Small hydrogen liquefaction device

Abstract

The invention relates to a small hydrogen liquefaction device which comprises a gas source, a pressure regulating valve, a flow meter, a cold box and a liquefaction flow path arranged in the cold box, the liquefaction flow path comprises a precooler, a first refrigeration unit, a second refrigeration unit and a liquid hydrogen container which are connected in sequence, the first refrigeration unit comprises a first refrigerator and a first heat exchanger on a cold head of the first refrigerator, and the second refrigeration unit comprises a second heat exchanger on a cold head of the second refrigerator. The first refrigerating unit comprises a first refrigerating machine and a first heat exchanger, the first heat exchanger is filled with an ortho-parahydrogen catalyst, the second refrigerating unit comprises a second refrigerating machine and a second heat exchanger on a cold head of the second refrigerating machine, and a pressure regulating valve and a flow meter are located outside the cold box and used for completing pressure regulation and flow metering at normal temperature; according to the invention, pressure regulation is carried out at a normal temperature end, and a multi-stage static cooling flow path without moving parts is constructed in a low-temperature area, so that the problems of poor reliability, short service life and the like caused by a low-temperature throttle valve are fundamentally eliminated, meanwhile, complete liquefaction of hydrogen is realized, waste of a gas source is avoided, the working pressure of the system is reduced, and the utilization rate of gas in a gas cylinder is also improved.

Description

Technical Field

[0001] This invention relates to the field of refrigeration and cryogenic technology, and specifically to a small hydrogen liquefaction device. Background Technology

[0002] Currently, in the field of small-scale hydrogen liquefaction, a common technical solution is to use high-pressure hydrogen combined with a cryogenic throttling valve (JT valve) to achieve final liquefaction. In this type of system, after the high-pressure feedstock hydrogen is pre-cooled and cryogenically cooled by a refrigerator, its phase change process depends on a throttling valve located in the cryogenic zone.

[0003] However, the introduction of this core component also brings a series of inherent technical challenges. First, due to the necessity of precise control of small flow rates, the valve core of this cryogenic throttling valve has an extremely small diameter and requires a long rod structure, making it a precision cryogenic moving part. Such components inevitably face reliability challenges under deep cryogenic conditions, including material embrittlement, jamming of moving parts, seal failure, and decreased adjustment accuracy due to lubrication problems. Simultaneously, the valve core is subjected to long-term scouring by high-speed fluid, leading to severe wear and shortened lifespan, thus increasing the manufacturing and maintenance costs of the equipment. Second, from a thermodynamic perspective, the throttling process itself dictates that its outlet will inevitably produce a gas-liquid two-phase flow. This means that some hydrogen cannot be liquefied, and the separated gas phase is usually forced to diffuse, resulting in direct waste of gas resources. Furthermore, because this scheme relies on high-pressure throttling, it has high requirements for the supply pressure of the gas source, causing the gas in the high-pressure hydrogen cylinder to be underutilized, with a considerable amount of residual gas remaining in the cylinder. This constitutes indirect waste of gas resources and increases operating costs. It is evident that existing technologies rely on a single cryogenic moving component for liquefaction, thus creating a difficult contradiction between reliability, efficiency, and economy. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a small-scale hydrogen liquefaction device, aiming to solve one or more of the problems mentioned in the background technology.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a small hydrogen liquefaction device, comprising: a gas source; a pressure regulating valve connected to the gas source for regulating the hydrogen pressure from the gas source to the system operating pressure at room temperature; a flow meter connected downstream of the pressure regulating valve; a cold box; and a liquefaction flow path, the liquefaction flow path comprising: a precooler disposed within the cold box, its inlet connected downstream of the flow meter for first-stage cooling of the hydrogen; a first refrigeration unit comprising a first refrigerator and a first heat exchanger, the first heat exchanger being disposed on the cold head of the first refrigerator and filled with a neutral hydrogen catalyst, the inlet of the first heat exchanger being connected to the outlet of the precooler; a second refrigeration unit comprising a second refrigerator and a second heat exchanger, the second heat exchanger being disposed on the cold head of the second refrigerator, the inlet of the second heat exchanger being connected to the outlet of the first heat exchanger; and a liquid hydrogen container disposed within the cold box, its inlet connected to the outlet of the second heat exchanger, wherein the pressure regulating valve and the flow meter are located outside the cold box.

