein the recycle stream comprises greater than 90% by volume of parahydrogen. [Aspect 10] separating the partially vaporized low-pressure hydrogen stream to produce a low-pressure hydrogen vapor stream and a low-pressure hydrogen liquid stream; splitting at least a portion of the low pressure hydrogen liquid stream to form a low pressure hydrogen return stream; 2. The method of claim 1, further comprising warming the low-pressure hydrogen return stream by indirect heat exchange and combining the low-pressure hydrogen vapor stream to produce the warmed low-pressure hydrogen stream. [Aspect 11] compressing at least a portion of the nitrogen stream through one or more compression stages to produce a compressed nitrogen stream; cooling the compressed nitrogen stream by indirect heat exchange to produce a cooled compressed nitrogen stream; expanding at least a portion of the cooled compressed nitrogen stream to produce a partially condensed nitrogen stream; separating the partially condensed nitrogen stream to produce a nitrogen vapor stream and a nitrogen liquid stream; warming and combining the nitrogen vapor stream and at least a portion of the nitrogen liquid stream by indirect heat exchange to produce a nitrogen return stream; wherein the nitrogen stream comprises the nitrogen return stream; 2. The method of claim 1, wherein the cooling duty for cooling the hydrogen feed by indirect heat exchange is at least partially provided by the nitrogen vapor stream and at least a portion of the nitrogen liquid stream. [Aspect 12] splitting at least a portion of the nitrogen liquid stream to produce a liquid nitrogen product; cooling a portion of the compressed nitrogen stream by indirect heat exchange and splitting to produce a cold nitrogen expander feed; expanding the cold nitrogen expander feed to produce a first cold medium pressure nitrogen stream; warming the first cold medium-pressure nitrogen stream by indirect heat exchange to produce a first medium-pressure nitrogen stream; providing a medium pressure nitrogen recycle stream to an intermediate stage of said one or more compression stages; 12. The method of claim 11, further comprising: wherein the medium-pressure nitrogen recycle stream comprises the first medium-pressure nitrogen stream. [Aspect 13] extracting a portion of said nitrogen stream from an intermediate stage of said one or more compression stages to produce a warm nitrogen expander feed; expanding the warm nitrogen expander feed to produce a second low temperature medium pressure nitrogen stream; warming the second cold medium-pressure nitrogen stream by indirect heat exchange to produce a second medium-pressure nitrogen recycle stream; 13. The method of claim 12, further comprising: wherein the medium-pressure nitrogen recycle stream comprises the second medium-pressure nitrogen recycle stream. [Aspect 14] expanding at least a portion of the cooled compressed nitrogen stream to produce a third low temperature medium pressure nitrogen stream; warming the third cold medium-pressure nitrogen stream by indirect heat exchange to produce a third medium-pressure nitrogen recycle stream; 14. The method of claim 13, further comprising: [Aspect 15] 1. A method for converting ortho-hydrogen to para-hydrogen in a hydrogen feed, the process comprising: cooling said hydrogen feed comprising ortho- and para-hydrogen by indirect heat exchange to form a low-temperature hydrogen stream; forming a cryogenic hydrogen stream having a pressure above a critical pressure and a temperature below a critical temperature; catalytically converting at least a portion of the ortho-hydrogen in the cryogenic hydrogen stream to para-hydrogen to produce a cryogenic hydrogen stream enriched in para-hydrogen; generating a cryogenic para-hydrogen enriched hydrogen stream having a pressure above the critical pressure and a temperature below the critical temperature; A method comprising:

Claims

1. 1. A method for liquefying hydrogen, comprising: cooling a hydrogen feed comprising ortho- and para-hydrogen by indirect heat exchange to form a low-temperature hydrogen stream; expanding at least a portion of the cryogenic hydrogen stream to produce a partially vaporized intermediate pressure hydrogen stream; separating the partially vaporized intermediate-pressure hydrogen stream to produce an intermediate-pressure hydrogen vapor stream and an intermediate-pressure hydrogen liquid stream; expanding at least a portion of the intermediate-pressure hydrogen liquid stream to produce a partially vaporized low-pressure hydrogen stream; warming the partially vaporized low-pressure hydrogen stream, or a stream derived from the partially vaporized low-pressure hydrogen stream, by indirect heat exchange to produce a warmed low-pressure hydrogen stream; warming the intermediate pressure hydrogen vapor stream by indirect heat exchange to produce a warmed intermediate pressure hydrogen stream; compressing and combining the warmed low-pressure hydrogen stream, the warmed intermediate-pressure hydrogen stream, and the warmed medium-pressure hydrogen stream to generate a recycle stream; cooling the recycle stream by indirect heat exchange to produce a cooled recycle stream; expanding at least a portion of the cooled recycle stream to produce a first low temperature medium pressure hydrogen stream; warming the first cold medium-pressure hydrogen stream by indirect heat exchange to produce the warmed medium-pressure hydrogen stream; wherein said intermediate-pressure hydrogen vapor stream at least partially provides a cooling duty for cooling said hydrogen feed by indirect heat exchange.

