Apparatus and process for hydrogen recirculation to avoid liquefier shutdown due to insufficient hydrogen supply

Abstract

To provide an apparatus and a process for hydrogen recirculation for avoiding shutdown of a liquefier caused by insufficient hydrogen supply.SOLUTION: Supplying a feed of hydrogen to a liquefaction unit, the liquefaction unit liquefying the hydrogen and outputting liquid hydrogen, wherein the liquid hydrogen is parahydrogen with a parahydrogen content between 80 and 100 mol%, and recycling the liquid hydrogen to the feed of the liquefaction unit in response to a determination that the feed of hydrogen has decreased below a preselected threshold; Wherein the liquid hydrogen is vaporized into a gaseous state and undergoes conversion from para-hydrogen to ortho-hydrogen to bring the para-hydrogen content of the recycled hydrogen recycled to the feed of the liquefaction unit to a para-hydrogen content of 20 to 30mol% para-hydrogen.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a process and apparatus for hydrogen liquefaction, and to a process and apparatus for recycling hydrogen for hydrogen liquefaction processing. [Background technology]

[0002] Hydrogen can be produced via the electrolysis of water. Examples of systems configured to help facilitate the production of hydrogen via electrolysis are disclosed in U.S. Patent No. 11,929,613 and U.S. Patent Application Publication Nos. 2022 / 0033983 and 2024 / 0141524.

[0003] Hydrogen can be liquefied. Liquefaction of hydrogen gas can include the use of one or more liquefiers. Examples of approaches used to liquefy hydrogen can be found in U.S. Patent Application Publication No. 2023 / 0175773 and U.S. Patent Nos. 3,092,461 and 7,559,213. Summary of the Invention

[0004] Hydrogen liquefaction often occurs in processes where relatively steady-state conditions are desired. For example, the hydrogen stream for liquefaction may be provided from at least one hydrogen production source that operates using a reliable supply of hydrogen-forming materials and a reliable power supply that may be provided by a conventional power source (e.g., electricity generated from the combustion of natural gas or other fossil fuels, hydrogen production provided by steam reforming that may be produced through the use of fossil fuel sources, etc.).

[0005] In contrast to this type of approach to hydrogen production, green hydrogen production can be provided by using renewable energy to power the production of hydrogen. Such systems can produce hydrogen gas using water electrolysis powered via renewable sources such as solar and / or wind power. However, this type of production process can be subject to significant production variability due to changing weather conditions, which can greatly affect the power available to support the electrolysis of water. In many cases, hydrogen production can vary significantly from day to day or even every few days depending on various weather conditions (e.g., duration of daylight versus duration of night, cloud cover, wind availability, etc.). Green hydrogen production systems have often found that there can be significant variations in hydrogen gas output, and that liquefiers that may be positioned to liquefy hydrogen gas from such production systems may often need to shut down due to a lack of sufficient hydrogen feed to support the liquefaction process. Shutdown of the liquefaction process can involve significant costs in terms of lost production. Shutting down such equipment also has staggering costs. For example, restarting the liquefaction process can take a relatively long time, resulting in lost production that can occur when renewable power is increased to help output enough hydrogen to feed the liquefaction system, start-up delays can affect the ability to efficiently utilize the hydrogen produced, and equipment degradation from regular changes in operating conditions can result in equipment having to be replaced more frequently or otherwise having a shorter operating life, which can increase maintenance costs because the process is less flexible and more prone to shutdowns or other problems due to equipment failure.

[0006] Conventionally, expensive storage units may be provided as a buffer between the hydrogen production system and the liquefaction system to help ensure that the liquefaction system can operate if hydrogen refueling is unavailable. However, this type of conventional approach may require significant capital costs associated with storage. Also, hydrogen storage may result in losses due to having to control over-pressurization of the hydrogen stored in the reservoir and other storage-related process complexities.

[0007] It has been found that these types of problems can be better addressed by providing an apparatus and process for recycling the hydrogen output from the liquefaction unit so that the liquid hydrogen can be vaporized and subsequently recycled back to the feed of the liquefaction unit to make up for the insufficient hydrogen feed. Surprisingly, it has been found that this type of approach in energy usage and process complexity related to the liquid hydrogen formed can be beneficial because it can avoid liquefaction unit shutdowns and also help reduce or limit storage amounts that may be desirable to help support liquefaction operations during periods of low hydrogen production.

[0008] Surprisingly, we have found that this type of approach can be particularly beneficial in embodiments where the hydrogen feed is provided by a production system powered by a renewable electricity source, where hydrogen production may fluctuate due to weather conditions, daylight conditions (e.g., daytime compared to nighttime, cloudy conditions, etc.), or other conditions that may affect the power available for hydrogen production. In such systems, where production may fluctuate frequently in some circumstances (e.g., at least three times per week, at least 12 times per month, at least 200 times per year, etc.), we have surprisingly found that it can be beneficial to incur the costs and production complexity associated with recirculating already liquefied hydrogen back into the liquefaction unit feed in order to avoid liquefaction unit shutdown due to insufficient hydrogen supply for certain periods (e.g., overnight, rainy days, etc.). This can be particularly challenging in situations where the period of zero production is short (e.g., due to temporary weather issues affecting power availability that may be lost for 2 to 12 hours). The duration of power non-availability can be much shorter than that required to provide for complete liquefaction process shutdown and subsequent startup, which can typically take the full 24 hours. Surprisingly, to avoid a prolonged shutdown process, it has been found that in such circumstances it can be much more beneficial to maintain the liquefaction process online in a full recycle mode of operation so that product capture can be more easily achieved after power availability is resumed to replenish hydrogen to the liquefaction process, while also avoiding product discharge (e.g., hydrogen product discharge).

[0009] It has been found that chillers capable of producing refrigeration for hydrogen liquefaction may require a heat load (e.g., to provide hydrogen) to remain online and maintain productivity if the liquefaction process needs to continue running while hydrogen production is stopped or substantially delayed due to an unexpected loss of power. Without the heat load, the liquefaction process would subcool all equipment above its design temperature, thereby necessitating process shutdown. Surprisingly, it has been found that recycling hydrogen output from the liquefaction process to the process feed can provide an alternative feed for feed hydrogen in the form of a recycle stream that can replace lost hydrogen feed that may occur when a lack of power availability causes a stoppage or significant reduction in hydrogen production, which may significantly reduce (or stop) the provision of feed hydrogen for liquefaction.

[0010] To make such recycling effective and avoid problems related to refrigeration machinery limitations, refrigeration duties, and cryogenic conditions in liquefaction units capable of outputting liquid hydrogen having a para-hydrogen content of at least 95 mole percent, it has also been surprisingly discovered that controlling the para-hydrogen and ortho-hydrogen content of the recycled hydrogen can provide improved performance that also avoids processing problems that could damage equipment, degrade equipment, and / or create unexpected failures that could result in production problems or liquefaction shutdowns resulting from the use of recycled hydrogen.

[0011] For example, it has been surprisingly discovered that the presence of a para-hydrogen content greater than 25 mole percent (mol%) in the feed to a liquefaction unit for hydrogen liquefaction can require significant adjustments to the liquefaction unit's cooling system. Typically, the hydrogen feed supplied for liquefaction has a para-hydrogen content of about 25 mol%. The conversion of ortho-hydrogen to para-hydrogen can release energy, and the para-hydrogen content of the hydrogen can increase as the hydrogen is cooled for liquefaction. The liquefaction unit's cooling system can be designed to absorb this heat resulting from the conversion of ortho-hydrogen to para-hydrogen to facilitate the cooling and liquefaction of the hydrogen. If the hydrogen feed supplied for liquefaction has a para-hydrogen content higher than expected (e.g., a para-hydrogen content significantly greater than 25 mol%, a para-hydrogen content greater than 25 mol%), the heat released from the conversion of ortho-hydrogen to para-hydrogen can be lower than the liquefaction unit is designed to accommodate due to the reduction in ortho-hydrogen available for conversion to para-hydrogen. Such a loss of heat can result in subcooling of the cooling system, which can cause equipment temperatures to fall below those that may be required for stable performance of the cryogenic machinery utilized in the liquefaction unit. When this occurs, it can result in equipment tripping or other problems that necessitate shutting down the liquefaction process. It has been discovered that this can be avoided by utilizing a para-hydrogen-to-ortho-hydrogen conversion unit to control the para-hydrogen content in the hydrogen recycled to the liquefaction unit and help better control the para-hydrogen content in the hydrogen feed, including the recycled hydrogen. Such a conversion unit can provide improved para-hydrogen content control of the feed hydrogen, including hydrogen recycled from the liquefaction unit, to avoid liquefaction shutdowns and equipment degradation, while also helping to avoid processing delays and reduced production efficiency that may result from having to repeatedly cycle the liquefaction unit between shutdown and operating states.

[0012] In a first aspect, a process for recycling hydrogen is provided. The process may include supplying a hydrogen feed to a liquefaction unit. The liquefaction unit may liquefy the hydrogen and output liquid hydrogen. The liquid hydrogen may have a para-hydrogen content of 80 mole percent (mol%) para-hydrogen to 100 mol% para-hydrogen. In response to determining that the hydrogen feed has decreased below a preselected threshold, the liquid hydrogen may be recycled to the liquefaction unit feed such that the liquid hydrogen is vaporized to a gaseous state and undergoes conversion from para-hydrogen to ortho-hydrogen, resulting in a para-hydrogen content of the recycled hydrogen recycled to the liquefaction unit feed of 20 mol% para-hydrogen to 30 mol% para-hydrogen.

[0013] In some embodiments, the hydrogen feed can have a preselected para-hydrogen content. For example, the hydrogen feed can have a para-hydrogen content within a preselected para-hydrogen content range of 20 mol percent para-hydrogen to 30 mol percent para-hydrogen (e.g., at or about 25 mol% para-hydrogen, in the range of 23 mol% para-hydrogen to 27 mol% para-hydrogen, etc.).

[0014] In some embodiments, the hydrogen feed may be provided by a hydrogen generation system that may be configured to operate through the use of renewable electricity.

[0015] In a second aspect, the process may also include stopping the recirculation of liquid hydrogen in response to determining that the hydrogen feed has increased above a preselected threshold. In some embodiments of the process, the recirculation and stopping of the recirculation may occur at multiple different operating cycles, for example, to compensate for the rate of the hydrogen feed provided to the liquefaction unit.

[0016] In a third aspect, recycling the liquid hydrogen can include supplying hydrogen having a para-hydrogen content of 80 mol% to 100 mol% stored in at least one storage tank to a conversion unit positioned to convert para-hydrogen to ortho-hydrogen and adjust the para-hydrogen content of the recycled hydrogen recycled to the liquefaction unit feed to between 20 mol% and 30 mol% para-hydrogen, and / or supplying liquid hydrogen output from the liquefaction unit to a heater in the recycle loop to vaporize the liquid hydrogen, and then passing the vaporized hydrogen to a conversion unit positioned to convert para-hydrogen to ortho-hydrogen and adjust the para-hydrogen content of the recycled hydrogen recycled to the liquefaction unit feed to between 20 mol% and 30 mol% para-hydrogen. In some embodiments, both of these steps can be performed. In other embodiments, only one of these steps can be performed.