[0006] Furthermore, it also includes a liquid nitrogen precooling system, which includes a liquid nitrogen storage tank located outside the cold box, and a liquid nitrogen regulating valve connected between the liquid nitrogen storage tank and the precooler, for providing liquid nitrogen cooling capacity to the precooler.

[0007] Furthermore, the cooling capacity of the precooler is provided by a small precooling refrigeration unit.

[0008] Furthermore, the first refrigeration unit and / or the second refrigeration unit are GM refrigeration units.

[0009] Furthermore, the system operates at a pressure of 5 bar to 15 bar.

[0010] Furthermore, the first refrigeration unit is configured to cool hydrogen to 20K to 25K.

[0011] Furthermore, the second refrigeration unit is configured to cool hydrogen to below 20K.

[0012] Furthermore, an electric heater is provided on the cold head of the second refrigeration unit.

[0013] Furthermore, the liquid hydrogen container is equipped with a temperature-type level gauge and a differential pressure-type level gauge.

[0014] It also includes a small-scale hydrogen liquefaction method, comprising the following steps: S01: At room temperature, adjust the hydrogen pressure from the high-pressure gas source to the system operating pressure of 5 bar to 15 bar; S02: Pressure-regulated hydrogen gas is introduced into the precooler to cool it to the liquid nitrogen temperature range; S03: The pre-cooled hydrogen gas is introduced into the heat exchanger of the first refrigeration unit, and the cooling capacity of the first refrigeration unit is used to cool it to 20K to 25K. During this process, the positive hydrogen in the hydrogen gas is converted into secondary hydrogen by means of the positive and secondary hydrogen catalysts packed in the heat exchanger. S04: The converted hydrogen gas is passed into the heat exchanger of the second refrigeration unit, and the cooling capacity of the second refrigeration unit is used to cool it to below 20K, so that it is completely liquefied into a saturated liquid. S05: The saturated liquid hydrogen is sent into a liquid hydrogen container for storage.

[0015] The small-scale hydrogen liquefaction device described in this invention has the following advantages: By placing the pressure regulation function in the normal temperature range and constructing a multi-stage static cooling liquefaction flow path with no moving parts in the low temperature range, the indispensable low-temperature throttling valve in the prior art is fundamentally eliminated, thereby completely solving the inherent problems of low reliability, short lifespan, and high maintenance costs. At the same time, this solution achieves complete liquefaction of hydrogen through direct cooling by a refrigerator, avoiding the gas source waste caused by the generation of gas-liquid two-phase flow in traditional throttling methods, and significantly improving the utilization rate of raw materials. In addition, the significant reduction in system operating pressure allows the gas in the high-pressure cylinder to be almost completely utilized, further improving the economy and practicality of the entire system. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the small-scale hydrogen liquefaction device of the present invention.

[0017] Explanation of reference numerals in the attached diagram: 1. Gas source; 2. Pressure reducing valve; 3. Pressure regulating valve; 4. Flow meter; 5. Cold box; 51. Precooler; 52. First refrigeration unit; 521. First heat exchanger; 53. Second refrigeration unit; 531. Second heat exchanger; 532. Electric heater; 6. Liquid hydrogen container; 7. Liquid nitrogen storage tank; 8. Regulating valve. Detailed Implementation

[0018] Typical embodiments embodying the features and advantages of the present invention will be described in detail in the following description. It should be understood that the present invention can have various variations in different embodiments without departing from the scope of the present invention, and the descriptions and illustrations herein are for illustrative purposes only and not intended to limit the present invention.

[0019] In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.

[0020] To further illustrate the principles and structure of the present invention, preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0021] like Figure 1 As shown, this embodiment of the invention provides a small hydrogen liquefaction device. Its core design lies in constructing a hydrogen liquefaction flow path without any moving parts in the low-temperature region, thereby fundamentally solving the technical bottlenecks of poor reliability, short lifespan, and low adjustment accuracy of moving parts such as low-temperature throttle valves in the prior art.

[0022] To achieve this objective, the overall architecture of the device is clearly divided into two main functional modules: one is a pressure pretreatment and metering module located outside the cold box 5, and the other is a multi-stage static cooling and liquefaction module highly integrated inside the vacuum-insulated cold box 5. These two modules are connected by pipelines to form a complete and highly reliable hydrogen liquefaction system.

