Hydrogen recirculation equipment and process to avoid liquefaction shutdowns caused by 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, as well as a process and apparatus for recirculating hydrogen for hydrogen liquefaction processing.

Background Art

[0002] Hydrogen can be produced via 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 may involve 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 Invention

[0004] In many cases, hydrogen liquefaction occurs in processes where relatively steady-state conditions are desired. For example, the stream of hydrogen 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 conventional power sources (e.g., electricity generated from the combustion of natural gas or other fossil fuels, hydrogen production provided by steam reforming that may be generated 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 hydrogen production. Such systems can produce hydrogen gas by utilizing the electrolysis of water 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 that can greatly affect the electricity available to support the electrolysis of water. Often, hydrogen production can vary significantly from day to day or from day to day depending on various weather conditions (e.g., the length of daytime relative to the length of nighttime, cloud cover, wind availability, etc.). Green hydrogen production systems have often been found to need to be shut down due to the significant fluctuations in hydrogen gas output and the fact that liquefiers, which may be positioned to liquefy the hydrogen gas from such production systems, often lack sufficient hydrogen feed to support the liquefaction process. Shutting down the liquefaction process can incur significant costs in terms of production losses. Shutting down such equipment also incurs other surprising costs. For example, restarting the liquefaction process may take a relatively long time, which could result in production losses that may occur when renewable power increases to support sufficient hydrogen output to supply the liquefaction system, and the startup delay could affect the ability to efficiently utilize the hydrogen produced. Also, equipment degradation resulting from periodic changes in operating conditions may necessitate more frequent equipment replacement or, otherwise, a shorter equipment lifespan, which can increase maintenance costs as it leads to less flexible processes that are more prone to shutdowns or other problems due to equipment failure.

[0006] Traditionally, expensive storage units may include a buffer between the hydrogen production system and the liquefaction system to help ensure that the liquefaction system can operate when hydrogen replenishment is unavailable. However, this type of conventional approach can require significant capital costs associated with storage. Furthermore, hydrogen storage can result in losses due to the need to control excessive pressurization of the hydrogen stored in the storage unit and the complexity of other storage-related processes.

[0007] We found that these types of problems can be better addressed by providing equipment and processes for recirculating the hydrogen output from the liquefaction unit so that the liquid hydrogen can be vaporized and then recirculated back to the liquefaction unit's feed to supplement insufficient hydrogen feed. Surprisingly, we found that this type of approach, in terms of energy use and process complexity related to the formed liquid hydrogen, can be beneficial because it can avoid liquefaction unit shutdowns and can help reduce or limit storage levels, which may be desirable to assist liquefaction operations during periods of low hydrogen production.

[0008] Surprisingly, we 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 energy 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 may affect the electricity available for hydrogen production. In such systems, production may fluctuate frequently in some situations (e.g., at least 3 times a week, at least 12 times a month, at least 200 times a year, etc.), and surprisingly, we found that it can be beneficial to bear the costs and production complexities associated with recirculating already liquefied hydrogen back into the feed of the liquefaction unit to avoid shutdowns of the liquefaction unit due to insufficient hydrogen supply for certain periods (e.g., nighttime, rainy days, etc.). This can be particularly challenging in situations where periods of zero production are short (e.g., due to temporary weather conditions affecting electricity use that may be lost for 2 to 12 hours). The duration of electricity non-use can typically be much shorter than when providing a complete shutdown and subsequent restart of the liquefaction process, which may take a full 24 hours. Surprisingly, we found that in these situations, it can be far more beneficial to keep the liquefaction process online in full recirculation mode to avoid prolonging the shutdown process. This makes it easier to capture the product after power is restored to replenish the liquefaction process with hydrogen, while simultaneously avoiding product emissions (e.g., hydrogen emissions).

[0009] It was found that a cooler capable of generating the cooling necessary for hydrogen liquefaction may require a thermal load (e.g., supplying hydrogen) to remain online and maintain productivity when the liquefaction process needs to continue running while hydrogen production is stopped or substantially delayed due to unexpected power loss. Without a thermal load, the liquefaction process would overcool all equipment above its design temperature, thereby requiring a process shutdown. Surprisingly, it was found that by recirculating the hydrogen output from the liquefaction process into the process feed, an alternative feed for feed hydrogen can be provided in the form of a recirculated stream that can replace the lost hydrogen feed that may occur when a shutdown or significant reduction in hydrogen production occurs, which could significantly reduce (or stop) the supply of feed hydrogen for liquefaction due to a lack of power availability.

[0010] To make this recirculation more effective and to avoid problems related to cooling equipment limitations, cooling operations, and cryogenic conditions in liquefaction units capable of outputting liquid hydrogen with at least 95 mole percent para-hydrogen content, we have also found that by controlling the para-hydrogen and ortho-hydrogen content of the recirculated hydrogen, it is possible to provide improved performance that avoids processing problems that can damage and degrade equipment and / or cause unexpected failures resulting from the use of recirculated hydrogen, which could lead to production problems or liquefaction shutdowns.

[0011] For example, surprisingly, we have found that if the feed for hydrogen liquefaction to the liquefaction unit contains more than 25 mol% para-hydrogen, significant adjustments to the liquefaction unit's cooling system may be necessary. Typically, the feed of hydrogen supplied for liquefaction has a para-hydrogen content of approximately 25 mol%. Energy may be released during the conversion of ortho-hydrogen to para-hydrogen, and as the hydrogen is cooled for liquefaction, the para-hydrogen content of the hydrogen may increase. The cooling system of the liquefaction unit can be designed to absorb this heat generated from the conversion of ortho-hydrogen to para-hydrogen, thereby facilitating the cooling and liquefaction of the hydrogen. If the feed of hydrogen supplied for liquefaction has a para-hydrogen content higher than expected (e.g., significantly more than 25 mol%), the heat released from the conversion of ortho-hydrogen to para-hydrogen may be lower than that the liquefaction unit is designed to accommodate, due to the reduction in ortho-hydrogen available for the conversion to para-hydrogen. This reduction in heat can lead to overcooling of the cooling system, potentially causing the equipment temperature to fall below the temperature required for stable performance of the cryogenic machinery used in the liquefaction unit. When this occurs, it can lead to equipment tripping or other problems that necessitate shutting down the liquefaction process. We have found that this can be avoided by using a para-hydrogen to ortho-hydrogen conversion unit to control the para-hydrogen content in the hydrogen recycled back into the liquefaction unit, thereby helping to better control the para-hydrogen content in the feed hydrogen, including the recycled hydrogen. These conversion units can also help avoid processing delays and reduced production efficiency that may arise from repeatedly cycling the liquefaction unit between shut-down and operating states, while preventing liquefaction shutdowns and equipment degradation.

[0012] In a first embodiment, a process for recirculating hydrogen is provided. This process may include supplying a hydrogen feed to a liquefaction unit. The liquefaction unit may liquefy the hydrogen to output liquid hydrogen. The liquid hydrogen may have a para-hydrogen content of 80 mole percent (mol%) to 100 mol%. In response to a determination that the hydrogen feed has decreased to below a pre-selected threshold, the liquid hydrogen is recirculated to the feed of the liquefaction unit, and as a result, the liquid hydrogen is vaporized into a gaseous state, undergoes conversion from para-hydrogen to ortho-hydrogen, and the para-hydrogen content of the recirculated hydrogen recirculated to the feed of the liquefaction unit can be 20 mol% to 30 mol%.

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

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

[0015] In a second embodiment, the process may also include stopping the recirculation of liquid hydrogen in response to a determination that the hydrogen feed has increased above a pre-selected threshold. In some embodiments of the process, recirculation and stopping of recirculation may occur in multiple different operating cycles, for example, to compensate for the rate of hydrogen feed supplied to the liquefaction unit.

[0016] In a third embodiment, the recirculation of liquid hydrogen may include supplying hydrogen with 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 recirculate the recirculated hydrogen to a para-hydrogen content of 20 mol% to 30 mol% para-hydrogen, and / or supplying the liquid hydrogen output from the liquefaction unit to a heater in the recirculation loop to vaporize the liquid hydrogen, and then passing the vaporized hydrogen through a conversion unit positioned to convert para-hydrogen to ortho-hydrogen and recirculate the recirculated hydrogen to a para-hydrogen content of 20 mol% to 30 mol% para-hydrogen. In some embodiments, both of these steps may be performed. In other embodiments, only one of these steps may be performed.

[0017] In a fourth embodiment, the process may include supplying liquid hydrogen with a para-hydrogen content of 80 mol% to 100 mol% output from a liquefaction unit to at least one storage tank of a hydrogen storage unit that is in fluid communication with the liquefaction unit. In some embodiments, the recirculation of liquid hydrogen may include adjusting at least one valve so that the liquid hydrogen output from the liquefaction unit cannot pass through at least one storage tank, and supplying the liquid hydrogen output from the liquefaction unit to a heater in the recirculation loop to vaporize the liquid hydrogen, and then passing the vaporized hydrogen through a conversion unit positioned to convert the para-hydrogen to ortho-hydrogen and recirculate the recirculated hydrogen to the feed of the liquefaction unit so that the para-hydrogen content of the recirculated hydrogen is 20 mol% to 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, which is positioned to convert para-hydrogen to ortho-hydrogen and recirculate the recirculated hydrogen to the feed of the liquefaction unit, so that the para-hydrogen content of the recirculated hydrogen is between 20 mol% and 30 mol% para-hydrogen. After determining that there is enough hydrogen recirculated to the liquefaction unit to compensate for the decrease in the hydrogen feed, the supply of hydrogen stored in at least one storage tank to the conversion unit can be ceased or stopped.

