Patent Publication Number: US-2023147955-A1

Title: Hydrogen Liquefaction with Stored Hydrogen Refrigeration Source

Description:
CLAIM OF PRIORITY 
     This application claims the benefit of U.S. Provisional Application No. 63/276,888, filed Nov. 8, 2021, the contents of which are hereby incorporated by reference. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure relates generally to systems and methods for liquefying hydrogen and, more particularly, to a system and method that liquefies hydrogen and uses hydrogen gas storage as a refrigerant source. 
     BACKGROUND 
     Industrial gases, such as natural gas or hydrogen, are advantageously stored or transported in a liquid state because they occupy a much smaller volume (natural gas for instance is 1/600 th  the gaseous state). The liquefied gases are then vaporized back to a gaseous state for use at a site or system. 
     Gaseous hydrogen is converted to liquefied hydrogen by cooling it to at least about −253° C. The typical process of cooling utilizes a high amount of energy and can be very expensive with regard to equipment costs. The process may include multiple refrigeration cycles and involve multiple stages of gas compression. 
     The use of letdown energy from high-pressure gases to provide refrigeration and reduce operating costs in a hydrogen liquefaction system is illustrated in U.S. Pat. No. 10,634,425 to Guillard et al. The &#39;425 patent uses letdown energy from high-pressure gases other than hydrogen to provide cooling in the warm end of the system and a methanol production unit as a source of a high-pressure hydrogen rich purge gas for letdown refrigeration energy to provide cooling in the cold end of the system. After use to provide cooling, the hydrogen rich stream is sent back to the methanol plant as low pressure fuel. 
     It is desirable to provide a hydrogen liquefaction system and method which lowers operational and equipment costs in at least some applications. 
     SUMMARY OF THE DISCLOSURE 
     There are several aspects of the present subject matter which may be embodied separately or together in the methods, devices and systems described and claimed below. These aspects may be employed alone or in combination with other aspects of the subject matter described herein, and the description of these aspects together is not intended to preclude the use of these aspects separately or the claiming of such aspects separately or in different combinations as set forth in the claims appended hereto. 
     In one aspect, a system for liquefying a hydrogen gas feed stream includes a cold box feed line configured to receive a cold box feed stream having a cold box feed stream pressure where the cold box feed stream includes at least the hydrogen gas feed stream. A heat exchanger system has a liquefier cooling passage in fluid communication with the cold box feed line and is configured to receive and cool a liquefier stream so that a product stream is formed. A product expansion device is in fluid communication with an outlet of the liquefier cooling passage and is configured to receive the product stream so that an expanded product stream is formed. 
     The heat exchanger system includes a refrigerant cooling passage configured to receive a refrigerant feed stream so that a cooled refrigerant feed stream is formed. A refrigerant expansion device is in fluid communication with the refrigerant cooling passage of the heat exchanger system so that an expanded refrigerant stream is formed. The heat exchanger system includes a refrigerant warming passage in fluid communication with an outlet of the refrigerant expansion device so that cooling is provided in the heat exchanger system. 
     The heat exchanger system includes a first hydrogen high-pressure refrigerant cooling passage configured to receive and cool a high-pressure hydrogen supplemental refrigerant feed stream so that a cooled hydrogen supplemental refrigerant stream is formed. A supplemental refrigerant expansion device has an inlet in fluid communication with the first hydrogen high-pressure refrigeration cooling passage so that an expanded hydrogen supplemental refrigerant stream is produced having a pressure not lower than the cold box feed stream pressure. The heat exchanger system includes a high-pressure hydrogen refrigerant warming passage in fluid communication with an outlet of the supplemental refrigerant expansion device and is configured to receive the expanded hydrogen supplemental refrigerant stream so that cooling is provided in the heat exchanger system and a high-pressure hydrogen product stream is formed that is at a pressure higher than the cold box feed stream pressure. 