[0023] Specifically, the device includes a gas source 1, a pressure reducing valve 2, a pressure regulating valve 3CV2001, and a flow meter 4 connected sequentially along the hydrogen flow direction, as well as a precooler 51, a first refrigeration unit 52, a second refrigeration unit 53, and a liquid hydrogen container 6, all housed within a cold box 5. After hydrogen flows out from the high-pressure gas source 1, its pressure regulation and metering are completed at room temperature. It then enters the cold box 5 at a stable low pressure, flows through each stage of the cooling units, and is gradually cooled to its liquefaction temperature through pure heat exchange, ultimately being collected in liquid form in the liquid hydrogen container 6.

[0024] Furthermore, the gas source 1 is typically a high-pressure hydrogen cylinder assembly with a pressure of approximately 150 bar (15 MPa). Directly introducing high-pressure hydrogen into the liquefaction system poses safety risks and places high pressure resistance requirements on subsequent components. Therefore, this invention incorporates a two-stage pressure regulating structure at the outlet of gas source 1, aiming to safely and smoothly reduce the pressure to a low level suitable for liquefaction.

[0025] Furthermore, firstly, a pressure reducing valve 2 is connected to the outlet of gas source 1. The main function of this pressure reducing valve 2 is to perform a preliminary, significant pressure reduction, which is a safety redundancy and coarse adjustment design. For example, it reduces the pressure of gas source 1 from 150 bar to a moderate and safer intermediate pressure range (such as 25-40 bar). This design significantly reduces the inlet pressure and operating pressure differential of the subsequent core pressure regulating valve 3CV2001, which not only improves the service life of CV2001, but also enhances the safety and stability of the entire pressure regulation section.

[0026] Furthermore, downstream of the pressure reducing valve 2, the pressure regulating valve 3CV2001 is connected. This valve is one of the key components of the present invention, and its core function is to precisely regulate and stabilize the pressure of hydrogen gas after preliminary pressure reduction at room temperature. It precisely regulates and stabilizes the intermediate pressure upstream at a preset system operating pressure. The system operating pressure is set at a relatively low level, preferably 5 bar to 15 bar, for example, about 10 bar. By placing this key function of final pressure setting at room temperature, we have successfully avoided a series of problems faced when using precision moving parts (such as cryogenic throttle valves) at low temperatures, such as material embrittlement, moving part jamming, seal failure, and loss of regulation accuracy due to lubricating oil freezing. This design directly addresses the core defects existing in the prior art: firstly, it fundamentally avoids the use of cryogenic long-stem throttle valves, which are difficult to manufacture, have poor regulation accuracy at low temperatures, and have a short service life; secondly, the significant reduction in system operating pressure reduces the pressure requirements of the upstream gas source 1, allowing the gas in the high-pressure hydrogen cylinder group to be almost completely released and fully utilized.

[0027] At the same time, combined with the multi-stage refrigeration direct cooling scheme adopted in the cold box 5, the hydrogen is completely liquefied at the outlet of the second refrigeration unit 53 and enters the liquid hydrogen container 6 as a single liquid phase. This successfully solves the second problem mentioned in the background technology: avoiding the waste of gas source 1 caused by the gas phase having to be released after high pressure throttling.

[0028] Furthermore, a flow meter 4 is connected downstream of the pressure regulating valve 3CV2001. After the system pressure is stabilized, the flow meter 4 can accurately monitor and measure the hydrogen entering the liquefaction system in real time under stable operating conditions. Crucially, the pressure reducing valve 2, pressure regulating valve 3CV2001, and flow meter 4 are all located outside the cold box 5. This layout makes these components, which may require regular maintenance, calibration, or operation, easily accessible, greatly improving the maintainability and ease of operation of the equipment.

[0029] The precooler 51, the first refrigeration unit 52, the second refrigeration unit 53, and the liquid hydrogen container 6 are all installed inside the vacuum-insulated cold box 5. The cold box 5 isolates convection and conduction heat transfer through high vacuum and usually has a built-in radiation screen to minimize the entry of heat from the external environment and ensure the maintenance of a low-temperature environment.