[0019] In the sixth embodiment, the recirculation of liquid hydrogen includes compressing the hydrogen before it is supplied to a conversion unit, which is positioned to convert para-hydrogen to ortho-hydrogen and recirculate the recirculated hydrogen to the feed of the liquefaction unit, so that the para-hydrogen content of the recirculated hydrogen is between 20 mol% and 30 mol% para-hydrogen.

[0020] In the seventh embodiment, the recirculation of liquid hydrogen may include supplying hydrogen with 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 into ortho-hydrogen and recirculate the recirculated hydrogen to a para-hydrogen content of 20 mol% to 30 mol% para-hydrogen, and / or supplying the liquid hydrogen output from the liquefaction unit to a heater in the recirculation loop to vaporize the liquid hydrogen, and then passing the vaporized hydrogen through a conversion unit positioned to convert para-hydrogen into ortho-hydrogen and recirculate the recirculated hydrogen to a para-hydrogen content of 20 mol% to 30 mol% para-hydrogen. Embodiments of this process may also include supplying liquid hydrogen stored in at least one storage tank to the liquefaction unit in response to the liquefaction unit being started when the liquefaction unit is at ambient temperature, in order to facilitate the operation of the liquefaction unit and the cooling of the liquefaction unit to its cryogenic operating temperature, and recirculating the hydrogen output from the liquefaction unit through a recirculation loop during startup.

[0021] In the eighth aspect, the process may be configured to utilize a controller having a processor connected to non-temporary memory. The controller is positioned and configured to determine whether the hydrogen feed has decreased to below a pre-selected threshold.

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

[0023] In a tenth embodiment, an apparatus for hydrogen recirculation 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 parahydrogen content of 80 mol% to 100 mol%. The apparatus may also include a conversion unit positioned to convert the parahydrogen in the hydrogen output by the liquefaction unit to orthohydrogen, so that the hydrogen output from the liquefaction unit can be recirculated to the feed inlet of the liquefaction unit with a parahydrogen content of 20 mol% to 30 mol%. Embodiments of the apparatus may be configured to implement an embodiment of a process for recirculating hydrogen.

[0024] In the eleventh embodiment, 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 the 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 embodiment, 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. In some embodiments, the converters may all operate in parallel. In other embodiments, some converters may operate in parallel and others in series. In yet another embodiment having multiple para-hydrogen to ortho-hydrogen converters, the converters may be arranged to operate in series.

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

[0027] In a fourteenth aspect, the present 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 may be connected between the liquefaction unit and the recirculation loop conduit heater. The recirculation loop conduit heater may be positioned to heat the 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. Alternatively (or in addition), the recirculation loop heater may be 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.

[0029] In a sixteenth aspect, the present 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 the 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. A second recirculation loop heater may be 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.

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

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

[0032] For example, in the 19th embodiment, the apparatus for hydrogen recirculation 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%. A conversion unit may be positioned to convert the para-hydrogen of the hydrogen output by the liquefaction unit to ortho-hydrogen so that the hydrogen output from the liquefaction unit can be recirculated 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. At least one storage tank may be positioned to output the hydrogen stored therein to supply hydrogen to the conversion unit in response to the hydrogen feed being below a pre-selected threshold. A recirculation loop conduit heater feed conduit may be connected between the liquefaction unit and a first recirculation loop conduit heater. A first recirculation loop conduit heater may be positioned to heat the liquid hydrogen output from the liquefaction unit to vaporize the liquid hydrogen into gaseous hydrogen. A first recirculation loop conduit heater may be positioned to supply gaseous hydrogen to the conversion unit. A second recirculation loop heater may be positioned to receive hydrogen from at least one storage tank and heat the hydrogen so that the hydrogen output from at least one storage tank supplied to the conversion unit can be supplied to the conversion unit as gaseous hydrogen.

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

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

[0035] It should be understood that embodiments of this process and apparatus can utilize various 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 automated process control system and / or a distributed control system (DCS). By utilizing various different conduit arrangements and process control systems, a specific set of design criteria can be met.

[0036] The apparatus for recirculating hydrogen, the process for recirculating hydrogen, the hydrogen liquefaction apparatus, the hydrogen liquefaction process, and the apparatus, processes, and systems for providing hydrogen recirculation to avoid liquefaction shutdown, as well as other details, purposes, and advantages of the methods for manufacturing and using them, will become apparent as the following description of certain exemplary embodiments thereof progresses. [Brief explanation of the drawing]

[0037] Exemplary embodiments of apparatus for recirculating hydrogen, processes for recirculating hydrogen, hydrogen liquefaction apparatus, hydrogen liquefaction processes, and apparatus, processes, and systems for hydrogen circulation that can avoid liquefaction shutdown, as well as methods for their manufacture and use, are shown in the drawings included herein. It is understood that the same reference numerals used in the drawings can identify the same components.

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

[0039] [Figure 2]This is a block diagram of a first exemplary execution mode of a first exemplary embodiment of the apparatus 1 for recirculating hydrogen (which may also be referred to as Figure 2 (FIG.2)). An exemplary embodiment of the process for recirculating hydrogen is also shown in this figure.

[0040] [Figure 3] This is a block diagram of a second exemplary execution mode of a first exemplary embodiment of the hydrogen recirculation apparatus 1 (which may also be referred to as Figure 3 (FIG.3)). An exemplary embodiment of the hydrogen recirculation process is also shown in this figure.

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

[0042] [Figure 5] This is a block diagram of the first exemplary execution mode of a second exemplary embodiment of the hydrogen recirculation apparatus 1 (which may also be referred to as Figure 5 (FIG. 5)). An exemplary embodiment of the hydrogen recirculation process is also shown in this figure.

[0043] [Figure 6] This is a block diagram of a second exemplary execution mode of a second exemplary embodiment of the hydrogen recirculation apparatus 1 (which may also be referred to as Figure 6 (FIG.6)). An exemplary embodiment of the hydrogen recirculation process is also shown in this figure.

[0044] [Figure 7]This flowchart (which may also be referred to as Figure 7 (FIG.7)) illustrates an exemplary embodiment of a process for hydrogen recirculation to prevent the liquefaction from shutting down. Embodiments of the hydrogen recirculation apparatus can perform this exemplary embodiment of the process. [Modes for carrying out the invention]

[0045] Referring to Figures 1-7, a device 1 for recirculating hydrogen can be used to recirculate the hydrogen output from the liquefaction unit 2 and supply it back to the liquefaction unit 2. In some embodiments, the device 1 may be configured to provide hydrogen recirculation in response to a decrease in the hydrogen feed supplied to the liquefaction unit 2 for hydrogen liquefaction, falling below a pre-selected supply rate (e.g., a pre-selected volumetric flow rate defining a threshold for the operation of hydrogen recirculation, a pre-selected mass flow rate defining a threshold for the operation of hydrogen recirculation, etc.). Hydrogen recirculation can be operated to help avoid the shutdown of the liquefaction unit 2 in response to low supply rate conditions, thereby avoiding production delays associated with the shutdown and subsequent startup of the liquefaction unit, as well as avoiding equipment degradation that may occur as a result of such operation involving a cycle between operating and shutdown operating conditions.

[0046] Surprisingly, we 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 energy 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 may affect the electricity available for hydrogen production. In such systems, in some situations, production may fluctuate frequently (e.g., 200 times or more per year), and surprisingly, we found that it can be beneficial to bear the costs and production complexities associated with using already liquefied hydrogen to be returned to the feed of the liquefaction unit 2 for recirculation in order to avoid shutdowns of the liquefaction unit due to insufficient hydrogen supply over certain periods (e.g., nighttime, rainy days, etc.).

[0047] A liquefaction unit 2, which may be supported by device 1 for hydrogen recirculation, may include one or more liquefiers or a row of one or more liquefiers for liquefying the hydrogen feed 15. The liquefaction unit 2 may be configured as a hydrogen liquefaction system (HLS), which may include, for example, a row 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 increase the para-hydrogen content of the liquefied hydrogen by converting ortho-hydrogen to para-hydrogen.

[0048] The liquefaction unit 2 may be configured to output a liquid hydrogen stream that may have a relatively high parahydrogen content. In some embodiments, the parahydrogen content of the liquid hydrogen output from the liquefaction unit may be at least 80 mol% parahydrogen or at least 95 mol% parahydrogen (e.g., 80 mol% to 100 mol% parahydrogen, 95 mol% to 100 mol% parahydrogen, etc.). While a suitable supply of hydrogen feed is being supplied to the liquefaction unit 2, the liquid hydrogen stream output from the liquefaction unit 2 may be supplied to a storage unit 4 for storage and subsequently supplied to one or more customers (e.g., via shipment of liquid hydrogen, transport of liquid hydrogen to another location or production facility, etc.). The storage unit 4 for liquid hydrogen may include at least one tank or other container for storing the liquid hydrogen at cryogenic temperatures to help maintain the liquid hydrogen in a liquid state.

