Apparatus and method for hydrogen recirculation to avoide shutdown of a liquefier by

Abstract

In some embodiments, an apparatus and method for recycling hydrogen may be provided such that hydrogen is recycled in a hydrogen liquefaction process to cope with unexpected loss of feed of hydrogen, and thus recycled hydrogen may be provided to avoid the liquefier operation must be shut down. Embodiments may utilize a parahydrogen to ortho-hydrogen conversion unit to facilitate such recycle of hydrogen to avoid liquefaction processing problems in liquefaction of the recycled hydrogen contained in the feed to cope with loss of feed hydrogen.

Description

Technical Field

[0001] The present invention relates to methods and apparatus for hydrogen liquefaction, and methods and apparatus for recycling hydrogen in hydrogen liquefaction processing. Background Technology

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

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

[0004] Hydrogen liquefaction typically occurs during processes requiring relatively stable conditions. For example, the hydrogen stream for liquefaction can be provided by at least one hydrogen production source that operates with a reliable supply of hydrogen-forming materials and a reliable power supply, which can be provided by conventional power sources (e.g., electricity generated from the combustion of natural gas or other fossil fuels, hydrogen production via steam reforming using fossil fuel sources, etc.).

[0005] In contrast to this type of hydrogen production method, green hydrogen production can be provided by using renewable power to power hydrogen production. Such systems can produce hydrogen through the electrolysis of water, powered by renewable energy sources such as solar and / or wind power. However, this type of production method can experience significant production fluctuations due to varying weather conditions, which can greatly affect the power available to support the electrolysis of water. Typically, hydrogen production can vary significantly daily or every few days, depending on various weather conditions (e.g., duration of daylight relative to nighttime duration, cloud cover, wind availability, etc.). We have found that green hydrogen production systems can frequently see significant variations in hydrogen output, and liquefaction plants that can be positioned to liquefy hydrogen from such production systems may need to be shut down frequently due to insufficient hydrogen feedstock to support liquefaction processing. Shutdowns of liquefaction processing can involve substantial costs in terms of lost production. There are other significant costs associated with downtime of such equipment. For example, restarting a liquefaction process can take a relatively long time, which may result in production losses when renewable power increases to support sufficient hydrogen output for feed into the liquefaction system, and delays during startup may affect the ability to effectively utilize the produced hydrogen. Furthermore, equipment degradation due to periodic changes in operating conditions can lead to more frequent equipment replacements or otherwise shorter operational lives, potentially increasing maintenance costs, reducing processing flexibility, and making downtime or other problems due to equipment failure more likely.

[0006] Conventionally, expensive storage units can be provided to act as a buffer between hydrogen production and liquefaction systems, helping to ensure the liquefaction system can operate should a hydrogen supply become unavailable. However, this type of conventional approach can require significant capital expenditures related to storage. Furthermore, hydrogen storage can lead to losses due to the need to control overpressure of stored hydrogen and other storage-related processing complexities.

[0007] We have found that these types of problems can be better addressed by providing an apparatus and method for recycling hydrogen output from a liquefaction unit, allowing liquid hydrogen to be vaporized and subsequently recycled back into the feed to the liquefaction unit to address hydrogen feed shortages. We have surprisingly found that this type of approach can be advantageous in terms of energy use and the process complexity associated with the liquid hydrogen produced, as it avoids liquefaction unit downtime and also helps mitigate or limit the amount of storage that may be needed to support liquefaction operations during periods of low hydrogen production rates.

[0008] We have found, surprisingly, that this type of approach can be particularly advantageous in implementations where hydrogen is fed through a production system powered by renewable energy sources, which may experience variable hydrogen production rates due to weather conditions, daylight conditions (e.g., daylight compared to night, cloudy conditions, etc.), or other conditions that may affect the power available for hydrogen production. In some cases, such systems may frequently experience variable production (e.g., at least 3 times per week, at least 12 times per month, at least 200 times per year, etc.), and we have found, surprisingly, that it can be beneficial to bear the costs and production complexities associated with recycling already liquefied hydrogen back to the liquefaction unit as feed to avoid liquefaction unit downtime due to insufficient hydrogen feed for extended periods (e.g., during nighttime, during rainy days, etc.). This can be particularly challenging in cases where there are short periods of zero production (e.g., this could be between 2 and 12 hours due to transient weather conditions affecting power availability). The duration of power unavailability can be much shorter than the time typically required for a complete liquefaction process shutdown and subsequent startup (which could potentially take a full 24 hours). We were surprised to find that, in such cases, keeping the liquefaction process online in full recycle mode may be more beneficial to avoid prolonged downtime, allowing the liquefaction process to catch up with production more easily once power availability is restored to supply hydrogen to the liquefaction process, while also avoiding product emissions (e.g., emissions of hydrogen products).

[0009] We determined that if the liquefaction process is to remain operational in the event that hydrogen production is halted or significantly slowed due to unexpected power loss, the refrigeration machinery that cools the hydrogen for liquefaction may require a heat load (e.g., feed hydrogen) to maintain online and productive capacity. Without a heat load, the liquefaction process would overcool all its equipment above its design temperature, necessitating a process shutdown. Surprisingly, we found that an alternative feed hydrogen could be provided as a recirculated stream, recycling hydrogen from the liquefaction process's output back into the process's feed, replacing the lost hydrogen feed that could occur if a lack of power availability leads to a halt in hydrogen production or a significant reduction in hydrogen production (which would significantly reduce (or stop) the supply of feed hydrogen for liquefaction).

[0010] To make such recycling effective, and also to avoid problems of refrigeration mechanical limitations, refrigeration loads, and cryogenic conditions in liquefaction units that can output liquid hydrogen with a content of at least 95 molar percentage of secondary hydrogen, we have also surprisingly discovered that the secondary and primary hydrogen contents of the recycled hydrogen can be controlled to provide improved performance. This also avoids processing problems that could damage, degrade, and / or cause unexpected failures that could lead to production problems or liquefaction shutdowns due to the use of recycled hydrogen.

[0011] For example, we have surprisingly found that a secondary hydrogen content exceeding 25 mol% in the feed of a liquefaction unit used for hydrogen liquefaction may require significant adjustments to the refrigeration system of the liquefaction unit. Typically, the hydrogen feed used for liquefaction has a secondary hydrogen content of approximately 25 mol%. The conversion of hydrogen from orthohydrogen to secondary hydrogen releases energy, and the secondary hydrogen content can increase as hydrogen is cooled for liquefaction. The refrigeration system of the liquefaction unit can be designed to absorb this heat generated from the conversion of orthohydrogen to secondary hydrogen to facilitate the cooling and liquefaction of hydrogen. If the hydrogen feed used for liquefaction has a higher secondary hydrogen content than expected (e.g., significantly greater than 25 mol%, exceeding 25 mol%, etc.), the heat released from the conversion of orthohydrogen to secondary hydrogen may be less than the amount the liquefaction unit is designed to contain due to the reduced availability of orthohydrogen for conversion. Such a reduction in heat can lead to overcooling of the refrigeration system, causing the temperature of the equipment to drop below the temperature required for the stable capacity of the cryogenic machinery utilized in the liquefaction unit. Such situations can lead to equipment tripping or other problems, requiring the liquefaction process to be shut down. We have found that such situations can be avoided by utilizing a secondary hydrogen to positive hydrogen conversion unit to help control the secondary hydrogen content in the hydrogen recycled to the liquefaction unit, thereby better controlling the secondary hydrogen content in the feed hydrogen, including recycled hydrogen. This type of conversion unit can help provide improved secondary hydrogen content control for the feed hydrogen, including hydrogen recycled from the liquefaction unit, to avoid liquefaction downtime and equipment degradation, while also avoiding processing delays and production efficiency losses that may occur due to the need to repeatedly cycle the liquefaction unit between shutdown and operation.

[0012] In a first aspect, a method for recycling hydrogen is provided. The method may include feeding hydrogen into a liquefaction unit. The liquefaction unit may liquefy the hydrogen to output liquid hydrogen. The liquid hydrogen may have a secondary hydrogen content between 80 mol% and 100 mol%. In response to determining that the hydrogen feed has decreased to or below a pre-selected threshold, the liquid hydrogen may be recycled into the feed of the liquefaction unit, such that the liquid hydrogen is vaporized into a gaseous state and undergoes a secondary hydrogen to positive hydrogen conversion, such that the secondary hydrogen content of the recycled hydrogen in the feed to the liquefaction unit has a secondary hydrogen content between 20 mol% and 30 mol%.

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

[0014] In some implementations, the hydrogen feed can be provided by a hydrogen generation system that can be configured to operate using renewable power.

[0015] In a second aspect, the method may further include stopping the recycling of liquid hydrogen in response to determining that the hydrogen feed has increased to or above a pre-selected threshold. In some embodiments of the method, recycling and stopping recycling may occur in multiple different operating cycles in response to, for example, the rate of hydrogen feed supplied to the liquefaction unit.