     In another aspect, a method for liquefying a hydrogen gas feed stream includes the steps of: receiving a cold box feed stream including at least the hydrogen gas feed stream into a heat exchanger system, where the cold box feed stream has a cold box feed stream pressure; cooling a liquefier feed stream that includes the cold box feed stream in a heat exchanger system to form a product stream; expanding the product stream to form an expanded product stream; cooling a refrigerant stream in the heat exchanger system to form a cooled refrigerant stream; expanding the cooled refrigerant stream to form a first expanded refrigerant stream; warming the first expanded refrigerant stream so that cooling is provided in the heat exchanger system; cooling a high-pressure hydrogen supplemental refrigerant feed stream in the heat exchanger system so that a cooled hydrogen supplemental refrigerant stream is formed; expanding the cooled hydrogen supplemental refrigerant stream to form an expanded hydrogen supplemental refrigerant stream having a pressure not lower than the cold box feed stream pressure; and warming the expanded supplemental hydrogen refrigerant stream so that cooling is provided in the heat exchanger system and a high-pressure hydrogen product stream is formed that is at a pressure higher than the cold box feed stream pressure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a process flow diagram and schematic illustrating an embodiment of the hydrogen liquefaction system of the disclosure. 
         FIG.  2    is a process flow diagram and schematic illustrating an alternative embodiment of the hydrogen liquefaction system of the disclosure. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     In accordance with the present disclosure, hydrogen gas from high-pressure storage(s), such as a hydrogen storage cavern, high-pressure cylinders, hydrogen pipeline, and/or other high-pressure storage or components, is used to provide refrigeration to a hydrogen liquefaction system. The high-pressure hydrogen then exits the system as a hydrogen stream that can be utilized by different systems and/or processes. Usage of a stored high-pressure hydrogen gas source, including the letdown energy provided by such a source, eliminates or greatly reduces the refrigeration requirement from other sources, reducing power required and operating cost. 
     A process flow diagram and schematic illustrating an embodiment of the hydrogen liquefaction system of the current disclosure is provided in  FIG.  1   . 
     It should be noted herein that the lines, conduits, piping, passages and similar structures and the corresponding streams are sometimes both referred to by the same element number set out in the figures. Also, as used herein, and as known in the art, a heat exchanger is that device or an area in the device wherein indirect heat exchange occurs between two or more streams at different temperatures, or between a stream and the environment. In addition, all heat exchangers referenced herein may be incorporated into one or more heat exchanger devices or may each be individual heat exchanger devices. As used herein, the terms “communication”, “communicating”, and the like generally refer to fluid communication unless otherwise specified. And although two fluids in communication may exchange heat upon mixing, such an exchange would not be considered to be the same as heat exchange in a heat exchanger, although such an exchange can take place in a heat exchanger. A heat exchange system or a heat exchanger system can include those items though not specifically described are generally known in the art to be part of a heat exchanger, such as expansion devices, flash valves, and the like. As used herein, the terms, “high”, “middle”, “warm”, “cold” and the like are relative to comparable streams, as is customary in the art. 
     With reference to the embodiment of  FIG.  1   , a hydrogen gas feed stream  3  is combined with a first hydrogen recycle stream and then a second medium-pressure hydrogen recycle stream  2 . The first hydrogen recycle stream is formed by compressing a low-pressure hydrogen recycle stream  1  in a first hydrogen compressor  101 . The resulting mixture, at approximately ambient temperature, is fed to a second hydrogen compressor  102 . The fluid exits the second hydrogen compressor as a hydrogen cold box feed stream  4 . 
     The hydrogen cold box feed stream  4  may have a pressure of about 200-600 psig, and preferably 250-400 psig. The first and second hydrogen compressors  101  and  102  can each consist of a single compressor or compressor stage or more than one compressor or compressor stage. Alternatively, the compressors  101  and  102  can represent stages of the same compressor with at least one interstage feed. If the pressure of the hydrogen feed  3  is high enough to feed the cold box, compression of that stream is not necessary, and it can be combined with the recycle streams downstream of the second compressor  102 , as indicated in phantom at  130  in  FIG.  1   . 