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

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

[0051] The hydrogen feed 15 that may be supplied may be powered by a renewable power source, which may cause hydrogen production to fluctuate due to weather conditions, daylight conditions (e.g., daytime compared to nighttime, cloudy conditions, etc.), or other conditions that may affect the electricity available for hydrogen production. In such systems, in some situations, production may fluctuate frequently as a specification (e.g., at least 3 times a week, at least 12 times a month, at least 200 times a year, etc.), and surprisingly, it has been found that it may be beneficial to bear 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 replenishment hydrogen flow to the hydrogen feed 15, thereby avoiding shutdown of the liquefaction unit 2 due to insufficient hydrogen supply for a certain period (e.g., nighttime, rainy days, etc.). Since hydrogen recirculation can be done through the use of hydrogen in storage 4 and / or through routing of hydrogen output from the liquefaction unit, the hydrogen is returned to the feed inlet of the liquefaction unit 2 instead of being routed to storage 4. This recirculation may involve vaporizing the liquid hydrogen output from the liquefaction unit so that the hydrogen that returns to the feed inlet of the liquefaction unit 2 and is recirculated is in a gaseous state (for example, hydrogen gas instead of liquid hydrogen).

[0052] The liquefaction unit 2 is capable of outputting liquid hydrogen having a para-hydrogen content of at least 95 mol percent. Surprisingly, it has also been found that by controlling the para-hydrogen and ortho-hydrogen content of the recirculated hydrogen supplied to the feed inlet of the liquefaction unit for recirculating the hydrogen output from the liquefaction unit 2, improved performance can be provided, avoiding processing problems that could damage and degrade the equipment and / or cause unexpected failures resulting from the use of recirculated hydrogen, such as production problems or liquefaction shutdowns. By controlling the para-hydrogen content of the recirculated hydrogen via the conversion unit 11, the recirculated hydrogen can have a pre-selected para-hydrogen content that is below 25 mol% para-hydrogen, below 30 mol% para-hydrogen, or below another suitable para-hydrogen content feed threshold that can be set to avoid the hydrogen containing the recirculated hydrogen being cooled by supercooling of the liquefaction equipment, along with any low-flow hydrogen that can be supplied from the hydrogen production system 20 as hydrogen feed 15.

[0053] Surprisingly, we found that if the feed to the liquefaction unit for hydrogen liquefaction contains more than 25 mol% or significantly more than 25 mol% para-hydrogen, significant adjustments to the cooling system of the liquefaction unit may be necessary. Typically, the feed of hydrogen supplied for liquefaction has a para-hydrogen content of approximately 25 mol%. Energy may be released during the conversion of ortho-hydrogen to para-hydrogen, and as the hydrogen is cooled for liquefaction, the para-hydrogen content of the hydrogen may increase. The cooling system of the liquefaction unit can be designed to absorb this heat generated from the conversion of ortho-hydrogen to para-hydrogen, thereby facilitating 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., significantly exceeding 25 mol%), the heat released from the conversion of ortho-hydrogen to para-hydrogen may be lower than that the liquefaction unit is designed to accommodate due to the reduction in ortho-hydrogen available for the conversion to para-hydrogen (this can only occur as a result of recirculating the hydrogen output from the liquefaction unit back into the feed of liquefaction unit 2 in an amount sufficient to significantly alter the para-hydrogen content in the hydrogen feed supplied to liquefaction unit 2). This reduction in heat may cause the cooling system to supercool the hydrogen during liquefaction, potentially causing the equipment temperature to fall below the temperature required for stable performance of the cryogenic machinery used in the liquefaction unit. We have found that when this type of thing happens, it can lead to equipment tripping or other problems that necessitate shutting down the liquefaction process.

[0055] We have found that these problems that can be caused by overcooling can be avoided by using a para-hydrogen to ortho-hydrogen conversion unit 11 (CVRT) to control the para-hydrogen content in the hydrogen recirculated to the feed inlet of the liquefaction unit 2, thereby helping to better control the para-hydrogen content in the feed of hydrogen, including the recirculated 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 recirculated hydrogen to ortho-hydrogen, so as to provide improved control of the para-hydrogen content in the feed hydrogen, including the hydrogen recirculated from the liquefaction unit, and also help to avoid processing delays and reduced production efficiency that may arise from the need to repeatedly cycle the liquefaction unit between a shut-down state and an operating state, while avoiding liquefaction shutdown and equipment degradation. This type of control of the para-hydrogen content in recirculated hydrogen can help control the para-hydrogen content of the hydrogen supplied to the feed inlet of the liquefaction unit 2 when there is no hydrogen feed 15 available from the hydrogen production system 20, or the flow rate of hydrogen feed from the hydrogen production system 20 is so low that recirculated hydrogen constitutes most of the total hydrogen supplied to the liquefaction unit 2 (e.g., at least 30% of the hydrogen is recirculated hydrogen, at least 50% of the hydrogen in the hydrogen feed is recirculated hydrogen, or 50% to 100% of the hydrogen supplied to the liquefaction unit 2 as hydrogen feed 15 is recirculated hydrogen), in situations where recirculated hydrogen constitutes all of the hydrogen supplied to the liquefaction unit 2. Examples of extremely low flow rates of hydrogen feed 15 include no feed at all, or a feed so low that the thermal load of hydrogen feed 15 falls below a pre-selected minimum threshold required by the cooling system of the liquefaction process to keep the cooling machinery operating within its predetermined temperature constraints.

[0056] Hydrogen recirculation is not always performed. Instead, hydrogen recirculation may be provided in response to a determination that the hydrogen feed 15 is below a predetermined hydrogen feed flow rate or is expected to be below a predetermined hydrogen feed flow rate for at least a predetermined low hydrogen feed period. In response to the detection of such conditions, hydrogen recirculation may be initiated or activated. Recirculated hydrogen may first be provided via the long recirculation loop LRP through the use of hydrogen stored in the storage unit 4, and then via the short recirculation loop SRP for the recirculation of hydrogen output from the liquefaction unit 2, resulting in such hydrogen avoiding supply to the storage unit 4 and instead being directly recirculated back to the feed inlet of the liquefaction unit 2. In other embodiments, recirculated hydrogen may always be provided via the short recirculation loop SRP or always via the long recirculation loop LRP (for example, there may be no switching of use between loops, and only the short recirculation loop SRP or the long recirculation loop LRP may exist). In yet another embodiment, recirculated hydrogen may first be supplied via a short recirculation loop (SRP) and / or a long recirculation loop (LRP) (e.g., a combination of stored hydrogen from the storage unit and liquid hydrogen output from the liquefaction unit to be recirculated instead of being sent to the storage unit 4), and then supplied via the short recirculation loop (SRP).

[0057] After it is detected that the hydrogen feed 15 supplied from the hydrogen production system 20 is equal to or greater than a predetermined hydrogen feed flow rate during a predetermined low hydrogen feed period, or is expected to be equal to or greater than a predetermined hydrogen feed flow rate, the recirculation of hydrogen may be stopped or delayed until the hydrogen feed flow rate supplied from the hydrogen production system 20 equals or greater than the predetermined hydrogen feed flow rate. This switching of operation between hydrogen recirculation and non-recirculation can be repeatedly provided when a low feed flow rate below a predetermined minimum threshold required for the operation of the liquefaction unit 2 may be detected during the course of a number of different operating cycles as a result of changes in weather conditions or other conditions that may affect hydrogen production in the hydrogen production system 20, which is positioned to supply hydrogen feed 15 to the liquefaction unit 2.

[0058] The recirculation of hydrogen can be dynamically adjusted to compensate for the low feed rate of hydrogen from the hydrogen production system 20. For example, if there is no hydrogen provided by the hydrogen production system 20, hydrogen recirculation can be provided at a higher capacity to supply sufficient hydrogen to the inlet of the liquefaction unit 2, allowing the unit to operate without needing to shut down at a pre-selected minimum operating capacity. If a hydrogen feed 15 exists but is extremely low and below a pre-selected minimum threshold, the amount of recirculated hydrogen can be varied to provide a hydrogen configuration such that the hydrogen feed supplied to the inlet 15b of the liquefaction unit is above a pre-selected minimum threshold.

[0059] Figures 1-6 illustrate different exemplary execution modes of different apparatuses for providing hydrogen recirculation. Embodiments of processes for hydrogen recirculation can also be understood from these drawings. The first exemplary embodiment in Figures 1-3 illustrates an exemplary recirculation process that may be provided in a situation where the liquefaction unit 2 can utilize an open-loop cooling system for liquefaction. The second exemplary embodiment in Figures 4-6 illustrates an exemplary recirculation process that may be provided in a situation where the liquefaction unit 2 can utilize a closed-loop cooling system for liquefaction.

[0060] The hydrogen feed 15 supplied to the liquefaction unit 2 may have a pre-selected feed pressure (e.g., over 100 kPa to 4000 kPa or other suitable feed pressure) and a pre-selected feed temperature (e.g., 0°C to 100°C, ambient temperature to less than 65°C, 0°C to 65°C, or other suitable temperature). The parahydrogen content of the hydrogen feed may also be within a pre-selected range of parahydrogen content (e.g., 20 mol% to 30 mol% parahydrogen content).

