Hydrogen liquefaction device and method for LNG (Liquefied Natural Gas) precooling and nitrogen cycle refrigeration

Abstract

The invention relates to the technical field of hydrogen liquefaction, in particular to an LNG (liquefied natural gas) precooling and nitrogen cycle refrigeration hydrogen liquefaction device and method.The LNG precooling and nitrogen cycle refrigeration hydrogen liquefaction device comprises a gas hydrogen flow channel and a plurality of heat exchangers arranged in the gas hydrogen flow channel at intervals in the conveying direction, and a liquid hydrogen storage device is connected behind the last-stage heat exchanger; at least the first-stage heat exchanger is connected with an LNG precooling pipe and used for precooling gas hydrogen entering the first-stage heat exchanger, at least the first-stage heat exchanger and the second-stage heat exchanger are communicated to a nitrogen cooling pipeline, and the nitrogen cooling pipeline is sequentially communicated with the multiple heat exchangers to form a circulation pipeline. According to the system and the method, nitrogen and LNG are used for assisting in providing cooling capacity for precooling hydrogen, hydrogen expansion is used for providing cooling capacity for liquefaction, the cooling capacity of flash steam is used for liquefaction, independent cooling capacity supply in the liquefaction process is reduced, and energy consumption is reduced; meanwhile, through multi-stage ortho-parahydrogen conversion and multi-stage turbine expansion, hydrogen conversion can be effectively improved.

Description

Technical Field

[0001] This invention relates to the field of hydrogen liquefaction technology, specifically to an apparatus and method for hydrogen liquefaction using LNG precooling and nitrogen cycle refrigeration. Background Technology

[0002] Hydrogen energy is a clean secondary energy source with abundant supply, green and low-carbon characteristics, and wide applications. It is an important alternative energy source in the construction of future energy systems and a key development direction for strategic emerging industries and future industries. Liquid hydrogen has significant advantages such as high hydrogen storage density, high transportation efficiency, and low storage and transportation pressure. The efficiency of transporting liquid hydrogen is 6 to 8 times higher than that of gaseous hydrogen. From a technical perspective, cryogenic liquid hydrogen has a greater cost advantage and is the inevitable choice for large-scale hydrogen energy applications in the future. Currently, domestic liquid hydrogen technology is still in its early stages. The cost of using liquid hydrogen for civilian purposes is too high, the efficiency is relatively low, the energy consumption is high, and the system is complex.

[0003] It is evident that current liquid hydrogen technology still has room for improvement and should be optimized to enhance its ease of application, reduce technical costs, and simplify related systems. Therefore, a more rational technical solution is needed to address the existing technical problems. Summary of the Invention

[0004] To overcome at least one of the aforementioned defects, this invention proposes an apparatus and method for hydrogen liquefaction using LNG precooling and nitrogen cycle refrigeration. The method employs multiple heat exchange processes to liquefy gaseous hydrogen, and the heat is converted and utilized multiple times during the liquefaction process to improve the heat utilization rate. LNG and liquid nitrogen are also used for auxiliary cooling and to form a cycle, thereby improving the efficiency of gaseous hydrogen liquefaction, simplifying the composition of the liquefaction system, and effectively controlling the applicable cost of the entire system.

[0005] To achieve the above objectives, the hydrogen liquefaction device disclosed in this invention can adopt the following technical solution:

[0006] An apparatus for hydrogen liquefaction using LNG precooling and nitrogen circulation cooling includes a gaseous hydrogen flow channel and a plurality of heat exchangers spaced apart along the conveying direction in the gaseous hydrogen flow channel. A liquid hydrogen storage device is connected after the final heat exchanger. At least one first-stage heat exchanger is connected to an LNG precooling pipeline for precooling the gaseous hydrogen entering the first-stage heat exchanger. At least the first-stage and second-stage heat exchangers are connected to a nitrogen cooling pipeline, which sequentially connects to multiple heat exchangers to form a circulation pipeline.

[0007] The aforementioned hydrogen liquefaction apparatus utilizes a multi-stage heat exchanger for progressive heat exchange. During this process, multiple stages of conversion between ortho- and para-hydrogen occur, enhancing the stability of the liquid hydrogen. Simultaneously, a portion of the gaseous hydrogen is expanded to provide cooling, and the flash vapor of the liquid hydrogen is used to further cool and liquefy the hydrogen. Finally, both the reheated gaseous hydrogen and the flash vapor are compressed and cooled before being used as feedstock hydrogen in subsequent liquefaction cycles, thus avoiding hydrogen waste. The liquefaction of gaseous hydrogen using this apparatus is not only simple to operate but also features a simple process, low cost, and a simple device structure.