[0016] In a third aspect, the recycling of liquid hydrogen may include feeding hydrogen stored in at least one storage tank, having a secondary hydrogen content between 80 mol% and 100 mol%, toward a conversion unit configured to convert secondary hydrogen to positive hydrogen, such that the secondary hydrogen content of the recycled hydrogen in the feed to the liquefaction unit has a secondary hydrogen content between 20 mol% and 30 mol%, and / or feeding liquid hydrogen from the liquefaction unit to a heater in a recycle loop to vaporize the liquid hydrogen, and subsequently conveying the vaporized hydrogen to a conversion unit configured to convert secondary hydrogen to positive hydrogen, such that the secondary hydrogen content of the recycled hydrogen in the feed to the liquefaction unit has a secondary hydrogen content between 20 mol% and 30 mol%. In some embodiments, both steps may be performed. In other embodiments, only one of these steps may be performed.

[0017] In a fourth aspect, the method may include feeding liquid hydrogen from the liquefaction unit, having a secondary hydrogen content between 80 mol% and 100 mol% of secondary hydrogen, into at least one storage tank in fluid communication with the liquefaction unit. In some embodiments, the recycling of liquid hydrogen may include regulating at least one valve such that liquid hydrogen from the liquefaction unit cannot be conveyed to at least one storage tank, and feeding liquid hydrogen from the liquefaction unit into a heater in the recycling loop to vaporize the liquid hydrogen, and subsequently conveying the vaporized hydrogen to a conversion unit configured to convert secondary hydrogen into positive hydrogen, such that the secondary hydrogen content of the recycled hydrogen in the feed to the liquefaction unit has a secondary hydrogen content between 20 mol% and 30 mol% of secondary hydrogen.

[0018] In a fifth aspect, the method may further include feeding hydrogen stored in at least one storage tank toward a conversion unit, which is configured to convert secondary hydrogen into positive hydrogen, such that the secondary hydrogen content of the recycled hydrogen in the feed to the liquefaction unit has a secondary hydrogen content between 20 mol% and 30 mol%. After determining that sufficient hydrogen has been recycled to the liquefaction unit to compensate for a reduction in the hydrogen feed, the feeding of hydrogen stored in at least one storage tank toward the conversion unit may be ceased or stopped.

[0019] In a sixth aspect, the recycling of liquid hydrogen may include compressing the hydrogen before feeding it into a conversion unit, which is configured to convert secondary hydrogen into positive hydrogen, such that the secondary hydrogen content of the recycled hydrogen in the feed to the liquefaction unit has a secondary hydrogen content between 20 mol% and 30 mol%.

[0020] In a seventh aspect, the recycling of liquid hydrogen may include feeding hydrogen stored in at least one storage tank having a secondary hydrogen content between 80 mol% and 100 mol% toward a conversion unit configured to convert secondary hydrogen to positive hydrogen, such that the secondary hydrogen content of the recycled hydrogen in the feed to the liquefaction unit has a secondary hydrogen content between 20 mol% and 30 mol%; and / or feeding liquid hydrogen from the liquefaction unit to a heater in the recycling loop to vaporize the liquid hydrogen, and subsequently conveying the vaporized hydrogen to a conversion unit configured to convert secondary hydrogen to positive hydrogen, such that the secondary hydrogen content of the recycled hydrogen in the feed to the liquefaction unit has a secondary hydrogen content between 20 mol% and 30 mol%. An embodiment of the method may further include: when the liquefaction unit is at ambient temperature, in response to the start-up of the liquefaction unit, feeding liquid hydrogen stored in at least one storage tank into the liquefaction unit to facilitate the operation of the liquefaction unit and cooling the liquefaction unit to a cryogenic operating temperature, and recirculating the hydrogen output from the liquefaction unit via a recirculation loop during start-up.

[0021] In an eighth aspect, the method can be configured to utilize a controller having a processor connected to a non-transitory memory. The controller can be positioned and configured to determine whether the hydrogen feed has decreased to or below a pre-selected threshold.

[0022] In the ninth aspect, the method of the first aspect may include one or more features of the second, third, fourth, fifth, sixth, seventh, and / or eighth aspects. However, other embodiments may also include other features. Examples of such other features include, for instance, the features of the exemplary embodiments discussed herein.

[0023] A tenth aspect provides an apparatus for hydrogen recirculation. Embodiments of the apparatus may include a liquefaction unit configured to liquefy a hydrogen feed to output a first liquid hydrogen stream for feeding the liquid hydrogen into at least one storage tank. The liquid hydrogen may have a secondary hydrogen content between 80 mol% and 100 mol%. The apparatus may further include a conversion unit positioned to convert the secondary hydrogen of the hydrogen output from the liquefaction unit into positive hydrogen, such that the hydrogen output from the liquefaction unit can be recycled back to the feed inlet of the liquefaction unit, wherein the secondary hydrogen content is between 20 mol% and 30 mol%. Embodiments of the apparatus may be configured to implement an embodiment of a method for hydrogen recirculation.

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

[0025] In a twelfth aspect, the conversion unit includes at least one secondary-to-positive hydrogen converter. In some embodiments, the conversion unit may include a single secondary-to-positive hydrogen converter. In other embodiments, the conversion unit may include multiple secondary-to-positive hydrogen converters. In some embodiments, all converters may operate in parallel. In other embodiments, some may operate in parallel while others may operate in series. In still other embodiments having multiple secondary-to-positive hydrogen converters, the converters may be arranged in series operation.

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

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

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

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

[0030] In a seventeenth aspect, the apparatus may include a compression system positioned upstream of the conversion unit for compressing hydrogen for feeding hydrogen into the conversion unit. The compression system may include a single compressor or a series of compressors. In some embodiments, the compression system may include at least one multi-stage compressor or a single-stage compressor.

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

[0032] For example, in the nineteenth aspect, the apparatus for hydrogen recirculation may include a liquefaction unit configured to liquefy a hydrogen feed to output a first liquid hydrogen stream for feeding the liquid hydrogen into at least one storage tank. The liquid hydrogen may have a secondary hydrogen content between 80 mol% and 100 mol%. A conversion unit may be positioned to convert the secondary hydrogen in the hydrogen output from the liquefaction unit into positive hydrogen, such that the hydrogen output from the liquefaction unit can be recirculated to the feed inlet of the liquefaction unit, wherein the secondary hydrogen content is between 20 mol% and 30 mol%. The conversion unit may include at least one secondary hydrogen to positive hydrogen converter. At least one storage tank may be positioned to output hydrogen stored therein in response to the hydrogen feed being at or below a pre-selected threshold for feeding hydrogen into the conversion unit. A recirculation loop conduit heater feed conduit may be connected between the liquefaction unit and the first recirculation loop conduit heater. The first recirculation loop conduit heater may be positioned to heat the liquid hydrogen output from the liquefaction unit to vaporize the liquid hydrogen into gaseous hydrogen. The first recirculation loop conduit heater can be positioned to feed gaseous hydrogen into the conversion unit. The second recirculation loop heater can be positioned to receive hydrogen from at least one storage tank and heat the hydrogen such that hydrogen to be fed into the conversion unit from at least one storage tank can be fed into the conversion unit as gaseous hydrogen.

[0033] In some implementations, the compression system can be located upstream of the conversion unit to compress the hydrogen for use as a feedstock into the conversion unit.

[0034] Implementation schemes of the apparatus and methods can utilize liquefaction units with different types of refrigeration systems. For example, in some implementations, the liquefaction unit may have a closed-loop refrigeration system. In other implementations, the liquefaction unit may have an open-loop refrigeration system.

[0035] It should be understood that implementations of this method and apparatus can utilize various conduit arrangements and process control elements. These implementations can utilize sensors (e.g., pressure sensors, temperature sensors, flow sensors, concentration sensors, etc.), controllers, valves, piping, and other process control elements. For example, some implementations can utilize automated process control systems and / or distributed control systems (DCS). A variety of different conduit arrangements and process control systems can be used to meet a specific set of design criteria.

[0036] Further details, objectives, and advantages of the apparatus for hydrogen recirculation, the method for hydrogen recirculation, the hydrogen liquefaction apparatus, the hydrogen liquefaction method, and the apparatus, method, and system for providing hydrogen recirculation to avoid liquefaction shutdown, as well as methods of manufacture and use thereof, will become apparent as a result of the following description of specific exemplary embodiments thereof. Attached Figure Description

[0037] Apparatus for hydrogen recirculation, methods for hydrogen recirculation, hydrogen liquefaction apparatuses, hydrogen liquefaction methods, and apparatuses, methods, and systems for hydrogen recirculation that can prevent liquefaction unit shutdown, as well as methods of manufacture and use thereof, are shown in the accompanying drawings contained herein. It should be understood that the same reference numerals used in the drawings may identify the same parts.

[0038] Figure 1 (Figure 1) (It can also be called) Figure 1 FIG. 1 is a block diagram of a first exemplary embodiment of a device 1 for hydrogen recycling. Some optional elements of this exemplary embodiment of the device are shown in... Figure 1 The figure is shown in dashed lines. An exemplary embodiment of a method for recycling hydrogen is also shown in the figure.

[0039] Figure 2 (It can also be called) Figure 2 This is a block diagram of a first exemplary embodiment of a first exemplary embodiment of an apparatus 1 for recycling hydrogen. An exemplary embodiment of a method for recycling hydrogen is also shown in the figure.

[0040] Figure 3 (It can also be called) Figure 3 This is a block diagram of a second exemplary embodiment of a first exemplary embodiment of an apparatus 1 for recycling hydrogen. An exemplary embodiment of a method for recycling hydrogen is also shown in the figure.

