Modular hydrogen liquefaction system

Abstract

Disclosed is a modular hydrogen liquefaction system. The modular hydrogen liquefaction system comprises one or more liquefaction devices arranged in parallel, wherein the hydrogen inlet of the liquefaction device is connected to a hydrogen gas source, and the product outlet of the liquefaction device is connected to one or more liquid hydrogen storage tanks that are connected in parallel; and each liquefaction device is of an integrated structure with functions of hydrogen cooling, liquefaction and completing ortho-para hydrogen conversion and is arranged to start-up and shut-down independently. The present disclosure achieves hydrogen liquefaction through numerous refrigeration units connected in series and parallel to form devices at different levels, effectively leveraging the benefits of large-scale standard refrigeration unit production to reduce equipment costs. By controlling the number of devices and refrigeration units activated at different levels, the present disclosure also enables a wide range of liquid hydrogen production capacity adjustments. Additionally, utilizing a regenerative refrigerator as the standard refrigeration unit allows for rapid cool-down and immediate shutdown, endowing the system with the advantage of quick startup and shutdown. These advantages make the present disclosure particularly suitable for using renewable energy sources to produce green liquid hydrogen.

Description

TECHNICAL FIELD

[0001] The present disclosure belongs to the technical field of cryogenic equipment, and particularly relates to a modular hydrogen liquefaction system.BACKGROUND

[0002] In recent years, to facilitate the achievement of carbon peaking and carbon neutrality, further promote the revolution in energy production and consumption, and establish a clean, low-carbon, safe, and efficient society, hydrogen energy has emerged as one of the long-term solutions to address current energy issues and realize the strategic goals of "dual carbon" (carbon peaking and carbon neutrality). Hydrogen energy is a secondary energy source that is abundant, green, low-carbon, and widely applicable. It also serves as a crucial and large-scale chemical raw material. Hydrogen produced by using renewable energy sources such as wind and solar power, also known as "green hydrogen," represents the primary future source of hydrogen energy. It can be utilized in the transportation, civilian, and energy storage sectors of electricity production, and is also expected to be used extensively in the chemical industry, such as replacing coke as a reducing agent.

[0003] To achieve a reasonable and economically viable price for hydrogen at the end-user level, thereby enabling large-scale market adoption, the key technical challenge lies in safe and efficient storage and transportation. High-pressurized hydrogen storage at the ambient temperaturehas the highest technical maturity, and has been widely used; however, its low storage and transportation density and high well-to-wheel costs render it uneconomical and unsuitable for large-scale application based on current technological trends. Material-based hydrogen storage technologies, including physical adsorption, chemical adsorption, and liquid organic hydrogen carrier (LOHC), are still at a relatively low level of technical maturity and lack economies of scale. They also suffer from issues such as high well-to-wheel energy consumption, high equipment and material costs, system complexity, and product purity concerns, making them impractical for large-scale application. On the other hand, thanks to the increasingly maturecryogenic, multilayer insulation, and vacuum technologies, storing and transporting cryogenic liquefied hydrogenoffers higher storage density and lower operating pressures. This reduces energy consumption and space costs per unit mass transported, making it a promising method for long-distance hydrogen transportation and large-scale storage. It represents the only technical pathway capable of achieving an economically viable price for hydrogen at the end-user level.

[0004] Using renewable energy sources such as wind and solar power to produce and liquefy hydrogen represents an important mode for future green hydrogen production. However, the intermittency of renewable energy power generation poses special requirements on the green hydrogen production systems (electrolyzer and hydrogen liquefaction systems) that are associated with downstream processes: 1. Adjustable capacity and rapid start-up / shutdown: If the green liquid hydrogen production system operates continuously and stably, it must either beequipped with an energy storage system that is large enough to supply sufficient power, or use electricity from the grid to maintain the production during periods of low electricity generation. However, the former method requires a high-cost energy storage system (currently still more expensive compared to the green hydrogen production system with the same installed capacity) and occupies a large area, significantly increasing capital expenditure (CAPEX) and, consequently,resulting in high hydrogen costs. The latter option involves grid electricity prices that are much higher than the off-grid prices, resulting in a steep increase in operating expenses (OPEX). Moreover, the entire system still imposes significant fluctuation impacts on the grid, failing to mitigate the impact of renewable energy intermittency on the grid through hydrogen production. Therefore, the green hydrogen production system (including electrolyzer and hydrogen liquefaction systems) needs to have adjustable capacity and rapid start-up / shutdown capabilities. By selecting appropriate capacity or start-up / shutdown strategies, it can match the intermittent renewable energy system and achieve a fully off-grid production mode. 2. Lower CAPEX: A green liquid hydrogen production system with adjustable capacity and rapid start-up / shutdown capabilities, also experiences a corresponding reduction in equipment utilization rate cooperating with intermittent renewable energy production. This makes the CAPEX of the green liquid hydrogen production system a more significant proportion of the terminal hydrogen cost composition, becoming the most crucial factor affecting hydrogen price. Therefore, to reduce the CAPEX of the green liquid hydrogen production system is a necessary condition for the green hydrogen production mode to be competitive in the market.

[0005] Hydrogen liquefaction is the most critical link in the green hydrogen industry chain, characterized by complex technological processes, high energy consumption, and substantial investment costs. Over the past few decades, numerous researchers have been focusing on enhancing the efficiency of liquefaction process that can effectively reduce both the OPEX directly and, indirectly, the CAPEX of a hydrogen liquefaction plant.

[0006] According to the different refrigerants and thermodynamic cycles, existing commercial liquefaction plants usually use either the helium-based reversedBrayton cycleor the hydrogen-based modified Claude cycle. The former is commonly used in small / medium-scale liquefaction systems with a capacity of less than 5 ton / day, while the latter is typically applied inlarge-scale liquefaction systems with a capacity exceeding 5 ton / day.

[0007] Conventional hydrogen liquefaction systems typically consist of a pre-cooling system, a main refrigeration system, a liquefaction system, and a set of cryogenic heat exchangers. The pre-cooling system usually usesa relatively mature process to achieve refrigeration at around 70-120 K, providing pre-cooling for the main refrigeration system and the liquefaction system. The main refrigeration system equipped with compressor(s) and expander(s), exchanges heat with the hydrogen in the liquefaction system through the cryogenic heat exchangers set, to cool the hydrogen, finally liquefy the hydrogen. Specifically, the compressor(s)compresses the refrigerant to a high pressure, providing high-pressurized refrigerant for the main refrigeration system cycle. Via the expander(s),the high-pressurized refrigerant expands to generatecooling, supplying cold energy to the liquefaction system. In the cryogenic heat exchanger set, a plurality of ortho-para hydrogen converters (which can be either continuous isothermal reactors or stepwise adiabatic reactors) are equipped to convert ortho-hydrogen to para-hydrogen until the equilibrium ratio of ortho- and para-hydrogen at the current heat exchanger temperature. The feed hydrogen supplied from the hydrogen source sequentially passes through the ortho-para hydrogen converters within the multistage heat exchangers and finally enters the liquid hydrogen storage tank in a liquid state, and finally flows out through the product outlet.

[0008] It is evident that conventional hydrogen liquefaction technology cannot meet the two requirements for green liquid hydrogen production from the off-grid renewable energy sources: Conventional hydrogen liquefaction technology employs large compressors, turbo-expanders, and heat exchangers. During the cool-down process, the flow rate is relatively low, causing the turbo-expander to operate far away from its normal conditions, resulting in a small circulating flow rate and correspondingly low refrigeration capacity. Consequently, the startup (cool-down) and shutdown processes require a significant amount of time (typically ranging from 6 to 18 hours). Furthermore, to protect the rotating equipment such as compressors and expanders, the startup and shutdown procedures are very complex. Although the use of variable frequency compressors or selectively shutting down a few of the parallel compressors can adjust the production capacity of the hydrogen liquefaction system to some extent, the adjustment range is relatively limited, and there is a noticeable decrease in energy efficiency.