[0030] Furthermore, the precooler 51 is the first-stage cooling device after hydrogen enters the cold box 5, and its function is to cool the hydrogen from room temperature to the liquid nitrogen temperature range. This process removes the sensible heat of the hydrogen from 300K to 80K, which is a key step in reducing the subsequent cryogenic refrigeration load. The source of cooling energy for the precooler 51 is flexible, and two main implementation methods are provided: Implementation Method 1: The system also includes a liquid nitrogen precooling system. This system comprises a liquid nitrogen storage tank 7 located outside the cold box 5, and a liquid nitrogen regulating valve 8 connected between the liquid nitrogen storage tank 7 and the precooler 51 via vacuum-insulated piping. Under the control of the regulating valve 8, liquid nitrogen enters the precooler 51, where it undergoes efficient indirect heat exchange with hydrogen flowing through the main path in its internal heat exchange channels. After absorbing heat, the liquid nitrogen vaporizes and is discharged, thus providing a stable and sufficient 80K level cooling capacity for the hydrogen. This solution offers a cost advantage when liquid nitrogen is readily available.

[0031] Implementation Method 2: In situations where liquid nitrogen is not readily available or where complete system self-sufficiency is desired, the precooler 51 can be designed as the cold head heat exchanger of a small precooling refrigerator (such as a GM refrigerator or a Stirling refrigerator). When the refrigerator is running, its cold head directly cools this heat exchanger, thereby providing the necessary precooling capacity for the flowing hydrogen. This approach enhances the system's independence and applicability.

[0032] Further, the hydrogen gas, cooled to approximately 80 K by the precooler 51, then enters the first refrigeration unit 52. The first refrigeration unit 52 includes a first refrigerator (preferably a GM refrigerator) and a first heat exchanger 521 disposed on the cold head of the first refrigerator. A key structural feature is that the interior of the first heat exchanger 521 is filled with particulate or specifically structured catalysts for the conversion of ortho- and para-hydrogen, such as high-surface-area iron oxide (Fe₂O₃) or iron hydroxide (Fe(OH)₃). Here, the hydrogen gas not only exchanges heat with the cold head of the first refrigerator, being further cooled to an intermediate temperature (e.g., 20 K to 25 K), but also, under the highly efficient catalytic action of the catalyst, the ortho-hydrogen molecules in the gas stream rapidly convert to para-hydrogen, approaching the equilibrium concentration at that temperature. The conversion of ortho-hydrogen to para-hydrogen is an exothermic process. Filling the heat exchanger with the catalyst in this temperature range means that this significant heat of conversion is removed in a timely manner at a relatively high temperature range (20K-25K), which is far more efficient than releasing the heat of conversion in a liquid hydrogen storage tank at a lower temperature. This greatly reduces the heat load that the second refrigeration unit 53 needs to bear, and is a key design to improve the overall energy efficiency of the system.

[0033] Furthermore, in order to initiate the secondary hydrogen conversion at an earlier stage and distribute the heat load, as a preferred embodiment, the secondary hydrogen conversion catalyst can also be packed inside the precooling heat exchanger. When the hydrogen is cooled to about 80K in the precooler 51, the conversion can begin under the action of the catalyst, removing some of the conversion heat in advance, making the heat distribution of the entire system more balanced and further improving efficiency.

[0034] Furthermore, the hydrogen that has undergone the n-to-paragonal conversion then flows into the second refrigeration unit 53. The second refrigeration unit 53 includes a second refrigerator (preferably a GM refrigerator) and a second heat exchanger 531 disposed on the cold head of the second refrigerator. The second heat exchanger 531 is explicitly not filled with any catalyst; its function is singular and focused: utilizing the lowest system cooling capacity provided by the second refrigerator, it cools the pre-cooled and converted hydrogen from 20K to 25K to below its boiling point (e.g., below 20K), completely liquefying it into a saturated liquid. Since the system pressure has been reduced at room temperature and most of the n-to-paragonal conversion heat has been removed in the previous stage, the liquefaction process here is smooth and efficient. Finally, the hydrogen flowing out of the outlet of the second heat exchanger 531 is saturated liquid hydrogen in a completely liquid phase, which contrasts sharply with the situation where traditional high-pressure throttling methods inevitably produce a two-phase flow of gas and liquid, thus achieving complete liquefaction of the raw material hydrogen and avoiding waste caused by gas phase emissions.

[0035] After complete liquefaction, the liquid hydrogen flows into and is stored in the liquid hydrogen container 6 under its own gravity or a slight pressure difference. The liquid hydrogen container 6 has a certain storage capacity to meet the high-frequency and random use of liquid hydrogen during experiments.