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

[0062] Referring to Figures 1-3, the hydrogen recirculation apparatus 1 can be configured to recirculate the hydrogen output from the liquefaction unit 2 as at least one stream of liquid hydrogen to the 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 any other loop (for example, 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 pre-selected feed flow rate, the liquid hydrogen output by the liquefaction unit 2 can be supplied to the storage unit 4 for storage in one or more liquid hydrogen storage tanks. The liquid hydrogen supplied into the storage unit 4 may be held at a pre-selected storage pressure (e.g., a pressure of 100 kPa to 150 kPa, or other suitable pressure). A liquid hydrogen storage feed conduit 3a is connected between the storage unit 4 and the liquefaction unit 2 to route the liquid hydrogen to the storage unit 4 for storage in one or more storage tanks. The liquid hydrogen held in the storage unit 4 can be supplied to one or more trailers for transport to customers via trucks, rail vehicles, or other types of vehicles, or it can be supplied to another process element of an industrial facility at another location for hydrogen use. As described above, the liquid hydrogen in the storage unit 4 may have a relatively high para-hydrogen content of at least 80 mol% or at least 95 mol%.

[0064] During operation, the hydrogen feed 15 may change significantly due to changes in production conditions in the hydrogen production system 20 (e.g., changes in weather conditions affecting the power available for water electrolysis). Such changes may cause a significant decrease in the hydrogen feed 15 provided by the hydrogen acid system 20, or even to cease being provided altogether. In response to detection that no hydrogen feed is being provided, or that the hydrogen feed is below a pre-selected threshold (e.g., a pre-selected volumetric flow rate defining a threshold for the activation of hydrogen recirculation, a pre-selected mass flow rate defining a threshold for the activation of hydrogen recirculation, etc.), at least a portion of the liquid hydrogen output from the liquefaction unit 2 can be recirculated. Recirculation may occur via 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 to route at least a portion of the liquid hydrogen output from the liquefaction unit 2 back to a feed conduit for hydrogen feeding to supply hydrogen to the feed inlet of the liquefaction unit 2. The short recirculation loop may include a recirculation loop conduit heater 5 positioned to heat the liquid hydrogen output from the liquefaction unit to vaporize the hydrogen into 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. In some embodiments, the heater 5 may be an ambient air vaporizer, an ambient air heat exchanger, a heat exchanger that utilizes water (e.g., water at ambient temperature, heated water, etc.) as a heating medium, or other suitable heat exchangers that can route the vaporized hydrogen stream 5b output from the heater to a conversion unit 11 that includes at least one para-hydrogen to ortho-hydrogen converter for adjusting the ortho-hydrogen and para-hydrogen content of the recirculated hydrogen to approximately 25 mol% para-hydrogen content.

[0066] For example, the heater 5 can fluidly communicate with the compression feed conduit 7b of the recirculating hydrogen conduit arrangement for the apparatus 1 to supply vaporized hydrogen to at least one compressor of the compression system (CS) (e.g., a first compressor C1, a second compressor C2, and / or a third compressor C3). The compression system 9 can compress hydrogen to a higher pressure to supply it to the feed inlet of the liquefaction unit 2 and to help pass it through the hydrogen conversion unit 11. The compression system 9 can output hydrogen gas to supply it to at least one para-hydrogen to ortho-hydrogen conversion device of the conversion unit 11 via the conversion unit feed conduit 9a located between the compression system 9 and the conversion unit 11. The conversion unit 11 can process hydrogen gas so that the para-hydrogen content of the hydrogen gas output from the conversion unit 11 is 25 mol% or less or 30 mol% or less (for example, 20 mol% to 30 mol% para-hydrogen and 80 mol% to 70 mol% ortho-hydrogen), thereby converting para-hydrogen to 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 the hydrogen feed 15 can be supplied to the feed inlet of the liquefaction unit. The conversion unit replenishment 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.

[0067] In some embodiments, the conversion unit replenishment conduit 11a can supply hydrogen output from the conversion unit 11 to a feed conduit, through which a hydrogen feed 15 can pass, be mixed inline with the hydrogen feed, and supplied to the inlet of the liquefaction unit 2 together with the hydrogen feed 15 that may be output from the hydrogen production system 20. Alternatively, the conversion unit replenishment conduit 11a can pass hydrogen through the feed inlet of the liquefaction unit and mix it with its hydrogen (if provided) from the hydrogen production system 20 in the feed inlet area of ​​the liquefaction unit 2.

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

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

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

[0071] The compression system 9 receives hydrogen from the heater 5 of the short recirculation loop SRP and / or the heater 7 of the long recirculation loop LRP, compresses the hydrogen, and can output the hydrogen to the conversion unit 11 (CVRT) via a conversion unit feed conduit 9a located between the compression system 9 and the conversion unit 11. The conversion unit 11 processes the hydrogen gas from the long recirculation loop LRP and / or a combination of hydrogen gas from the short recirculation loop SRP and the long recirculation loop LRP to convert para-hydrogen to ortho-hydrogen so that the para-hydrogen content of the hydrogen gas output from the conversion unit 11 is 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 a 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 embodiments, the hydrogen to be recirculated may first be supplied through at least one storage tank of the hydrogen storage unit 4, and then entirely through a short recirculation loop (SRP), so that the recirculated hydrogen avoids being supplied to the storage unit 4 during such recirculation after the initial supply of hydrogen from the storage unit 4 occurs. In other embodiments, the recirculated hydrogen may first be supplied through at least one storage tank of the hydrogen storage unit 4, as well as through routing of liquid hydrogen output from the liquefaction unit to the short recirculation loop (SRP). After a sufficient amount of hydrogen for recirculation has been supplied, the hydrogen recirculation may then be entirely supplied through the short recirculation loop (SRP), so that the recirculated hydrogen avoids being supplied to the storage unit 4 during such recirculation after the initial supply of hydrogen from the storage unit 4 occurs. In yet another embodiment, the short recirculation loop (SRP) may not be provided, and only a long recirculation loop (LRP) may be used for hydrogen recirculation.

[0073] In embodiments where both short recirculation loops (SRP) and long recirculation loops (LRP) can be utilized, the heater 5 of the short recirculation loop (SRP) can be considered as the first recirculation loop heater of the first recirculation loop, and the heater 7 of the long recirculation loop (LRP) can be considered as the second heater of the second recirculation loop. Alternatively, the heater 7 of the long recirculation loop (LRP) can be considered as the first heater of the first recirculation loop, and the heater 5 of the short recirculation loop (SRP) can be considered as the second recirculation loop heater of the second recirculation loop. Each heater assists in heating the hydrogen output from the liquefaction unit (2) (for example, immediately after output or after the hydrogen has been stored in the hydrogen storage unit (4)) so that gaseous hydrogen can be supplied to the conversion unit (11) for hydrogen recirculation.

[0074] Embodiments of apparatus 1 may be configured in conjunction with an open-loop cooling system OLP of the liquefaction unit 2. The open-loop cooling 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 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 at a higher pressure than the first hydrogen stream 23, for supply to the compression system 9 for compression and for subsequent supply back to the liquefaction unit for use in cooling that occurs during liquefaction. To facilitate an open-loop cooling scheme in which hydrogen can be used as a refrigerant, the compression system 9 for the cooling system may be utilized. Compressed hydrogen used as a refrigerant in the open-loop cooling 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 cooling system of the liquefaction unit 2.

[0075] At least one storage tank in the hydrogen storage unit 4 may also be fluidly connected to 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 exhaust through at least one exhaust conduit VT. For example, hydrogen can be exhausted in situations where the hydrogen output from liquefaction unit 2 cannot meet a pre-selected hydrogen content specification. In some embodiments, such exhaust may occur downstream of at least one heater (e.g., heater 5 for short recirculation loop SRP, heater 7 for long recirculation loop LRP, ambient air heater for exhaust conduit, etc.) so that the exhausted hydrogen is heated to an exhaust temperature suitable for exhaust into 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 2a of liquid hydrogen and a second stream 2b of liquid hydrogen. In some embodiments, these streams of liquid hydrogen may be mixed together via a mixing device (e.g., an in-line mixer, a mixing vessel, etc.) for supply to a short recirculation loop SRP or to a hydrogen storage unit 4.

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

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

[0080] In some embodiments, at least one trailer 8 can be connected to a long recirculation loop (LRP). Trailer 8 can be positioned to receive hydrogen from a storage unit to replenish hydrogen at another location. Trailer (TRLR) can be positioned to contain alternative hydrogen gas and supply hydrogen to the recirculation loop when constituent hydrogen is required and the supply of liquid hydrogen in the hydrogen storage unit 4 is insufficient, providing recirculation to the liquefaction unit 2 and providing a sufficient hydrogen composition to compensate for a reduction in the flow of hydrogen feed 15 that can initiate hydrogen recirculation. For example, trailer 8 can be fluidly connected to a short recirculation loop (SRP) or a long recirculation loop (LRP) to supply 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] Figure 2 illustrates an exemplary working configuration of the apparatus 1 shown in Figure 1. The compression system 9 may include a first compressor C1 and a second compressor C2, and hydrogen gas output from the liquefaction unit 2 as part of an open-loop cooling system may include a first hydrogen stream 23, which may be at a lower pressure, for compression by the first compressor C1 and subsequent supply to the compression system 9 for further compression via the second compressor C2 of the compression system 9. The liquefaction unit 2 may output a second hydrogen stream 25, which may be at a higher pressure than the first hydrogen stream 23, and this stream may be supplied to the second compressor C2 of the compression system 9, where it is compressed and subsequently supplied back to the liquefaction unit and / or back to the conversion unit 11 for recirculation for use in cooling that occurs during liquefaction (if the use of a recirculation loop is used due to the low level of hydrogen feed supplied to the liquefaction unit 2).