[0009] The core components of conventional hydrogen liquefaction plants, such as compressors, heat exchangers, and turbo-expanders, are all large, custom-made parts available in limited quantities, leading to long delivery times and high prices. As a typical chemical engineering project, both the equipment and engineering require custom design. The entire project, from contract negotiation, conceptual design, construction, to final commissioning and operation, requires a very long project time (24 to 36 months). The non-standard products and customized engineering inevitably result in high CAPEX.SUMMARY

[0010] Based on the demand for green liquid hydrogen production mode associated with the off-grid renewable energy, the present disclosure proposes a modular hydrogen liquefaction system that features adjustable production capacity, rapid startup and shutdown capabilities, low CAPEX, and the ability to quickly deployment. To achieve this, the present disclosure adopts the following technical solution: A modular hydrogen liquefaction system, comprising: one or more liquefaction devices arranged in parallel, wherein a hydrogen inlet of the liquefaction device is connected to a hydrogen gas source, and a product outlet of the liquefaction device is connected to one or more liquid hydrogen storage tanks that are connected in parallel; and each liquefaction device is of an integrated structure with functions of hydrogen cooling, liquefaction and ortho-para hydrogen conversion and is arranged to start-up and shut-down independently.

[0011] The hydrogen gas source and the liquid hydrogen storage tank can be independently arranged, and can also be part of the present disclosure. When the system is used as a component of the present disclosure, the modular hydrogen liquefaction system comprises a hydrogen gas source, a liquefaction device and a liquid hydrogen storage tank, the hydrogen gas source, the liquefaction device and the liquid hydrogen storage tank are sequentially connected through pipelines. Room-temperature hydrogen from the hydrogen gas source is cooled, liquefied, and subjected to ortho-para hydrogen conversion through the liquefaction device before flowing into the liquid hydrogen storage tank for storage.

[0012] The liquefaction system in the present disclosure comprises one or more (quantified as k, where k≥1) liquefaction devices connected in parallel. These liquefaction devices are standardized skid-mounted units, adopting standard container dimensions and interfaces, with each device capable of independent operation to cool, liquefy, and complete the ortho-para hydrogen conversion of a certain flow rate of hydrogen. The liquid hydrogen product outlets of the paralleled liquefaction devices converge into a single main pipeline via piping, which is then connected to the liquid hydrogen storage tank. This design offers the following advantages: 1. A plurality of devices connected in parallel enable larger hydrogen liquefaction capacity; 2. Independent operation of one or more devices allows for a wide range of capacity adjustment without compromising system energy efficiency; 3. Users can flexibly and conveniently expand or reduce system capacity, thereby mitigating investment risks; 4. Standardized devices facilitate large-scale production, significantly reducing equipment costs; 5. The complexity of system installation is minimized, leading to reduced constructioncosts and time; 6. Skid-mounted devices are convenient for inventory management, transportation, lifting, and layout.

[0013] Preferably, the liquefaction device comprises: a pre-cooling unit for pre-cooling hydrogen; a cryogenic liquefaction conversion unit for liquefying pre-cooled hydrogen and converting the pre-cooled hydrogen to liquid hydrogen and performing ortho-para hydrogen conversion; an expansion unit for reducing pressure of the hydrogen after cryogenic liquefaction and ortho-para hydrogen conversion, wherein an outlet of the expansion unit is used as a product outlet and is connected to the liquid hydrogen storage tank; and a compression unit for providing compression works tothe cryogenic liquefaction conversion unit.

[0014] The compression unit is connected to a standard refrigeration unit in the cryogenic liquefaction conversion unit by means of a pipeline.

[0015] Preferably, the pre-cooling unit comprises: a pre-cooling heat exchanger; a pre-cooling cold source for providing cooling for the pre-cooling heat exchanger; and a purifier and a pre-cooling-stage ortho-para hydrogen converter that are sequentially connected to a hydrogen flow channel of the pre-cooling heat exchanger.

[0016] The pre-cooling heat exchanger comprises a hydrogen flow channel and a pre-cooling refrigerant flow channel; and the pre-cooling cold source provides pre-cooling to the hydrogen via the pre-cooling refrigerant. The flow channel of the pre-cooling stage ortho-para hydrogen converter is provided withortho-para hydrogen catalyst inside. In actual connection, the interface of the hydrogen gas source, the hydrogen flow channel of the pre-cooling heat exchanger, the purifier, and the pre-cooling stage ortho-para hydrogen converter are connected through pipelines; the pre-cooling cold source is connected to a cold end inlet of the pre-cooling refrigerant flow channel of the pre-cooling heat exchanger via pipelines, and the pre-cooling refrigerant flows through the pre-cooling refrigerant flow channel of the pre-cooling heat exchanger to provide cooling for the hydrogen flowing through the hydrogen flow channel of the pre-cooling heat exchanger, the purifier, and the pre-cooling stage ortho-para hydrogen converter. During actual operation, the room-temperature hydrogen with a pressure of P supply from the hydrogen gas source is first precooled to the pre-cooling temperature T preC through the pre-cooling heat exchanger; then passes through the purifier to remove the gaseous and solid impurities from the feed hydrogen, preventing blockage of subsequent processes and ensuring the purity of the liquid hydrogen product; the precooled and purified feed hydrogen enters the pre-cooling-stage ortho-para hydrogen converter, where the ortho-para conversion occurs with the assistance of the ortho-para hydrogen catalyst, causing the para-hydrogen content in the hydrogen to approach its equilibrium concentration at the pre-cooling temperature T preC and restoring the hydrogen temperature to the pre-cooling temperature T preC .

[0017] Preferably, the purifier is a cryogenic purification adsorber. The purifier can be a single cryogenic purification adsorber or two or more cryogenic purification adsorbers configured in parallel. Further preferably, the purifier comprises two cryogenic purification adsorbers that are switched through valves and alternately connected to the pipeline. The two cryogenic purification adsorbers, connected in parallel, form a typical temperature swing adsorption (TSA) unit. When one of the cryogenic purification adsorbers is connected to the pipeline, the other one that is not connected is purged and heated by clean inert hot gas to achieve regeneration, thereby enhancing the operating efficiency of the hydrogen cryogenic purification adsorber.

[0018] The pre-cooling-stage ortho-para hydrogen converter and its corresponding pre-cooling heat exchanger can adopt either an integrated structure or a mutually independent structure. The former is continuous isothermal reactor, essentially involving the filling of a catalyst within the flow channel of a cryogenic heat exchanger; here, the reactor serves as the heat exchanger, simultaneously completing the ortho-para hydrogen catalytic reaction and achieving cooling of the in-flow hydrogen. The latter is adiabatic stepwise reactor, essentially comprising a separate adiabatic container provided with catalyst; in this case, hydrogen first passes through the corresponding cryogenic heat exchanger for cooling before entering the reactor for the ortho-para reaction, resulting in a temperature increase, and then passes through a subsequent cryogenic heat exchanger for further cooling. The continuous isothermal reactor offers higher efficiency and a more compact structure compared to the adiabatic stepwise reactor, while the adiabatic stepwise reactor is simpler in terms of manufacturing and processing. Both structures can be applied in the technical solution of the present disclosure.

[0019] Depending on the different conditions at the site where the hydrogen liquefaction system is located, the pre-cooling cold source can be either an open-loop cryogensystem or a closed-loop cryogenic refrigeration pre-cooling system. The open-loop cryogen system utilizes liquid nitrogen or liquefied natural gas (LNG) as the cooling medium. The former is particularly suitable for situations where stable and inexpensive liquid nitrogen is available on-site, such as when there is a nearby air separation unit capable of providing a stable and cost-effective supply of liquid nitrogen. The latter is especially suitable for applications like LNG ports where it is necessary to recover the cold energy from the vaporization of LNG. The closed-loop cryogenic refrigeration pre-cooling system can be a reversed-Brayton cycle refrigeration system, acascaded mixture refrigeration system, or a regenerative refrigeration system, which are suitable for scenarios where electricity is inexpensive or where it is difficult to obtain cryogen such as liquid nitrogen or LNG on-site.