[0008] Furthermore, during the cooling process of gaseous hydrogen, the conversion from orthohydrogen to parahydrogen occurs at multiple points. This conversion can be facilitated through the coordination of the device, and the specific scheme is not limited to one particular method. Here, we optimize and propose one feasible option: at least at the first-stage heat exchanger, second-stage heat exchanger, and third-stage tube heat exchanger, orthohydrogen-parahydrogen converters are installed and connected to gaseous hydrogen channels. The gaseous hydrogen channels guide the gaseous hydrogen into the orthohydrogen-parahydrogen converters for conversion treatment, and then guide the gaseous hydrogen back to the corresponding heat exchanger for heat exchange again. When using this scheme, the conversion of orthohydrogen to parahydrogen causes the temperature of the gaseous hydrogen to rise, so it is guided back to the heat exchanger for further cooling.

[0009] Furthermore, during the continuous cooling process, the expansion of some gaseous hydrogen provides cooling to promote hydrogen liquefaction. This can be achieved through various methods and is not limited to a single approach. Here, we optimize the process and propose one feasible option: Turbine expanders are installed at least at the third, fourth, and final heat exchangers. The gaseous hydrogen flow path is connected to branched hydrogen refrigerant pipelines and then to the turbine expanders. The turbine expanders are connected to hydrogen expansion pipelines and several heat exchangers. The hydrogen expansion pipelines are connected to a refrigerant compressor and a hydrogen cooler to generate supplementary gaseous hydrogen feedstock. With this approach, the gaseous hydrogen in the hydrogen expansion pipeline, after receiving cooling, experiences a temperature rise. Through the action of the refrigerant compressor and hydrogen cooler, it is converted back to the temperature and pressure values ​​of the feedstock hydrogen and mixed with it before entering the liquefaction unit.

[0010] Furthermore, in this invention, a portion of flash vapor is generated in the liquid hydrogen storage device. The cooling capacity of this flash vapor can also be used for the liquefaction of gaseous hydrogen. The specific method is not limited to one particular method. Here, an optimization is proposed, and one feasible option is as follows: the liquid hydrogen storage device is equipped with a flash vapor pipeline that is sequentially connected to several heat exchangers, and the flash vapor pipeline extends to a refrigerant compressor and a hydrogen cooler to generate supplementary gaseous hydrogen feedstock. When this scheme is adopted, the flash vapor pipeline can provide cooling capacity to some heat exchangers or to all heat exchangers. After the flash vapor provides cooling capacity, the temperature rises and it is converted into gaseous hydrogen. Through the action of the refrigerant compressor and the hydrogen cooler, the temperature and pressure can be readjusted to the feedstock hydrogen value.

[0011] Furthermore, nitrogen circulation cooling can provide cooling capacity to the heat exchanger, promoting the conversion of gaseous hydrogen to liquid hydrogen. The nitrogen circulation cooling method is not limited to a single approach; here, an optimization is proposed, suggesting one feasible option: the nitrogen cooling pipeline passes through the corresponding connected heat exchangers twice, and the nitrogen cooling pipeline connects the nitrogen intake tank, the nitrogen compressor, and the nitrogen cooler. With this scheme, the nitrogen cooling pipeline can continuously enter multiple heat exchangers and, after adjustment, re-enter multiple heat exchangers, thereby maximizing the cooling capacity and promoting the conversion of gaseous hydrogen to liquid hydrogen.

[0012] Furthermore, to optimize the nitrogen cooling pipeline for enhanced cooling capacity, one feasible option is to install a throttling valve on the nitrogen cooling pipeline. Using this approach, the throttling valve restricts the flow of nitrogen in the cooling pipeline, promoting nitrogen subcooling and providing cooling capacity.

[0013] Furthermore, after gaseous hydrogen is converted into liquid hydrogen, it can be transported externally as a liquid hydrogen product: the liquid hydrogen storage equipment is equipped with a product transport pipeline.

[0014] In addition to the hydrogen liquefaction apparatus disclosed above, this invention also provides a method for hydrogen liquefaction, which will be described below.

[0015] A method for hydrogen liquefaction using LNG precooling and nitrogen cycle refrigeration, employing the aforementioned hydrogen liquefaction apparatus, comprising:

[0016] After the raw hydrogen is mixed with the circulating hydrogen, it is pre-cooled at the first heat exchanger and then enters several heat exchangers in sequence for heat exchange and cooling. The temperature decreases in sequence and it is finally liquefied and stored and transported.