[0041] Figure 4 (It can also be called) Figure 4 This is a block diagram of a second exemplary embodiment of a device 1 for hydrogen recirculation. Different compressors are used in... Figure 4 The figure is shown in dashed lines because at least one such compressor may be optional for this particular embodiment. An exemplary embodiment of a method for hydrogen recycling is also shown in the figure.

[0042] Figure 5 (It can also be called) Figure 5 This is a block diagram of a first exemplary embodiment of a second exemplary embodiment of an apparatus 1 for recycling hydrogen. An exemplary embodiment of a method for recycling hydrogen is also shown in the figure.

[0043] Figure 6 (It can also be called) Figure 6 This is a block diagram of a second exemplary embodiment of a second exemplary embodiment of an apparatus 1 for recycling hydrogen. An exemplary embodiment of a method for recycling hydrogen is also shown in the figure.

[0044] Figure 7(It can also be called) Figure 7 This is a flowchart illustrating an exemplary embodiment of a method for preventing liquefier operation from being shut down during hydrogen recirculation. Embodiments of the apparatus for hydrogen recirculation can implement this exemplary embodiment of the method. Detailed Implementation

[0045] refer to Figures 1 to 7 The hydrogen feed can be returned to the liquefaction unit 2 by using device 1 for hydrogen recirculation. In some embodiments, device 1 can be configured to provide hydrogen recirculation in response to a reduction in the hydrogen feed 15 supplied to the liquefaction unit 2 to a preselected feed rate (e.g., a preselected volumetric flow rate defining a threshold for actuating hydrogen recirculation, a preselected mass flow rate defining a threshold for actuating hydrogen recirculation, etc.). Hydrogen recirculation can be actuated to help avoid shutdown of the liquefaction unit 2 in response to low feed rate conditions, thereby avoiding production delays associated with liquefaction unit shutdown and subsequent startup, as well as equipment degradation that may occur due to such operations involving cycling between actuated and shutdown operating conditions.

[0046] We have found, surprisingly, that this type of approach may be particularly advantageous in implementations where the hydrogen feed 15 is provided by a production system powered by renewable energy, which may experience variable hydrogen production rates due to weather conditions, daylight conditions (e.g., daytime compared to nighttime, cloudy conditions, etc.), or other conditions that may affect the power available for hydrogen production. In some cases, such systems may frequently experience variable production (e.g., 200 times or more per year), and we have found, surprisingly, that it may be beneficial to bear the costs and production complexities associated with using already liquefied hydrogen as feed for recycling back to liquefaction unit 2 in order to avoid downtime of the liquefaction unit due to insufficient hydrogen feed for a period of time (e.g., during nighttime, during rainy days, etc.).

[0047] The liquefaction unit 2, which may be supported by the device 1 for hydrogen recycling, may include one or more liquefiers or one or more rows of liquefiers for liquefying the hydrogen feed 15. The liquefaction unit 2 may be configured, for example, as a hydrogen liquefaction system (HLS), which may include one or more rows of liquefiers. The hydrogen liquefaction system (HLS) may include a series of expanders and hydrogen liquefaction heat exchangers. Some embodiments of the liquefaction system may also include a positive hydrogen to secondary hydrogen conversion unit to convert the positive hydrogen in the liquefied hydrogen into secondary hydrogen, thereby increasing the secondary hydrogen content of the liquefied hydrogen.

[0048] The liquefaction unit 2 can be configured to output a stream of liquid hydrogen, which may have a relatively high secondary hydrogen content. In some embodiments, the secondary hydrogen content of the liquid hydrogen output from the liquefaction unit may be at least 80 mol% secondary hydrogen or at least 95 mol% secondary hydrogen (e.g., between 80 mol% and 100 mol% secondary hydrogen, between 95 mol% and 100 mol% secondary hydrogen, etc.). During operation in which a suitable hydrogen feed supply is fed into the liquefaction unit 2, the stream of liquid hydrogen output from the liquefaction unit 2 may be fed into a storage device 4 for storage and subsequent supply to one or more customers (e.g., via shipping the liquid hydrogen, transporting the liquid hydrogen to another location or production facility, etc.). The storage device 4 for the liquid hydrogen may include at least one tank or other container for storing the liquid hydrogen at cryogenic temperatures to help keep the liquid hydrogen in a liquid state.

[0049] The hydrogen feed 15 supplied to liquefaction unit 2 may comprise hydrogen that is entirely gaseous (e.g., 100% gaseous), or may comprise a stream of hydrogen that is predominantly gaseous (e.g., a stream of gaseous hydrogen having liquid hydrogen between 0% and 1% by volume). The hydrogen feed 15 may be a common hydrogen product comprising, for example, a concentration of 25 mol% secondary hydrogen and 75 mol% orthohydrogen. The hydrogen feed 15 may be provided via at least one hydrogen production system 20. The hydrogen production system 20 may include a hydrogen generation system (HGS) that may include one or more electrolyzers capable of forming hydrogen from the electrolysis of water. In some embodiments, the electrolyzers of such a hydrogen production system 20 may be powered by at least one renewable energy source (e.g., solar, wind, hydropower, combinations thereof) to provide the feed of green hydrogen produced via renewable power.

[0050] The hydrogen feed provided by the hydrogen production system 20 may have a secondary hydrogen content of about 25 mol% secondary hydrogen, with the balance being positive hydrogen. For example, the hydrogen feed 15 provided by the hydrogen production system 20 may have a secondary hydrogen content between 20 mol% and 30 mol% (e.g., 25 mol% or about 25 mol%), and the positive hydrogen content may be between 80 mol% and 70 mol% (e.g., 75 mol% or about 75 mol%).

[0051] The hydrogen feedstock 15 can be powered by renewable energy sources, which may experience variable hydrogen production rates due to weather conditions, daylight conditions (e.g., daylight compared to night, cloudy conditions, etc.), or other conditions that may affect the power available for hydrogen production. In some cases, such systems may be designed to frequently experience variable production (e.g., at least 3 times per week, at least 12 times per month, at least 200 times per year, etc.), and we have surprisingly found that to avoid downtime of liquefaction unit 2 due to insufficient hydrogen feedstock for a period of time (e.g., during nighttime, during rainy days, etc.), it may be beneficial to bear the costs and production complexities associated with recycling the liquefied hydrogen output from liquefaction unit 2 back to hydrogen feedstock 15 to provide a supplemental hydrogen flow to support the operation of liquefaction unit 15. Hydrogen recycling can be achieved by using hydrogen within storage unit 4 and / or by route-fed hydrogen output from liquefaction unit 2, such that hydrogen is transported back to the feedstock of liquefaction unit 2, rather than being route-fed to storage unit 4. This recycling can involve the vaporization of liquid hydrogen output from the liquefaction unit, so that the hydrogen recycled back to the feed inlet of liquefaction unit 2 is in a gaseous state (e.g., hydrogen gas instead of liquid hydrogen).

[0052] Liquefaction unit 2 can output liquid hydrogen with a secondary hydrogen content of at least 95 mol% . Regarding the recycling of hydrogen from liquefaction unit 2, we have surprisingly discovered that the secondary and primary hydrogen contents of the recycled hydrogen fed into the liquefaction unit's inlet can be controlled to provide improved performance. This also avoids processing problems that could damage, degrade, and / or cause unexpected malfunctions that could lead to production issues or liquefaction shutdowns due to the use of recycled hydrogen. The secondary hydrogen content of the recycled hydrogen can be controlled via the conversion unit 11 such that the recycled hydrogen, together with any low-flow hydrogen that can be supplied as feed 15 from the hydrogen production system 20, can have a preselected secondary hydrogen content of 25 mol% or less, 30 mol% or less, or another suitable secondary hydrogen content feed threshold or less, which can be set to prevent the liquefaction equipment from being overcooled by cooling the hydrogen including the recycled hydrogen.

[0053] We have surprisingly found that a secondary hydrogen content exceeding 25 mol% or significantly exceeding 25 mol% in the feed of a liquefaction unit used for hydrogen liquefaction may require significant modifications to the refrigeration system of the liquefaction unit. Typically, the hydrogen feed used for liquefaction has a secondary hydrogen content of approximately 25 mol%. The conversion of hydrogen from orthohydrogen to secondary hydrogen releases energy, and the secondary hydrogen content can increase as hydrogen is cooled for liquefaction. The refrigeration system of the liquefaction unit can be designed to absorb this heat generated from the conversion of orthohydrogen to secondary hydrogen to facilitate the cooling and liquefaction of the hydrogen.

[0054] If the hydrogen feed to liquefaction unit 2 for liquefaction has a higher secondary hydrogen content than expected (e.g., significantly greater than 25 mol% secondary hydrogen content, exceeding 25 mol% secondary hydrogen content, etc.), the heat released from the conversion of orthohydrogen to secondary hydrogen may be less than the amount the liquefaction unit is designed to hold due to the reduced amount of orthohydrogen available for conversion (this may occur solely because hydrogen output from the liquefaction unit is recycled back to the feed to liquefaction unit 2 in sufficient quantities to significantly alter the secondary hydrogen content in the hydrogen feed to liquefaction unit 2). Such a reduction in heat can cause the refrigeration system to overcool the hydrogen during liquefaction, resulting in the equipment temperature dropping below the temperature required for the stable capacity of the cryogenic machinery utilized in the liquefaction unit. We have determined that this type of situation could lead to equipment tripping or other problems, requiring the liquefaction process to be shut down.