[0020] As a specific preferred solution, the pre-cooling cold source is provided by the following pre-cooling circulation system: a turbo-compressor for compressing a pre-cooling refrigerant to high pressure; a driving motor for driving the turbo-compressor; a water cooler for cooling a high-pressurized gas output from the turbo-compressor; a cryogenic turbo-expander for expanding and cooling the pre-cooling refrigerant output from an in-flow channel of the pre-cooling heat exchanger; and a hydrogen flow channel, the in-flow channel for the pre-cooling refrigerant and a return-flow channel for the pre-cooling refrigerant are arranged in the pre-cooling heat exchanger; wherein an inlet of the in-flow channel for the pre-cooling refrigerant is connected to an outlet of the water cooler, an outlet of the in-flow channel for the pre-cooling refrigerant is connected to an inlet of the cryogenic turbo-expander, an inlet of the return-flow channel for the pre-cooling refrigerant is connected to an outlet of the cryogenic turbo-expander, and an outlet of the return-flow channel for the pre-cooling refrigerant is connected to aninlet of the turbo-compressor.

[0021] Further preferably, the turbo-compressor recovers expansion work generated by the cryogenic turbo-expander through a connecting shaft connected between the turbo-compressor and the cryogenic turbo-expander.

[0022] Preferably, the liquefaction device further comprises a vacuum-insulated cold-box and a radiation shield. The radiation shield, the pre-cooling unit (cryogenic section), the expansion unit, and the cryogenic section of the cryogenic liquefaction conversion unit (including the cold finger of the standard refrigeration unit and the ortho-para hydrogen converter) are installed within the vacuum-insulated cold-box. The inner portion of the vacuum-insulated cold-box is evacuated to minimize convective and conductive heat leaks from the ambient. The lowest temperature sections of the expansion unit and the cryogenic liquefaction conversion unit are positioned within the radiation shield. The radiation shield is constructed from a thin metal shell with good thermal conductivity, and its surface is polished to achieve a high reflectivity. It is thermally connected to the pre-cooling cold source and is cooled to the pre-cooling temperature T preC by the pre-cooling refrigerant. The radiation shield surrounds the lowest temperature (cold head) sections of the expansion unit and the cryogenic cooling sub-device, further reducing the radiation heat leaks from room temperature to these components.

[0023] Preferably, the radiation shield is thermallyconnected to the pre-cooling unit.

[0024] Preferably, the liquid hydrogen transfer pipeline connecting the liquefaction device and the liquid hydrogen storage tank is a vacuum-insulated dual-walled pipeline.

[0025] Preferably, the cryogenic liquefaction conversion unit is composed of one or more cryogenicliquefaction sets arranged in parallel, each cryogenicliquefaction set is composed of one or more cryogenic cooling sub-devices arranged in series, and each cryogenic cooling sub-device comprises a standard refrigeration unit and an ortho-para hydrogen converter thermally connected to a cold end of the standard refrigeration unit.

[0026] Further preferably, for each cryogenicliquefaction set, the hydrogen flow channels of the ortho-para hydrogen converters are sequentially connected in series according to the hydrogen flow direction, and the cold head temperatures of the standard refrigeration units or the temperatures of the ortho-para hydrogen converters are sequentially reduced.

[0027] Furthermore, in the present disclosure, the cryogenic liquefaction conversion unit comprises one or more (denoted as m, where m≥1) cryogenicliquefaction sets. When a plurality of cryogenicliquefaction sets are employed, the plurality of cryogenicliquefaction sets are connected in parallel to each other. The feed hydrogen from the pre-cooling unit is divided into m paths, each connected to a respective cryogenicliquefaction set. Each cryogenicliquefaction set includes one or more (denoted as n, where n≥1) cryogenic cooling sub-devices connected in series. Each cryogenic cooling sub-device comprises a standard refrigeration unit and an ortho-para hydrogen converter. The ortho-para hydrogen converter is installed at the cold end of the standard refrigeration unit and comprises a refrigerant flow channel and a hydrogen flow channel. The refrigerant of the standard refrigeration unit flows directly within the refrigerant flow channel of the ortho-para hydrogen converter, providing cooling for the hydrogen and the ortho-para hydrogen reaction. The hydrogen flow channel of the ortho-para hydrogen converter is provided with ortho-para hydrogen catalyst to catalyze the ortho-para hydrogen reaction.

[0028] The hydrogen flow channels of the ortho-para hydrogen converters in the plurality of (n) cryogenic cooling sub-devices are sequentially connected in series. The n standard refrigeration units operate at successively decreasing temperatures, T c,1 >T c,2 > ... >T c,n-1 >T c,n . During actual operation, the cryogenic hydrogen from the pre-cooling unit, with a temperature of T preC and a para-hydrogen concentration close to the equilibrium para-hydrogen concentration at the pre-cooling temperature T preC , sequentially passes through the n ortho-para hydrogen converters connected in series in each cryogenicliquefaction set. The hydrogen is gradually cooled in the hydrogen flow channels of the n ortho-para hydrogen converters and undergoes progressive ortho-para hydrogen conversion with the assistance of the ortho-para hydrogen catalyst, reaching a temperature of T preExp and a pressure of p preExp before throttling, with a para-hydrogen concentration exceeding 95%. The design has the following advantages: 1. The use of a large number of standardized cryogenic cooling sub-devices facilitates mass standardized production and installation, resulting in significantly equipment cost reduction; 2. Independent operation of one or more of the paralleled cryogenicliquefaction sets allows for a wide range of capacity adjustment without affecting system energy efficiency; 3. The series connection of the plurality of cryogenic cooling sub-devices reduces the heat exchange temperature difference between the refrigerant and hydrogen in each ortho-para hydrogen converter, improving system energy efficiency; 4. The design of the ortho-para hydrogen converter minimizes the heat transfer path between the refrigerant and hydrogen (separated only by one heat exchange wall), which reduces the heat exchange temperature difference and enhancing system energy efficiency; 5. The independent standard refrigeration units improve system stability; even if individual refrigeration units fail, only the liquefaction capacity will be affected, without causing the entire system to shut down; 6. The independent standard refrigeration units can be maintained and replaced separately, enhancing maintenance convenience, and reducing the OPEX.

[0029] Preferably, to enhance the heat exchange efficiency within the ortho-para hydrogen converter, both the refrigerant flow channel and the hydrogen flow channel of the ortho-para hydrogen converter are provided with enhanced heat transfer structures, such as fins. The inlet and outlet of the hydrogen flow channel are provided with filters of appropriate pore size to prevent ortho-para hydrogen catalyst particles from entering the piping system. The ortho-para hydrogen catalyst within the hydrogen flow channel of the ortho-para hydrogen converter can be arranged in various configurations: 1. The ortho-para hydrogen catalyst completely fills the flow channel: The advantage is that the filling process is simple, ensuring sufficient catalyst for complete reaction; 2. The ortho-para hydrogen catalyst partially fills the flow channel: The advantage is that the filling process is simple as well, and as hydrogen flows, it lifts the catalyst particles within the flow channel, enabling thorough contact and heat transfer with the hydrogen, which is conducive to a complete reaction; 3. The ortho-para hydrogen catalyst is filled in segments, with filters of appropriate pore size used to secure each segment of catalyst, reducing contamination from microparticles generated by catalyst particle wear and fragmentation; 4. The ortho-para hydrogen catalyst is adhered to the surface of the flow channel and the surface of the enhanced heat transfer structures using adhesive: The advantage is low flow resistance and adequate heat transfer;

[0030] Preferably, the standard refrigeration unit is a regenerative refrigerator, specifically including the Gifford-McMahon (GM) refrigerator, Stirling refrigerator, Solvay refrigerator, GM-type pulse tube refrigerator, or Stirling-type pulse tube refrigerator. The advantages of using such a regenerative refrigerator are as follows: 1. The regenerative refrigerators offer considerable cooling efficiency in the temperature range between liquid nitrogen and liquid hydrogen; 2. The core components of the regenerative refrigerators are structurally simple and do not require high precisionmanufacturing or particularly expensive materials, making them particularly suitable for large-scale mass production, thereforethe cost per standard refrigeration unit can be significantly reduced; 3. The regenerative refrigerators are quite reliable, with the Gifford-McMahon refrigerator, Solvay refrigerator, and GM-type pulse tube refrigerator offering a maintenance-free operating period (MFOP) exceeding 2 years, while the MFOP of the Stirling refrigerator or Stirling-type pulse tube refrigerator can exceed 5 years; 4. The regenerative refrigerators typically utilize piston expansion, which provides a substantial flow-rate and considerable cooling capacity during the cool-down process, inherently enabling rapid cool-down and facilitating quick start-up and shutdown of the system.