[0017] In a fourth aspect, the process may include feeding liquid hydrogen output from the liquefier, having a para-hydrogen content of 80 mol% to 100 mol%, to at least one storage tank of a hydrogen storage section in fluid communication with the liquefaction unit. In some embodiments, recycling the liquid hydrogen may include adjusting at least one valve to prevent the liquid hydrogen output from the liquefaction unit from passing through the at least one storage tank, feeding the liquid hydrogen output from the liquefaction unit to a heater in a recirculation loop to vaporize the liquid hydrogen, and subsequently passing the vaporized hydrogen to a conversion unit positioned to convert the para-hydrogen to ortho-hydrogen such that the para-hydrogen content of the recycled hydrogen recycled to the liquefaction unit feed is between 20 mol% para-hydrogen and 30 mol% para-hydrogen.

[0018] In a fifth aspect, the process may also include supplying hydrogen stored in at least one storage tank to a conversion unit positioned to convert para-hydrogen to ortho-hydrogen such that the para-hydrogen content of the recycled hydrogen recycled to the liquefaction unit feed is between 20 mol% para-hydrogen and 30 mol% para-hydrogen. After determining that sufficient hydrogen is being recycled to the liquefaction unit to compensate for the reduction in the hydrogen feed, the supply of hydrogen stored in the at least one storage tank to the conversion unit may be ceased or stopped.

[0019] In a sixth embodiment, recycling the liquid hydrogen includes compressing the hydrogen before it is fed to a conversion unit positioned to convert the para-hydrogen to ortho-hydrogen to bring the para-hydrogen content of the recycled hydrogen recycled to the liquefaction unit feed to between 20 mol% para-hydrogen and 30 mol% para-hydrogen.

[0020] In a seventh aspect, recycling the liquid hydrogen may include supplying hydrogen having a para-hydrogen content of 80 mol% to 100 mol% stored in at least one storage tank to a conversion unit positioned to convert the para-hydrogen to ortho-hydrogen such that the para-hydrogen content of the recycled hydrogen recycled to the liquefaction unit feed is between 20 mol% para-hydrogen and 30 mol% para-hydrogen, and / or supplying the liquid hydrogen output from the liquefaction unit to a heater in the recycle loop to vaporize the liquid hydrogen, and subsequently passing the vaporized hydrogen to a conversion unit positioned to convert the para-hydrogen to ortho-hydrogen such that the para-hydrogen content of the recycled hydrogen recycled to the liquefaction unit feed is between 20 mol% para-hydrogen and 30 mol% para-hydrogen. Embodiments of the process may also include, in response to start-up of the liquefaction unit when the liquefaction unit is at ambient temperature, supplying liquid hydrogen stored in at least one storage tank to the liquefaction unit to facilitate operation of the liquefaction unit and cooling of the liquefaction unit to a cryogenic operating temperature, and recirculating hydrogen output from the liquefaction unit through a recirculation loop during start-up.

[0021] In an eighth aspect, the process can be configured to utilize a controller having a processor coupled to a non-transitory memory, the controller positioned and configured to determine whether the hydrogen feed has decreased below a preselected threshold.

[0022] In a ninth aspect, the process of the first aspect can include one or more features of the second, third, fourth, fifth, sixth, seventh, and / or eighth aspects. Still other embodiments can include other features. Examples of such other features include, for example, features of the exemplary embodiments discussed herein.

[0023] In a tenth aspect, an apparatus for hydrogen recycling is provided. Embodiments of the apparatus may include a liquefaction unit configured to liquefy a hydrogen feed and output a first stream of liquid hydrogen to supply the liquid hydrogen to at least one storage tank. The liquid hydrogen may have a para-hydrogen content of 80 mole percent (mol%) to 100 mol%. The apparatus may also include a conversion unit positioned to convert para-hydrogen in the hydrogen output by the liquefaction unit to ortho-hydrogen such that the hydrogen output from the liquefaction unit can be recycled to a feed inlet of the liquefaction unit with a para-hydrogen content of 20 mol% to 30 mol%. Embodiments of the apparatus may be configured to implement embodiments of a process for recycling hydrogen.

[0024] In an eleventh aspect, the apparatus may include a recirculation loop conduit heater feed conduit connected between the liquefaction unit and the recirculation loop conduit heater. The recirculation loop conduit heater may be positioned to heat liquid hydrogen output from the liquefaction unit to vaporize the liquid hydrogen into gaseous hydrogen. The recirculation loop conduit heater may be positioned to supply the gaseous hydrogen to the conversion unit.

[0025] In a twelfth aspect, the conversion unit includes at least one para-hydrogen to ortho-hydrogen converter. In some embodiments, the conversion unit may include a single para-hydrogen to ortho-hydrogen converter. In other embodiments, the conversion unit may include multiple para-hydrogen to ortho-hydrogen converters. The converters may all operate in parallel in some embodiments. In other embodiments, some converters may operate in parallel and other converters may operate in series. In yet other embodiments having multiple para-hydrogen to ortho-hydrogen converters, the converters may be arranged to operate in series.

[0026] In a thirteenth aspect, the apparatus may include at least one storage tank positioned to output hydrogen stored therein to supply hydrogen to the conversion unit. In some embodiments, the storage tank may also be utilized to receive and store liquid hydrogen output from the liquefaction unit.

[0027] In a fourteenth aspect, the apparatus may include a recirculation loop heater positioned to receive hydrogen from the at least one storage tank and heat the hydrogen such that the hydrogen output from the at least one storage tank supplied to the conversion unit is supplied to the conversion unit as gaseous hydrogen.

[0028] In a fifteenth aspect, a recirculation loop conduit heater feed conduit can be connected between the liquefaction unit and the recirculation loop conduit heater. The recirculation loop conduit heater can be positioned to heat liquid hydrogen output from the liquefaction unit to vaporize the liquid hydrogen into gaseous hydrogen. The recirculation loop conduit heater can be positioned to supply gaseous hydrogen to the conversion unit. Alternatively (or in addition), the recirculation loop heater can be positioned to receive and heat hydrogen from at least one storage tank such that hydrogen output from the at least one storage tank supplied to the conversion unit is supplied to the conversion unit as gaseous hydrogen.

[0029] In a sixteenth aspect, the apparatus may include a recirculation loop conduit heater feed conduit connected between the liquefaction unit and a first recirculation loop conduit heater. The first recirculation loop conduit heater may be positioned to heat liquid hydrogen output from the liquefaction unit to vaporize the liquid hydrogen into gaseous hydrogen, and the first recirculation loop conduit heater may be positioned to supply the gaseous hydrogen to the conversion unit. The second recirculation loop heater may be positioned to receive and heat hydrogen from the at least one storage tank such that hydrogen output from the at least one storage tank supplied to the conversion unit is supplied to the conversion unit as gaseous hydrogen.

[0030] In a seventeenth aspect, the apparatus can include a compression system positioned upstream of the conversion unit to compress hydrogen for supply to the conversion unit. The compression system can include a single compressor or a train of compressors. In some embodiments, the compression system can include at least one multi-stage compressor or a single-stage compressor.

[0031] In an eighteenth aspect, the device of the tenth aspect may include one or more features of the eleventh, twelfth, thirteenth, fourteenth, fifteenth, sixteenth, and / or seventeenth aspects. Still other embodiments may include other features. Examples of such other features include, for example, features of the exemplary embodiments discussed herein.

[0032] For example, in a nineteenth embodiment, an apparatus for hydrogen recycling may include a liquefaction unit configured to liquefy a hydrogen feed and output a first stream of liquid hydrogen to supply the liquid hydrogen to at least one storage tank. The liquid hydrogen may have a para-hydrogen content of 80 mol% to 100 mol%. The conversion unit may be positioned to convert para-hydrogen in the hydrogen output by the liquefaction unit to ortho-hydrogen such that the hydrogen output from the liquefaction unit can be recycled to the feed inlet of the liquefaction unit with a para-hydrogen content of 20 mol% to 30 mol%. The conversion unit may include at least one para-hydrogen to ortho-hydrogen converter. The at least one storage tank may be positioned to output hydrogen stored therein to supply hydrogen to the conversion unit in response to the hydrogen feed being equal to or less than a preselected threshold. A recirculation loop conduit heater feed conduit may be connected between the liquefaction unit and the first recirculation loop conduit heater. The first recirculation loop conduit heater may be positioned to heat liquid hydrogen output from the liquefaction unit to vaporize the liquid hydrogen into gaseous hydrogen. The first recirculation loop conduit heater may be positioned to supply gaseous hydrogen to the conversion unit. The second recirculation loop heater may be positioned to receive and heat hydrogen from the at least one storage tank that supplies the conversion unit so that the hydrogen output from the at least one storage tank can be supplied to the conversion unit as gaseous hydrogen.

[0033] In some embodiments, a compression system may be positioned upstream of the conversion unit to compress hydrogen for supply to the conversion unit.

[0034] Embodiments of the apparatus and embodiments of the process can utilize liquefaction units with different types of cooling systems. For example, in some embodiments, the liquefaction unit can have a closed-loop cooling system. In other embodiments, the liquefaction unit can have an open-loop cooling system.

[0035] It should be understood that embodiments of the present process and apparatus can utilize a variety of conduit arrangements and process control elements. Embodiments may utilize sensors (e.g., pressure sensors, temperature sensors, flow sensors, concentration sensors, etc.), controllers, valves, piping, and other process control elements. Some embodiments may utilize, for example, an automatic process control system and / or a distributed control system (DCS). A variety of different conduit arrangements and process control systems can be utilized to meet a particular set of design criteria.

[0036] Other details, objects, and advantages of the apparatus for recycling hydrogen, the process for recycling hydrogen, the hydrogen liquefaction apparatus, the hydrogen liquefaction process, and the apparatus, process, and system for providing hydrogen recycling and avoiding liquefaction machine shutdowns, and methods of making and using them, will become apparent as the following description of certain exemplary embodiments thereof proceeds. [Brief explanation of the drawings]

[0037] Exemplary embodiments of apparatus for recycling hydrogen, processes for recycling hydrogen, hydrogen liquefaction apparatus, hydrogen liquefaction processes, and apparatus, processes, and systems for hydrogen circulation that can avoid liquefaction machine shutdowns, and methods of making and using the same, are shown in the drawings included herein, it being understood that like reference numerals used in the drawings may identify like components.

[0038] [Figure 1] FIG. 1 is a block diagram of a first exemplary embodiment of an apparatus 1 for recycling hydrogen (which may also be referred to as FIG. 1). Some optional elements of the exemplary embodiment of the apparatus are shown in dashed lines in FIG. 1. An exemplary embodiment of a process for recycling hydrogen is also illustrated in this figure.