[0055] We have found that by utilizing a secondary hydrogen to positive hydrogen conversion unit 11 (CVRT) to help control the secondary hydrogen content of the hydrogen being recycled to the feed inlet of liquefaction unit 2, thereby better controlling the secondary hydrogen content in the hydrogen feed (which includes recycled hydrogen fed to the feed inlet of liquefaction unit 2), such problems that may be caused by over-refrigeration can be avoided. This type of conversion unit 11 (CVRT) may include one or more secondary hydrogen to positive hydrogen converters to convert secondary hydrogen in the recycled hydrogen to positive hydrogen, helping to provide improved secondary hydrogen content control for the feed hydrogen, including hydrogen recycled from the liquefaction unit, to avoid liquefaction downtime and equipment degradation, while also avoiding processing delays and production efficiency losses that may occur due to the need to repeatedly cycle the liquefaction unit between shutdown and operation states. When there is no hydrogen feed 15 available from the hydrogen production system 20, or when there is a very low rate of hydrogen feed from the hydrogen production system 20 such that recycled hydrogen constitutes a significant portion of the total hydrogen fed to the liquefaction unit (e.g., at least 30% of the hydrogen is recycled hydrogen, at least 50% of the hydrogen feed is recycled hydrogen, and between 50% and 100% of the hydrogen fed to the liquefaction unit 2 as hydrogen feed 15 is recycled hydrogen, etc.), this type of control over the secondary hydrogen content in the recycled hydrogen can help control the secondary hydrogen content in the hydrogen fed to the inlet of the liquefaction unit 2 in cases where recycled hydrogen constitutes all the hydrogen fed to the liquefaction unit 2. An example of a very low feed rate for the hydrogen feed 15 could be no feed at all, or a feed so low that the heat load of the hydrogen feed 15 drops below a pre-selected minimum threshold required by the refrigeration system of the liquefaction process to keep the refrigeration machinery operating within its predetermined temperature limits.

[0056] Hydrogen recycling may not occur continuously. Instead, hydrogen recycling can be provided in response to determining that the hydrogen feed 15 is at or below a pre-selected hydrogen feed rate or is expected to be at or below a pre-selected hydrogen feed rate for at least a pre-selected low hydrogen feed period. Hydrogen recycling can be initiated or actuated in response to the detection of such a condition. Recycled hydrogen can initially be provided via a long recirculation loop (LRP) using hydrogen stored in storage unit 4, and subsequently via a short recirculation loop (SRP) for the recycling of hydrogen output from liquefaction unit 2, such that this hydrogen bypasses feeding into storage unit 4 and is instead recycled directly back to the inlet of liquefaction unit 2. In other embodiments, recycled hydrogen may always be provided via the short recirculation loop (SRP) or always via the long recirculation loop (LRP) (e.g., there may be no usage switching between loops, and only the short recirculation loop (SRP) or the long recirculation loop (LRP) may be present). In other embodiments, the recycled hydrogen may initially be supplied via a short recycle loop (SRP) and / or a long recycle loop (LRP) (e.g., a combination of stored hydrogen from the storage unit and liquid hydrogen output from the liquefaction unit is recycled instead of being sent to storage unit 4), and may subsequently be supplied via the short recycle loop (SRP).

[0057] After detecting that the hydrogen feed 15 supplied by the hydrogen production system 20 is at or above a pre-selected hydrogen feed rate, or is expected to remain at or above a pre-selected hydrogen feed rate for an extended period beyond a pre-selected low hydrogen feed time, hydrogen recycling can be terminated or slowed down until the hydrogen feed rate supplied by the hydrogen production system 20 is at or above the pre-selected hydrogen feed rate. Because low feed rates below a predetermined minimum threshold required for the operation of the liquefaction unit 2 may be detected during many different operating cycles due to varying weather conditions or other conditions that may affect hydrogen production at the hydrogen production system 20, which is positioned to supply hydrogen to the liquefaction unit 2, such switching between hydrogen recycling and non-recycling operations can be repeatedly provided.

[0058] To address low feed rates of hydrogen from hydrogen production system 20, hydrogen recycling can be dynamically adjusted. For example, when hydrogen is unavailable from hydrogen production system 20, hydrogen recycling can be provided at a higher capacity to supply sufficient hydrogen to the inlet of liquefaction unit 2, allowing the unit to operate without having to shut down at a pre-selected minimum operating capacity. If hydrogen feed 15 is present but very low and below a pre-selected minimum threshold, the amount of recycled hydrogen can be varied to supplement hydrogen supply, such that the hydrogen feed to inlet 15b of the liquefaction unit is at or above the pre-selected minimum threshold.

[0059] Figures 1 to 6Different exemplary embodiments of various devices for providing hydrogen recycling are shown. Implementations of methods for hydrogen recycling can also be understood from these figures. Figures 1 to 3 The first exemplary embodiment illustrates an exemplary recycling process that can be provided in a case where the liquefaction unit 2 can be liquefied using an open-loop refrigeration system. Figures 4 to 6 The second exemplary embodiment illustrates an exemplary recycling process that can be provided in a case where the liquefaction unit 2 can utilize a closed-loop refrigeration system for liquefaction operations.

[0060] The hydrogen feed 15 into liquefaction unit 2 can be at a pre-selected feed pressure (e.g., between 100 kPa and 4000 kPa or other suitable feed pressures) and a pre-selected feed temperature (e.g., between 0°C and 100°C, between ambient temperature and below 65°C, between 0°C and 65°C or other suitable temperatures). The secondary hydrogen content of the hydrogen feed can also be within a pre-selected range (e.g., between 20 mol% and 30 mol%).

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

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

[0063] When the hydrogen feed rate 15 to liquefaction unit 2 is at or above a pre-selected feed rate, the liquid hydrogen output from liquefaction unit 2 can be fed to storage device 4 for retention in one or more liquid hydrogen storage tanks. The liquid hydrogen fed therein can be retained at a pre-selected storage pressure (e.g., between 100 kPa and 150 kPa or other suitable pressure). A liquid hydrogen storage device feed conduit 3a can be connected between storage device 4 and liquefaction unit 2 to route liquid hydrogen to storage device 4 for storage in one or more storage tanks. The liquid hydrogen retained in storage device 4 can be fed to one or more trailers for transport to customers via trucks, railcars, or other types of transport, or can be fed to another process element in an industrial facility located elsewhere for hydrogen use. As described above, the liquid hydrogen in storage device 4 can have a relatively high secondary hydrogen content of at least 80 mol% or at least 95 mol%.

[0064] During operation, the hydrogen feed 15 may vary significantly due to changing production conditions at the hydrogen production system 20 (e.g., weather conditions affecting the available power for water electrolysis, etc.). Such changes may result in a significant reduction or cessation of hydrogen feed 15 from the hydrogen production system 20. In response to the detection of no hydrogen feed or hydrogen feed at or below a pre-selected threshold (e.g., a pre-selected volumetric flow rate defining a threshold for actuating hydrogen recirculation, a pre-selected mass flow rate defining a threshold for actuating hydrogen recirculation, etc.), at least some of the liquid hydrogen output from the liquefaction unit 2 can be recirculated. Recirculation may occur via a first recirculation loop and / or a second recirculation loop (e.g., a short recirculation loop SRP and / or a long recirculation loop LRP).

[0065] For example, a short recirculation loop (SRP) can be provided for routing at least a portion of the liquid hydrogen output from liquefaction unit 2 back along a path to the feed conduit for hydrogen feed, so as to return the hydrogen feed to the inlet of 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 liquefaction unit 2 and recirculation loop conduit heater 5. In some embodiments, heater 5 may be an ambient air vaporizer, an ambient air heat exchanger, a heat exchanger using water as a heating medium (e.g., water at ambient temperature, heated water, etc.), or other suitable heat exchangers that can use the heating medium to heat liquid hydrogen to vaporize the hydrogen, for outputting a vaporized hydrogen stream 5b from the heater for route delivery to conversion unit 11, which includes at least one secondary hydrogen to positive hydrogen converter for adjusting the positive hydrogen content and secondary hydrogen content of the recycled hydrogen to about 25 mol% secondary hydrogen content.

[0066] For example, heater 5 may be in fluid communication with a compression feed conduit 7b arranged in the recirculation conduit of device 1 to feed 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). Compression system 9 may compress hydrogen to a higher pressure for feeding into the inlet of liquefaction unit 2 and to facilitate hydrogen passage through conversion unit 11. Compression system 9 may output hydrogen gas to feed the gas via conversion unit feed conduit 9a positioned between compression system 9 and conversion unit 11 to at least one secondary hydrogen to positive hydrogen conversion device of conversion unit 11. Conversion unit 11 may process the hydrogen gas to convert secondary hydrogen to positive hydrogen such that the secondary hydrogen content of the hydrogen gas output from conversion unit 11 has a secondary hydrogen content not exceeding 25 mol% or not exceeding 30 mol% (e.g., secondary hydrogen between 20 mol% and 30 mol% and positive hydrogen between 80 mol% and 70 mol%, etc.). Hydrogen with an improved secondary hydrogen content can be output from conversion unit 11 and fed into a feed conduit, through which hydrogen feed 15 can be fed into the inlet of the liquefaction unit. Conversion unit supply conduit 11a can be connected between liquefaction unit 2 and conversion unit 11 to feed hydrogen output from conversion unit into liquefaction unit.