     The hydrogen cold box feed  4  is cooled in a first heat exchanger  103  to about 80° K to form a first adsorber feed steam  5  that is fed to a first adsorber system  104  that removes trace impurities to prevent freezing of impurities and subsequent plugging of a heat exchanger passage. The first adsorber system  104  shown in  FIG.  1    generally consists of parallel vessels and switching valves to allow for regeneration of a saturated adsorbent vessel in continuous operation. Suitable adsorber systems are well known in the art. 
     The stream exiting the first adsorber is split or divided into a liquefier feed stream  6  and a hydrogen refrigerant stream  7 . Preferably approximately 20% of the stream will become the liquefier feed  6  and the remainder will become the hydrogen refrigerant  7 . 
     The liquefier feed  6  is cooled further in a second heat exchanger  106  that contains a second heat exchanger catalyst passage  107  that contains ortho-para conversion catalyst. The ortho-para conversion catalyst converts a portion of the ortho-hydrogen to para-hydrogen in the liquefaction process to minimize volatilization of the liquid product. Alternatively, one or more catalytic reactors outside of the heat exchangers can be used. Suitable catalysts, such as iron oxide, chromium oxide, or vanadium oxide, are well known in the art. 
     The liquefier feed  6  exits the second heat exchanger  106  as a cooled liquefier feed stream  8 . The cooled liquefier feed  8  is cooled further in a third heat exchanger  109 , a fourth heat exchanger  112  and a fifth heat exchanger  116  containing a third heat exchanger catalyst passage  110 , a fourth heat exchanger catalyst passage  113 , and a fifth heat exchanger catalyst passage  117 , respectively, to produce a cold high-pressure hydrogen stream  11 . Alternatively, one or more catalytic reactors outside of the heat exchangers can be used in place of catalysts within heat exchanger passages  110 ,  113  and/or  117 . 
     A single heat exchanger or more than three heat exchangers may be substituted for the third through fifth heat exchangers ( 109 ,  112  and  116 ) in alternative embodiments of the system. Indeed, a single heat exchanger or a heat exchanger system may be substituted for, or may incorporate any or all of, the first through fifth heat exchangers ( 103 ,  106 ,  109 ,  112  and/or  116 ). 
     The cold high-pressure hydrogen stream  11  is expanded across a product expansion device  118  to further cool it and produce a mixed-phase product stream or two-phase hydrogen stream  12  that is fed to a hydrogen product separator  119 . The product expansion device  118 , as in the case of any of the expansion devices or valves disclosed in  FIG.  1   , may be a Joule-Thomson valve or any other type of expansion valve or expansion device known in the art including, but not limited to, a turbine or an orifice. The product separator  119 , as in the case of any of the separators disclosed in  FIG.  1   , may be an accumulation drum or any other separation vessel or other type of separation device known in the art including, but not limited to a cyclonic separator, a distillation unit, a coalescing separator or a mesh or vane type mist eliminator. 
     A liquid hydrogen product stream  13  exits the bottom of the hydrogen product separator  119  while a saturated hydrogen vapor stream  14  exits the top. The saturated hydrogen vapor stream  14  is warmed in the fifth heat exchanger  116 , where it provides refrigeration to assist in the production of the cold high-pressure hydrogen stream  11 , and exits as a warmed hydrogen vapor stream  15 . 
     The hydrogen refrigerant  7  is cooled in the second heat exchanger  106  and the third heat exchanger  109  to produce cooled hydrogen refrigerant streams  16  and  17 , respectively. A first portion  18  of the cooled hydrogen refrigerant stream  17  is cooled further in the fourth heat exchanger  112  to produce a cold high-pressure hydrogen refrigerant stream  20  while the remainder or second portion  19  of the cooled hydrogen refrigerant  17  is fed to a cold expansion device, such as cold expansion turbine  111 , where it is expanded to a lower pressure and exits at a lower temperature as a cold turbine product  29 . 
     The cold high-pressure hydrogen refrigerant stream  20  is expanded across a refrigerant expansion device  114  to further cool it and produce a mixed-phase or two-phase hydrogen refrigerant stream  21  that is fed to a hydrogen refrigerant separator  115 . A liquid hydrogen refrigerant stream  22  exits the bottom of the hydrogen refrigerant separator  115  and is fed to the fifth heat exchanger  116  where much of it is vaporized to provide refrigeration to the fifth heat exchanger  116  and exits as a mixed-phase hydrogen refrigerant stream  23  that is fed to the hydrogen refrigerant separator  115 . 