[0039] [Figure 2]FIG. 2 is a block diagram of a first exemplary implementation of a first exemplary embodiment of an apparatus 1 for recycling hydrogen. An exemplary embodiment of a process for recycling hydrogen is also illustrated in this figure.

[0040] [Figure 3] FIG. 3 is a block diagram of a second exemplary implementation of a first exemplary embodiment of an apparatus 1 for recycling hydrogen. An exemplary embodiment of a process for recycling hydrogen is also illustrated in this figure.

[0041] [Figure 4] FIG. 4 (which may also be referred to as FIG. 4) is a block diagram of a second exemplary embodiment of an apparatus 1 for recycling hydrogen. Different compressors are shown in dashed lines in FIG. 4 because at least one such compressor may be optional for this particular embodiment. An exemplary embodiment of a process for recycling hydrogen is also illustrated in this figure.

[0042] [Figure 5] FIG. 5 is a block diagram of a first exemplary implementation of a second exemplary embodiment of an apparatus 1 for recycling hydrogen. An exemplary embodiment of a process for recycling hydrogen is also illustrated in this figure.

[0043] [Figure 6] FIG. 6 is a block diagram of a second exemplary implementation of a second exemplary embodiment of an apparatus 1 for recycling hydrogen. An exemplary embodiment of a process for recycling hydrogen is also illustrated in this figure.

[0044] [Figure 7]7 is a flowchart illustrating an exemplary embodiment of a process for hydrogen recycling to prevent liquefier operation from shutting down (which may also be referred to as FIG. 7). An embodiment of an apparatus for hydrogen recycling can perform this exemplary embodiment of the process. DETAILED DESCRIPTION OF THE INVENTION

[0045] 1-7 , an apparatus 1 for recirculating hydrogen can be utilized to recirculate hydrogen output from a liquefaction unit 2 and supply the hydrogen back to the liquefaction unit 2. In some embodiments, the apparatus 1 can be configured to provide hydrogen recirculation in response to a decrease in the hydrogen feed provided to the liquefaction unit 2 for liquefaction of the hydrogen below a preselected feed rate (e.g., a preselected volumetric flow rate defining a threshold for operation of the hydrogen recirculation, a preselected mass flow rate defining a threshold for operation of the hydrogen recirculation, etc.). The hydrogen recirculation can be operated to help avoid a shutdown of the liquefaction unit 2 in response to a low feed rate condition, thereby avoiding production delays associated with liquefaction unit shutdown and subsequent startup, as well as equipment degradation that can result from such operations involving cycling between operational and shutdown operating conditions.

[0046] It has been surprisingly found that this type of approach can be particularly beneficial in embodiments where the hydrogen feed 15 is provided by a production system powered by a renewable power source where hydrogen production can fluctuate due to weather conditions, daylight conditions (e.g., daytime compared to nighttime, cloudy conditions, etc.), or other conditions that can affect the power available for hydrogen production. In such systems, where production can fluctuate frequently (e.g., 200 or more times per year), it has been surprisingly found that it can be beneficial to incur the costs and production complexities associated with using already liquefied hydrogen to recycle back into the feed of the liquefaction unit 2 in order to avoid liquefaction unit shutdowns due to insufficient hydrogen supply for certain periods (e.g., nighttime, rainy days, etc.).

[0047] Liquefaction unit 2, which may be supported by apparatus 1 for hydrogen recycle, may include one or more liquefiers or a train of one or more liquefiers for liquefying hydrogen feed 15. Liquefaction unit 2 may be configured as a hydrogen liquefaction system (HLS), which may include, for example, a train of one or more liquefiers. The hydrogen liquefaction system (HLS) may include an array of expanders and hydrogen liquefaction heat exchangers. Some embodiments of the liquefaction system may also include an ortho-hydrogen to para-hydrogen conversion unit to convert ortho-hydrogen in the liquefied hydrogen to para-hydrogen to increase the para-hydrogen content of the liquefied hydrogen.

[0048] Liquefaction unit 2 may be configured to output a liquid hydrogen stream that may have a relatively high para-hydrogen content. In some embodiments, the para-hydrogen content of the liquid hydrogen output from the liquefaction unit may be at least 80 mol% para-hydrogen or at least 95 mol% para-hydrogen (e.g., 80 mol% para-hydrogen to 100 mol% para-hydrogen, 95 mol% para-hydrogen to 100 mol% para-hydrogen, etc.). During operation, when a suitable make-up of hydrogen feed is provided to liquefaction unit 2, the liquid hydrogen stream output from liquefaction unit 2 may be provided to storage 4 for storage, and then supplied to one or more customers (e.g., via shipping of the liquid hydrogen, transport of the liquid hydrogen to another location or production facility, etc.). Storage 4 for the liquid hydrogen may include at least one tank or other vessel for cryogenically storing the liquid hydrogen to help maintain the liquid hydrogen in a liquid state.

[0049] The hydrogen feed 15 supplied to the liquefaction unit 2 can include hydrogen that is entirely gaseous (e.g., 100% gaseous) or can include a primarily gaseous hydrogen stream (e.g., a gaseous hydrogen stream with 0 vol% to 1 vol% liquid hydrogen). The hydrogen feed 15 can be, for example, a normal hydrogen product containing a concentration of 25 mol% para-hydrogen and 75 mol% ortho-hydrogen. The hydrogen feed 15 can be provided via at least one hydrogen production system 20. The hydrogen production system 20 can include a hydrogen generation system (HGS), which can include one or more electrolyzers capable of forming hydrogen from the electrolysis of water. In some embodiments, the electrolyzers of such hydrogen production system 20 can be powered by at least one renewable power source (e.g., solar power, wind power, hydroelectric power, a combination thereof, etc.) to provide a feed of green hydrogen produced via renewable electricity.

[0050] The para-hydrogen content of the hydrogen feed provided by hydrogen production system 20 can be about 25 mol% para-hydrogen, with the remainder being ortho-hydrogen. For example, hydrogen feed 15 provided by hydrogen production system 20 can have a para-hydrogen content of 20 mol% to 30 mol% (e.g., 25 mol% or about 25 mol%), and the ortho-hydrogen content of the hydrogen can be 80 mol% to 70 mol% (e.g., 75 mol% or about 75 mol%).

[0051] The hydrogen feed 15 that may be provided may be powered by a renewable power source whose hydrogen production may fluctuate due to weather conditions, daylight conditions (e.g., daytime compared to nighttime, cloudy conditions, etc.), or other conditions that may affect the power available for hydrogen production. In such systems, in some circumstances, specifications may indicate frequent fluctuations in production (e.g., at least three times per week, at least 12 times per month, at least 200 times per year, etc.), and it has surprisingly been found that it may be beneficial to incur the costs and production complexity associated with supporting the operation of the liquefaction unit 15 by recirculating already liquefied hydrogen output from the liquefaction unit 2 back to the hydrogen feed 15 to provide a supplemental hydrogen flow to the hydrogen feed 15, thereby avoiding shutdown of the liquefaction unit 2 due to insufficient hydrogen supply for certain periods of time (e.g., overnight, on rainy days, etc.). Hydrogen recycling may occur via the use of hydrogen within the storage 4 and / or via routing of hydrogen output from the liquefaction unit such that the hydrogen is returned to the feed inlet of the liquefaction unit 2 instead of being routed to the storage 4. This recirculation may involve vaporizing the liquid hydrogen output from the liquefaction unit so that the hydrogen recycled back to the feed inlet of the liquefaction unit 2 is in a gaseous state (e.g., hydrogen gas instead of liquid hydrogen).

[0052] Liquefaction unit 2 can output liquid hydrogen having a para-hydrogen content of at least 95 mole percent. To recycle the hydrogen output from liquefaction unit 2, it has surprisingly been discovered that controlling the para-hydrogen and ortho-hydrogen content of the recycled hydrogen supplied to the feed inlet of the liquefaction unit can provide improved performance, avoiding processing issues that could damage or degrade equipment and / or result in unexpected failures that could cause production problems or liquefaction shutdowns resulting from the use of recycled hydrogen. Controlling the para-hydrogen content of the recycled hydrogen via conversion unit 11 can enable the recycled hydrogen, along with any low flow rate hydrogen that may be provided as hydrogen feed 15 from hydrogen production system 20, to have a preselected para-hydrogen content of 25 mole percent or less para-hydrogen, 30 mole percent or less para-hydrogen, or another suitable para-hydrogen content feed threshold that can be set to avoid subcooling the liquefaction equipment and causing hydrogen, including the recycled hydrogen, to cool.

[0053] Surprisingly, it has been discovered that the presence of a para-hydrogen content greater than or significantly greater than 25 mole percent (mol%) in a feed to a liquefaction unit for hydrogen liquefaction can require significant adjustments to the liquefaction unit's cooling system. Typically, hydrogen feeds supplied for liquefaction have a para-hydrogen content of about 25 mol%. The conversion of hydrogen from ortho-hydrogen to para-hydrogen can release energy, and as the hydrogen is cooled for liquefaction, the para-hydrogen content of the hydrogen can increase; the liquefaction unit's cooling system can be designed to absorb this heat resulting from the conversion of ortho-hydrogen to para-hydrogen to facilitate the cooling and liquefaction of the hydrogen.

[0054] If the hydrogen feed supplied to liquefaction unit 2 for liquefaction has a higher-than-expected para-hydrogen content (e.g., a para-hydrogen content significantly greater than 25 mol%, a para-hydrogen content greater than 25 mol%, etc.), the heat released from the conversion of ortho-hydrogen to para-hydrogen may be lower than what the liquefaction unit is designed to accommodate due to a reduction in ortho-hydrogen available for conversion to para-hydrogen (this could only occur as a result of recycling hydrogen output from the liquefaction unit back to the liquefaction unit 2 feed in an amount sufficient to significantly alter the para-hydrogen content in the hydrogen feed supplied to liquefaction unit 2). This reduction in heat could cause the cooling system to subcool the hydrogen during liquefaction, which could cause equipment temperatures to fall below those required for stable performance of the cryogenic machinery utilized in the liquefaction unit. It has been determined that this type of occurrence could result in equipment tripping or other problems that necessitate shutting down the liquefaction process.