[0082] As can be understood from the exemplary execution shown in Figure 2, the apparatus 1 for hydrogen recirculation may not utilize a phase separation system PS. The first and second streams of liquid hydrogen 2a and 2b are output from the liquefaction unit 2 and then merged and supplied to the hydrogen storage unit 4 via the liquid hydrogen storage unit 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 a short recirculation loop via a recirculation loop conduit heater feed conduit that can be connected to the liquid hydrogen storage unit feed conduit 3a and / or connected between the liquefaction unit 2 and the heater 5 of 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 available. In such embodiments, liquid hydrogen from at least one storage tank of the hydrogen storage unit 4 can output hydrogen for supply to the conversion unit via the long recirculation loop (LRP) conduit arrangement. Hydrogen from at least one trailer 8 may also be used to help provide a stream of hydrogen to the liquefaction unit when the hydrogen feed provided by the hydrogen production system 20 is too little or absent, thereby recirculating hydrogen and assisting the operation of the liquefaction unit.

[0084] As best seen from the exemplary execution configuration shown in Figure 3, the compression system 9 may include a first compressor C1 as a low-pressure compressor, a second compressor C2 as an intermediate-pressure compressor, and a third compressor C3 as a high-pressure compressor. Such a configuration may be used in a high-pressure liquefaction unit 2 that can utilize the high-pressure, low-pressure, and intermediate-pressure cooling elements of its cooling system for hydrogen liquefaction. The liquefaction unit 2 can output a first hydrogen stream 23, which may be at a lower pressure, for compression by the first compressor C1 and for supply to the compression system 9 for further compression via the subsequent second and third compressors 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 the pressure of the first hydrogen stream 23, and this stream may be supplied to a second compressor C2 of the compression system 9, where it is compressed, compressed by a third compressor C3, and subsequently supplied to the liquefaction unit and / or returned to the conversion unit 11 for recirculation for use in cooling during liquefaction (if the use of a recirculation loop is utilized due to a low level of hydrogen feed supplied to the liquefaction unit 2). Another second hydrogen stream 25 may be output from the cooling system of the liquefaction unit 2, which may be at a high pressure higher than the pressure of the first hydrogen stream 23 and higher than the intermediate pressure of the other second hydrogen stream 25, and this may be supplied to a third compressor C3 of the compression system 9, where it is compressed, and subsequently supplied to the liquefaction unit and / or returned to the conversion unit 11 for recirculation for use in cooling during liquefaction (if the use of a recirculation loop is utilized due to a low level of hydrogen feed supplied 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., 3 vol% hydrogen gas to 10 vol% hydrogen gas, 5 vol% hydrogen gas to 25 vol% hydrogen gas, more than 0 vol% gas to 40 vol% gas, etc.). The liquid hydrogen stream containing hydrogen gas can be supplied to a phase separation system PS, which then passes through a phase separator PH, where a considerable 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 can be recirculated back to the feed inlet of the liquefaction unit 2, for example, by supplying this stream to a compression system 9 and routing it to the inlet of the liquefaction unit 2, or it can be supplied to the cooling system of the liquefaction unit. Such routing may occur when the device has an insufficient hydrogen feed from the hydrogen production system, or while the hydrogen feed from the hydrogen production system 20 is above a pre-selected feed rate for the normal operation of the liquefaction unit that does not recirculate hydrogen.

[0087] Hydrogen that is mostly liquid (e.g., at least 95 vol% liquid hydrogen) or completely liquid hydrogen can be output from the phase separator PH via the 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 supplied to the liquefaction unit via a hydrogen gas return conduit connected between the subcooler 3 and the liquefaction unit 2. As described above, such hydrogen gas flow may be supplied to the cooling system of the liquefaction unit, routed back to the liquefaction unit as a low-pressure hydrogen vapor stream LPV, and recirculated back to the feed inlet of the liquefaction unit 2 (e.g., by being supplied 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, when the apparatus has an insufficient feed of hydrogen from the hydrogen production system. Such routing may also occur when the apparatus has an sufficient feed of hydrogen from the hydrogen production system 20 that is above a pre-selected feed flow rate for normal operation of the liquefaction unit without recirculation of hydrogen.

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

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

[0090] In such a closed-loop cooling system environment, the recirculation conduit arrangement for hydrogen recirculation can utilize different compression system arrangements. For example, there may be a compressor 41 located upstream of the conversion unit 11 to compress hydrogen for supply to the conversion unit 11 and then recirculate it to the feed inlet of the liquefaction unit 2. As another example, there may be a compressor 43 located downstream of the heater 7 through which hydrogen from at least one storage tank of the hydrogen storage unit 4 passes, is heated, and recirculated to the feed inlet of the liquefaction unit 2 via the conversion unit 11. In embodiments where multiple such compressors can be used, the 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 the hydrogen to a second-higher pressure (e.g., high or medium pressure) for recirculation.

[0091] In yet another configuration, the feed conduit for the hydrogen feed 15 supplied to the liquefaction unit 2 may include a feed compressor. In such a configuration, the excess capacity of the feed compressor, which may exist due to a decrease in the hydrogen feed from the hydrogen production system 20, can be utilized to help drive the flow of hydrogen to recirculate through the short recirculation loop (SRP) and / or the long recirculation loop (LRP).

[0092] In some exemplary execution configurations, such as the one shown in Figure 5, a low-pressure compressor LC downstream of the heater 7 can be used to receive hydrogen from the hydrogen storage unit 4 and / or at least one trailer 8, supply it to the conversion unit 11, and recirculate the hydrogen to the liquefaction unit 2. A recirculation loop conduit heater output conduit 7a is connected between the recirculation loop conduit heater 7 and the compressor 43 and can supply hydrogen to the compressor in preparation for output to be supplied to the conversion unit 11 via a conversion unit feed conduit 9a located between the compressor 43 and the conversion unit 11.

[0093] Hydrogen that can be recirculated through the short recirculation loop SRP is output from the heater 5 in the conduit arrangement for the loop and can be 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 executions, such as the exemplary execution in 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 compression feed conduit 7b which can be connected between the 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 cooling embodiment in Figure 1 (but without receiving hydrogen streams from the cooling system of the liquefaction unit 2 and compressing these streams).

[0095] As described above, different exemplary embodiments and executions of the apparatus 1 may be configured to provide hydrogen recirculation in response to the hydrogen feed 15 supplied to the liquefaction unit 2 for hydrogen liquefaction decreasing below a pre-selected feed flow rate (e.g., a pre-selected volumetric flow rate defining a threshold for the activation of hydrogen recirculation, a pre-selected mass flow rate defining a threshold for the activation of hydrogen recirculation, etc.). Hydrogen recirculation can be operated to help avoid the shutdown of the liquefaction unit 2 in response to low supply rate conditions, thereby avoiding production delays associated with the shutdown and subsequent startup of the liquefaction unit, as well as avoiding equipment degradation that may occur as a result of such operation involving a cycle between operating and shutdown operating conditions.

[0096] As shown in Figures 1-6, a controller CTRL can be provided to detect these conditions for the operation of hydrogen recirculation via one or more sensors that can be positioned to monitor or measure the flow of hydrogen feed 15 at position 15a upstream of where the recirculation flow can be supplied to the inlet of the liquefaction unit 2 via the conversion unit supply conduit 11a and / or the flow of hydrogen feed at the inlet 15b of the liquefaction unit 2. One or more sensors may be, for example, flow sensors and / or pressure sensors. The controller CTRL can be communicatively connected to the sensors and receive data from the sensors to determine whether the hydrogen feed is below a pre-selected threshold for the operation of hydrogen recirculation. The controller CTRL may similarly or alternatively receive data from one or more sensors or other elements of the hydrogen production system 20 that can provide inputs indicating when the hydrogen feed can decrease to a pre-selected threshold for hydrogen recirculation.

[0097] The controller CTRL may also be communicably 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 activating hydrogen recirculation to the inlet of the liquefaction unit. The controller can use this flow data to communicate with valves in one or more recirculation loops and recirculate appropriate portions of liquid hydrogen to compensate for any lack of sufficient hydrogen feed supplied to the hydrogen production system 20. Valve V can be dynamically adjusted to compensate for changing hydrogen feed conditions 15, so that the portion of water being recirculated can be adjusted from no hydrogen recirculation to complete recirculation of output hydrogen to compensate for the detected flow rate of hydrogen feed 15 supplied by the hydrogen production system 20.

[0098] The controller CTRL may be a computer device comprising a processor and at least one transceiver connected to non-temporary memory. The controller CTRL may also be communicatively connected to a valve to actuate valve adjustment for hydrogen recirculation.