     The hydrogen refrigerant vapor stream  24  exiting the hydrogen refrigerant separator  115  combines with the warmed hydrogen vapor  15  to form a cold low-pressure hydrogen refrigerant stream  25 . The cold low-pressure hydrogen refrigerant stream  25  and the cold turbine product stream  29  are heated in the fourth heat exchanger  112  and the third heat exchanger  109  to form a warm low-pressure hydrogen refrigerant stream  27  and a warm turbine product  31 . The warm low-pressure hydrogen refrigerant stream  27  is heated further in the second heat exchanger  106  and the first heat exchanger  103  to form the low-pressure hydrogen recycle stream  1 . The warm turbine product stream  31  is heated further in the first heat exchanger  103  to form the medium-pressure hydrogen recycle stream  2 . 
     A high-pressure hydrogen supplemental refrigeration feed stream  41  at a pressure higher than about 600 psig, typically about 1000-2000 psig, is cooled in the first heat exchanger  103  and fed as stream  42  to a second adsorber system  105  operating at a higher pressure and similar temperature to the first adsorber system  104  to form a purified high-pressure hydrogen stream  43  that is cooled further in the second heat exchanger  106  to form a warm expansion turbine feed  44  that is fed to a warm expansion device, such as warm expansion turbine  108 . The warm expansion turbine  108  operates at a higher temperature, a higher inlet pressure, and a higher outlet pressure than the cold expansion turbine  111  and forms a warm expansion turbine product  45 , which is at a higher pressure than the hydrogen cold box feed  4  pressure. The warm expansion turbine product  45  is heated in the third heat exchanger  109  and the first heat exchanger  103  forming a high-pressure hydrogen product  47  that is at a pressure lower than the high-pressure stored hydrogen feed  41  but higher than the hydrogen cold box feed  4  pressure. The high-pressure hydrogen product  47  can be fed to a gas turbine, a chemical process, a pipeline, an energy production process, hydrogen storage, or other application. Alternatively, the high-pressure hydrogen product  47  may be fed to a gas turbine that is used to power compressor stages or compressors  101  and/or  102 . 
     Additional refrigeration may be provided to the process using an external refrigerant, such as liquid or gaseous nitrogen. A second heat exchanger refrigerant stream  51 , such as liquid nitrogen or another refrigeration source, is heated in the second heat exchanger  106  and/or the first heat exchanger  103 , to provide additional cooling. A first heat exchanger refrigerant stream  54 , such as cold gaseous nitrogen or another refrigeration source, is heated in the first heat exchanger  103  to provide additional cooling. 
     As noted previously, heat exchangers  103 ,  106 ,  109 ,  112  and  116  could be incorporated into a heat exchanger system. Such a heat exchanger system may include, as examples only, a single heat exchanger, separate heat exchangers (as illustrated in  FIG.  1   ), or combined in multiple heat exchangers (for example,  103  and  106  combined in a first heat exchanger with  109 ,  112  and  116  combined in a second heat exchanger). In addition, the number of heat exchangers may vary from the number shown in  FIG.  1    in alternative embodiments of the system of the disclosure. Furthermore, any of the heat exchangers could be split into more than one exchanger. 
     In an alternative embodiment, a portion of the high-pressure hydrogen product  47  can be used as the cold box feed  4 , as illustrated in phantom at  132  in  FIG.  1   . This may still save hydrogen compression power and cost when compared to a typical hydrogen liquefaction process, but may not provide the high-pressure gas product that can be used as a gas turbine feed. 
     In another alternative embodiment, a portion of the warm expansion turbine product stream  45  can be cooled further and expanded in either a valve or expander to provide additional refrigeration in heat exchangers  109  and/or  106  and/or  103  as stream  45  is already cold and available at high pressure. 
     The embodiments of the system and process of the disclosure presented above therefore take advantage of the energy stored in a high-pressure storage system such as a hydrogen cavern, pipeline, stationary storage system or other high pressure hydrogen storage to provide refrigeration for a liquefaction system, increasing system efficiency and saving equipment and/or operating costs. The hydrogen product ( 47  in  FIG.  1   ) which is not recycled can provide a hydrogen source for an additional system or process. 