[0031] The expansion unit can be a single one, and the hydrogen pipelines from m parallel cryogenicliquefaction sets converge and connect to the inlet of the expansion unit, while the outlet of the expansion unit is connected to the liquid hydrogen product outlet; by setting up a common expansion unit for m parallel cryogenicliquefaction sets, such design has the advantage of lower cost.

[0032] Preferably, m expansion units are provided, each with its inlet connected to the hydrogen pipeline from one of the m parallel cryogenicliquefaction sets, and the outlets of all the expansion units converge and then connect to the liquid hydrogen product outlet; by setting up a separate expansion unit for each cryogenicliquefaction set, such design improves system reliability, and independent control of the expansion units also allows for system capacity adjustment and independent maintenance of each device.

[0033] The expansion unit can be a capillary tube, a throttle valve, or an expander. Preferably, the expansion unit is an adjustable throttle valve with a shut-off function.

[0034] As a specific preferred solution, the expansion units are a plurality of throttle valves arranged in parallel, each of the throttle valve is connected to the plurality of cryogenicliquefaction sets of the corresponding cryogenic liquefaction conversion unit.

[0035] Preferably, the product outlets of the liquefaction device are connected to a plurality of (j, where j≥2) parallel liquid hydrogen storage tanks. The main pipeline for liquid hydrogen products from the liquefaction system is divided into j lines, each connected to a respective liquid hydrogen storage tank through cryogenic valves. The liquid hydrogen produced by the liquefaction device is stored sequentially in each tank, and a full-filled liquid hydrogen storage tank cantransfer liquid hydrogen within it to a liquid hydrogen tanker / ship for further transportation to the end customers of liquid hydrogen. With this design, by closing the cryogenic valves, the liquid hydrogen storage tank that is undergoing transfer operations can be disconnected from the liquefaction system, while the liquid hydrogen produced by the liquefaction system can still be stored in other liquid hydrogen storage tanks, ensuring the continuity of liquid hydrogen production and storage.

[0036] Further preferably, the liquid hydrogen storage tank is a tank container. When a tank container is full-filledwith liquid hydrogen, it can be transported to the liquid hydrogen end customers by container trailers / ships. The transported tank container is then replaced with a new empty one, which is connected to the liquefaction device. The adoption of standardized tank containers eliminates the need for transferring liquid hydrogen from stationary liquid hydrogen storage vesselsto liquid hydrogen tankers / ships, thereby reducing the boil-off loss during the process. For large-scale applications, a combination of numerous standardized tank containers with container trailers / ships offers a cost advantage over a combination of semi-customized stationary storage tanks with liquid hydrogen tankers / ships.

[0037] During the transfer of the liquid hydrogen from the storage tanks, the replacement of the tank containers, or long-term storage, a certain amount of the liquid hydrogen will vaporize, causing an increase in pressure within the liquid hydrogen storage tanks. This will eventually trigger the safety relief system, resulting in hydrogen loss via venting. To re-liquefy the boil-off hydrogen from the liquid hydrogen storage tanks, it is preferable to connect a boil-off vapor return line from the top of the liquid hydrogen storage tanks to one or more of the liquefaction devices. That is, a top of the liquid hydrogen storage tank is provided with a boil-off vapor return line, and the boil-off vapor return line is connected to a hydrogen pipeline in one or more of the liquefaction devices.

[0038] As an optimized solution, within the liquefaction device, the boil-off vapor return line is connected to a cryogenic compressor and then to the pipeline between the penultimate (ordered according to the hydrogen flow direction) and the last cryogenic cooling sub-devices in one or more cryogenicliquefaction sets. The boil-off hydrogen is compressed to high pressure by the cryogenic compressor and then mixed with the incoming feed hydrogen, entering the final cryogenic cooling sub-device to be cooled and liquefied.

[0039] Alternatively, as another optimized solution, within the liquefaction device, the boil-offvapor return line is connected to the low-pressure inlet of an ejector. The high-pressure inlet of the ejector is connected to the feed hydrogen pipeline from the ortho-para hydrogen converter in the second last cryogenic cooling sub-device of one or more cryogenicliquefaction sets. The outlet of the ejector is connected to the ortho-para hydrogen converter in the last cryogenic cooling sub-device of the cryogenicliquefaction set. The ejector utilizes a high-flowrate, high-pressurized feed hydrogen stream as the main flow to pump and mix with the low-flowrate, low-pressurized boil-off hydrogen. The two hydrogen streams mix in the ejector and then enter the last cryogenic cooling sub-device to be cooled and liquefied. Compared to cryogenic compressors, ejectors have no moving parts, are cost-effective, and offer high reliability.

[0040] The compression unit is a compressor set composed of a plurality of compressors, and the plurality of compressors respectively provide compression work for the cryogenic liquefaction conversion unit.

[0041] Preferably, the compressor unit comprises m*n independent compression units, each compression unit is individually connected to respective standard refrigeration units. By adopting this technical solution, it becomes easy to switch each standard refrigeration unit on or off. The smaller compression units are more conducive to large-scale mass production, thereby reducing costs.

[0042] Preferably, a hydrogen pipeline and a cold refrigerant pipeline are arranged in the cold end of the standard refrigeration unit, one part or all of the hydrogen pipeline is provided with an ortho-para hydrogen catalyst, and the part or all of the hydrogen pipeline simultaneously forms the ortho-para hydrogen converter.

[0043] Compared with the prior art, the beneficial effects of the present disclosure are as follows: The present disclosure achieves hydrogen liquefaction through numerous refrigeration units connected in series and parallel to form devices at different levels, effectively leveraging the benefits of large-scale standard refrigeration unit production to significantly reduce equipment costs. By controlling the number of devices and refrigeration units activated at different levels, the present disclosure also enables a wide range of liquid hydrogen production capacity adjustments. Additionally, utilizing a regenerative refrigerator as the standard refrigeration unit allows for rapid cool-down and immediate shutdown, endowing the system with the advantage of quick startup and shutdown. These advantages make the present disclosure particularly suitable for using the renewable energy sources to produce green liquid hydrogen.BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Fig. 1 is a schematic diagram of the first embodiment of a modular hydrogen liquefaction system according to the present disclosure. Fig. 2 is a schematic diagram of the first embodiment of the liquefaction system in a modular hydrogen liquefaction system according to the present disclosure. Fig. 3 is a schematic diagram of the second embodiment of the liquefaction system ina modular hydrogen liquefaction system according to the present disclosure. Fig. 4 is a schematic diagram of the second embodiment of a modular hydrogen liquefaction system according to the present disclosure. Fig. 5 is a schematic diagram of the first embodiment of the liquefaction system in the second embodiment of a modular hydrogen liquefaction system according to the present disclosure. Fig. 6 is a schematic diagram of the second embodiment of the liquefaction system in the second embodiment of a modular hydrogen liquefaction system according to the present disclosure.