[0099] The controller CTRL may be configured to respond to a determination that the hydrogen feed is too low (e.g., decreasing below a pre-selected feed rate, decreasing below a pre-selected feed rate, and that low rate may persist for at least a pre-selected hydrogen recirculation period) 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 a configuration of the controller CTRL may be implemented via automatic process control logic defined in code in the controller's non-temporary memory, which may be executed by the controller's processor.

[0100] For example, in some embodiments, the controller CTRL can communicate with the valve V of the liquid hydrogen storage feed conduit 3a to close this valve V, and open the valve V of 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, allowing hydrogen with reduced para-hydrogen content to be returned to the feed inlet of the liquefaction unit for recirculation. The controller CTRL can also communicate with the valve V of the storage tank recirculation conduit 4c located between the hydrogen storage unit 4 and the heater 7 to open this valve V to replenish hydrogen from the hydrogen storage unit 4 to the conversion unit 11, allowing hydrogen with reduced para-hydrogen content to be returned to the feed inlet for the liquefaction unit for recirculation. The controller CTRL can also communicate with the valve V of the conversion unit replenishment conduit 11a to open this valve V, facilitating the supply of hydrogen to the feed inlet of the liquefaction unit for recirculation after the para-hydrogen content of the hydrogen has been adjusted via the conversion unit 11. After a sufficient amount of hydrogen has been supplied 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 the valve V, thereby allowing the short recirculation loop SRP to be used solely for hydrogen recirculation until the hydrogen feed from the hydrogen production system 20 increases to a desired level.

[0101] In other configurations where a short recirculation loop (SRP) may not be provided, the controller (CTRL) can communicate with a valve V on the storage tank recirculation conduit 4c located between the hydrogen storage unit 4 and the heater 7 to open this valve V, thereby supplying hydrogen from the hydrogen storage unit 4 to the conversion unit 11 and allowing the hydrogen with reduced para-hydrogen content to be recirculated back to the feed inlet for the liquefaction unit. The controller (CTRL) can also communicate with a valve V on the conversion unit supply conduit 11a to open this valve V, facilitating the supply of hydrogen to the feed inlet of the liquefaction unit for recirculation after the para-hydrogen content of the hydrogen has been adjusted via the conversion unit 11. The controller (CTRL) can also communicate with a valve V on the storage tank recirculation conduit 4c to close that valve V, and similarly, communicate with a valve V on the conversion unit supply 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 the cessation of hydrogen recirculation.

[0102] In other configurations where the long recirculation loop LRP may not be available, the controller CTRL can communicate with the valve of the liquid hydrogen storage feed conduit 3a to close this valve V, and open the valve V of 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, allowing the hydrogen with reduced para-hydrogen content to be returned to the feed inlet of the liquefaction unit and recirculated. The controller CTRL can communicate with the valve V of the recirculation loop conduit heater feed conduit 5a to close that valve V, and similarly, can communicate with the valve V of the conversion unit supply conduit 11a to close that valve V after the hydrogen feed from the hydrogen production system 20 has increased to a desired level that facilitates the cessation of hydrogen recirculation.

[0103] Controller CTRL communicates with different valves to adjust their positions to partially open and / or closed to supplement the flow rate of hydrogen feed 15 provided by the hydrogen production system 20 and to explain how that flow rate compares to a pre-selected minimum threshold flow rate. In the absence of a hydrogen feed, the hydrogen recirculation valve V can be fully open to provide, for example, a hydrogen recirculation flow to compensate for the lack of hydrogen feed from the hydrogen production system 20. In the presence of a hydrogen feed but significantly below the pre-selected minimum threshold flow rate, the hydrogen recirculation valve may be partially open (but not as open as when no hydrogen feed is provided) to provide a hydrogen recirculation flow that can provide a supplemental hydrogen flow to compensate for the deviation from the pre-selected minimum threshold flow rate. In the absence of a hydrogen feed but only slightly below the pre-selected minimum threshold flow rate, the hydrogen recirculation valve may be partially open to a smaller extent to provide a hydrogen recirculation flow that can compensate for this slight deviation from the pre-selected minimum threshold flow rate.

[0104] Furthermore, surprisingly, we found that the use of short recirculation loops (SRP) and long recirculation loops (LRP) can offer several other advantages. For example, during the startup of the 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, while the short recirculation loop (SRP) can be used to help accelerate the cooling rate of the liquefaction equipment in liquefaction unit 2. This type of approach to cooling the liquefaction unit during startup can make it possible to perform such cooling with little to no exhaust (for example, due to the absence of impurities in the hydrogen used to facilitate the cooling of liquefaction unit 2).

[0105] Embodiments of Apparatus 1 may offer operational flexibility in response to turndown or other low hydrogen production conditions. For example, liquefaction unit 2 can be kept cryogenically via the 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 be performed even when there may be no hydrogen feed, and allows for a rapid transition of the liquefaction unit to process hydrogen without significant operational delays that could affect yield or production efficiency when hydrogen production through the hydrogen production system increases due to increased available power or other circumstances.

[0106] Embodiments may be configured so that the liquefaction unit can utilize minimal or relatively low power when hydrogen recirculation is utilized. For example, by utilizing the reserve capacity of the cooling compressor, the operation of the liquefaction unit can be assisted when the hydrogen feed from the production system 20 is low, and the liquid hydrogen can also be recompressed when the liquid hydrogen is flushed to a pressure close to ambient pressure, in order to help keep the power consumption for liquefaction operations low. This may occur while hydrogen recirculation can provide a heat load that can absorb the cooling generated by operating the liquefaction unit cooling system to enable the liquefaction unit 2 to maintain cryogenic temperatures when the hydrogen feed from the hydrogen production system 20 is low (e.g., below a pre-selected minimum flow rate or a pre-selected minimum threshold flow rate) or no hydrogen feed from the hydrogen production system 20.

[0107] Referring to Figure 7, the process for hydrogen recirculation is illustrated. This embodiment of the process can be utilized by running and operating an embodiment of Apparatus 1.

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

[0109] In the second step S2, the flow of liquid hydrogen output from the liquefaction unit 2 can be adjusted to recirculate the hydrogen to the feed inlet of the liquefaction unit. Recirculation may be carried out so that the hydrogen undergoes conversion from para-hydrogen to ortho-hydrogen to reduce the para-hydrogen content of the recirculated hydrogen, as discussed above. Recirculation may 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, using both loops, etc.), as discussed above. Hydrogen recirculation can be activated and controlled so that the amount of recirculated hydrogen provides a sufficient compensatory hydrogen flow rate to compensate for any deviation between the feed flow of hydrogen provided by the hydrogen production system 20 and a pre-selected minimum threshold. For example, when the flow rate of hydrogen from the hydrogen production system 20 may increase (but still fall below a pre-selected minimum threshold), hydrogen recirculation can be adjusted to compensate for these changes, as discussed above, by controlling one or more valves, compressor operation, or other parameters. Similarly, when the hydrogen flow rate from the hydrogen production system 20 may decrease (for example, to a flow rate even lower than a pre-selected minimum threshold), hydrogen recirculation can be adjusted to compensate for these changes by controlling one or more valves, compressor operation, or other parameters, as discussed above.

[0110] In the third step S3, it may be determined that the hydrogen feed is above a pre-selected threshold, and as a result, further hydrogen recirculation may not be permitted. In response to such detection, hydrogen recirculation may be stopped. Examples of such cessation of hydrogen recirculation can be understood from the above. The controller CTRL can be used, for example, to activate such cessation of hydrogen recirculation as described above.

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

[0112] The storage unit 4 for liquid hydrogen may be positioned to receive hydrogen from multiple different liquefaction units 2 or from only a single unit. In embodiments in which the storage unit 4 can receive liquid hydrogen from multiple different liquefaction units, the hydrogen stored therein may be provided to recirculate the hydrogen to one or more of the different liquefaction units in response to a decrease in the hydrogen feed supplied to the liquefaction units to a predetermined threshold or below.

[0113] The embodiments may offer operational flexibility in response to turndown or other low hydrogen production conditions. For example, the embodiments of this process may allow the liquefaction unit 2 to be kept cryogenically low by recirculating hydrogen through a first and / or second recirculation loop to avoid the need for the liquefaction unit 2 to shut down. This type of operation can be performed even when there may be no hydrogen feed, and allows the liquefaction unit to be quickly transitioned to process hydrogen without significant operational delays that could affect yield or production efficiency when hydrogen production through the hydrogen production system increases due to increased available power or other circumstances.

[0114] Embodiments of this process may be implemented so that the liquefaction unit 2 can utilize minimal or relatively low power while hydrogen recirculation is taking place. For example, when the hydrogen feed from the production system is low and hydrogen recirculation is taking place, the reserve capacity of the cooling compressor can be used to support the operation of the liquefaction unit. By utilizing this excess compression capacity, the liquid hydrogen may be assisted in recompressing when the liquid hydrogen is flushed to a pressure close to ambient pressure, in order to help keep the power consumption for liquefaction operations low. This may occur while hydrogen recirculation provides a heat load that can absorb the cooling generated by operating the liquefaction unit cooling system to enable the liquefaction unit 2 to maintain cryogenic temperatures when the hydrogen feed from the hydrogen production system 20 is low or absent.