[0067] In some embodiments, the conversion unit supply conduit 11a can feed hydrogen from the conversion unit 11 into a feed conduit, through which hydrogen feed 15 can be mixed online with hydrogen from the hydrogen production system 20 and fed together to the inlet of the liquefaction unit 2. Alternatively, the conversion unit supply conduit 11a can deliver hydrogen to the inlet of the liquefaction unit for mixing with hydrogen from the hydrogen production system 20 (if supplied) at the inlet area of ​​the liquefaction unit 2.

[0068] A long recirculation loop (LRP) can be provided, which is also used to route at least a portion of the liquid hydrogen output from the liquefaction unit 2 back to the feed conduit for hydrogen feed, to return the hydrogen feed to the feed inlet of the liquefaction unit 2, or as an alternative to using a short recirculation loop (SRP). The long recirculation loop (LRP) may include at least one storage tank of the storage device 4, which feeds the hydrogen stored in the tank to the heater 7 via a storage tank recirculation conduit 4c positioned between the hydrogen storage device 4 and the heater 7.

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

[0070] The recirculation loop conduit heater 7 can be positioned to further heat the hydrogen output from the storage device 4, so that the hydrogen is gaseous, for feeding into 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 an ambient air vaporizer, an ambient air heat exchanger, a heat exchanger using water as a heating medium (e.g., ambient temperature water, heated water, etc.), or other suitable heat exchanger that can use the heating medium to heat liquid hydrogen to vaporize the hydrogen, for outputting a stream of gaseous hydrogen from the heater 7 for route delivery to the conversion unit 11, which includes at least one secondary hydrogen to positive hydrogen converter for adjusting the positive hydrogen content and secondary hydrogen content of the recirculated hydrogen to about 25 mol% secondary hydrogen content.

[0071] Compression system 9 can receive hydrogen from heater 5 of short recirculation loop (SRP) and / or heater 7 of long recirculation loop (LRP) to compress the hydrogen and output it to conversion unit 11 (CVRT) via conversion unit feed conduit 9a positioned between compression system 9 and conversion unit 11. Conversion unit 11 can process hydrogen from long recirculation loop (LRP) and / or a combination of hydrogen from short recirculation loop (SRP) and long recirculation loop (LRP) to convert secondary hydrogen to positive hydrogen, such that the secondary hydrogen content of the hydrogen output from conversion unit 11 has a secondary hydrogen content of no more than 25 mol% or no more than 30 mol% (e.g., secondary hydrogen between 20 mol% and 30 mol% and positive hydrogen between 80 mol% and 70 mol%). Hydrogen with improved secondary hydrogen content can be output from conversion unit 11 for feeding into feed conduit 15, through which hydrogen feed 15 can be fed into the inlet of liquefaction unit. The conversion unit supply conduit 11a can be connected between the liquefaction unit 2 and the conversion unit 11 to feed hydrogen from the conversion unit to the liquefaction unit.

[0072] In some embodiments, the recycled hydrogen may initially be supplied via at least one storage tank of the hydrogen storage unit 4, and subsequently entirely via a short recycle loop (SRP), such that during such recycles, the recycled hydrogen bypasses the feed to the storage unit 4 after the initial supply of hydrogen from the storage unit 4. In other embodiments, the recycled hydrogen may initially be supplied via at least one storage tank of the hydrogen storage unit 4 and via a route transported from the liquefaction unit to the short recycle loop (SRP). After a sufficient amount of hydrogen has been supplied for recycle, hydrogen recycle may subsequently be supplied entirely via the short recycle loop (SRP), such that during such recycles, the recycled hydrogen bypasses the feed to the storage unit 4 after the initial supply of hydrogen from the storage unit 4. In still other embodiments, the short recycle loop (SRP) may not be provided, and only the long recycle loop (LRP) may be used for hydrogen recycle.

[0073] In an embodiment that can utilize both a short recirculation loop (SRP) and a long recirculation loop (LRP), 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 helps to heat the hydrogen output from the liquefaction unit 2 (e.g., shortly after being output or after the hydrogen is stored in the hydrogen storage device 4), so that gaseous hydrogen can be fed into the conversion unit 11 for hydrogen recycling.

[0074] An embodiment of device 1 can be configured for use in conjunction with an open-loop refrigeration system (OLP) of liquefaction unit 2. The open-loop refrigeration system (OLP) may include a liquefaction unit that outputs at least one first hydrogen stream 23, which may be at a lower pressure, for feeding into a compression system for compression by at least one low-pressure compressor of compression system 9. 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 feeding into compression system 9 for compression therein, and subsequently for feeding back into the liquefaction unit for refrigeration that will also occur during liquefaction. Utilization of compression system 9 for a refrigeration system can be provided to facilitate an open-loop refrigeration scheme in which hydrogen can be used as a refrigerant. Compressed hydrogen to be used as a refrigerant in the open-loop refrigeration system (OLP) can be output from compression system 9 for feeding as a refrigerant into the liquefaction unit heat exchanger via at least one refrigerant feed conduit 9b connected between compression system 9 and the refrigeration system of liquefaction unit 2.

[0075] At least one storage tank of the hydrogen storage device 4 can be fluidly connected to the refrigeration system of the liquefaction unit 2 to also provide hydrogen as a refrigerant. For example, a hydrogen refrigerant feed conduit 21 can be connected between the storage tank of the hydrogen storage device 4 and the refrigeration system of the liquefaction unit 2 to feed hydrogen from the hydrogen storage device 4 to the refrigeration system of the liquefaction unit 2.

[0076] Device 1 can also be configured to facilitate discharge via at least one discharge duct VT. For example, hydrogen can be discharged if the hydrogen already output from liquefaction unit 2 does not meet a pre-selected hydrogen content specification. In some embodiments, such discharge can occur downstream of at least one heater (e.g., heater 5 of short recirculation loop SRP, heater 7 of long recirculation loop LRP, ambient air heater of discharge duct, etc.), such that the discharged hydrogen is warmed to a suitable discharge temperature for release into the outside atmosphere.

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

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

[0079] In some implementations, the phase separation system PS can be positioned to facilitate Joule-Thomson cooling of liquid hydrogen via depressurization. Partially flashed cold vapor (e.g., hydrogen) that may form can be output as a hydrogen stream 3c and sent to, for example, an open-loop refrigeration system. Alternatively, the hydrogen vapor can be routed from the phase separation system as a low-pressure hydrogen vapor stream LPV to a compression system 9 for recirculation back to the inlet of liquefaction unit 2 or the refrigeration system of liquefaction unit 2 via the compression system 9.

[0080] In some embodiments, at least one trailer 8 may be connected to a long recirculation loop (LRP). The trailer 8 may be positioned to receive hydrogen from a storage unit for supplying hydrogen to another location. The trailer (TRLR) may alternatively comprise hydrogen and be positioned to feed hydrogen into the recirculation loop in cases where replenishment is needed and there is an insufficient supply of liquid hydrogen in the hydrogen storage unit 4 for recirculation to the liquefaction unit 2, to provide sufficient hydrogen replenishment in response to a reduction in the flow rate of the hydrogen feed 15, which can actuate hydrogen recirculation. For example, the trailer 8 may be fluidly connected to a short recirculation loop (SRP) or a long recirculation loop (LRP) for supplying hydrogen for feeding hydrogen to the conversion unit 11 to regulate the secondary and primary hydrogen content of the hydrogen to be recirculated to the inlet of the liquefaction unit 2.

[0081] Figure 2 It shows Figure 1An exemplary embodiment of the apparatus 1 shown is described. The compression system 9 may include a first compressor C1 and a second compressor C2, and the hydrogen output from the liquefaction unit 2, which is part of an open-loop refrigeration system, may include a first hydrogen stream 23, which may be at a lower pressure, for feeding into the compression system 9 for compression by the first compressor C1, and subsequently undergoing further compression via the second compressor C2 of the compression system 9. The liquefaction unit 2 may also output a second hydrogen stream 25, which may be at a higher pressure than the first hydrogen stream 23, for feeding into the second compressor C2 of the compression system 9 for compression therein, and subsequently being fed back into the liquefaction unit for refrigeration that also occurs during liquefaction; and / or a conversion unit 11 for recycling (in the case of utilizing a recirculation loop due to the low level of hydrogen feed supplied to the liquefaction unit 2).

[0082] As from Figure 2 As can be understood from the exemplary embodiment shown, the apparatus 1 for hydrogen recycling may not utilize the phase separation system PS. A first liquid hydrogen stream 2a and a second liquid hydrogen stream 2b may be output from the liquefaction unit 2 and subsequently combined to be fed into the hydrogen storage unit 4 via the liquid hydrogen storage unit feed conduit 3a. In response to a decrease in the hydrogen feed rate, at least some of the liquid hydrogen may also be routed to a short recycling loop via the recirculation loop conduit heater feed conduit 5a, which may be connected to the liquid hydrogen storage unit feed conduit 3a and / or may be connected between the liquefaction unit 2 and the heater 5 of the recirculation loop conduit heater feed conduit 5a.