[0055] It has been discovered that such problems that may be caused by excessive cooling can be avoided by utilizing a para-hydrogen to ortho-hydrogen conversion unit 11 (CVRT) to control the para-hydrogen content in the hydrogen recycled to the feed inlet of the liquefaction unit 2 and to help better control the para-hydrogen content in the feed hydrogen, including the recycled hydrogen, supplied to the feed inlet of the liquefaction unit 2. Such a conversion unit 11 (CVRT) may include one or more para-hydrogen to ortho-hydrogen converters for converting para-hydrogen in the recycled hydrogen to ortho-hydrogen, to provide improved para-hydrogen content control of the feed hydrogen, including hydrogen recycled from the liquefaction unit, to avoid liquefaction shutdowns and equipment degradation, while also helping to avoid processing delays and reduced production efficiency that may result from having to repeatedly cycle the liquefaction unit between shutdown and operating states. This type of control of the para-hydrogen content in the recycle hydrogen can help control the para-hydrogen content of the hydrogen supplied to the feed inlet of liquefaction unit 2 in situations where recycle hydrogen constitutes all of the hydrogen supplied to liquefaction unit 2, when there is no hydrogen feed 15 available from hydrogen production system 20 or the hydrogen feed flow rate from hydrogen production system 20 is so low that recycle hydrogen constitutes a substantial portion of the total hydrogen supplied to the liquefaction unit (e.g., at least 30% of the hydrogen is recycle hydrogen, at least 50% of the hydrogen in the hydrogen feed is recycle hydrogen, 50% to 100% of the hydrogen supplied to liquefaction unit 2 as hydrogen feed 15 is recycle hydrogen, etc.). An example of a very low flow rate of hydrogen feed 15 would be no feed at all or a feed so low that the heat load of hydrogen feed 15 is below a preselected minimum threshold required by the liquefaction process refrigeration system to keep the refrigeration machinery operating within its predetermined temperature constraints.

[0056] Hydrogen recirculation does not occur all the time. Instead, hydrogen recirculation may be provided in response to a determination that the hydrogen feed 15 is at or below a preselected hydrogen feed rate, or is expected to be at or below a preselected hydrogen feed rate, for at least a preselected low hydrogen feed period. In response to detection of such a condition, hydrogen recirculation may be initiated or activated. Recycled hydrogen may initially be provided via the long recirculation loop LRP through use of hydrogen stored in storage 4, and then may be provided via the short recirculation loop SRP for recirculation of the hydrogen output from liquefaction unit 2, such that such hydrogen avoids being fed to storage 4 and instead is recycled directly back to the feed inlet of liquefaction unit 2. In other embodiments, recycled hydrogen may always be provided via the short recirculation loop SRP or always via the long recirculation loop LRP (e.g., there may be only the short recirculation loop SRP or the long recirculation loop LRP, without switching use between the loops). In yet other embodiments, recycled hydrogen may be initially provided via the short recirculation loop SRP and / or the long recirculation loop LRP (e.g., a combination of stored hydrogen from storage and liquid hydrogen output from a liquefaction unit that is recycled instead of sent to storage 4), and then provided via the short recirculation loop SRP.

[0057] After the hydrogen feed 15 provided from the hydrogen production system 20 is detected to be at or above the preselected hydrogen feed rate, or expected to be at or above the preselected hydrogen feed rate, for a preselected low hydrogen feed period, hydrogen recirculation may be stopped or delayed until the hydrogen feed rate provided from the hydrogen production system 20 is at or above the preselected hydrogen feed rate. This switching of operation between hydrogen recirculation and non-recirculation may be provided repeatedly over the course of multiple different operating cycles when a low feed rate below a predetermined minimum threshold required for operation of the liquefaction unit 2 may be detected as a result of changing weather conditions or other conditions that may affect hydrogen production at the hydrogen production system 20 positioned to replenish the hydrogen feed 15 to the liquefaction unit 2.

[0058] Hydrogen recirculation to compensate for low hydrogen feed flow rates from hydrogen production system 20 can be dynamically adjusted to compensate for the low feed flow rate. For example, if there is no hydrogen provided by hydrogen production system 20, hydrogen recirculation can be provided at a higher capacity to provide enough hydrogen to the inlet of liquefaction unit 2 to allow the unit to operate at a preselected minimum operating capacity without having to shut down. If hydrogen feed 15b is present but is very low and below a preselected minimum threshold, the amount of hydrogen recirculated can be varied to provide a hydrogen makeup such that the hydrogen feed provided to liquefaction unit inlet 15b is at or above a preselected minimum threshold.

[0059] Figures 1-6 illustrate different exemplary implementations of different apparatus for providing hydrogen recirculation. Process embodiments for hydrogen recirculation can also be understood from these figures. The first exemplary embodiment of Figures 1-3 illustrates an exemplary recirculation process that may be provided in situations where the liquefaction unit 2 can utilize an open-loop cooling system for the liquefaction operation. The second exemplary embodiment of Figures 4-6 illustrates an exemplary recirculation process that may be provided in situations where the liquefaction unit 2 can utilize a closed-loop cooling system for the liquefaction operation.

[0060] The hydrogen feed 15 supplied to the liquefaction unit 2 can be at a preselected feed pressure (e.g., greater than 100 kPa to 4000 kPa or other suitable feed pressure) and a preselected feed temperature (e.g., 0°C to 100°C, a temperature from ambient to less than 65°C, a temperature from 0°C to 65°C, or other suitable temperature). The para-hydrogen content of the hydrogen feed can also be within a preselected para-hydrogen content range (e.g., a para-hydrogen content of 20 mol% to 30 mol%).

[0061] The liquid hydrogen output from liquefaction unit 2 may have a preselected liquid hydrogen output pressure (e.g., a pressure of 200 kPa, a pressure between 200 kPa and greater than 500 kPa, a pressure between 350 kPa and 425 kPa, or other suitable pressure) and a preselected liquid hydrogen output temperature (e.g., a temperature between −230° C. and −250° C., cryogenic temperatures, etc.). For example, the hydrogen output pressure may be the inlet feed pressure of hydrogen feed 15 minus the pressure drop across liquefaction unit 2. The para-hydrogen content of the liquid hydrogen output from liquefaction unit 2 may also be within a preselected para-hydrogen content range (e.g., a para-hydrogen content of 80 mol% to 100 mol%, a para-hydrogen content of 95 mol% to 100 mol%, etc.).

[0062] 1-3, the apparatus 1 for hydrogen recirculation can be configured to recirculate hydrogen output from the liquefaction unit 2 as at least one stream of liquid hydrogen to a feed inlet of the liquefaction unit 2 via a first recirculation conduit arrangement and / or a second recirculation conduit arrangement. The first recirculation conduit arrangement can be a short recirculation loop SRP or a long recirculation loop LRP, and the second recirculation conduit arrangement can be another loop (e.g., when the first recirculation conduit arrangement is a short recirculation loop SRP, the second recirculation conduit arrangement can be a long recirculation loop LRP, and when the first recirculation conduit arrangement is a long recirculation loop LRP, the second recirculation conduit arrangement can be a short recirculation loop SRP).

[0063] When the hydrogen feed 15 supplied to the liquefaction unit 2 is equal to or greater than a preselected feed flow rate, the liquid hydrogen output by the liquefaction unit 2 can be fed to storage 4 for holding in one or more liquid hydrogen storage tanks. The liquid hydrogen supplied thereto may be held at a preselected storage pressure (e.g., a pressure of 100 kPa to 150 kPa, or other suitable pressure). A liquid hydrogen storage feed conduit 3a can be connected between storage 4 and the liquefaction unit 2 to route the liquid hydrogen to storage 4 for storage in one or more storage tanks. The liquid hydrogen held in storage 4 can be fed to one or more trailers for transport to customers via truck, railcar, or other type of vehicle, or to another process element of an industrial facility elsewhere for use of the hydrogen. As noted above, the liquid hydrogen in storage 4 can have a relatively high para-hydrogen content, at least 80 mol% or at least 95 mol%.

[0064] During operation, hydrogen feed 15 may vary significantly due to changes in production conditions at hydrogen production system 20 (e.g., changes in weather conditions affecting the available power for water electrolysis). Such changes may cause hydrogen feed 15 provided by hydrogen acid system 20 to be significantly reduced or no longer provided. In response to detecting that the hydrogen feed is not being provided or that the hydrogen feed is below a preselected threshold (e.g., a preselected volumetric flow rate defining a threshold for activation of hydrogen recirculation, a preselected mass flow rate defining a threshold for activation of hydrogen recirculation, etc.), at least a portion of the liquid hydrogen output from liquefaction unit 2 may be recirculated. Recirculation may occur through the use of a first recirculation loop and / or a second recirculation loop (e.g., a short recirculation loop SRP and / or a long recirculation loop LRP).

[0065] For example, a short recirculation loop SRP can be provided for routing at least a portion of the liquid hydrogen output from the liquefaction unit 2 back to the feed conduit for feeding hydrogen to supply the hydrogen to the feed inlet of the liquefaction unit 2. The short recirculation loop can include a recirculation loop conduit heater 5 positioned to heat the liquid hydrogen output from the liquefaction unit to vaporize the hydrogen to a gaseous state, and a recirculation loop conduit heater feed conduit 5a connected between the liquefaction unit 2 and the recirculation loop conduit heater 5. The heater 5 can, in some embodiments, be an ambient air vaporizer, an ambient air heat exchanger, a heat exchanger utilizing water (e.g., ambient temperature water, heated water, etc.) as a heating medium, or other suitable heat exchanger utilizing a heating medium to heat the liquid hydrogen and vaporize the hydrogen, outputting a vaporized hydrogen stream 5b from the heater that can be routed to a conversion unit 11 including at least one para-to-ortho-hydrogen converter for adjusting the ortho- and para-hydrogen content of the recycled hydrogen to about 25 mol% para-hydrogen content.

[0066] For example, heater 5 may be in fluid communication with compressed feed conduit 7b of a recirculating hydrogen conduit arrangement for apparatus 1 to supply vaporized hydrogen to at least one compressor (e.g., first compressor C1, second compressor C2, and / or third compressor C3) of a compression system (CS). Compression system 9 may compress hydrogen to a higher pressure to supply to a feed inlet of liquefaction unit 2 and to facilitate passage through hydrogen conversion unit 11. Compression system 9 may output hydrogen gas to supply the gas to at least one para-hydrogen to ortho-hydrogen conversion device of conversion unit 11 via conversion unit feed conduit 9a positioned between compression system 9 and conversion unit 11. Conversion unit 11 can process hydrogen gas to convert para-hydrogen to ortho-hydrogen so that the hydrogen gas output from conversion unit 11 has a para-hydrogen content of 25 mol% or less or 30 mol% or less (e.g., 20 mol% to 30 mol% para-hydrogen and 80 mol% to 70 mol% ortho-hydrogen). The hydrogen gas with the altered para-hydrogen content can be output from conversion unit 11 and supplied to a feed conduit, through which hydrogen feed 15 can be supplied to the feed inlet of the liquefaction unit. Conversion unit supply conduit 11a is connected between liquefaction unit 2 and conversion unit 11 and supplies hydrogen output from the conversion unit to the liquefaction unit.

[0067] In some embodiments, conversion unit make-up conduit 11a can supply hydrogen output from conversion unit 11 to a feed conduit through which hydrogen feed 15 can be mixed in-line with the hydrogen feed and supplied to the inlet of liquefaction unit 2 along with hydrogen feed 15 that can be output from hydrogen production system 20. Alternatively, conversion unit make-up conduit 11a can pass hydrogen to the feed inlet of the liquefaction unit and mix it with the hydrogen from hydrogen production system 20 (if provided) at the feed inlet region of liquefaction unit 2.