     As noted previously, the hydrogen stream  5  entering the first adsorber  104  of  FIG.  1    is split into a liquefier feed stream  6  and a hydrogen refrigerant stream  7  with approximately 20% of the stream  5  preferably becoming the liquefier feed  6  and the remainder becoming the hydrogen refrigerant  7 . This is a much higher fraction of hydrogen to be liquefied than is typical of a standard hydrogen liquefaction process that is not integrated with high-pressure storage. 
     In addition, the embodiment of  FIG.  1    takes advantage of the energy stored in a high-pressure storage system such as a hydrogen cavern, pipeline, stationary hydrogen storage system or other high-pressure storage system to provide refrigeration for a liquefier while still recovering the hydrogen at a pressure higher than the cold box feed pressure. This is a significant advantage where a cavern, pipeline, or other high-pressure storage system and liquefier are located at the same place. 
     Even if the recovered hydrogen (stream  47 ) is not at a higher pressure than the cold box feed  4 , using the outlet hydrogen somewhere other than recycling it back to the liquefier may also be useful. 
     Example 
     The following example provides more information on one configuration of the invention. It is not intended to limit the disclosed invention or the scope of the disclosure. In the embodiment of  FIG.  1   , 4886 lbmol/hr of hydrogen cold box feed stream  4  consisting of normal hydrogen is fed to the process of this embodiment after exiting the second hydrogen compressor  102 , which raises the pressure of the feed gas 4 to 360 psig. Operating at elevated pressure enables the cryogenic liquefaction process. 
     The first heat exchanger  103  in this embodiment decreases the temperature of the stream to 81 K. Trace impurities are removed in the first adsorber system  104  and the stream is split into the liquefier feed  6  (1000 lbmol/hr) and the hydrogen refrigerant stream  7  (3886 lbmol/hr). This results in a split of 20-21% of the feed stream sent to the liquefier, which is higher than conventional hydrogen liquefiers known in the art. The liquefier feed  6  is cooled from 81 K to produce the cold high-pressure hydrogen stream  11  at 22 K in the heat exchangers  106 ,  109 ,  112 , and  116 . This stream is expanded to 45 psia in the product expansion device  118  to form the liquid hydrogen product stream  13 . 
     The hydrogen refrigerant stream  7  is cooled in heat exchangers  106  and  109  to produce the cooled hydrogen refrigerant stream  17  at 51 K, which is split into a first portion  18  (351 lbmol/hr), which is cooled to 27 K in heat exchanger  112 , and a second portion  19  (3553 lbmol/hr), which is fed to the cold expansion turbine  111 . The second portion  19  is expanded from 356 psia to 35 psia in the turbine and cooled from 51 K to 24 K. This cold turbine product  29  is used to provide refrigeration in the heat exchangers. The first portion  18  is cooled in heat exchanger  112  to produce the cold high-pressure hydrogen refrigerant stream  20  at 27 K, which is expanded from 356 psia to 18 psia in the refrigerant expansion valve device  114  and cooled from 27 K to 21 K, and partially condensed. The partially condensed stream is mixed with the mixed-phase hydrogen refrigerant stream  23  and separated in the hydrogen refrigerant separator  115  to form the liquid hydrogen refrigerant stream  22  (1170 lbmol/hr) and the hydrogen refrigerant vapor stream  24  (351 lbmol/hr). The liquid hydrogen refrigerant stream is partially vaporized to provide cooling in the coldest heat exchanger  116  and returns to the hydrogen refrigerant separator. The refrigerant vapor stream provides cooling in the other heat exchangers  112 ,  109 ,  106 , and  103 . Additional refrigeration is provided by liquid nitrogen  51  (106 lbmol/hr) and cold nitrogen vapor  54  (961 lbmol/hr). 
     The high-pressure stored hydrogen feed  41 , in this example, feeds 2780 lbmol/hr at 300 K and 2000 psia of normal hydrogen to the heat exchanger system and is cooled to 79 K and fed to the warm expansion turbine  108 , where it is expanded to 500 psia and cooled to 55 K. This is a sufficiently low temperature to provide refrigeration to the system and actually replace a standard warm expander of the prior art. Furthermore, the stream is recovered from the cold box at 498 psia as the high-pressure hydrogen product  47 . Recovering this stream at a pressure not lower than the cold box feed may provide the combined benefits of recovering a hydrogen stream at high pressure for use outside the liquefier and reducing the refrigeration requirement when compared to conventional hydrogen liquefaction processes. 
     Conditions and compositions of selected streams for the above Example are shown in Table 1. 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                 Stream 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
                 11 
                 12 
               