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

[0116] As yet another example, certain features described individually or as part of one embodiment are intended to be combined with other individually described features or parts of other embodiments. Therefore, further embodiments can be provided by combining elements and actions of the various embodiments described herein. For this reason, while certain exemplary embodiments of processes, apparatus, systems, and methods of manufacturing and using them have been shown and described above, it should be clearly understood that the present invention is not limited thereto and can be embodied and practiced in various other ways within the scope of the following claims. This disclosure includes the following embodiments of the invention: <Aspect 1> It is a process for recirculating hydrogen. The hydrogen feed is supplied to the liquefaction unit, The liquefaction unit liquefies the hydrogen and outputs liquid hydrogen, wherein the output liquid hydrogen has a para-hydrogen content of 80 mole percent (mol%) to 100 mol%. A process comprising: in response to a determination that the hydrogen feed has decreased to below a pre-selected threshold, recirculating the liquid hydrogen to the feed of the liquefaction unit, thereby vaporizing the liquid hydrogen into a gaseous state, undergoing conversion from para-hydrogen to ortho-hydrogen, and recirculating the recirculated hydrogen to the feed of the liquefaction unit, wherein the para-hydrogen content of the recirculated hydrogen is set to 20 mol% para-hydrogen to 30 mol% para-hydrogen. <Aspect 2> The process according to embodiment 1, wherein the hydrogen feed has a parahydrogen content within a pre-selected range of 20 mole percent parahydrogen to 30 mole percent parahydrogen. <Aspect 3> The process according to embodiment 1, comprising stopping the recirculation of the liquid hydrogen in response to a determination that the feed of the hydrogen has increased to a pre-selected threshold. <Aspect 4> The aforementioned recirculation of liquid hydrogen To a conversion unit positioned to convert the aforementioned parahydrogen into orthohydrogen and recirculate the recirculated hydrogen to the feed of the liquefaction unit, the parahydrogen content of the recirculated hydrogen is set to be 20 mol% to 30 mol%, and / or to supply hydrogen with a parahydrogen content of 80 mol% to 100 mol% stored in at least one storage tank, and / or The process according to embodiment 1, comprising supplying the liquid hydrogen output from the liquefaction unit to a heater in a recirculation loop to vaporize the liquid hydrogen, and then passing the vaporized hydrogen through a conversion unit positioned to convert the para hydrogen to ortho hydrogen and recirculate the recirculated hydrogen to the feed of the liquefaction unit, such that the para hydrogen content of the recirculated hydrogen is between 20 mol% and 30 mol% para hydrogen. <Aspect 5> The process includes supplying the liquid hydrogen output from the liquefaction unit, which has a para-hydrogen content of 80 mole percent (mol%) to 100 mol%, to at least one storage tank in the hydrogen storage unit that is in fluid communication with the liquefaction unit, The aforementioned recirculation of liquid hydrogen is Adjusting at least one valve so that the liquid hydrogen output from the liquefaction unit cannot pass through at least one storage tank, The process according to embodiment 1, comprising supplying the liquid hydrogen output from the liquefaction unit to a heater in a recirculation loop to vaporize the liquid hydrogen, and then passing the vaporized hydrogen through a conversion unit positioned to convert the para hydrogen to ortho hydrogen and recirculate the recirculated hydrogen to the feed of the liquefaction unit, such that the para hydrogen content of the recirculated hydrogen is between 20 mol% and 30 mol% para hydrogen. <Aspect 6> To supply hydrogen stored in at least one storage tank to a conversion unit that is positioned to convert the para-hydrogen into ortho-hydrogen and recirculate the recirculated hydrogen to the feed of the liquefaction unit, such that the para-hydrogen content of the recirculated hydrogen is between 20 mol% and 30 mol% para-hydrogen, The process according to embodiment 5, comprising determining that sufficient hydrogen has been recirculated to the liquefaction unit to compensate for the decrease in the hydrogen feed, and then ceasing to supply the hydrogen stored in the at least one storage tank to the conversion unit. <Aspect 7> The aforementioned recirculation of liquid hydrogen is The process according to embodiment 1, comprising compressing the hydrogen before it is supplied to a conversion unit which is positioned to convert the para hydrogen into ortho hydrogen and recirculate the recirculated hydrogen to the feed of the liquefaction unit, so that the para hydrogen content of the recirculated hydrogen is between 20 mol% para hydrogen and 30 mol% para hydrogen. <Aspect 8> The aforementioned recirculation of liquid hydrogen is To a conversion unit positioned to convert the para-hydrogen into ortho-hydrogen and recirculate the recirculated hydrogen to the feed of the liquefaction unit, the para-hydrogen content of the recirculated hydrogen is to be 20 mol% to 30 mol%, and / or to supply hydrogen with a para-hydrogen content of 80 mol% to 100 mol%, stored in at least one storage tank, to a conversion unit, and / or The process includes supplying the liquid hydrogen output from the liquefaction unit to a heater in the recirculation loop to vaporize the liquid hydrogen, and then passing the vaporized hydrogen through a conversion unit that is positioned to convert the para-hydrogen to ortho-hydrogen and recirculate the recirculated hydrogen to the feed of the liquefaction unit, so that the para-hydrogen content of the recirculated hydrogen is between 20 mol% and 30 mol% para-hydrogen. The aforementioned process method, The process according to embodiment 1, comprising supplying liquid hydrogen stored in at least one storage tank to the liquefaction unit in response to the activation of the liquefaction unit when the liquefaction unit is at ambient temperature, in order to facilitate the operation of the liquefaction unit and the cooling of the liquefaction unit to its cryogenic operating temperature, and recirculating the hydrogen output from the liquefaction unit through the recirculation loop during the activation. <Pattern 9> The process according to embodiment 8, wherein a controller having a processor connected to non-temporary memory is positioned and configured to determine whether the hydrogen feed has decreased to below a pre-selected threshold. <Aspect 10> A device for hydrogen recirculation, 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, wherein the liquid hydrogen has a para-hydrogen content of 80 mol% to 100 mol%, An apparatus comprising: a conversion unit positioned to convert parahydrogen to orthohydrogen in the hydrogen output by the liquefaction unit, so that the hydrogen output from the liquefaction unit can be recirculated to the feed inlet of the liquefaction unit with a parahydrogen content of 20 mol% to 30 mol%. <Aspect 11> The recirculation loop conduit heater feed conduit is connected between the liquefaction unit and the recirculation loop conduit heater, and the recirculation loop conduit heater is positioned to heat the liquid hydrogen output from the liquefaction unit and vaporize the liquid hydrogen into gaseous hydrogen. The apparatus according to embodiment 10, wherein the recirculation loop conduit heater is positioned to supply the gaseous hydrogen to the conversion unit. <Aspect 12> The apparatus according to embodiment 10, wherein the conversion unit includes at least one para-hydrogen to ortho-hydrogen converter. <Aspect 13> The apparatus according to embodiment 10, comprising at least one storage tank, wherein the at least one storage tank is positioned to output the hydrogen stored therein and supply the hydrogen to the conversion unit. <Aspect 14> The apparatus according to embodiment 13, further comprising 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. <Aspect 15> A recirculation loop conduit heater feed conduit connected between the liquefaction unit and the recirculation loop conduit heater, wherein the recirculation loop conduit heater is positioned to heat the liquid hydrogen output from the liquefaction unit to vaporize the liquid hydrogen into gaseous hydrogen, and the recirculation loop conduit heater is positioned to supply the gaseous hydrogen to the conversion unit, and / or The apparatus according to embodiment 10, further comprising 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. <Aspect 16> A recirculation loop conduit heater feed conduit connected between the liquefaction unit and the first recirculation loop conduit heater, wherein the first recirculation loop conduit heater is positioned to heat the liquid hydrogen output from the liquefaction unit to vaporize the liquid hydrogen into gaseous hydrogen, and the first recirculation loop conduit heater is positioned to supply the gaseous hydrogen to the conversion unit, and The apparatus according to embodiment 10, further comprising a second 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. <Aspect 17> The apparatus according to embodiment 10, further comprising a compression system positioned upstream of the conversion unit to compress the hydrogen in order to supply the hydrogen to the conversion unit. <Aspect 18> A device for hydrogen recirculation, 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, wherein the liquid hydrogen has a para-hydrogen content of 80 mol% to 100 mol%, A conversion unit positioned to convert para-hydrogen to ortho-hydrogen in the hydrogen output by the liquefaction unit so that the hydrogen output from the liquefaction unit can be recirculated to the feed inlet of the liquefaction unit with a para-hydrogen content of 20 mol% to 30 mol%, wherein the conversion unit includes at least one para-hydrogen to ortho-hydrogen converter. The at least one storage tank, the at least one storage tank being positioned to output the hydrogen stored therein in response to the hydrogen feed being below a pre-selected threshold, and to supply the hydrogen to the conversion unit, A recirculation loop conduit heater feed conduit connected between the liquefaction unit and the first recirculation loop conduit heater, wherein the first recirculation loop conduit heater is positioned to heat the liquid hydrogen output from the liquefaction unit to vaporize the liquid hydrogen into gaseous hydrogen, and the first recirculation loop conduit heater is positioned to supply the gaseous hydrogen to the conversion unit, An apparatus comprising: a second recirculation loop heater positioned to receive hydrogen from the at least one storage tank and heat the hydrogen so that hydrogen output from the at least one storage tank supplied to the conversion unit can be supplied to the conversion unit as gaseous hydrogen. <Aspect 19> The apparatus according to embodiment 18, further comprising a compression system positioned upstream of the conversion unit to compress the hydrogen in order to supply the hydrogen to the conversion unit. <Aspect 20> The apparatus according to embodiment 18, wherein the liquefaction unit has a closed-loop cooling system or an open-loop cooling system.