[0036] To ensure the system operates stably and safely for a long time under extreme low temperature conditions, this invention integrates multi-level safety and control designs in addition to the core liquefaction function.

[0037] Furthermore, the freezing point of liquid hydrogen is approximately 13.8K. To prevent the liquid hydrogen from solidifying and clogging the flow channels in the second heat exchanger 531 due to excessively low temperatures caused by control fluctuations or unexpected operating conditions, an electric heater is installed on the cold head of the second refrigeration unit 53. This electric heater does not operate continuously but intelligently starts, stops, and adjusts its power based on signals from a temperature sensor installed on or near the cold head. When the temperature falls below a set safety threshold, the electric heater automatically starts, injecting an appropriate amount of heat to precisely control the cold head temperature within a safe range, effectively preventing hydrogen solidification.

[0038] Furthermore, to accurately monitor the inventory of liquid hydrogen and ensure the continuity and safety of the experiment, the liquid hydrogen container 6 is equipped with level monitoring devices (not shown in the figure) at 10%, 50%, and 90% liquid levels. These include a temperature-type level gauge and a differential pressure-type level gauge. The temperature-type level gauge measures the liquid level based on the temperature difference between the gas and liquid phases, while the differential pressure-type level gauge measures the level based on the hydrostatic pressure of the liquid column. These two types of level gauges, based on different physical principles, can operate simultaneously, and their readings can be compared and verified. When one exhibits a deviation or malfunction, the other can serve as a reference, thereby greatly ensuring the accuracy, reliability, and redundancy of the liquid level measurement data, providing a solid data foundation for precise control and safety early warning during the experiment.

[0039] Furthermore, to ensure the long-term stability of the liquid hydrogen product during storage and avoid evaporation losses caused by the exothermic conversion of neutral and parahydrogen, in another preferred embodiment, a neutral-parahydrogen conversion catalyst can also be placed inside the liquid hydrogen container 6. This allows the stored liquid hydrogen to always maintain a parahydrogen equilibrium state, achieving an effect similar to "zero-evaporation storage," which is particularly suitable for applications requiring long-term storage or with extremely high requirements for product purity and stability.

[0040] Furthermore, a pre-cooling stage discharge pipeline (not shown) is installed on the liquid hydrogen container. The discharge pipeline is connected to an ambient temperature valve and an ambient temperature flow meter (not shown). A heating tape (not shown) is installed at the part of the discharge pipeline that exits the cold box. A thermometer (not shown) is installed before the valve. It is used to interlock with the heating tape. When the temperature is low, the heating tape is turned on, and when the temperature is high, the heating tape is turned off to ensure the operating temperature range of the ambient temperature valve and the flow meter.

[0041] In operation, the small-scale hydrogen liquefaction device of this invention first safely and precisely reduces the pressure of high-pressure hydrogen to a stable low-pressure state (~10 bar) at room temperature through a two-stage pressure regulation system consisting of "pressure reducing valve 2 + pressure regulating valve 3CV2001". Subsequently, the hydrogen enters the vacuum insulated cold box 5 and undergoes three stages in sequence: "liquid nitrogen temperature zone pre-cooling", "intermediate deep cooling with positive and negative hydrogen catalytic conversion", and "final liquefaction cooling". During this process, by placing all pressure regulation functions in the room temperature zone and adopting a pure heat exchange architecture consisting of multi-stage static heat exchangers directly coupled with the cold head of the refrigerator in the low-temperature zone, the design goal of "no moving parts between the hydrogen source flow path from the inlet of the pre-cooler 51 to the inlet of the liquid hydrogen container 6" is successfully achieved. This system is not only simple in structure, convenient to control, highly reliable, and low in maintenance cost, but also achieves complete liquefaction of hydrogen, with the utilization rate of gas source 1 being close to 100%, making it very suitable for small-scale, high-frequency liquid hydrogen demand scenarios at the laboratory level.