               
                   
               
               
                 Temperature [K] 
                 293 
                 293 
                 293 
                 294 
                 81 
                 81 
                 79 
                 22 
                 23 
               
               
                 Pressure [psia] 
                 15 
                 32 
                 32 
                 360 
                 358 
                 358 
                 358 
                 335 
                 45 
               
               
                 Molar Flow [lbmole/hr] 
                 352 
                 3535 
                 1000 
                 4886 
                 4886 
                 3886 
                 1000 
                 1000 
                 1000 
               
               
                 Liquid Fraction 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 1.00 
                 1.00 
               
               
                 Para Hydrogen [Mole %] 
                 75.0 
                 75.0 
                 75.0 
                 75.0 
                 75.0 
                 75.0 
                 75.0 
                 0.5 
                 0.5 
               
               
                 Ortho Hydrogen [Mole %] 
                 25.0 
                 25.0 
                 25.0 
                 25.0 
                 25.0 
                 25.0 
                 25.0 
                 99.5 
                 99.5 
               
               
                 Nitrogen [Mole %] 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                   
               
               
                 Stream 
                 13 
                 17 
                 18 
                 19 
                 20 
                 21 
                 22 
                 23 
                 25 
               
               
                   
               
               
                 Temperature [K] 
                 22 
                 51 
                 51 
                 51 
                 27 
                 21 
                 21 
                 21 
                 21 
               
               
                 Pressure [psia] 
                 45 
                 356 
                 356 
                 356 
                 356 
                 18 
                 17 
                 17 
                 17 
               
               
                 Molar Flow [lbmole/hr] 
                 1000 
                 3884 
                 351 
                 3533 
                 351 
                 351 
                 1170 
                 1170 
                 351 
               
               
                 Liquid Fraction 
                 1.00 
                 0.00 
                 0.00 
                 0.00 
                 1.00 
                 0.81 
                 1.00 
                 0.77 
                 0.00 
               
               
                 Para Hydrogen [Mole %] 
                 0.5 
                 75.0 
                 75.0 
                 75.0 
                 75.0 
                 75.0 
                 75.0 
                 75.0 
                 75.0 
               
               
                 Ortho Hydrogen [Mole %] 
                 99.5 
                 25.0 
                 25.0 
                 25.0 
                 25.0 
                 25.0 
                 25.0 
                 25.0 
                 25.0 
               
               
                 Nitrogen [Mole %] 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                   
               
               
                 Stream 
                 29 
                 41 
                 44 
                 45 
                 47 
                 51 
                 53 
                 54 
                 55 
               
               
                   
               
               
                 Temperature [K] 
                 24 
                 300 
                 79 
                 54 
                 293 
                 51 
                 53 
                 54 
                 55 
               
               
                 Pressure [psia] 
                 35 
                 2000 
                 1997 
                 500 
                 498 
                 16 
                 14 
                 20 
                 18 
               
               
                 Molar Flow [lbmole/hr] 
                 3533 
                 2780 
                 2780 
                 2780 
                 2780 
                 106 
                 106 
                 961 
                 961 
               
               
                 Liquid Fraction 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 1.00 
                 0.00 
                 0.00 
                 0.00 
               
               
                 Para Hydrogen [Mole %] 
                 75.0 
                 75.0 
                 75.0 
                 75.0 
                 75.0 
                 0.0 
                 0.0 
                 0.0 
                 0.0 
               
               
                 Ortho Hydrogen [Mole %] 
                 25.0 
                 25.0 
                 25.0 
                 25.0 
                 25.0 
                 0.0 
                 0.0 
                 0.0 
                 0.0 
               
               
                 Nitrogen [Mole %] 
                 0 
                 0 
                 0 
                 0 
                 0 
                 100 
                 100 
                 100 
                 100 
               
               
                   
               
            
           
         
       
     