[0068] In addition to or instead of using a short recirculation loop SRP, a long recirculation loop LRP can be provided for routing at least a portion of the liquid hydrogen output from the liquefaction unit 2 back to the feed conduit for feeding hydrogen to supply hydrogen back to the feed inlet of the liquefaction unit 2. The long recirculation loop LRP can include at least one storage tank of the storage 4 and supply hydrogen stored in the tank to the heater 7 via a storage tank recirculation conduit 4c positioned between the hydrogen storage 4 and the heater 7.

[0069] The hydrogen output from storage 4 may include vapor that may collect in the storage tank, which may be output from vapor conduit 4a connected between storage tank recirculation conduit 4c and the storage tank of hydrogen storage 4. The hydrogen output from storage may also include liquid hydrogen that may be output from liquid hydrogen conduit 4b, which may be connected between the storage unit and vaporizer 6 (VP), which may be positioned to vaporize the liquid hydrogen to provide gaseous hydrogen to storage tank recirculation conduit 4c via vaporizer output conduit 4d connected between vaporizer 6 and storage tank recirculation conduit 4c.

[0070] Recirculation loop conduit heater 7 can be positioned to further heat the hydrogen output from storage 4 so that it becomes gaseous hydrogen for supply to at least one compressor of compression system 9 via recirculation loop conduit heater output conduit 7a, which is connected between compression feed conduit 7b and recirculation loop conduit heater 7. Heater 7 can, in some embodiments, be an ambient air vaporizer, an ambient air heat exchanger, a heat exchanger utilizing water (e.g., ambient temperature water, heated water, etc.) as a heating medium, or other suitable heat exchanger that utilizes a heating medium to heat liquid hydrogen to vaporize the hydrogen and output a gaseous hydrogen stream from heater 7 that can be routed to conversion unit 11, which includes at least one para-to-ortho-hydrogen converter, for adjusting the ortho- and para-hydrogen content of the recirculated hydrogen to about 25 mol% para-hydrogen content.

[0071] The compression system 9 can receive hydrogen from the heater 5 of the short recycle loop SRP and / or the heater 7 of the long recycle loop LRP, compress the hydrogen, and output the hydrogen to the conversion unit 11 (CVRT) via a conversion unit feed conduit 9a positioned between the compression system 9 and the conversion unit 11. The conversion unit 11 can process hydrogen gas from the long recycle loop LRP and / or a combination of hydrogen gas from the short recycle loop SRP and the long recycle loop LRP to convert para-hydrogen to ortho-hydrogen such that the hydrogen gas output from the conversion unit 11 has a para-hydrogen content of 25 mol% or less or 30 mol% or less (e.g., 20 mol% to 30 mol% para-hydrogen and 80 mol% to 70 mol% ortho-hydrogen). The hydrogen gas with the modified para-hydrogen content can be output from the conversion unit 11 and supplied to a feed conduit through which hydrogen feed 15 can be supplied to the feed inlet of the liquefaction unit. The conversion unit supply conduit 11a is connected between the liquefaction unit 2 and the conversion unit 11 and supplies hydrogen output from the conversion unit to the liquefaction unit.

[0072] In some implementations, the recycled hydrogen may be initially provided through at least one storage tank of the hydrogen storage unit 4 and then provided entirely through the short recirculation loop SRP, such that the recycled hydrogen is avoided from being supplied to the storage unit 4 during such recirculation after the initial provision of hydrogen from the storage unit 4 has occurred. In other implementations, the recycled hydrogen may be initially provided through at least one storage tank of the hydrogen storage unit 4 and via routing of the liquid hydrogen output from the liquefaction unit to the short recirculation loop SRP. After a sufficient amount of hydrogen has been provided for recirculation, the hydrogen may then be provided entirely through the short recirculation loop SRP, such that the recycled hydrogen is avoided from being supplied to the storage unit 4 during such recirculation after the initial provision of hydrogen from the storage unit 4 has occurred. In still other implementations, the short recirculation loop SRP may not be provided, and only the long recirculation loop LRP may be utilized for hydrogen recirculation.

[0073] In embodiments that may utilize both a short recirculation loop SRP and a long recirculation loop LRP, heater 5 of the short recirculation loop SRP can be considered a first recirculation loop heater for the first recirculation loop, and heater 7 of the long recirculation loop LRP can be considered a second heater for the second recirculation loop. Alternatively, heater 7 of the long recirculation loop LRP can be considered a first heater for the first recirculation loop, and heater 5 of the short recirculation loop SRP can be considered a second recirculation loop heater for the second recirculation loop. Each heater helps heat the hydrogen output from liquefaction unit 2 (e.g., immediately after output or after the hydrogen is stored in hydrogen storage 4) so ​​that the gaseous hydrogen can be supplied to conversion unit 11 for hydrogen recirculation.

[0074] Embodiments of the apparatus 1 may be configured for use with an open-loop refrigeration system OLP of the liquefaction unit 2. The open-loop refrigeration system OLP may include a liquefaction unit that outputs at least one first hydrogen stream 23, which may be at a lower pressure, for supply to the compression system 9 for compression by at least one low-pressure compressor of the compression system 9. The liquefaction unit 2 may also output one or more second hydrogen streams 25, each of which may be at a higher pressure than the pressure of the first hydrogen stream 23, for supply to the compression system 9 for compression and subsequent supply back to the liquefaction unit 9 for use in cooling generated during liquefaction. A compression system 9 for the refrigeration system may be utilized to facilitate an open-loop refrigeration scheme in which hydrogen is used as a refrigerant. Compressed hydrogen used as a refrigerant in the open-loop refrigeration system OLP may be output from the compression system 9 and supplied as a refrigerant to the liquefaction unit heat exchanger via at least one refrigerant feed conduit 9b connected between the compression system 9 and the refrigeration system of the liquefaction unit 2.

[0075] At least one storage tank of the hydrogen storage unit 4 may also be in fluid communication with the cooling system of the liquefaction unit 2 to provide hydrogen as a refrigerant. For example, a hydrogen refrigerant feed conduit 21 may be connected between the storage tank of the hydrogen storage unit 4 and the cooling system of the liquefaction unit 2 to supply hydrogen from the hydrogen storage unit 4 to the cooling system of the liquefaction unit 2.

[0076] Apparatus 1 may also be configured to facilitate venting via at least one exhaust conduit VT. For example, in situations where the hydrogen being output from liquefaction unit 2 fails to meet a preselected hydrogen content specification, the hydrogen may be vented. Such venting may, in some embodiments, occur downstream of at least one heater (e.g., heater 5 of the short recirculation loop SRP, heater 7 of the long recirculation loop LRP, ambient air heater of the exhaust conduit, etc.) so that the vented hydrogen is warmed to a suitable exhaust temperature for venting to the external atmosphere.

[0077] In some embodiments, the liquefaction unit 2 may be configured to output two or more streams of liquid hydrogen. For example, the liquefaction unit 2 may output a first stream of liquid hydrogen 2a and a second stream of liquid hydrogen 2b. These streams of liquid hydrogen may, in some embodiments, be mixed together via a mixing device (e.g., an in-line mixer, a mixing vessel, etc.) for feeding into the short recirculation loop SRP or into the hydrogen storage 4.

[0078] Some embodiments may utilize a phase separation system PS to provide liquid hydrogen to storage 4 and / or the short recycle loop SRP, and to return hydrogen gas that may be output from liquefaction unit 2 to liquefaction unit 2 for use as a refrigerant in a refrigeration system and / or to the liquefaction unit for liquefaction. For example, phase separation system PS may output hydrogen gas stream 3c for provision to the liquefaction unit via a hydrogen gas return conduit connected between phase separation system PS and liquefaction unit 2. In some embodiments, a portion of the liquid hydrogen output from phase separation system PS for supply to hydrogen storage 4 may be returned to phase separation system PS for use as a refrigerant or otherwise to support the phase separation process via phase separation conduit 3d connected between the phase separation system and liquid hydrogen storage feed conduit 3a.

[0079] The phase separation system PS may, in some embodiments, be positioned to facilitate Joule-Thomson cooling of the liquid hydrogen via reduced pressure. The partially flashed, cool vapor (e.g., hydrogen gas) that may be formed may be output, for example, as hydrogen gas stream 3c and sent to an open-loop refrigeration system. Alternatively, the hydrogen vapor may be routed from the phase separation system to compression system 9 as a low-pressure hydrogen vapor stream LPV for recirculation via compression system 9 back to the feed inlet of liquefaction unit 2 or the refrigeration system of liquefaction unit 2.

[0080] In some embodiments, at least one trailer 8 can be connected to the long recirculation loop LRP. The trailer 8 can be positioned to receive hydrogen from storage for replenishment of hydrogen at another location. The trailer (TRLR) can alternatively contain hydrogen gas when make-up hydrogen is needed and supply hydrogen to the recirculation loop when there is insufficient liquid hydrogen replenishment in the hydrogen storage 4, providing recirculation to the liquefaction unit 2 and providing sufficient hydrogen make-up to compensate for a reduction in the flow of hydrogen feed 15 that could trigger hydrogen recirculation. For example, the trailer 8 can be fluidly connected to the short recirculation loop SRP or the long recirculation loop LRP to provide hydrogen to the conversion unit 11 to adjust the para-hydrogen and ortho-hydrogen content of the hydrogen recirculated to the feed inlet of the liquefaction unit 2.

[0081] 2 illustrates an exemplary implementation of the apparatus 1 shown in FIG. 1. Compression system 9 may include a first compressor C1 and a second compressor C2, and hydrogen gas output from liquefaction unit 2 as part of an open-loop refrigeration system may include a first hydrogen stream 23, which may be at a lower pressure, in preparation for compression by first compressor C1 and subsequent delivery to compression system 9 for further compression via second compressor C2 of compression system 9. Liquefaction unit 2 may output a second hydrogen stream 25, which may be at a higher pressure than the pressure of first hydrogen stream 23, which may be delivered to second compressor C2 of compression system 9, where it may be compressed and subsequently delivered to the liquefaction unit for use in cooling generated during liquefaction and / or back to conversion unit 11 for recycle (if use of a recycle loop is employed due to the low level of hydrogen feed provided to liquefaction unit 2).

[0082] 2, the apparatus 1 for hydrogen recirculation may not utilize a phase separation system PS. The first and second streams of liquid hydrogen 2a, 2b may be output from the liquefaction unit 2 and then combined and fed to the hydrogen storage 4 via the liquid hydrogen storage feed conduit 3a. In response to a decrease in the hydrogen feed flow rate, at least a portion of this liquid hydrogen may also be routed to the short recirculation loop via a recirculation loop conduit heater feed conduit that may be connected to the liquid hydrogen storage feed conduit 3a and / or connected between the liquefaction unit 2 and the recirculation loop conduit heater feed conduit 5a.