[0083] In other configurations, the Short Recircuit Loop (SRP) may not be provided. Instead, only the Long Recircuit Loop (LRP) can be utilized. In such embodiments, liquid hydrogen from at least one storage tank of the hydrogen storage unit 4 can be supplied as feed to the conversion unit via the LRP conduit. Hydrogen from at least one trailer 8 can also be used to help supply a hydrogen stream to the liquefaction unit for hydrogen recycling to support its operation when the feed of hydrogen to be supplied by the hydrogen production system 20 is too low or absent.

[0084] As from Figure 3As can be understood from the example embodiment shown, the compression system 9 may include a first compressor C1 as a low-pressure compressor, a second compressor C2 as a medium-pressure compressor, and a third compressor C3 as a high-pressure compressor. Such a configuration can be used for a high-pressure liquefaction unit 2, which can liquefy hydrogen using the high-pressure, low-pressure, and medium-pressure refrigeration elements of its refrigeration system. The liquefaction unit 2 may output a first hydrogen stream 23, which may be at a lower pressure, for feeding into the compression system 9 for compression by the first compressor C1, and subsequently undergoing further compression via the second compressor C2 and the third compressor C3 of the compression system 9. The liquefaction unit 2 may also output a second hydrogen stream 25, which may be at an intermediate pressure higher than the first hydrogen stream 23, for feeding into the second compressor C2 of the compression system 9 for compression therein, and subsequently compressed by the third compressor C3, for subsequent feeding back into the liquefaction unit for refrigeration that also occurs during liquefaction; and / or a conversion unit 11 for recycling (in the case of utilizing a recirculation loop due to the low level of hydrogen feed supplied to the liquefaction unit 2). Another second hydrogen stream 25 can be output from the refrigeration system of the liquefier 2, which can be at a high pressure higher than the first hydrogen stream 23 and also higher than the intermediate pressure of the other second hydrogen stream 25, for feeding into the third compressor C3 of the compression system 9 for compression therein, for subsequent feeding back to the liquefaction unit for refrigeration that also occurs during liquefaction; and / or the conversion unit 11 for recycling (in the case of the use of a recycling loop due to the 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 the single-phase separator PH, or it may include only the subcooler 3 without using an upstream phase separator.

[0086] For example, the liquefaction unit can output a liquid hydrogen stream that also includes hydrogen (e.g., between 3 volume percentage (volume%) and 10 volume percentage hydrogen, between 5 volume percentage and 25 volume percentage hydrogen, between greater than 0 volume percentage and 40 volume percentage gas, etc.). The liquid hydrogen stream, including hydrogen, can be fed into the phase separation system PS, so that it passes through the phase separator PH, and a large amount of hydrogen can be 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 can be returned to the liquefaction unit as a low-pressure hydrogen vapor stream LPV for recycling back to the inlet of the liquefaction unit 2, or for use in a refrigeration system fed into the liquefaction unit via a compression system 9, for example, for routed delivery to the inlet of the liquefaction unit 2. Such route-based delivery can occur when the device has insufficient hydrogen feed from the hydrogen generation system, and can also occur when the hydrogen feed from the hydrogen generation system 20 is at or above the pre-selected feed rate for normal operation of the liquefaction unit without hydrogen recirculation.

[0087] Most or all of the liquid hydrogen (e.g., at least 95% by volume) can be output from the phase separator PH for feeding into the subcooler 3 via the phase separator output conduit 3b connected between the phase separator PH and the subcooler 3. Additional hydrogen can be output from the subcooler 3 as a hydrogen stream 3c for supplying the liquefaction unit via a hydrogen return conduit connected between the subcooler 3 and the liquefaction unit 2. As described above, such a hydrogen stream can be fed into the refrigeration system of the liquefaction unit, or it can be routed back to the liquefaction unit as a low-pressure hydrogen vapor stream LPV for recirculation back to the feed port of the liquefaction unit 2 (e.g., by being fed into the compression system 9 for subsequent feeding into the feed port of the liquefaction unit 2 or the refrigeration system of the liquefaction unit 2). For example, such routed delivery can occur when the device has insufficient feed of hydrogen from the hydrogen generation system. Such route-based delivery can also occur when the plant has a sufficient feed of hydrogen from the hydrogen production system 20, at or above the pre-selected feed rate for normal operation of the liquefaction unit, without hydrogen recycling.

[0088] Cooled liquid hydrogen can be output from the subcooler 3 and fed towards the hydrogen storage unit 4 and / or the short recirculation loop (SRP) via the 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 can be returned to the subcooler 3 via the phase separation conduit 3d connected between the phase separation system and the liquid hydrogen storage unit feed conduit 3a to facilitate hydrogen subcooling.

[0089] As from Figures 4 to 6It is understood that the embodiment of the device 1 for hydrogen recirculation can also be used in conjunction with a liquefaction unit 2, which can utilize a closed-loop refrigeration system (CLP). Such a closed-loop refrigeration system (CLP) can have a dedicated closed-loop compressor 31 (CP) to help drive the refrigerant flow in the closed-loop arrangement for hydrogen liquefaction. In this configuration, the liquefaction unit 2 may not receive hydrogen from the compressor of the hydrogen storage device 4 and / or the recirculation conduit; other hydrogen can also be used as refrigerant for the refrigeration system via the recirculation conduit. Conversely, the refrigerant utilized by the refrigeration system for the liquefaction unit can be provided in a closed-loop arrangement.

[0090] In such closed-loop refrigeration system environments, the recirculation conduit arrangement for hydrogen recirculation can utilize different compression system arrangements. For example, a compressor 41 located upstream of the conversion unit 11 can be present to compress hydrogen for feeding into the conversion unit 11 and subsequently recirculating to the inlet of the liquefaction unit 2. As another example, a compressor 43 located downstream of the heater 7 can be present, through which hydrogen from at least one storage tank of the hydrogen storage device 4 can be heated for recirculation via the conversion unit 11 to the inlet of the liquefaction unit 2. In embodiments where multiple such compressors can be used, compressor 43 can be a low-pressure compressor LC, and an additional compressor 41 downstream of this compressor can be a high-pressure compressor (HC) that can further compress the hydrogen to a second higher pressure for recirculation (e.g., high or medium pressure).

[0091] In other arrangements, the feed conduit 15 for the hydrogen supplied to the liquefaction unit 2 may include a feed compressor. In such configurations, the excess capacity of the feed compressor, which may exist due to a reduction in the hydrogen feed from the hydrogen production system 20, can be used to help drive the hydrogen stream being recirculated via the short recirculation loop (SRP) and / or the long recirculation loop (LRP).

[0092] In some exemplary implementations (such as) Figure 5 In the exemplary embodiment shown, a low-pressure compressor LC can be used downstream of the heater 7 to receive hydrogen from the hydrogen storage device 4 and / or at least one trailer 8 for feeding into the conversion unit 11 for recirculation to the liquefaction unit 2. A recirculation loop conduit heater output conduit 7a can be connected between the recirculation loop conduit heater 7 and the compressor 43 to feed hydrogen to the compressor for output via a conversion unit feed conduit 9a positioned between the compressor 43 and the conversion unit 11 for feeding into the conversion unit 11.

[0093] Hydrogen that can be recycled via the short recirculation loop (SRP) can be output from the heater 5, which is arranged in conduits for the loop, and fed into the conversion unit 11 via the 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 transported to the conversion unit 11 along the route.

[0094] In other exemplary implementations (such as...) Figure 6 In an exemplary embodiment, the high-pressure compressor HC can 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 can be positioned as compressor system 9, similar to... Figure 1 The positioning of the compression system 9 in the open-loop refrigeration implementation scheme (but does not receive hydrogen flow from the refrigeration system of liquefaction unit 2 for compression of these flow).

[0095] As described above, various exemplary embodiments and implementations of device 1 can be configured to provide hydrogen recirculation in response to a reduction of the hydrogen feed 15 supplied to the liquefaction unit 2 for hydrogen liquefaction to a preselected feed rate (e.g., a preselected volumetric flow rate defining a threshold for actuating hydrogen recirculation, a preselected mass flow rate defining a threshold for actuating hydrogen recirculation, etc.). Hydrogen recirculation can be actuated to help avoid shutdown of the liquefaction unit 2 in response to low feed rate conditions, thereby avoiding production delays associated with liquefaction unit shutdown and subsequent startup, as well as equipment degradation that may occur due to such operations involving cycling between actuated and shutdown operating conditions.

[0096] like Figures 1 to 6 As shown, a controller CTRL can be provided to detect such conditions for actuating hydrogen recirculation via one or more sensors. These sensors can be positioned to monitor or measure the flow rate of hydrogen feed 15 at location 15a and / or the hydrogen feed flow rate at the inlet 15b of the liquefaction unit 2, upstream of the location where the recirculation flow can be fed into the inlet of the liquefaction unit 2 via the conversion unit supply conduit 11a. For example, the one or more sensors can be flow sensors and / or pressure sensors. The controller CTRL can communicatively connect to the sensors to receive data from them to determine whether the hydrogen feed is at or below a pre-selected threshold for actuating hydrogen recirculation. The controller CTRL can also, or alternatively, receive data from one or more sensors or other elements of the hydrogen production system 20 that can provide input indicating when the hydrogen feed can be reduced to the pre-selected threshold for actuating hydrogen recirculation.