[0045] The corresponding relationship between reference signs and component names is as follows: 1, hydrogen gas source; 2, liquefaction system; 2.1~2.k, liquefaction device; 3, liquid hydrogen storage tank set; 3.1~3.j, liquid hydrogen storage tank; 21, pre-cooling unit; 22, cryogenic liquefaction conversion unit; 22.1.~22.m, cryogenic liquefaction set; 23, expansion unit; 24, liquid hydrogen product outlet; 25, compression unit; 26, vacuum-insulated cold-box; 27, radiation shield; 28, boil-off vapor return line; 31.cryogenic valve; 32, gas return control valve; 211, pre-cooling cold source; 212, pre-cooling heat exchanger; 212a / b, first-stage / second-stage pre-cooling heat exchanger; 213, purifier; 213a / b, cryogenic purification adsorber; 214, pre-cooling-stage ortho-para hydrogen converter; 215, cooling heat exchanger for the radiation shield; 221, cryogenic cooling sub-device; 222, standard refrigeration unit; 223, ortho-para hydrogen converter; 231, throttle valve; 251, compressor set; 252, high-pressure gas supply line; and 253, low-pressure gas return line. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0046] To make the objectives, technical solutions, and advantages of the embodiments of the present disclosure clearer, the following provides a further detailed description of the embodiments of the present disclosure with reference to the accompanying drawings. However, the described embodiments are only part of the embodiments of the present disclosure, not all of them. Based on the embodiments of the present disclosure, other embodiments derived from non-creative efforts by a person skilled in the art fall within the scope of protection of the present disclosure.Embodiment 1:

[0047] As shown in Fig. 1, a modular hydrogen liquefaction system comprises a hydrogen gas source 1, a liquefaction system 2 and aliquid hydrogen storage tank set 3, the hydrogen gas source 1, the liquefaction system 2 and the liquid hydrogen storage tank set 3 are sequentially connected through pipelines.

[0048] The liquefaction system 2 comprises one or more (k≥1) liquefaction devices (2.1~2.k) connected in parallel. The liquefaction devices 2.1~2.k are standardized skid-mounted units, integrating components such as pre-cooling, liquefaction, and conversion components, intermediate piping, and control valves into a single entity, adopting standard container dimensions. Each device can operate independently, cooling and liquefying hydrogen at a certain flow-rate and completing the ortho-para hydrogen conversion. The liquid hydrogen storage tank set 3 comprises two or more (j≥2) liquid hydrogen storage tanks (3.1~3.j) connected in parallel; and the liquid hydrogen storage tanks 3.1∼3.j are tank containers.

[0049] The pipelines from the liquid hydrogen product outlets 24 of each liquefaction device 2.1~2.k in the liquefaction system 2 are converged into major pipeline for liquid hydrogen product, which is then divided into j pipelines, each connecting to the respective liquid hydrogen storage tanks 3.1~3.j. The pipelines between the liquefaction system 2 and the liquid hydrogen storage tanks 3.1~3.j are vacuum-insulated dual-walled cryogenic liquid hydrogen pipelines.

[0050] The working principle of hydrogen liquefaction using this embodiment is as follows: The feed hydrogen from the hydrogen gas source 1, at an ambient temperature of T amb (263∼313 K) and a pressure of P supply (10∼26 bar), and with a para-hydrogen concentration of approximately 25%, is divided into k pathways. Through each pathway, the hydrogen enters into the respective liquefaction devices 2.1~2.k within the liquefaction system 2, where it is cooled, liquefied, and undergoes the ortho-para hydrogen conversion process. Subsequently, the liquefied hydrogen flows into the liquid hydrogen storage tanks 3.1~3.j for storage. The product liquid hydrogen flowing out of the liquefaction devices 2.1~2.k has a pressure of p store (1~6 bar), a temperature of T product , and a para-hydrogen concentration of ≥95%. The mentioned product liquid hydrogen is subcooled, i.e. the temperature of the product liquid hydrogen is lower than the saturation temperature of hydrogen at its pressure (T product <T sat (p store )). By controlling the opening and closing of the cryogenic valves 31, the product liquid hydrogen is sequentially filled into each of the liquid hydrogen storage tanks 3.1~3.j. The tank containers filled with liquid hydrogen are transported to the liquid hydrogen end-users by container trailers, and the empty tank containers spots are loaded with new empty containers, which are then connected to the liquefaction system.

[0051] The liquid hydrogen production capacity of the entire modular hydrogen liquefaction system can be adjusted within a wide range by activating different numbers of liquefaction devices. Since each liquefaction device operates independently, the overall energy efficiency of the system does not significantly change due to capacity adjustments.Embodiment 2:

[0052] As shown in Fig. 2, the liquefaction device in the modular hydrogen liquefaction system comprises a pre-cooling unit 21, a cryogenic liquefaction conversion unit 22, an expansion unit 23, a liquid hydrogen product outlet 24, and a compression unit 25. The pre-cooling unit 21 comprises a pre-cooling cold source 211, a pre-cooling heat exchanger 212, a purifier 213, and a pre-cooling-stage ortho-para hydrogen converter 214. The pre-cooling-stage ortho-para hydrogen converter 214 is provided with ortho-para hydrogen catalyst. The pre-cooling heat exchanger 212 is provided with a hydrogen flow channel for hydrogen to pass through and a pre-cooling refrigerant flow channel for the pre-cooling refrigerant to pass through. The cryogenic liquefaction conversion unit 22 comprises one or more (m≥1) independent cryogenicliquefaction sets 22.1~22.m connected in parallel. Each cryogenicliquefaction set comprises one or more (n≥1) independent cryogenic cooling sub-devices 221 connected in series. The cryogenic cooling sub-device 221 comprises a standard refrigeration unit 222 and an ortho-para hydrogen converter 223. The ortho-para hydrogen converter 223 comprises a refrigerant flow channel and a hydrogen flow channel, and the hydrogen flow channel is provided with the ortho-para hydrogen catalyst inside.

[0053] The hydrogen gas source 1, the hydrogen flow channel of the pre-cooling heat exchanger 212, the purifier 213, and the pre-cooling-stage ortho-para hydrogen converter 214 are connected in sequence through pipelines or directly through sealed interfaces. The pre-cooling cold source is connected to the cold end inlet of the pre-cooling refrigerant flow channel of the pre-cooling heat exchanger through a pipeline. The pre-cooling refrigerant flows through the pre-cooling refrigerant flow channel of the pre-cooling heat exchanger, providing cooling for the hydrogen flowing through the hydrogen flow channel of the pre-cooling heat exchanger, the purifier, and the pre-cooling-stage ortho-para hydrogen converter. The outlet pipeline of the pre-cooling-stage ortho-para hydrogen converter 214 is divided into m pathways, which are connected in parallel to m cryogenicliquefaction sets22.1~22.m. In each cryogenicliquefaction set, n ortho-para hydrogen converters 223 are connected in series through pipelines. Each ortho-para hydrogen converter 223 is connected to the cold end of the standard refrigeration unit 222. The refrigeration in the standard refrigeration unit 222 flows through the refrigerant flow channel of the ortho-para hydrogen converter 223, providing cooling. The outlet pipelines of the m parallel cryogenicliquefaction sets are connected to the expansion unit 23, and the outlet of the expansion unit 23 is connected to the liquid hydrogen product outlet 24. The compression unit 25 is connected to the m*n standard refrigeration units 222 through gas supply lines, driving the standard refrigeration units 222 to provide cryogenic refrigeration.