[0083] In other configurations, a short recirculation loop SRP may not be provided. Instead, only a long recirculation loop LRP may be utilized. In such an embodiment, liquid hydrogen from at least one storage tank of hydrogen storage 4 may output hydrogen for supplying the conversion unit via the long recirculation loop LRP conduit arrangement. Hydrogen from at least one trailer 8 may also be utilized to help provide a hydrogen stream to the liquefaction unit during periods when the hydrogen feed provided by hydrogen production system 20 is too low or absent, thereby recycling hydrogen to support the operation of the liquefaction unit.

[0084] 3, the compression system 9 may include a first compressor C1 as the low-pressure compressor, a second compressor C2 as the intermediate-pressure compressor, and a third compressor C3 as the high-pressure compressor. Such a configuration may be utilized in a high-pressure liquefaction unit 2 that can utilize the high-pressure, low-pressure, and intermediate-pressure refrigeration elements of its refrigeration system for liquefying hydrogen. The liquefaction unit 2 may output a first hydrogen stream 23, which may be at a lower pressure, in preparation for compression by the first compressor C1 and subsequent feeding into the compression system 9 for further compression via the second compressor C2 and third compressor C3 of the compression system 9. The liquefaction unit 2 may output a second hydrogen stream 25, which may be at an intermediate pressure higher than that of the first hydrogen stream 23, and this stream may be fed to the second compressor C2 of the compression system 9, where it is compressed, and then compressed by the third compressor C3, and then fed to the liquefaction unit for use in the cooling generated during liquefaction and / or back to the conversion unit 11 for recycle (if the use of a recycle loop is utilized due to the low level of hydrogen feed provided to the liquefaction unit 2). Another second hydrogen stream 25 may be output from the refrigeration system of the liquefaction unit 2, which may be at a high pressure higher than that of the first hydrogen stream 23 and higher than the intermediate pressure of the other second hydrogen stream 25, and this stream may be fed to the third compressor C3 of the compression system 9, where it is compressed, and then fed to the liquefaction unit for use in the cooling generated during liquefaction and / or back to the conversion unit 11 for recycle (if the use of a recycle loop is utilized due to the low level of hydrogen feed provided to the liquefaction unit 2).

[0085] The phase separation system PS may include a phase separator PH and a subcooler 3 (SC). In other embodiments, the phase separation system may include only a single phase separator PH or only a subcooler 3 without an upstream phase separator.

[0086] For example, the liquefaction unit may output a liquid hydrogen stream that also contains hydrogen gas (e.g., between 3 volume percent (vol%) hydrogen gas and 10 vol% hydrogen gas, between 5 vol% hydrogen gas and 25 vol% hydrogen gas, between greater than 0 vol% and 40 vol% hydrogen gas, etc.). The liquid hydrogen stream that also contains hydrogen gas can be fed to a phase separation system PS, such that it passes through a phase separator PH, where a substantial amount of hydrogen gas is separated from the liquid hydrogen and returned to the liquefaction unit 2 via a vapor return conduit 2v connected between the liquefaction unit 2 and the phase separator PH. This hydrogen vapor returns to the liquefaction unit as a low-pressure hydrogen vapor stream LPV and may be recycled back to the feed inlet of the liquefaction unit 2 or fed to the liquefaction unit's cooling system, for example, by feeding the stream to a compression system 9 and routing it to the inlet of the liquefaction unit 2. Such routing may occur when the apparatus has an insufficient hydrogen feed from the hydrogen production system, and may also occur while the hydrogen feed from the hydrogen production system 20 is at or above the preselected feed flow rate for normal operation of the liquefaction unit without recirculating hydrogen.

[0087] Predominantly liquid hydrogen (e.g., at least 95 vol% liquid hydrogen) or completely liquid hydrogen can be output from the phase separator PH via a phase separator output conduit 3b connected between the phase separator PH and the subcooler 3. Additional hydrogen gas may be output from the subcooler 3 as a hydrogen gas stream 3c and provided to the liquefaction unit via a hydrogen gas return conduit connected between the subcooler 3 and the liquefaction unit 2. As described above, such a hydrogen gas stream may be fed to the liquefaction unit's cooling system or routed back to the liquefaction unit as a low-pressure hydrogen vapor stream LPV and recycled back to the feed inlet of the liquefaction unit 2 (e.g., by being fed to the compression system 9 and subsequently to the feed inlet of the liquefaction unit 2 or the cooling system of the liquefaction unit 2). Such routing may occur, for example, if the apparatus has an insufficient hydrogen feed from the hydrogen generation system. Such routing may also occur when the apparatus has a sufficient hydrogen feed from the hydrogen production system 20 that is equal to or exceeds a preselected feed flow rate for normal operation of the liquefaction unit without hydrogen recirculation.

[0088] The cooled liquid hydrogen may be output from the subcooler 3 and supplied to the hydrogen storage 4 and / or the short recirculation loop SRP via a subcooler output conduit connected between the subcooler 3 and the liquid hydrogen storage feed conduit 3a. A portion of the liquid hydrogen passing through the hydrogen storage feed conduit 3a may be returned to the subcooler 3 via a phase separation conduit 3d connected between the phase separation system and the liquid hydrogen storage feed conduit 3a to facilitate subcooling of the hydrogen.

[0089] As can be seen from FIGS. 4-6 , embodiments of the apparatus 1 for hydrogen recirculation can also be used in conjunction with a liquefaction unit 2 that may utilize a closed-loop refrigeration system CLP. Such a closed-loop refrigeration system CLP may have a dedicated closed-loop compressor 31 (CP) to help drive the flow of refrigerant in a closed-loop configuration for liquefying hydrogen. In such a configuration, the liquefaction unit 2 may not receive hydrogen from the hydrogen storage 4 and / or other compressors in a recirculation conduit through which hydrogen may pass as refrigerant for the refrigeration system. Instead, the refrigerant utilized for the liquefaction unit's refrigeration system may be provided in a closed-loop configuration.

[0090] In such a closed-loop refrigeration system environment, the recycle conduit arrangement for hydrogen recirculation may utilize different compression system arrangements. For example, there may be a compressor 41 positioned upstream of conversion unit 11 to compress hydrogen for supply to conversion unit 11 and subsequent recycle to the feed inlet of liquefaction unit 2. As another example, there may be a compressor 43 positioned downstream of heater 7 through which hydrogen from at least one storage tank of hydrogen storage 4 passes, is heated, and recirculated via conversion unit 11 to the feed inlet of liquefaction unit 2. In embodiments that may utilize multiple such compressors, compressor 43 may be a low-pressure compressor LC, and an additional compressor 41 downstream of this compressor may be a high-pressure compressor (HC) that can further compress hydrogen to a second-higher pressure (e.g., high or intermediate pressure) for recirculation.

[0091] In yet another arrangement, the feed conduit for the hydrogen feed 15 that replenishes the liquefaction unit 2 may include a feed compressor. In such a configuration, excess capacity in the feed compressor that may be present due to a reduced hydrogen feed from the hydrogen production system 20 may be utilized to help drive the flow of hydrogen that is recycled through the short recirculation loop SRP and / or the long recirculation loop LRP.

[0092] 5 , a low-pressure compressor LC may be utilized downstream of the heater 7 to receive hydrogen from hydrogen storage 4 and / or at least one trailer 8, supply hydrogen to the conversion unit 11, and recycle hydrogen to the liquefaction unit 2. A recirculation loop conduit heater output conduit 7a may be connected between the recirculation loop conduit heater 7 and the compressor 43 to supply hydrogen to the compressor for output to supply the conversion unit 11 via a conversion unit feed conduit 9a positioned between the compressor 43 and the conversion unit 11.

[0093] Hydrogen that can be recycled through the short recirculation loop SRP can be output from the heater 5 of the conduit arrangement for that loop and supplied to the conversion unit 11 via a conduit connection between the heater 5 and the conversion unit feed conduit 9a so that the vaporized hydrogen stream 5b output from the heater 5 can be routed to the conversion unit 11.

[0094] In other exemplary implementations, such as that of Figure 6, the high-pressure compressor HC may be positioned to receive hydrogen from the short recirculation loop SRP and / or the long recirculation loop LRP via a compressed feed conduit 7b that may be connected between this compressor 41 and the heater 5 of the short recirculation loop SRP and / or the heater 7 of the long recirculation loop LRP. In such a configuration, the high-pressure compressor HC may be positioned as a compressor system 9 similar to the positioning of the compression system 9 in the open-loop refrigeration embodiment of Figure 1 (but without receiving hydrogen streams from the refrigeration system of the liquefaction unit 2 and compressing these streams).

[0095] As described above, different exemplary embodiments and implementations of apparatus 1 may be configured to provide hydrogen recirculation in response to the hydrogen feed 15 provided to liquefaction unit 2 for liquefaction of hydrogen decreasing below a preselected feed flow rate (e.g., a preselected volumetric flow rate defining a threshold for activation of hydrogen recirculation, a preselected mass flow rate defining a threshold for activation of hydrogen recirculation, etc.). The hydrogen recirculation may be operated to help avoid shutdown of liquefaction unit 2 in response to a low feed rate condition, thereby avoiding production delays associated with liquefaction unit shutdown and subsequent startup, as well as equipment degradation that may result from such operation involving cycling between operational and shutdown operating conditions.

[0096] As shown in FIGS. 1-6 , a controller CTRL may be provided to detect such conditions for operation of the hydrogen recycle system via one or more sensors that may be positioned to monitor or measure the flow of the hydrogen feed 15 at a location 15 a upstream of where the recycle stream may be supplied to the inlet of the liquefaction unit 2 via the conversion unit make-up conduit 11 a and / or the flow of the hydrogen feed at the inlet 15 b of the liquefaction unit 2. The one or more sensors may be, for example, flow sensors and / or pressure sensors. The controller CTRL may be communicatively coupled to the sensors and receive data from the sensors to determine whether the hydrogen feed is below a preselected threshold for operation of the hydrogen recycle system. The controller CTRL may also or alternatively receive data from one or more sensors or other elements of the hydrogen production system 20 that may provide inputs indicating when the hydrogen feed may be reduced to a preselected threshold for operation of the hydrogen recycle system.

[0097] The controller CTRL may also be communicatively connected to one or more sensors positioned to monitor or measure the flow of liquid hydrogen output from the liquefaction unit 2 for use in controlling valve V for actuation of hydrogen recirculation to the inlet of the liquefaction unit. The controller may utilize such flow data to communicate with one or more recirculation loop valves to recirculate an appropriate portion of the liquid hydrogen to compensate for a lack of sufficient hydrogen feed provided to the hydrogen production system 20. Valve V may be dynamically adjusted to compensate for changing hydrogen feed 15 conditions such that the portion of the recirculated water may be adjusted from no hydrogen recirculation to full recirculation of the output hydrogen to compensate for the detected flow rate of the hydrogen feed 15 provided by the hydrogen production system 20.