     In another embodiment, hydrogen refrigerant passes through a series of expanders that operate at different pressures and/or temperatures or is fed to more than one set of expanders in parallel that also operate at different temperatures. In this case, the expander for the hydrogen supplemental refrigeration stream would be added to a standard hydrogen liquefaction process. Although this would represent additional capital cost, operating and power costs may be reduced compared to the standard process known in the art. As hydrogen liquefaction becomes more common, these processes could become larger and the operating cost reduction could justify additional capital cost. The additional higher-temperature hydrogen refrigerant expanders may also increase operating flexibility to adjust for fluctuating pressure in the high-pressure hydrogen storage source. This could be beneficial because hydrogen storage pressures, such as those in caverns or pipelines, fluctuate with varying supply and demand. 
     In an alternative embodiment, with reference to  FIG.  1   , a higher-temperature hydrogen expander, indicated in phantom at  134  in  FIG.  1   , receives a portion of the cooled hydrogen refrigerant stream  16  and returns the expanded/cooled stream  136  to refrigeration stream  30  and/or expanded/cooled stream  138  to refrigeration stream  26 . The higher-temperature hydrogen expander  134  may be a turbine or any other expansion device known in the art. As a result, the high-pressure expander  108  is in parallel with the higher-temperature hydrogen expander  134  and takes some, but not all, of the refrigeration load. This means the additional capital cost of a third expander system would be required to save the power cost of part of the higher-temperature expander  134 . The relative importance of capital cost compared to operating cost decreases as plant size increases, so this approach becomes more economical as plant size increases. 
     In the embodiment of  FIG.  2   , a closed refrigeration loop is shown instead of a hydrogen refrigeration system that mixes with the feed. The closed refrigeration loop can use helium, hydrogen, mixtures of helium and neon, or other appropriate refrigerants that do not solidify at the lowest temperatures in the loop. All reference numbers that are repeated in  FIG.  2    represent the same streams or equipment shown in  FIG.  1   . 
     In contrast to the embodiment of  FIG.  1   , in the embodiment of  FIG.  2   , the warmed hydrogen vapor  15  does not mix with another stream before being heated in the heat exchanger system. In the heat exchanger configuration shown in  FIG.  2   , the warmed hydrogen vapor  15  is heated to a first  61 , second  62 , and third  63  hydrogen vapor recycle stream in the heat exchanger system before exiting as a hydrogen recycle stream  64 , comparable to the low-pressure hydrogen recycle stream  1  in  FIG.  1   , but with a lower flow rate. 
     The primary difference between the two process configurations of  FIG.  1    and  FIG.  2    is the closed-loop refrigeration cycle in the embodiment of  FIG.  2   . In the closed-loop refrigeration cycle of  FIG.  2   , a warm low-pressure refrigerant  71  is compressed in refrigerant compressor  201  to form a warm high-pressure refrigerant  72 , which is partially cooled in the heat exchanger system to about 80 K to form a refrigerant adsorber feed stream  73 . The refrigerant adsorber feed stream  73  is fed to a low-temperature refrigerant adsorption system  202  that removes impurities from the refrigerant that could have been introduced to the closed loop to produce a refrigerant adsorber product stream  74 . The low-temperature refrigerant adsorption system  202  can be smaller and regenerated much less frequently than the other adsorption systems because there is no continuous introduction of impurities into the stream. 
     The refrigerant adsorber product steam  74  is cooled further in the heat exchanger system to produce a first  75  and second  76  cooled refrigerant stream. In one embodiment, a portion of the first cooled refrigerant stream  141  is expanded in a first refrigerant expander  140  to produce a first low-pressure refrigerant stream  142 , which provides cooling to the heat exchanger system. This expander provides additional refrigeration if the warm expansion turbine  108  does not provide enough refrigeration. 
     A portion of the second cooled refrigerant stream  77  is expanded in a second refrigerant expander  203  to produce a second low-pressure refrigerant stream  78 , which provides cooling to the heat exchanger system. The remainder of the second cooled refrigerant stream  82  is cooled further in the heat exchanger system to produce a cold high-pressure refrigerant stream  83 , which is expanded in a third refrigerant expander  204  to produce a third low-pressure refrigerant stream  84 , which provides cooling to the heat exchanger system. The third low-pressure refrigerant stream  84  is partially warmed in the heat exchanger system to produce a warm third low-pressure refrigerant  85 , which mixes with the second low-pressure refrigerant stream  78  to produce a combined low-pressure refrigerant  86  that is heated to a first  79 , second  80 , and third  81  warmed refrigerant stream in the heat exchanger system before exiting as the warm low-pressure refrigerant  71 . 
     In one alternative to the configuration shown in  FIG.  2   , the second and third refrigerant expanders  203  and  204  can operate in series instead of in parallel. In this case, the second low-pressure refrigerant stream  78  is fed to the third refrigerant expander  204  as a series expander feed  87 . In this case, there is no second cooled refrigerant stream  82 . In another alternative, valves or other pressure-reducing devices can be used instead of expanders. 
     One advantage of the closed-loop refrigeration system is that ortho-para conversion of the cold box feed  4  can begin at a higher temperature. In this case, because the entire stream is being liquefied, it is advantageous to begin ortho-para conversion in the first heat exchanger  103  by packing an ortho-para conversion catalyst  120  into the lower-temperature portion of the cold box feed passage. This allows for conversion of the 75% ortho-hydrogen feed to about 50% ortho-hydrogen before entering the first adsorber system  104 . 
     While the preferred embodiments of the disclosure have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made therein without departing from the spirit of the disclosure, the scope of which is defined by the following claims.