[0054] The working principle of hydrogen liquefaction using this embodiment is as follows: The feed hydrogen from the hydrogen gas source 1, at an ambient temperature of T amb (263∼313 K) and a pressure of P supply (10∼26 bar), containing approximately 25% para-hydrogen, first enters the hydrogen flow channel of the pre-cooling heat exchanger 212. It is pre-cooled to a pre-cooling temperature of T preC , which ranges between 60 to 150 K depending on the different forms of the pre-cooling cold source and the pre-cooling refrigerant. The pre-cooled hydrogen then enters the purifier 213 to remove the residual gaseous impurity such as water, CO 2 , N 2 , as well as solid particles. Subsequently, it enters the pre-cooling-stage ortho-para hydrogen converte 214, where the ortho-para hydrogen conversion is completed with the aid of the ortho-para hydrogen catalyst in the reactor, and it is re-cooled to the pre-cooling temperature T preC . The amount of catalyst in the pre-cooling-stage ortho-para hydrogen converte 214 should be sufficient to ensure that the hydrogen leaving the pre-cooling unit 21 is as close as possible to equilibrium hydrogen (i.e., the para-hydrogen concentration is as close as possible to the equilibrium para-hydrogen concentration at the pre-cooling temperature T preC ). The hydrogen leaving the pre-cooling unit 21 is divided into m paths, each of them entering one of the m parallel cryogenicliquefaction sets 22.1~22.m. In the cryogenic liquefaction conversion unit 22, each of the n standard refrigeration units 222 in each cryogenicliquefaction set operates at successively decreasing temperatures T c,1 >T c,2 > ... >T c,n-1 >T c,n . The hydrogen passes through n series-connected ortho-para hydrogen converters 223; each ortho-para hydrogen converter 223 is connected to the cold end of the standard refrigeration unit 222, and the cooling generated by the standard refrigeration unit 222 is transferred to the hydrogen flowing in the hydrogen flow channel of the ortho-para hydrogen converter 223 through the flow of its refrigerant in the refrigerant flow channel. The hydrogen is gradually cooled in the hydrogen flow channels of the n ortho-para hydrogen converters, and with the aid of the ortho-para hydrogen catalyst, a gradual ortho-para hydrogen conversion is achieved, reaching the pre-expansion temperature of T preExp and a pressure of p preExp (p preExp = P supply -Δp, where Δp is the pressure drop of hydrogen passing through the pre-cooling unit 21 and the cryogenic liquefaction conversion unit 22), and a para-hydrogen concentration over than 95%. At this point, the hydrogen is subcooled.

[0055] The hydrogen, cooled to a subcooled state in the cryogenic liquefaction conversion unit 22, enters the expansion unit 23. Depending on the different choices of the expansion unit, the pressure reduction process of hydrogen in the expansion unit 23 to p product may undergo isentropic expansion, isenthalpic expansion, or a polytropic process somewhere between the two. The temperature of the hydrogen may decrease (the expansion tends to isentropic) or increase (the expansion tends to isenthalpic). The temperature of the hydrogen that leaves the expansion unit 23 is T product , thus the hydrogen remains subcooled liquid with a certain degree of subcooling. This ensures that the liquid hydrogen remains in a liquid form during its transfer to the liquid hydrogen storage tanks 3.1~3.j. After expansion, the subcooled liquid hydrogen product is finally delivered through the liquid hydrogen product outlet to the downstream pipeline and ultimately stored in the liquid hydrogen storage tanks.

[0056] In the modular hydrogen liquefaction system, the standard refrigeration unit 222 included in the cryogenic liquefaction conversion unit 22 is a regenerative refrigerator, specifically which can be a Gifford-McMahon refrigerator, a Stirling refrigerator, a Solvay refrigerator, a GM-type pulse tube refrigerator, or a Stirling-type pulse tube refrigerator. The compression unit 25 is connected to all standard refrigeration units 222 through a gas supply line and is used to drive the regenerative refrigerator, providing cooling capacity to the ortho-para hydrogen converter 223 to achieve hydrogen cooling and the ortho-para hydrogen conversion reaction.

[0057] The compression unit 25 can employ an integrated compressor set or a plurality of independent compressors, each with its own compression function, or it can be a large single compressor. Preferably, an integrated compressor set or a plurality of independent compressors are used for ease of control and to ensure overall energy efficiency. In particular, when it is necessary to shut down one or more cryogenicliquefaction sets, using an integrated compressor set allows for the shutdown of the corresponding compressor set without affecting the energy efficiency of the entire compression unit.Embodiment 3:

[0058] As shown in Fig. 3, in the modular hydrogen liquefaction system, a more detailed schematic of the liquefaction system 2 is illustrated, where the pre-cooling cold source 211 adopts a turbo-Brayton cycle refrigeration system, the standard refrigeration unit 222 employs a Gifford-McMahon refrigerator, the compression unit 25 consists of a plurality of independent compressor units, and the expansion unit 23 utilizes a plurality of parallel throttling control valves as expansion elements. The system is thermally insulated using a vacuum-insulatedcold-box 26 and a radiation shield 27. The difference from Embodiment 2 lies in the following: The pre-cooling heat exchanger 212 is a series-connected two-stage pre-cooling structure, comprising a first-stage pre-cooling heat exchanger 212a and a second-stage pre-cooling heat exchanger 212b. The cryogenic adsorption purifier 213 is composed of two parallel cryogenic adsorption purifiers, the cryogenic adsorption purifier213a and the cryogenic adsorption purifier213b.

[0059] Meanwhile, in the embodiment, the pre-cooling system 21 adopts a nitrogen turbo-Brayton refrigeration cycle as the pre-cooling cold source 211, which includes a driving motor 2111, a turbo-compressor 2112, a water cooler 2113, a cryogenicturbo-expander 2114, a connecting shaft 2115, and acooling heat exchanger for the radiation shield 215. The aforementioned components are connected in the following sequence: the high-pressure outlet of the turbo-compressor 2112, the water cooler 2113, the inlet of the pre-cooling refrigerant in-flow channel at the hot end of the first-stage pre-cooling heat exchanger 212a, the outlet of the pre-cooling refrigerant in-flow channel at the cold end of the first-stage pre-cooling heat exchanger 212a, the inlet of the pre-cooling refrigerant in-flow channel at the hot end of the second-stage pre-cooling heat exchanger 212b, the outlet of the pre-cooling refrigerant in-flow channel at the cold end of the second-stage pre-cooling heat exchanger 212b, the inlet of the cryogenicturbo-expander 2114, the outlet of the cryogenicturbo-expander 2114, the cooling heat exchanger for the radiation shield 215, the inlet of the pre-cooling refrigerant return-flow channel at the cold end of the second-stage pre-cooling heat exchanger 212b, the outlet of the pre-cooling refrigerant return-flow channel at the hot end of the second-stage pre-cooling heat exchanger 212b, the inlet of the pre-cooling refrigerant return-flow channel at the cold end of the first-stage pre-cooling heat exchanger 212a, the outlet of the pre-cooling refrigerant return-flow channel at the hot end of the first-stage pre-cooling heat exchanger 212a, and finally back to the low-pressure inlet of the turbo-compressor 2112, forming a closed loop. The turbo-compressor 2112 and the cryogenicturbo-expander 2114 are mechanically coupled through the connecting shaft 2115, and the connecting shaft 2115 is provided with a driving motor 2111.

[0060] In the embodiment, the working principle of the pre-cooling cold source 211 using a turbo-Brayton cycle refrigeration system is as follows: The pre-cooling refrigerant is compressed to high pressure by the turbo-compressor 2112, and the heat generated during compression is removed by the water cooler 2113 and the pre-cooling refrigerant is cooled down to around ambient temperature. After compression and cooling, the pre-cooling refrigerant enters the first-stage pre-cooling heat exchanger 212a and the second-stage pre-cooling heat exchanger 212b successively, where it is cooled by the returning cold refrigerant to approximately 100~120 K. Subsequently, the pre-cooling refrigerant enters the cryogenicturbo-expander 2114 for expansion refrigeration. Depending on the refrigerant and the pressure after expansion, the temperature of the pre-cooling refrigerant can ultimately drop to around 80~100 K. The cryogenic, low-pressure pre-cooling refrigerant then returns successively to the cooling heat exchanger for the radiation shield 215, the second-stage pre-cooling heat exchanger 212b, and the first-stage pre-cooling heat exchanger 212a to precool the incoming high-pressure refrigerant and feed hydrogen, warming up to around ambient temperature before exiting the first-stage pre-cooling heat exchanger 212a and finally returning to the low-pressure inlet of the turbo-compressor 2112. The driving motor 2111 provides the main driving force to drive the turbo-compressor 2112, while the expansion work of the cryogenicturbo-expander 2114 is recovered through the connecting shaft 2115 to provide auxiliary driving force for the turbo-compressor 2112.