2. further comprising catalytically converting at least a portion of the ortho-hydrogen to para-hydrogen in the low temperature hydrogen stream; 10. The method of claim 1, wherein the pressure of the cryogenic hydrogen stream is above the critical pressure and the temperature of the cryogenic hydrogen stream is below the critical temperature.

3. further comprising splitting a portion of the intermediate-pressure hydrogen vapor stream and / or the warmed intermediate-pressure hydrogen stream to generate a purge gas stream; the hydrogen feed and the purge gas stream comprise one or more light gases selected from the group consisting of helium and neon; 10. The method of claim 1, wherein the purge gas stream is enriched in light gases relative to the hydrogen feed.

4. catalytically converting at least a portion of the ortho-hydrogen in the hydrogen feed to para-hydrogen; 10. The method of claim 1, further comprising catalytically converting at least a portion of the orthohydrogen in the cooled recycle stream to parahydrogen.

5. 10. The method of claim 1, further comprising separating the hydrogen feed while cooling to form a cold hydrogen stream enriched in hydrogen relative to the hydrogen feed and a waste stream depleted in hydrogen relative to the hydrogen feed.

6. expanding at least a portion of the low temperature hydrogen stream to produce a second medium pressure hydrogen stream; 10. The method of claim 1, further comprising warming and combining the second medium-pressure hydrogen stream and the first cold medium-pressure hydrogen stream by indirect heat exchange to produce the warmed medium-pressure hydrogen stream.

7. expanding at least a portion of the cooled recycle stream to produce a cold recycle stream; The method of claim 1 further comprising combining the cold recycle stream with the cold hydrogen stream.

8. 10. The method of claim 1, wherein the recycle stream comprises greater than 90% by volume of parahydrogen.

9. separating the partially vaporized low-pressure hydrogen stream to produce a low-pressure hydrogen vapor stream and a low-pressure hydrogen liquid stream; splitting at least a portion of the low pressure hydrogen liquid stream to form a low pressure hydrogen return stream; 10. The method of claim 1, further comprising warming the low-pressure hydrogen return stream by indirect heat exchange and combining it with the low-pressure hydrogen vapor stream to produce the warmed low-pressure hydrogen stream.

10. compressing at least a portion of the nitrogen stream through one or more compression stages to produce a compressed nitrogen stream; cooling the compressed nitrogen stream by indirect heat exchange to produce a cooled compressed nitrogen stream; expanding at least a portion of the cooled compressed nitrogen stream to produce a partially condensed nitrogen stream; separating the partially condensed nitrogen stream to produce a nitrogen vapor stream and a nitrogen liquid stream; warming and combining the nitrogen vapor stream and at least a portion of the nitrogen liquid stream by indirect heat exchange to produce a nitrogen return stream; wherein the nitrogen stream comprises the nitrogen return stream; 2. The method of claim 1, wherein the cooling duty for cooling the hydrogen feed by indirect heat exchange is provided at least in part by the nitrogen vapor stream and at least a portion of the nitrogen liquid stream.

11. splitting at least a portion of the nitrogen liquid stream to produce a liquid nitrogen product; cooling a portion of the compressed nitrogen stream by indirect heat exchange and splitting to produce a cold nitrogen expander feed; expanding the cold nitrogen expander feed to produce a first cold medium pressure nitrogen stream; warming the first cold medium-pressure nitrogen stream by indirect heat exchange to produce a first medium-pressure nitrogen stream; providing a medium pressure nitrogen recycle stream to an intermediate stage of said one or more compression stages; 11. The method of claim 10, further comprising: wherein the medium-pressure nitrogen recycle stream comprises the first medium-pressure nitrogen stream.

12. extracting a portion of said nitrogen stream from an intermediate stage of said one or more compression stages to produce a warm nitrogen expander feed; expanding the warm nitrogen expander feed to produce a second low temperature medium pressure nitrogen stream; warming the second cold medium-pressure nitrogen stream by indirect heat exchange to produce a second medium-pressure nitrogen recycle stream; and wherein the medium-pressure nitrogen recycle stream comprises the second medium-pressure nitrogen recycle stream.

13. expanding at least a portion of the cooled compressed nitrogen stream to produce a third low temperature medium pressure nitrogen stream; warming the third cold medium-pressure nitrogen stream by indirect heat exchange to produce a third medium-pressure nitrogen recycle stream; and wherein the medium-pressure nitrogen recycle stream comprises the third medium-pressure nitrogen recycle stream.

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