[0042] It also includes a small-scale hydrogen liquefaction method, comprising the following steps: S01: At room temperature, adjust the hydrogen pressure from the high-pressure gas source to the system operating pressure of 5 bar to 15 bar; S02: Pressure-regulated hydrogen gas is introduced into the precooler to cool it to the liquid nitrogen temperature range; S03: The pre-cooled hydrogen gas is introduced into the heat exchanger of the first refrigeration unit, and the cooling capacity of the first refrigeration unit is used to cool it to 20K to 25K. During this process, the positive hydrogen in the hydrogen gas is converted into secondary hydrogen by means of the positive and secondary hydrogen catalysts packed in the heat exchanger. S04: The converted hydrogen gas is passed into the heat exchanger of the second refrigeration unit, and the cooling capacity of the second refrigeration unit is used to cool it to below 20K, so that it is completely liquefied into a saturated liquid. S05: The saturated liquid hydrogen is sent into a liquid hydrogen container for storage.

[0043] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A small-scale hydrogen liquefaction device, characterized in that, include: Gas source; A pressure regulating valve, connected to the gas source, is used to regulate the hydrogen pressure from the gas source to the system operating pressure at room temperature; A flow meter is connected downstream of the pressure regulating valve; Cold box; And a liquefaction flow path, the liquefaction flow path including: A precooler, located inside the cold box, has its inlet connected downstream of the flow meter and is used for the first-stage cooling of hydrogen. The first refrigeration unit includes a first refrigeration unit and a first heat exchanger. The first heat exchanger is disposed on the cold head of the first refrigeration unit and is filled with a neutral hydrogen catalyst. The inlet of the first heat exchanger is connected to the outlet of the precooler. The second refrigeration unit includes a second refrigeration unit and a second heat exchanger. The second heat exchanger is disposed on the cold head of the second refrigeration unit, and the inlet of the second heat exchanger is connected to the outlet of the first heat exchanger. A liquid hydrogen container is disposed inside the cold box, and its inlet is connected to the outlet of the second heat exchanger; The pressure regulating valve and the flow meter are located outside the cold box.

2. The small-scale hydrogen liquefaction device as described in claim 1, characterized in that, It also includes a liquid nitrogen precooling system, which includes a liquid nitrogen storage tank located outside the cold box and a liquid nitrogen regulating valve connected between the liquid nitrogen storage tank and the precooler for providing liquid nitrogen cooling capacity to the precooler.

3. The small-scale hydrogen liquefaction device as described in claim 1, characterized in that, The cooling capacity of the precooler is provided by a low-temperature mixed working fluid or a GM refrigerator.

4. The small-scale hydrogen liquefaction device as described in claim 1, characterized in that, The first refrigeration unit and / or the second refrigeration unit is any one of the following: GM refrigeration unit, Stirling refrigeration unit, pulse tube refrigeration unit, and thermoacoustic refrigeration unit.

5. The small-scale hydrogen liquefaction device as described in claim 1, characterized in that, The system operates at pressures ranging from 2 bar to 15 bar.

6. The small-scale hydrogen liquefaction device as described in claim 1, characterized in that, The first refrigeration unit is configured to cool hydrogen to 20K to 25K.

7. The small-scale hydrogen liquefaction device as described in claim 1, characterized in that, The second refrigeration unit is configured to cool hydrogen to below 20K.

8. The small-scale hydrogen liquefaction device as described in claim 1, characterized in that, An electric heater is installed on the cold head of the second refrigeration unit.

9. The small-scale hydrogen liquefaction device as described in claim 1, characterized in that, The liquid hydrogen container is equipped with a temperature-type level gauge and a differential pressure level gauge.

10. A small-scale hydrogen liquefaction method, characterized in that, Includes the following steps: S01: At room temperature, adjust the hydrogen pressure from the high-pressure gas source to the system operating pressure of 2 bar to 15 bar; S02: Pressure-regulated hydrogen gas is introduced into the precooler to cool it to the liquid nitrogen temperature range; S03: The pre-cooled hydrogen gas is introduced into the heat exchanger of the first refrigeration unit, and the cooling capacity of the first refrigeration unit is used to cool it to 20K to 25K. During this process, the positive hydrogen in the hydrogen gas is converted into secondary hydrogen by means of the positive and secondary hydrogen catalysts packed in the heat exchanger. S04: The converted hydrogen gas is passed into the heat exchanger of the second refrigeration unit, and the cooling capacity of the second refrigeration unit is used to cool it to below 20K, so that it is completely liquefied into a saturated liquid. S05: The saturated liquid hydrogen is sent into a liquid hydrogen container for storage.

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