[0061] The embodiment provides a more detailed description of the pre-cooling process flow for hydrogen. The hydrogen gas source 1 is connected to the hydrogen flow channel inlet of the hot end of the first-stage pre-cooling heat exchanger 212a. The incoming feed hydrogen passes through the hydrogen flow channels of the first-stage pre-cooling heat exchanger 212a and the second-stage pre-cooling heat exchanger 212b in sequence, and then connects to the parallel cryogenic adsorption purifiers 213a and 213b. Here, the cryogenic adsorption purifiers 213a and 213b constitute a typical temperature swing adsorption (TSA) unit. The two purifiers are switched through valves and alternately connected to the pipeline, while the purifier not connected to the pipeline is purged and heated by clean inert hot gas for regeneration. After being connected in parallel, the cryogenic purification adsorbers 213a and 213b are connected to the inlet of the hot end of the second-stage pre-cooling heat exchanger 212b through pipelines and enter the pre-cooling-stage ortho-para hydrogen converter 214 located in the second-stage pre-cooling heat exchanger 212b. In this embodiment, the pre-cooling-stage ortho-para hydrogen converter 214 is an isothermal reactor coupled within the second-stage pre-cooling heat exchanger 212b, where catalyst particles are filled in the heat exchange channels of the heat exchanger to achieve the ortho-para hydrogen catalytic reaction while exchanging heat. This type of isothermal reactor features high reaction efficiency and low irreversible losses. After leaving the pre-cooling-stage ortho-para hydrogen converter 214, the feed hydrogen is connected to the inlet of the first ortho-para hydrogen converter 223 in each parallel cryogenicliquefaction set22.1~22.m.

[0062] In the embodiment, the cold end of the standard refrigeration unit 222, which employs a Gifford-McMahon (GM) refrigerator, is connected to the ortho-para hydrogen converter 223. When the GM refrigerator is in operation, its refrigerant expands at the cold end and alternately flows through the refrigerant flow channels in the ortho-para hydrogen converter 223, providing the necessary cooling for the ortho-para hydrogen reaction of the hydrogen flowing through the hydrogen flow channels of the ortho-para hydrogen converter 223. With each pass through a ortho-para hydrogen converter 223, the hydrogen is gradually cooled and the ortho-para hydrogen reaction is completed. After passing through n series-connected ortho-para hydrogen converters 223, the hydrogen reaches a pre-expansion temperature of T preExp and a pressure of p preExp (where p preExp = P supply - Δp, and Δp represents the pressure drop along the path as the hydrogen flows through the pre-cooling unit 21 and the cryogenic liquefaction conversion unit 22), with a para-hydrogen concentration over than 95%. At this point, the hydrogen is in a subcooled state.

[0063] In the embodiment, the compression unit 25 consists of m*n independently operating compressor units 251. Each compressor unit 251 is connected to the Gifford-McMahon (GM) refrigerator of each standard refrigeration unit 222 via a high-pressure gas supply line 252 and a low-pressure gas return line 253, serving to drive the GM refrigerator. The design of independent compressor units 251 facilitates large-scale and batch production, thereby reducing the cost of the compression unit. Additionally, the independent operation of each compressor unit 251 enables the independent start-up and shutdown of each standard refrigeration unit 222, allowing the system to adjust operating conditions over a wider range and enhancing overall reliability.

[0064] The embodiment provides a more detailed description of the expansion unit 23: The expansion unit 23 comprises m independent adjustable throttle valves 231 with cutoff capability. The hydrogen from the final ortho-para hydrogen converter 223 in each of the m paralleled cryogenicliquefaction sets (22.1~22.m) is connected to one of the m independent throttle valves 231. The m streams of hydrogen undergo isenthalpic throttling expansion in the m throttle valves 231, reducing the pressure from p preExp to p product and slightly increasing the temperature from T preExp to T product . The throttled hydrogen remains as a liquid with a certain degree of subcooling. After the m streams of throttled hydrogen converge into one, they are connected to the liquid hydrogen product interface 24.

[0065] To reduce heat leakage from the environment to the cryogenic components of the system, the embodiment also employs a vacuum-insulated cold-box 26 and a radiation shield 27 for system insulation. The radiation shield 27, the pre-cooling unit 21, the expansion unit 23, and the cryogenic portions of the cryogenic cooling sub-device (including the cold fingers of the standard refrigeration units and the ortho-para hydrogen converters) are installed inside the vacuum-insulated cold-box 26. The inner portion of the vacuum-insulated cold-box 26 is evacuated to minimize convective and conductive heat leakage from the environment. The radiation shield 27 is made of a thin, thermally conductive metal shell with a polished surface that provides high reflectivity. It is thermally connected to the cooling heat exchanger for the radiation shield 215 and is cooled to the pre-cooling temperature T preC . The radiation shield encloses the lowest temperature portions of the expansion unit and the cryogenic cooling sub-device, further reducing radiative heat leakage from the ambient temperature to these components.Embodiment 4:

[0066] As shown in Fig. 4, a modular hydrogen liquefaction system employing a boil-off vapor return line to recover and reliquefy boil-off hydrogen. During transfer (move liquid hydrogen from a stationary storage tank into transport vehicles such as tankers or ships), replacement of the tank containers, or long-term storage in the liquid hydrogen storage tank group 3, part of the liquid hydrogen evaporates, causing an pressure increasing within the liquid hydrogen storage tanks. This will ultimately trigger the safety relief system, resulting in hydrogen loss via venting. In this embodiment, a boil-off vapor return line is used to recover the boil-off hydrogen from the liquid hydrogen storage tank with excessively high pressure due to flash evaporation and return it to one of the liquefaction devices (any one of the liquefaction devices 2.1~2.k) in the liquefaction system 2 for re-liquefaction. The difference between this embodiment and embodiment 2 lies in the inclusion of a boil-off vapor return line 28 and a gas return control valve 32. The boil-off vapor return line is led out from the top of each liquid hydrogen storage tank, passes through the gas return control valve 32, and then j lines from various liquid hydrogen storage tanks converge into one line, which is connected to one of the liquefaction devices in the liquefaction system 2.

[0067] Taking the return to the liquefaction device 2.1 as an example, the working principle of the embodiment is as follows: When the pressure in the liquid hydrogen storage tank exceeds the set value p reV,high,set , the cryogenic valve 31 closes and the gas return control valve 32 opens, allowing the boil-off hydrogen in the liquid hydrogen storage tank to flow back to the liquefaction device 2.1 through the boil-off vapor return line 28. The boil-off hydrogen returning to the liquefaction device 2.1 is then reliquefied, and its working principle will be described in detail in Embodiments 5 and 6. As the boil-off hydrogen continues to flow out of the liquid hydrogen storage tank, the pressure inside the tank gradually decreases. When the pressure falls below the set value p reV,low,set , the cryogenic valve 31 opens and the gas return control valve 32 closes, stopping the return of gas to the liquid hydrogen storage tank and allowing it to continue receiving liquid hydrogen products from the liquefaction system 2.Embodiment 5:

[0068] As shown in Fig. 5, a more detailed schematic of the liquefaction system 2 in a modular hydrogen liquefaction system that employs a boil-off vapor return line to recover and reliquefy boil-off hydrogen is presented. The difference from Embodiment 3 lies in the inclusion of a boil-off vapor return line 28 and an ejector 291 in this embodiment. The boil-off vapor return line 28 is connected to the low-pressure inlet of the ejector 291, while the high-pressure inlet of the ejector 291 is connected to the hydrogen flow channel outlet of the ortho-para hydrogen converter 223 in the penultimate cryogenic cooling sub-device 221(1.n-1) of the cryogenicliquefaction set 22.1 (although it could also be any one of the modules from the cryogenicliquefaction set22.2∼22.m). The outlet of the ejector 291 is connected to the hydrogen flow channel inlet of the ortho-para hydrogen converter 223 in the final cryogenic cooling sub-device 221(1.n) of the cryogenicliquefaction set 22.1. The ejector utilizes a high flow rate, high-pressurized feed hydrogen stream as the primary flow to pump the low flow rate, low-pressurized boil-off hydrogen. The two hydrogen streams mix in the ejector before entering the final ortho-para hydrogen converter 223, where they are cooled and liquefied.Embodiment 6:

[0069] As shown in Fig. 6, a detailed schematic of an alternative technical solution for the liquefaction system 2 in a modular hydrogen liquefaction system that employs a boil-off vapor return line to recover and reliquefy boil-off hydrogen is presented. The difference from Embodiment 5 lies in the replacement of the ejector 291 with a cryogenic compressor 292 in this Embodiment. The boil-off vapor return line 28 is connected to the low-pressure inlet of the cryogenic compressor 292, while the high-pressure outlet of the cryogenic compressor 292 is connected to the hydrogen flow channel outlet of the ortho-para hydrogen converter 223 in the penultimate cryogenic cooling sub-device 221(1.n-1) of the cryogenicliquefaction set 22.1. After the feed hydrogen and the compressed boil-off hydrogen converge, they enter the hydrogen flow channel of the ortho-para hydrogen converter 223 in the final cryogenic cooling sub-device 221(1.n) of the cryogenicliquefaction set 22.1, where they are cooled and liquefied.

Claims

1. A modular hydrogen liquefaction system, comprising: one or more liquefaction devices arranged in parallel, wherein the liquefaction device comprises a hydrogen inlet and a product outlet, the hydrogen inlet is connected to a hydrogen gas source, and the product outlet is connected to one or more liquid hydrogen storage tanks that are connected in parallel; each liquefaction device comprises an integrated structure, and the integrated structureis used for hydrogen cooling, liquefaction, and completing ortho-para hydrogen conversion, andis arranged to start-up and shut-down independently.

2. The modular hydrogen liquefaction system according to claim 1, wherein the liquefaction device comprises: a pre-cooling unit for pre-cooling hydrogen; a cryogenic liquefaction conversion unit for liquefying pre-cooled hydrogen and converting the pre-cooled hydrogen to liquid hydrogen and performing ortho-para hydrogen conversion; an expansion unit for reducing pressure of the hydrogen after cryogenic liquefaction and ortho-para hydrogen conversion, wherein an outlet of the expansion unit is connected to the liquid hydrogen storage tank; and a compression unit for providing compression works to the cryogenic liquefaction conversion unit.

3. The modular hydrogen liquefaction system according to claim 2, wherein the pre-cooling unit comprises: a pre-cooling heat exchanger; a pre-cooling cold source for providing cooling for the pre-cooling heat exchanger; and a purifier and a pre-cooling-stage ortho-para hydrogen converter that are sequentially connected to a hydrogen flow channel of the pre-cooling heat exchanger.

4. The modular hydrogen liquefaction system according to claim 3, wherein the pre-cooling cold source is provided by the following pre-cooling circulation system: a turbo-compressor for compressing a pre-cooling refrigerant to high pressure; a driving motor for driving the turbo-compressor; a water cooler for cooling a high-pressurized gas output from the turbo-compressor; a cryogenic turbo-expander for expanding and cooling the pre-cooling refrigerant output from an in-flow channel of the pre-cooling heat exchanger; and a hydrogen flow channel, the in-flow channel for the pre-cooling refrigerant and a return-flow channel for the pre-cooling refrigerant are arranged in the pre-cooling heat exchanger; wherein an inlet of the in-flow channel for the pre-cooling refrigerant is connected to an outlet of the water cooler, an outlet of the in-flow channel for the pre-cooling refrigerant is connected to an inlet of the cryogenic turbo-expander, an inlet of the return-flow channel for the pre-cooling refrigerant is connected to anoutlet of the cryogenic turbo-expander, and an outlet of the return-flow channel for the pre-cooling refrigerant is connected to an inlet of the turbo-compressor.

5. The modular hydrogen liquefaction system according to claim 4, wherein the turbo-compressor recovers expansion work generated by the cryogenic turbo-expander through a connecting shaftconnected between the turbo-compressor and the cryogenic turbo-expander.

6. The modular hydrogen liquefaction system according to claim 2, wherein the liquefaction device further comprises a vacuum-insulated cold-box and a radiation shield, and the radiation shield is thermally connected to the pre-cooling unit; the expansion unit and the lowest temperature portion of the cryogenic liquefaction conversion unit are arranged in the radiation shield; and the radiation shield, the cryogenic portion of the pre-cooling unit and the cryogenic portion of the cryogenic liquefaction conversion unit are arranged in the vacuum-insulated cold-box.

7. The modular hydrogen liquefaction system according to claim 2, wherein the cryogenic liquefaction conversion unit is composed of one or more cryogenic liquefaction sets arranged in parallel, each cryogenicliquefaction set is composed of one or more cryogenic cooling sub-devices arranged in series, and each cryogenic cooling sub-device comprises a standard refrigeration unit and an ortho-para hydrogen converter thermally connected to a cold end of the standard refrigeration unit.

8. The modular hydrogen liquefaction system according to claim 7, wherein for each cryogenicliquefaction set, the hydrogen flow channels of the ortho-para hydrogen converters are sequentially connected in series according to the hydrogen flow direction, and the cold head temperatures of the standard refrigeration units or the temperatures of the ortho-para hydrogen converters are sequentially reduced.

9. The modular hydrogen liquefaction system according to claim 1, wherein the liquid hydrogen storage tank is a tank container.

10. The modular hydrogen liquefaction system according to claim 1, wherein a top of the liquid hydrogen storage tank is provided with a boil-off vapor return line, and the boil-off vapor return line is connected to a hydrogen pipeline in one or more of the liquefaction devices.

11. The modular hydrogen liquefaction system according to claim 7, wherein a top of the liquid hydrogen storage tank is provided with a boil-off vapor return line, and the boil-off vapor return line is connected to a hydrogen pipeline in one or more of the liquefaction devices; the modular hydrogen liquefaction system further comprises a cryogenic compressor, wherein an inlet of the cryogenic compressor is connected to the boil-off vapor return line, and an outlet of the cryogenic compressor is connected to a pipeline between the last and the penultimatecryogenic cooling sub-devices in the one or more cryogenicliquefaction sets; or, the modular hydrogen liquefaction system further comprises an ejector, wherein a low-pressure inlet of the ejector is connected to the boil-off vapor return line, a high-pressure inlet of the ejector is connected to an outlet pipeline of the penultimatecryogenic cooling sub-device in the one or more cryogenicliquefaction sets, and an outlet of the ejector is connected to an inlet pipeline of the lastcryogenic cooling sub-device in the corresponding cryogenicliquefaction set.

12. The modular hydrogen liquefaction system according to claim 2, wherein the compression unit is a compressor set composed of a plurality of compressors, and the plurality of compressors respectively provide compression work for the cryogenic liquefaction conversion unit.

13. The modular hydrogen liquefaction system according to claim 7, wherein the expansion unit is a plurality of throttle valves arranged in parallel, and each throttle valve is respectively connected to a corresponding outlet of the cryogenicliquefaction set.

14. The modular hydrogen liquefaction system according to claim 7, wherein a hydrogen pipeline and a cold refrigerant pipeline are arranged in the cold end of the standard refrigeration unit, one part or all of the hydrogen pipeline is provided with an ortho-para hydrogen catalyst, and the part or all of the hydrogen pipeline simultaneously forms the ortho-para hydrogen converter.

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