Claims

1. It is a process for recirculating hydrogen. The hydrogen feed is supplied to the liquefaction unit, The liquefaction unit liquefies the hydrogen and outputs liquid hydrogen, wherein the output liquid hydrogen has a para-hydrogen content of 80 mole percent (mol%) to 100 mol%. A process comprising: in response to a determination that the hydrogen feed has decreased to below a pre-selected threshold, recirculating the liquid hydrogen to the feed of the liquefaction unit, thereby vaporizing the liquid hydrogen into a gaseous state, undergoing conversion from para-hydrogen to ortho-hydrogen, and recirculating the recirculated hydrogen to the feed of the liquefaction unit to a para-hydrogen content of 20 mol% to 30 mol%.

2. The process according to claim 1, wherein the hydrogen feed has a parahydrogen content within a pre-selected range of 20 mole percent parahydrogen to 30 mole percent parahydrogen.

3. The process according to claim 1, comprising stopping the recirculation of the liquid hydrogen in response to a determination that the feed of the hydrogen has increased to a pre-selected threshold.

4. The aforementioned recirculation of liquid hydrogen To a conversion unit positioned to convert the aforementioned parahydrogen into orthohydrogen and recirculate the recirculated hydrogen to the feed of the liquefaction unit so that the parahydrogen content of the recirculated hydrogen is 20 mol% to 30 mol%, hydrogen with a parahydrogen content of 80 mol% to 100 mol stored in at least one storage tank is supplied, and / or The process according to claim 1, comprising supplying the liquid hydrogen output from the liquefaction unit to a heater in a recirculation loop to vaporize the liquid hydrogen, and then passing the vaporized hydrogen through a conversion unit positioned to convert the para hydrogen to ortho hydrogen and recirculate the recirculated hydrogen to the feed of the liquefaction unit, such that the para hydrogen content of the recirculated hydrogen is between 20 mol% and 30 mol% para hydrogen.

5. The process includes supplying the liquid hydrogen output from the liquefaction unit, which has a para-hydrogen content of 80 mole percent (mol%) to 100 mol%, to at least one storage tank in the hydrogen storage unit that is in fluid communication with the liquefaction unit, The aforementioned recirculation of liquid hydrogen is Adjusting at least one valve so that the liquid hydrogen output from the liquefaction unit cannot pass through at least one storage tank, The process according to claim 1, comprising supplying the liquid hydrogen output from the liquefaction unit to a heater in a recirculation loop to vaporize the liquid hydrogen, and then passing the vaporized hydrogen through a conversion unit positioned to convert the para hydrogen to ortho hydrogen and recirculate the recirculated hydrogen to the feed of the liquefaction unit, such that the para hydrogen content of the recirculated hydrogen is between 20 mol% and 30 mol% para hydrogen.

6. To supply hydrogen stored in at least one storage tank to a conversion unit positioned to convert the para-hydrogen into ortho-hydrogen and recirculate the recirculated hydrogen to the feed of the liquefaction unit, such that the para-hydrogen content of the recirculated hydrogen is 20 mol% to 30 mol% para-hydrogen, The process according to claim 5, further comprising determining that sufficient hydrogen has been recirculated to the liquefaction unit to compensate for the decrease in the hydrogen feed, and then ceasing to supply the hydrogen stored in the at least one storage tank to the conversion unit.

7. The aforementioned recirculation of liquid hydrogen is The process according to claim 1, comprising compressing the hydrogen before it is supplied to a conversion unit which is positioned to convert the para hydrogen into ortho hydrogen and recirculate the recirculated hydrogen to the feed of the liquefaction unit, so that the para hydrogen content of the recirculated hydrogen is between 20 mol% and 30 mol% para hydrogen.

8. The aforementioned recirculation of liquid hydrogen is To a conversion unit positioned to convert the parahydrogen into orthohydrogen and recirculate the recirculated hydrogen to the feed of the liquefaction unit, the parahydrogen content of the recirculated hydrogen is to be between 20 mol% and 30 mol%, and / or to supply hydrogen with a parahydrogen content of 80 mol% to 100 mol stored in at least one storage tank, and / or The process includes supplying the liquid hydrogen output from the liquefaction unit to a heater in the recirculation loop to vaporize the liquid hydrogen, and then passing the vaporized hydrogen through a conversion unit that is positioned to convert the para-hydrogen to ortho-hydrogen and recirculate the recirculated hydrogen to the feed of the liquefaction unit, so that the para-hydrogen content of the recirculated hydrogen is between 20 mol% and 30 mol% para-hydrogen. The aforementioned process method, The process according to claim 1, comprising supplying liquid hydrogen stored in at least one storage tank to the liquefaction unit in response to the activation of the liquefaction unit when the liquefaction unit is at ambient temperature, in order to facilitate the operation of the liquefaction unit and the cooling of the liquefaction unit to its cryogenic operating temperature, and recirculating the hydrogen output from the liquefaction unit through the recirculation loop during the activation.

9. The process according to claim 8, wherein a controller having a processor connected to non-temporary memory is positioned and configured to determine whether the hydrogen feed has decreased to below a pre-selected threshold.

10. A device for hydrogen recirculation, 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, wherein the liquid hydrogen has a para-hydrogen content of 80 mol% to 100 mol%, The system includes a conversion unit positioned to convert the parahydrogen of the hydrogen output by the liquefaction unit into orthohydrogen, so that the hydrogen output from the liquefaction unit can be recirculated to the feed inlet of the liquefaction unit with a parahydrogen content of 20 mol% to 30 mol%, and The recirculation loop conduit heater feed conduit is connected between the liquefaction unit and the recirculation loop conduit heater, and the recirculation loop conduit heater is positioned to heat the liquid hydrogen output from the liquefaction unit and vaporize the liquid hydrogen into gaseous hydrogen. An apparatus in which the recirculation loop conduit heater is positioned to supply the gaseous hydrogen to the conversion unit.

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

12. The apparatus according to claim 10, comprising at least one storage tank, wherein the at least one storage tank is positioned to output the hydrogen stored therein and supply the hydrogen to the conversion unit.

13. The apparatus according to claim 12, further comprising 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.

14. A device for hydrogen recirculation, 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, wherein the liquid hydrogen has a para-hydrogen content of 80 mol% to 100 mol%, The system includes a conversion unit positioned to convert the parahydrogen of the hydrogen output by the liquefaction unit into orthohydrogen, so that the hydrogen output from the liquefaction unit can be recirculated to the feed inlet of the liquefaction unit with a parahydrogen content of 20 mol% to 30 mol%, and A recirculation loop conduit heater feed conduit connected between the liquefaction unit and the first recirculation loop conduit heater, wherein the first recirculation loop conduit heater is positioned to heat the liquid hydrogen output from the liquefaction unit to vaporize the liquid hydrogen into gaseous hydrogen, and the first recirculation loop conduit heater is positioned to supply the gaseous hydrogen to the conversion unit, and An apparatus comprising a second 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.

15. The apparatus according to claim 10, further comprising a compression system positioned upstream of the conversion unit to compress the hydrogen in order to supply the hydrogen to the conversion unit.

16. A device for hydrogen recirculation, 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, wherein the liquid hydrogen has a para-hydrogen content of 80 mol% to 100 mol%, A conversion unit positioned to convert parahydrogen to orthohydrogen in the hydrogen output by the liquefaction unit so that the hydrogen output from the liquefaction unit can be recirculated to the feed inlet of the liquefaction unit with a parahydrogen content of 20 mol% to 30 mol%, wherein the conversion unit includes at least one parahydrogen to orthohydrogen converter. The at least one storage tank, the at least one storage tank being positioned to output the hydrogen stored therein and supply the hydrogen to the conversion unit in response to the hydrogen feed being below a pre-selected threshold, A recirculation loop conduit heater feed conduit connected between the liquefaction unit and the first recirculation loop conduit heater, wherein the first recirculation loop conduit heater is positioned to heat the liquid hydrogen output from the liquefaction unit to vaporize the liquid hydrogen into gaseous hydrogen, and the first recirculation loop conduit heater is positioned to supply the gaseous hydrogen to the conversion unit, An apparatus comprising: a second recirculation loop heater positioned to receive hydrogen from the at least one storage tank and heat the hydrogen so that the hydrogen output from the at least one storage tank supplied to the conversion unit can be supplied to the conversion unit as gaseous hydrogen.

17. The apparatus according to claim 16, further comprising a compression system positioned upstream of the conversion unit to compress the hydrogen in order to supply the hydrogen to the conversion unit.

18. The apparatus according to claim 16, wherein the liquefaction unit has a closed-loop cooling system or an open-loop cooling system.

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