[0098] The controller CTRL may be a computing device including a processor and at least one transceiver connected to non-transitory memory. The controller CTRL may also be communicatively connected to the valves to actuate the valve adjustments for hydrogen recirculation.

[0099] The controller CTRL may be configured to respond to a determination that the hydrogen feed is too low (e.g., has decreased below a preselected feed flow rate, has decreased below a preselected feed flow rate and may be at that low flow rate for at least a preselected hydrogen recirculation period, etc.) by communicating with different valves V to adjust the flow of hydrogen output from the liquefaction unit 2 through the short recirculation loop SRP and / or the long recirculation path LRP. Such configuration of the controller CTRL may be implemented via automated process control logic defined in code in the non-transitory memory of the controller that may be executed by the processor of the controller.

[0100] For example, in some embodiments, the controller CTRL can communicate with a valve V in the liquid hydrogen storage feed conduit 3a to close the valve V and open a valve V in the recirculation loop conduit heater feed conduit 5a connected between the liquefaction unit 2 and the recirculation loop conduit heater 5 to activate the recirculation of hydrogen output from the liquefaction unit to the conversion unit 11 and recirculate hydrogen with reduced para-hydrogen content back to the feed inlet of the liquefaction unit. The controller CTRL can also communicate with a valve V in the storage tank recirculation conduit 4c positioned between the hydrogen storage 4 and the heater 7 to open the valve V to refuel hydrogen from the hydrogen storage 4 to the conversion unit 11 and recirculate hydrogen with reduced para-hydrogen content back to the feed inlet for the liquefaction unit. The controller CTRL can also communicate with a valve V in the conversion unit refueling conduit 11a to open the valve V to facilitate the supply of hydrogen to the feed inlet of the liquefaction unit for recirculation of the hydrogen after its para-hydrogen content has been adjusted through the conversion unit 11. After a sufficient amount of hydrogen has been provided from the storage tank 4 to compensate for the reduced amount of hydrogen received from the hydrogen production system 20, the controller CTRL can communicate with the valve V of the storage tank recirculation conduit 4c to close that valve V so that the short recirculation loop SRP can then be used solely for hydrogen recirculation until the hydrogen feed from the hydrogen production system 20 increases to a desired level.

[0101] In other arrangements where a short recirculation loop SRP may not be provided, the controller CTRL may communicate with a valve V in a storage tank recirculation conduit 4c positioned between the hydrogen storage 4 and the heater 7 to open the valve V to replenish hydrogen from the hydrogen storage 4 to the conversion unit 11 and recycle hydrogen with reduced para-hydrogen content back to the feed inlet for the liquefaction unit. The controller CTRL may also communicate with a valve V in a conversion unit replenishment conduit 11a to open the valve V to facilitate supplying hydrogen to the feed inlet of the liquefaction unit for recirculation after the para-hydrogen content of the hydrogen has been adjusted through the conversion unit 11. The controller CTRL may communicate with a valve V in the storage tank recirculation conduit 4c to close the valve V, and similarly, with a valve V in the conversion unit replenishment conduit 11a to close the valve V after the feed of hydrogen from the hydrogen production system 20 has increased to a desired level to facilitate discontinuing hydrogen recirculation.

[0102] In yet another arrangement where a long recirculation loop LRP may not be utilized, the controller CTRL may communicate with the valve in the liquid hydrogen storage feed conduit 3a to close that valve V and open the valve in the recirculation loop conduit heater feed conduit 5a connected between the liquefaction unit 2 and the recirculation loop conduit heater 5 to activate the recirculation of hydrogen output from the liquefaction unit to the conversion unit 11 and recirculate hydrogen with reduced para-hydrogen content back to the feed inlet of the liquefaction unit. The controller CTRL may communicate with the valve in the recirculation loop conduit heater feed conduit 5a to close that valve V and similarly communicate with the valve in the conversion unit make-up conduit 11a to close that valve V after the hydrogen feed from the hydrogen production system 20 has increased to a desired level to facilitate discontinuing the hydrogen recirculation.

[0103] The controller CTRL communicates with the different valves to adjust their positions to somewhat open and / or closed positions to compensate for the flow rate of the hydrogen feed 15 being provided by the hydrogen production system 20 and how that flow rate compares to a preselected minimum threshold flow rate. In situations where there is no hydrogen feed, the valve V for recirculating hydrogen can be fully open, for example, to provide a hydrogen recirculation flow to compensate for the lack of hydrogen feed from the hydrogen production system 20. In situations where there is a hydrogen feed but it is significantly below the preselected minimum threshold flow rate, the valve for recirculating hydrogen need not be in a fully open position but may be partially open (but not as open as when no hydrogen feed is being provided) to provide a hydrogen recirculation flow that can provide a compensating hydrogen flow to compensate for the deviation from the preselected minimum threshold flow rate. In situations where the hydrogen feed is only slightly below the preselected minimum threshold flow rate, the valve for recirculating hydrogen may be partially open to a lesser extent to provide a hydrogen recirculation flow that can provide compensation for this slight deviation from the preselected minimum threshold flow rate.

[0104] It has also been surprisingly discovered that the utilization of a short recirculation loop SRP and a long recirculation loop LRP can provide several other advantages. For example, during start-up of a liquefaction unit, which is initially at ambient temperature, the long recirculation loop LRP can provide pure hydrogen for use in cooling down the liquefaction unit equipment, and the short recirculation loop SRP can be utilized to help speed up the cooling of the liquefaction equipment of liquefaction unit 2. This type of approach to cooling the liquefaction unit during start-up of liquefaction unit operation can allow such cooling to occur without or with minimal exhaust (e.g., due to the absence of impurities in the hydrogen utilized to facilitate cooling of liquefaction unit 2).

[0105] Embodiments of apparatus 1 may provide operational flexibility in response to turndown or other low hydrogen production conditions. For example, liquefaction unit 2 may be kept cryogenic through use of apparatus 1 to recirculate hydrogen through the long recirculation loop LRP and / or short recirculation loop SRP to avoid the need for liquefaction unit 2 to shut down. This type of operation can occur even when no hydrogen feed may be present, allowing the liquefaction unit to be rapidly transitioned to process hydrogen when hydrogen production through the hydrogen production system increases due to increased available power or other circumstances without significant delays in operation that could affect yield or production efficiency.

[0106] Embodiments may be configured to allow the liquefaction unit to utilize minimal or relatively low power when hydrogen recirculation is utilized. For example, reserve capacity in the refrigeration compressor may be utilized to assist in operation of the liquefaction unit during periods of low hydrogen feed from the production system 20, and liquid hydrogen may also be recompressed when flashed to near ambient pressure to help keep power consumption for the liquefaction operation low. This may occur while hydrogen recirculation may provide a heat load that can absorb cooling generated by operating the liquefaction unit refrigeration system to enable the liquefaction unit 2 to maintain cryogenic temperatures with low or no hydrogen feed from the hydrogen production system 20 (e.g., hydrogen feed from a hydrogen generation system (HGS) below a preselected minimum flow rate or a preselected minimum threshold flow rate).

[0107] 7, a process for hydrogen recycling is illustrated, and embodiments of the apparatus 1 can be implemented and operated to utilize embodiments of this process.

[0108] For example, in a first step S1, it may be determined that the feed of hydrogen from the hydrogen production system 20 is below a preselected threshold (e.g., a feed of hydrogen that is 30% of a preselected feed flow rate of hydrogen provided to the liquefaction unit, a feed of hydrogen that is 20% of a preselected feed flow rate of hydrogen provided to the liquefaction unit 2, etc.). This feed of hydrogen may be a feed of hydrogen sent to the liquefaction unit 2 to liquefy the hydrogen. The controller CTRL may make such determinations, for example, as discussed above. Such determinations may be based on sensor data or other data related to the production of hydrogen and the supply of that hydrogen to the liquefaction unit 2.

[0109] In a second step S2, the flow of liquid hydrogen output from the liquefaction unit 2 can be adjusted to recycle the hydrogen to the feed inlet of the liquefaction unit. The recirculation can be performed such that the hydrogen undergoes para-to-ortho-hydrogen conversion to reduce the para-hydrogen content of the recycled hydrogen, as discussed above. The recirculation can occur via a first recirculation loop and / or a second recirculation loop (e.g., using only the short recirculation loop SRP, using only the long recirculation loop LRP, utilizing both loops, etc.), as discussed above. The hydrogen recirculation can be operated and controlled so that the amount of recycled hydrogen provides a make-up hydrogen flow rate sufficient to compensate for deviations between the hydrogen feed flow provided by the hydrogen production system 20 and a preselected minimum threshold. For example, when the hydrogen flow rate from the hydrogen production system 20 may increase (but still be below the preselected minimum threshold), the hydrogen recirculation can be adjusted to compensate for such changes, as discussed above, by controlling one or more valves, compressor operation, or other parameters. Similarly, when the flow rate of hydrogen from hydrogen production system 20 may decrease (e.g., to a flow rate further below a preselected minimum threshold), hydrogen recirculation can be adjusted to compensate for such changes by controlling one or more valves, compressor operation, or other parameters, as discussed above.

[0110] In a third step S3, it may be determined that the hydrogen feed is above a preselected threshold, thereby disallowing further hydrogen recirculation. In response to such detection, hydrogen recirculation may be stopped. Examples of such cessation of hydrogen recirculation may be seen from above. A controller CTRL may be utilized to actuate such cessation of hydrogen recirculation, for example, as described above.

[0111] The process may then return to the first step S1 when the hydrogen feed may again decrease below a preselected threshold. In some embodiments where hydrogen production is powered by renewable power sources, such as solar and / or wind power, this process may occur multiple times per week or more frequently.

[0112] The storage 4 for liquid hydrogen may be positioned to receive hydrogen from multiple different liquefaction units 2 or from only a single unit. In embodiments where the storage 4 is capable of receiving liquid hydrogen from multiple different liquefaction units, the hydrogen stored therein may be provided for recycling hydrogen to one or more of the different liquefaction units in response to the feed of hydrogen supplied to the liquefaction unit decreasing to or below a preselected threshold.

[0113] Embodiments may provide operational flexibility in response to turndown or other low hydrogen production conditions. For example, embodiments of the present process may enable liquefaction unit 2 to be kept cryogenically low via hydrogen recirculation through the first recirculation loop and / or the second recirculation loop to avoid the need for liquefaction unit 2 to shut down. This type of operation can occur even when there may not be a hydrogen feed, allowing the liquefaction unit to be quickly transitioned to process hydrogen when hydrogen production through the hydrogen production system increases due to increased available power or other circumstances without significant delays in operation that could affect yield or production efficiency.

[0114] Embodiments of the present process may be implemented to allow liquefaction unit 2 to utilize minimal or relatively low power when hydrogen recirculation is occurring. For example, reserve capacity in the refrigeration compressor may be utilized to support liquefaction unit operation while hydrogen feed from the production system is low and hydrogen recirculation is occurring. This excess compression capacity may be utilized to assist in recompressing liquid hydrogen when it is flashed to near ambient pressure to help keep power consumption for the liquefaction operation low. This may occur while hydrogen recirculation may provide a heat load that can absorb the cooling generated by operating the liquefaction unit refrigeration system to enable liquefaction unit 2 to maintain cryogenic temperatures with low or no hydrogen feed from the hydrogen production system 20.