[0097] The controller CTRL can also communicatively connect to one or more sensors positioned to monitor or measure the flow rate of liquid hydrogen output from liquefaction unit 2 for use in controlling valve V, which actuates the recirculation of hydrogen to the inlet of the liquefaction unit. The controller can utilize this flow data to communicate with valves in one or more recirculation loops for appropriate portions of liquid hydrogen recirculation in response to a lack of sufficient hydrogen feed from hydrogen production system 20. Valve V can be dynamically adjusted to accommodate changes in hydrogen feed conditions 15, allowing the recirculated portion of hydrogen to be adjusted from no hydrogen recirculation to full recirculation of output hydrogen, in response to the detected flow rate of hydrogen feed 15 provided by hydrogen production system 20.

[0098] The controller CTRL can be a computer device, including a processor connected to non-transitory memory and at least one transceiver. The controller CTRL can also be communicatively connected to a valve to actuate valve regulation for hydrogen recirculation.

[0099] The controller CTRL can be configured to regulate the hydrogen flow output from liquefaction unit 2 via communication with different valves V, in response to a determination that the hydrogen feed is too low (e.g., reduced to below a pre-selected feed rate, reduced to below a pre-selected feed rate and possibly at that lower rate for at least a pre-selected hydrogen recirculation period, etc.) through the short recirculation loop (SRP) and / or long recirculation path (LRP). Such configuration of the controller CTRL can be implemented via automated process control logic defined in code in the controller's non-transitory memory and executable by the controller's processor.

[0100] For example, in some embodiments, the controller CTRL can communicate with valve V of the liquid hydrogen storage unit feed conduit 3a to close valve V and open valve V of the recirculation loop conduit heater feed conduit 5a connecting the liquefaction unit 2 and the recirculation loop conduit heater 5, to initiate the recirculation of hydrogen output from the liquefaction unit to the conversion unit 11, for the hydrogen to be recirculated back to the liquefaction unit's inlet with a reduced secondary hydrogen content. The controller CTRL can also communicate with valve V of the storage tank recirculation conduit 4c located between the hydrogen storage unit 4 and the heater 7 to open valve V to supply hydrogen from the hydrogen storage unit 4 to the conversion unit 11, for the hydrogen to be recirculated back to the liquefaction unit's inlet with a reduced secondary hydrogen content. The controller CTRL can also communicate with valve V of the conversion unit supply conduit 11a to open valve V to facilitate the feeding of hydrogen to the liquefaction unit's inlet for hydrogen recirculation after the secondary hydrogen content of the hydrogen has been regulated via the conversion unit 11. After a sufficient amount of hydrogen is supplied from storage tank 4 to replenish the reduced amount of hydrogen received from hydrogen production system 20, controller CTRL can communicate with valve V of storage tank recirculation conduit 4c to close valve V, so that short recirculation loop SRP can then be dedicated to hydrogen recirculation until the hydrogen feed from hydrogen production system 20 increases to the desired level.

[0101] In other arrangements where a short recirculation loop (SRP) may not be provided, the controller CTRL can communicate with valve V of the storage tank recirculation conduit 4c located between the hydrogen storage unit 4 and the heater 7 to open valve V to supply hydrogen from the hydrogen storage unit 4 to the conversion unit 11 for recirculation back to the liquefaction unit inlet with a reduced secondary hydrogen content. The controller CTRL can also communicate with valve V of the conversion unit supply conduit 11a to open valve V to facilitate the feeding of hydrogen to the liquefaction unit inlet for hydrogen recirculation after the secondary hydrogen content of the hydrogen has been adjusted via the conversion unit 11. The controller CTRL can communicate with valve V of the storage tank recirculation conduit 4c to close valve V, and can also communicate with valve V of the conversion unit supply conduit 11a to close valve V after the hydrogen feed from the hydrogen production system 20 has increased to a desired level, also facilitating the cessation of hydrogen recirculation.

[0102] In some other arrangements where a long recirculation loop (LRP) may not be utilized, the controller CTRL can communicate with a valve on the liquid hydrogen storage unit feed duct 3a to close valve V and open valve V on the recirculation loop heater feed duct 5a connecting the liquefaction unit 2 and the recirculation loop heater 5, thereby initiating the recirculation of hydrogen from the liquefaction unit to the conversion unit 11, allowing hydrogen to be recirculated back to the liquefaction unit feed inlet with a reduced secondary hydrogen content. The controller CTRL can also communicate with valve V on the recirculation loop heater feed duct 5a to close valve V, and can also communicate with valve V on the conversion unit supply duct 11a to close valve V after the hydrogen feed from the hydrogen production system 20 has increased to a desired level, thus facilitating the cessation of hydrogen recirculation.

[0103] The controller CTRL can communicate with different valves to adjust their positions to more or less open and / or closed positions in response to the flow rate of the hydrogen feed 15 provided by the hydrogen production system 20, and the comparison of that flow rate with a pre-selected minimum threshold flow rate. In the absence of hydrogen feed, the valve V for hydrogen recirculation can be fully open, for example, to provide a recirculated hydrogen flow to compensate for the lack of hydrogen feed from the hydrogen production system 20. In the presence of hydrogen feed but at a flow rate significantly lower than the pre-selected minimum threshold flow rate, the valve for hydrogen recirculation can be partially open (but less open than when no hydrogen feed is provided), but not necessarily in a fully open position, to provide a recirculated hydrogen flow that can provide supplemental hydrogen flow to compensate for deviations from the pre-selected minimum threshold flow rate. In cases where the hydrogen feed rate is only slightly below a pre-selected minimum threshold flow rate, the valve for hydrogen recirculation can be partially opened to a smaller extent to provide a recirculated hydrogen flow that can compensate for this slight deviation from the pre-selected minimum threshold flow rate.

[0104] We have also surprisingly discovered that utilizing short recirculation loop (SRP) and long recirculation loop (LRP) can provide several other benefits. For example, during the startup of the liquefaction unit, initially at ambient temperature, the long recirculation loop (LRP) can provide pure hydrogen for cooling the liquefaction unit equipment, and the short recirculation loop (SRP) can be used to help accelerate the cooling of the liquefaction unit 2. This type of method for cooling the liquefaction unit after its operational startup allows such cooling to occur with no emissions or minimal emissions (e.g., due to the lack of impurities in the hydrogen used to facilitate the cooling of liquefaction unit 2).

[0105] The implementation of Unit 1 can provide operational flexibility in response to reduced or other low hydrogen production conditions. For example, liquefaction unit 2 can be maintained at a cryogenic temperature via a long recirculation loop (LRP) and / or a short recirculation loop (SRP) using Unit 1 for hydrogen recirculation, to avoid the need for shutdown of liquefaction unit 2. This type of operation can occur even when there may be no hydrogen feed, allowing the liquefaction unit to be quickly switched to hydrogen processing when hydrogen production via the hydrogen production system increases due to increased available power or other circumstances, without significant lag in operation that could affect yield or production efficiency.

[0106] The implementation scheme can be configured such that the liquefaction unit can utilize minimum or relatively low power when utilizing hydrogen recycling. For example, when the hydrogen feed from production system 20 is low, the spare capacity of the refrigeration compressor can be used to help operate the liquefaction unit, and when the liquid hydrogen is flashed to near atmospheric pressure, it can be recompressed to help keep the power drawdown for liquefaction operations low. This may occur when hydrogen recycling can provide a heat load that can absorb the refrigeration generated by the operating liquefaction unit's refrigeration system, allowing the liquefaction unit 2 to maintain a cryogenic temperature in the event of low hydrogen feed from hydrogen production system 20 (e.g., hydrogen feed from the hydrogen generation system (HGS) below a pre-selected minimum flow rate or a pre-selected minimum threshold flow rate) or no hydrogen feed from the hydrogen production system.

[0107] refer to Figure 7 A method for hydrogen recycling is shown. An embodiment of apparatus 1 can be implemented and operated to utilize this method.

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

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

[0110] In the third step S3, it can be determined that the hydrogen feed is at or above a pre-selected threshold, such that hydrogen recycling is no longer guaranteed. In response to this detection, hydrogen recycling can be terminated. An example of such a stop to hydrogen recycling can be understood from the above. For example, as described above, the controller CTRL can be used to actuate such a stop to hydrogen recycling.

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

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

[0113] The implementation scheme can provide operational flexibility in response to reduced or other low hydrogen production conditions. For example, an implementation of the method can allow liquefaction unit 2 to be maintained at a cryogenic temperature via hydrogen recirculation through a first recirculation loop and / or a second recirculation loop, to avoid the need to shut down liquefaction unit 2. This type of operation can occur even when there may be no hydrogen feed, allowing the liquefaction unit to be quickly switched to hydrogen processing when hydrogen production via the hydrogen production system increases due to increased available power or other circumstances, without significant lag in operation that could affect yield or production efficiency.

[0114] An implementation of this method can be made such that liquefaction unit 2 can utilize minimum or relatively low power when hydrogen recirculation is also occurring. For example, when the hydrogen feed from the production system is low and hydrogen recirculation is in progress, the spare capacity of the refrigeration compressor can be used to assist in operating the liquefaction unit. This excess compression capacity can be used to help recompress the liquid hydrogen when it is flashed to near atmospheric pressure, in order to help keep the power drawdown for liquefaction operations low. This may occur when hydrogen recirculation can provide a heat load that can absorb the refrigeration generated by the operating liquefaction unit's refrigeration system, allowing liquefaction unit 2 to maintain a low temperature even with a low hydrogen feed from hydrogen production system 20 or no hydrogen feed from the hydrogen production system.

[0115] It should also be understood that the implementation schemes of apparatus 1 and method can be modified to meet a specific set of criteria for different implementation schemes of the apparatus or method. For example, the arrangement of valves, sensors, pipes, and other conduit elements (e.g., conduit connection mechanisms, pipelines, seals, valves, etc.) used to interconnect different units of the apparatus for fluid communication between different components can be arranged to meet a specific facility layout design that takes into account the available area of ​​the apparatus, the equipment size of the apparatus, the preferred type of automated process control scheme and / or distributed control scheme, and other design considerations. The size or type of equipment can also be modified to meet a specific set of design criteria.

[0116] As yet another example, it is contemplated that specific features described individually or as part of an embodiment may be combined with other individually described features or as part of other embodiments. Therefore, elements and actions of the various embodiments described herein may be combined to provide additional embodiments. Thus, while certain exemplary embodiments of methods, apparatuses, systems, and methods of making and using the same have been shown and described above, it should be clearly understood that the invention is not limited thereto, but may be practiced and implemented differently in other ways within the scope of the appended claims.

Claims

1. A method for recycling hydrogen, comprising: The hydrogen feedstock is fed into the liquefaction unit; The liquefaction unit liquefies hydrogen to output liquid hydrogen, which has a secondary hydrogen content between 80 mol% and 100 mol%. In response to determining that the hydrogen feed has decreased to or below a pre-selected threshold, the liquid hydrogen is recycled back into the feed of the liquefaction unit, causing the liquid hydrogen to be vaporized into a gaseous state and undergo a secondary hydrogen to positive hydrogen conversion, such that the secondary hydrogen content of the recycled hydrogen in the feed of the liquefaction unit has a secondary hydrogen content between 20 mol% and 30 mol%.

2. The method of claim 1, wherein the hydrogen feed has a secondary hydrogen content within a pre-selected range of 20 mol% secondary hydrogen and 30 mol% secondary hydrogen.

3. The method according to claim 1, comprising: In response to determining that the hydrogen feed has increased to at or above the pre-selected threshold, the recycling of the liquid hydrogen is stopped.

4. The method of claim 1, wherein the recycling of the liquid hydrogen comprises: Hydrogen with a secondary hydrogen content between 80 mol% and 100 mol% stored in at least one storage tank is fed toward a conversion unit, which is configured to convert the secondary hydrogen into positive hydrogen, such that the secondary hydrogen content of the recycled hydrogen in the feed to the liquefaction unit is between 20 mol% and 30 mol%. And / or Liquid hydrogen from the liquefaction unit is fed into a heater in the recirculation loop to vaporize it, and the vaporized hydrogen is then conveyed to the conversion unit, which is configured to convert secondary hydrogen into positive hydrogen, such that the secondary hydrogen content of the recirculated hydrogen in the feed to the liquefaction unit is between 20 mol% and 30 mol% secondary hydrogen.

5. The method according to claim 1, comprising: The liquid hydrogen output from the liquefier, having a secondary hydrogen content between 80 mol% and 100 mol%, is fed into at least one storage tank of a hydrogen storage device in fluid communication with the liquefaction unit. and The recycling of the liquid hydrogen mentioned above includes: Adjust at least one valve so that the liquid hydrogen output from the liquefaction unit cannot be transferred to the at least one storage tank; as well as Liquid hydrogen output from the liquefaction unit is fed into a heater in the recirculation loop to vaporize the liquid hydrogen, and the vaporized hydrogen is then conveyed to a conversion unit, which is configured to convert the secondary hydrogen into positive hydrogen, such that the secondary hydrogen content of the recirculated hydrogen in the feed to the liquefaction unit has a secondary hydrogen content between 20 mol% and 30 mol%.

6. The method of claim 5, further comprising: Hydrogen stored in at least one storage tank is fed toward a conversion unit, which is configured to convert the secondary hydrogen into positive hydrogen, such that the secondary hydrogen content of the recycled hydrogen in the feed to the liquefaction unit is between 20 mol% and 30 mol% secondary hydrogen. After determining that sufficient hydrogen has been recycled to the liquefaction unit to cope with the reduction in the hydrogen feed, the feeding of the hydrogen stored in the at least one storage tank toward the conversion unit is stopped.

7. The method of claim 1, wherein the recycling of the liquid hydrogen comprises: The hydrogen is compressed before being fed into the conversion unit, which is configured to convert the secondary hydrogen into positive hydrogen, such that the secondary hydrogen content of the recycled hydrogen in the feed to the liquefaction unit is between 20 mol% and 30 mol% secondary hydrogen.

8. The method of claim 1, wherein the recycling of the liquid hydrogen comprises: Hydrogen with a secondary hydrogen content between 80 mol% and 100 mol% stored in at least one storage tank is fed toward a conversion unit, which is configured to convert the secondary hydrogen into positive hydrogen, such that the secondary hydrogen content of the recycled hydrogen in the feed to the liquefaction unit is between 20 mol% and 30 mol%. And / or Liquid hydrogen output from the liquefaction unit is fed into a heater in the recirculation loop to vaporize the liquid hydrogen, and the vaporized hydrogen is then conveyed to the conversion unit, which is configured to convert the secondary hydrogen into positive hydrogen, such that the secondary hydrogen content of the recirculated hydrogen in the feed to the liquefaction unit has a secondary hydrogen content between 20 mol% and 30 mol%. The method also includes: When the liquefaction unit is at ambient temperature, in response to the start-up of the liquefaction unit, liquid hydrogen stored in at least one storage tank is fed into the liquefaction unit to facilitate the operation of the liquefaction unit and cool the liquefaction unit to a cryogenic operating temperature, and hydrogen output from the liquefaction unit is recirculated via the recirculation loop during the start-up.

9. The method of claim 8, wherein a controller having a processor connected to a non-transitory memory is positioned and configured to determine whether the hydrogen feed has been reduced to or below the pre-selected threshold.

10. An apparatus for hydrogen recirculation, comprising: A liquefaction unit configured to liquefy a hydrogen feed to output a first liquid hydrogen stream for feeding liquid hydrogen into at least one storage tank, the liquid hydrogen having a secondary hydrogen content between 80 mol% and 100 mol%. and A conversion unit is configured to convert secondary hydrogen from the hydrogen output from the liquefaction unit into positive hydrogen, such that the hydrogen output from the liquefaction unit can be recycled back to the feed inlet of the liquefaction unit, wherein the secondary hydrogen content is between 20 mol% and 30 mol%.

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

12. The apparatus of claim 10, wherein the conversion unit comprises at least one secondary hydrogen to positive hydrogen converter.

13. The apparatus of claim 10, comprising: The at least one storage tank is positioned to output hydrogen stored therein to feed the hydrogen into the conversion unit.

14. The apparatus of claim 13, comprising: A recirculation loop heater is configured to receive hydrogen from the at least one storage tank and heat the hydrogen such that hydrogen to be fed into the conversion unit from the at least one storage tank is fed into the conversion unit as gaseous hydrogen.

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

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

17. The apparatus of claim 10, comprising: A compression system, located upstream of the conversion unit, is used to compress the hydrogen for feeding the hydrogen into the conversion unit.

18. An apparatus for hydrogen recirculation, comprising: A liquefaction unit configured to liquefy a hydrogen feed to output a first liquid hydrogen stream for feeding liquid hydrogen into at least one storage tank, the liquid hydrogen having a secondary hydrogen content between 80 mol% and 100 mol%. A conversion unit is configured to convert secondary hydrogen from hydrogen output from the liquefaction unit into positive hydrogen, such that hydrogen output from the liquefaction unit can be recycled back to the feed inlet of the liquefaction unit, wherein the secondary hydrogen content is between 20 mol% and 30 mol%, and the conversion unit includes at least one secondary hydrogen to positive hydrogen converter. The at least one storage tank is positioned to output hydrogen stored therein in response to the hydrogen feed being at or below a pre-selected threshold, so as to feed the hydrogen to the conversion unit; A recirculation loop conduit heater feed conduit is connected between the liquefaction unit and a first recirculation loop conduit heater, the first recirculation loop conduit heater being positioned to heat liquid hydrogen output from the liquefaction unit to vaporize the liquid hydrogen into gaseous hydrogen, and the first recirculation loop conduit heater being positioned to feed the gaseous hydrogen into the conversion unit; as well as A second recirculation loop heater is positioned to receive hydrogen from the at least one storage tank and heat the hydrogen such that hydrogen to be fed into the conversion unit from the at least one storage tank can be fed into the conversion unit as gaseous hydrogen.

19. The apparatus of claim 18, comprising: A compression system, located upstream of the conversion unit, is used to compress the hydrogen for feeding the hydrogen into the conversion unit.

20. The apparatus of claim 18, wherein the liquefaction unit has a closed-loop refrigeration system or an open-loop refrigeration system.

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