[0115] It should also be understood that modifications to embodiments of the apparatus 1 and process can be made to meet a particular set of criteria for different embodiments of the apparatus or process. For example, the placement of valves, sensors, piping, and other conduit elements (e.g., conduit connections, tubing, seals, valves, etc.) for interconnecting different units of the apparatus for fluid communication of fluid flow between the different elements can be arranged to meet a particular facility layout design that anticipates the available area of ​​the apparatus, the sized equipment of the apparatus, the preferred type of automated process control scheme and / or distributed control scheme, and other design considerations. The size or type of equipment can also be modified to meet a particular set of design criteria.

[0116] As yet another example, it is contemplated that particular features described either individually or as part of an embodiment can be combined with other individually described features or parts of other embodiments. Accordingly, elements and acts of various embodiments described herein can be combined to provide further embodiments. Thus, while certain exemplary embodiments of processes, apparatus, systems, and methods of making and using them have been shown and described above, it is to be clearly understood that the invention is not limited thereto and may be variously embodied and carried out within the scope of the following claims.

Claims

1. 1. A process for recycling hydrogen, comprising: providing a hydrogen feed to a liquefaction unit; the liquefaction unit liquefies the hydrogen and outputs liquid hydrogen, the liquid hydrogen having a para-hydrogen content of 80 mole percent (mol%) to 100 mol% para-hydrogen; in response to determining that the hydrogen feed has decreased below a preselected threshold, recirculating the liquid hydrogen to the feed of the liquefaction unit such that the liquid hydrogen is vaporized to a gaseous state and undergoes conversion of para-hydrogen to ortho-hydrogen, resulting in a para-hydrogen content of the recycled hydrogen recycled to the feed of the liquefaction unit of between 20 mol% para-hydrogen and 30 mol% para-hydrogen.

2. 10. The process of claim 1, wherein the hydrogen feed has a para-hydrogen content within a preselected para-hydrogen content range of 20 mole percent para-hydrogen to 30 mole percent para-hydrogen.

3. 2. The process of claim 1, including stopping the recirculation of the liquid hydrogen in response to determining that the hydrogen feed has increased above the preselected threshold.

4. The recirculation of the liquid hydrogen comprises: supplying hydrogen having a para-hydrogen content of between 80 mol% and 100 mol% stored in at least one storage tank to a conversion unit positioned to convert the para-hydrogen to ortho-hydrogen such that the para-hydrogen content of recycle hydrogen recycled to the feed of the liquefaction unit is between 20 mol% para-hydrogen and 30 mol% para-hydrogen; and / or 2. The process of claim 1, comprising: feeding liquid hydrogen output from the liquefaction unit to a heater in a recycle loop to vaporize the liquid hydrogen; and subsequently passing the vaporized hydrogen to the conversion unit positioned to convert the para-hydrogen to ortho-hydrogen such that the para-hydrogen content of the recycled hydrogen recycled to the feed of the liquefaction unit is between 20 mol% para-hydrogen and 30 mol% para-hydrogen.

5. supplying the liquid hydrogen output from a liquefier having a para-hydrogen content of 80 mole percent (mol%) to 100 mol% para-hydrogen to at least one storage tank of a hydrogen storage section in fluid communication with the liquefaction unit; The recirculation of the liquid hydrogen comprises: adjusting at least one valve to prevent the liquid hydrogen output from the liquefaction unit from passing through the at least one storage tank; 2. The process of claim 1, comprising: feeding liquid hydrogen output from the liquefaction unit to a heater in a recycle loop to vaporize the liquid hydrogen; and subsequently passing the vaporized hydrogen to the conversion unit positioned to convert the para-hydrogen to ortho-hydrogen such that the para-hydrogen content of the recycled hydrogen recycled to the feed of the liquefaction unit is between 20 mol% para-hydrogen and 30 mol% para-hydrogen.

6. supplying hydrogen stored in at least one storage tank to a conversion unit positioned to convert the para-hydrogen to ortho-hydrogen such that the para-hydrogen content of the recycled hydrogen recycled to the feed of the liquefaction unit is between 20 mol% para-hydrogen and 30 mol% para-hydrogen; 6. The process of claim 5, further comprising: ceasing the supply of the hydrogen stored in the at least one storage tank to the conversion unit after determining that sufficient hydrogen is being recycled to the liquefaction unit to compensate for the reduction in the hydrogen feed.

7. The recirculation of the liquid hydrogen comprises:

2. The process of claim 1, comprising compressing the hydrogen before it is fed to a conversion unit positioned to convert the para-hydrogen to ortho-hydrogen to bring the para-hydrogen content of the recycled hydrogen recycled to the feed of the liquefaction unit to between 20 mol% para-hydrogen and 30 mol% para-hydrogen.

8. The recirculation of the liquid hydrogen comprises: supplying hydrogen having a para-hydrogen content of between 80 mol% and 100 mol% stored in at least one storage tank to a conversion unit positioned to convert the para-hydrogen to ortho-hydrogen such that the para-hydrogen content of the recycled hydrogen recycled to the feed of the liquefaction unit is between 20 mol% para-hydrogen and 30 mol% para-hydrogen; and / or supplying liquid hydrogen output from the liquefaction unit to a heater in a recycle loop to vaporize the liquid hydrogen, and then passing the vaporized hydrogen through the conversion unit positioned to convert the para-hydrogen to ortho-hydrogen such that the para-hydrogen content of the recycled hydrogen recycled to the feed of the liquefaction unit is between 20 mol% para-hydrogen and 30 mol% para-hydrogen; The process also comprises:

2. The process of claim 1, comprising: in response to start-up of the liquefaction unit when the liquefaction unit is at ambient temperature, supplying liquid hydrogen stored in at least one storage tank to the liquefaction unit to facilitate operation of the liquefaction unit and cooling of the liquefaction unit to a cryogenic operating temperature; and recirculating the hydrogen output from the liquefaction unit through the recirculation loop during the start-up.

9. 9. The process of claim 8, wherein a controller having a processor coupled to a non-transitory memory is positioned and configured to determine whether the hydrogen feed has decreased below the preselected threshold.

10. 1. An apparatus for hydrogen recycling, comprising: a liquefaction unit configured to liquefy a hydrogen feed and output a first stream of liquid hydrogen to supply the liquid hydrogen to at least one storage tank, the liquid hydrogen having a para-hydrogen content of 80 mole percent (mol%) to 100 mol%; a conversion unit positioned to convert para-hydrogen in the hydrogen output by the liquefaction unit to ortho-hydrogen such that the hydrogen output from the liquefaction unit can be recycled to the feed inlet of the liquefaction unit with a para-hydrogen content of 20 mol% to 30 mol%.

11. a recirculation loop conduit heater feed conduit connected between the liquefaction unit and a recirculation loop conduit heater, the recirculation loop conduit heater positioned to heat liquid hydrogen output from the liquefaction unit to vaporize the liquid hydrogen into gaseous hydrogen; 11. The apparatus of claim 10, wherein the recirculation loop conduit heater is positioned to supply the gaseous hydrogen to the conversion unit.

12. 11. The apparatus of claim 10, wherein the conversion unit comprises at least one para-hydrogen to ortho-hydrogen converter.

13. 11. The apparatus of claim 10, comprising the at least one storage tank, the at least one storage tank positioned to output hydrogen stored therein to supply the hydrogen to the conversion unit.

14. 14. The apparatus of claim 13, comprising a recirculation loop heater positioned to receive hydrogen from the at least one storage tank and heat the hydrogen output from the at least one storage tank supplied to the conversion unit such that the hydrogen is supplied to the conversion unit as gaseous hydrogen.

15. a recirculation loop conduit heater feed conduit connected between the liquefaction unit and a recirculation loop conduit heater, the recirculation loop conduit heater positioned to heat liquid hydrogen output from the liquefaction unit to vaporize the liquid hydrogen into gaseous hydrogen, and the recirculation loop conduit heater positioned to supply the gaseous hydrogen to the conversion unit; and / or 11. The apparatus of claim 10, comprising a recirculation loop heater positioned to receive hydrogen from the at least one storage tank and heat the hydrogen output from the at least one storage tank supplied to the conversion unit such that the hydrogen is supplied to the conversion unit as gaseous hydrogen.

16. a recirculation loop conduit heater feed conduit connected between the liquefaction unit and a first recirculation loop conduit heater, the first recirculation loop conduit heater positioned to heat liquid hydrogen output from the liquefaction unit to vaporize the liquid hydrogen into gaseous hydrogen, and the first recirculation loop conduit heater positioned to supply the gaseous hydrogen to the conversion unit; and 11. The apparatus of claim 10, comprising a second recirculation loop heater positioned to receive hydrogen from the at least one storage tank and heat the hydrogen output from the at least one storage tank supplied to the conversion unit such that the hydrogen is supplied to the conversion unit as gaseous hydrogen.

17. 11. The apparatus of claim 10, comprising a compression system positioned upstream of the conversion unit to compress the hydrogen for supply to the conversion unit.

18. 1. An apparatus for hydrogen recycling, comprising: a liquefaction unit configured to liquefy a hydrogen feed and output a first stream of liquid hydrogen to supply the liquid hydrogen to at least one storage tank, the liquid hydrogen having a para-hydrogen content of 80 mole percent (mol%) to 100 mol%; a conversion unit positioned to convert para-hydrogen in the hydrogen output by the liquefaction unit to ortho-hydrogen such that the hydrogen output from the liquefaction unit can be recycled to a feed inlet of the liquefaction unit with a para-hydrogen content of 20 mol% to 30 mol%, the conversion unit comprising at least one para-hydrogen to ortho-hydrogen converter; the at least one storage tank positioned to output hydrogen stored therein to supply the hydrogen to the conversion unit in response to the hydrogen feed being at or below a preselected threshold; a recirculation loop conduit heater feed conduit connected between the liquefaction unit and a first recirculation loop conduit heater, the first recirculation loop conduit heater positioned to heat liquid hydrogen output from the liquefaction unit to vaporize the liquid hydrogen into gaseous hydrogen, and the first recirculation loop conduit heater positioned to supply the gaseous hydrogen to the conversion unit; and a second recirculation loop heater positioned to receive hydrogen from the at least one storage tank and heat the hydrogen output from the at least one storage tank supplied to the conversion unit so that the hydrogen can be supplied to the conversion unit as gaseous hydrogen.

19. 20. The apparatus of claim 18, comprising a compression system positioned upstream of the conversion unit to compress the hydrogen for supply to the conversion unit.

20. 20. The apparatus of claim 18, wherein the liquefaction unit comprises a closed-loop or open-loop cooling system.

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