[0017] After hydrogen is output from several of the heat exchangers, it passes through a positive and negative hydrogen converter to convert a portion of the positive hydrogen into negative hydrogen. After releasing heat and heating up, it returns to the heat exchanger to cool down.

[0018] After hydrogen is output from several heat exchangers, a portion of the hydrogen is diverted to the turbine expander for cooling and liquefaction, and then flows through several heat exchangers via the hydrogen expansion pipeline to provide cooling capacity. Finally, the hydrogen is reheated, compressed and cooled to become circulating hydrogen.

[0019] Hydrogen is output from the final heat exchanger and cooled and compressed by the turbine expander before entering the liquid hydrogen storage device. The flash vapor generated at the liquid hydrogen storage device is guided and transported through the flash vapor pipeline and passes through several heat exchangers to provide cooling. The flash vapor is then reheated, compressed and cooled before being used as circulating hydrogen.

[0020] Nitrogen refrigeration circulation pipelines were formed at several heat exchangers to cool the hydrogen flowing through them.

[0021] Furthermore, during the staged cooling process, the heat exchange cooling rate of hydrogen can employ various schemes and is not limited to a single one. Here, we optimize and propose one feasible option: hydrogen is cooled to -150℃ to -155℃ via the first-stage heat exchanger, to -190℃ via the second-stage heat exchanger, to -200℃ to -220℃ via the third-stage heat exchanger, to -228℃ to -248℃ via the fourth-stage heat exchanger, and then liquefied and subcooled to -253℃ via the final-stage heat exchanger; the pressure of the raw hydrogen is greater than or equal to 1.4 MPa, and the pressure at the outlet of the final-stage heat exchanger is 15 kPa to 120 kPa. With this scheme, each heat exchanger can reduce the temperature of gaseous hydrogen to the set range, making implementation easier and ensuring the stability of liquid hydrogen, thus simplifying the processing technology.

[0022] Furthermore, when using nitrogen for refrigeration, various schemes can be adopted for nitrogen delivery control. Here, we optimize and propose one feasible option: Nitrogen is pressurized to 2.3MPa–3MPa, sequentially enters several heat exchangers for liquefaction and subcooling, and then re-enters the heat exchangers for cooling after being throttled and subcooled by a throttling valve. The reheated nitrogen then enters the next cycle. Using this scheme, nitrogen circulates for refrigeration within the circulation pipeline.

[0023] Compared with the prior art, some of the beneficial effects of the technical solution disclosed in this invention include:

[0024] This invention utilizes nitrogen and LNG to provide cooling to promote the liquefaction of gaseous hydrogen, and uses expansion to provide some of the cooling capacity of gaseous hydrogen for liquefaction, as well as the cooling capacity of flash vapor for liquefaction, thereby reducing the need for separate cooling supply during the liquefaction process and lowering energy consumption. At the same time, through multi-stage ortho- and para-hydrogen conversion and multi-stage turbine expansion, the hydrogen conversion rate can be effectively improved, which facilitates the improvement of conversion efficiency. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the components and process flow of a hydrogen liquefaction device.

[0027] In the above attached figures, the meanings of each label are as follows:

[0028] 1. Refrigerant compressor; 2. Hydrogen cooler; 3. First-stage heat exchanger; 4. Second-stage heat exchanger; 5. Third-stage heat exchanger; 6. Fourth-stage heat exchanger; 7. Final-stage heat exchanger; 8. First-stage anisotropic hydrogen converter; 9. Second-stage anisotropic hydrogen converter; 10. Third-stage anisotropic hydrogen converter; 11. First turbine expander unit; 12. Second turbine expander unit; 13. Liquid hydrogen storage equipment; 14. Third turbine expander unit; 15. LNG precooling pipe; 16. Nitrogen intake tank; 17. Nitrogen compressor; 18. Nitrogen cooler; 19. Throttling valve; 20. Feed pipe; 21. Product delivery pipe; 22. Natural gas pipeline; 23. First hydrogen refrigerant pipeline; 24. First hydrogen expansion pipeline; 25. Second hydrogen refrigerant pipeline; 26. Second hydrogen expansion pipeline. Detailed Implementation

[0029] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments.

[0030] In view of the fact that existing hydrogen conversion devices have relatively complex structures, complex conversion processes, and low conversion efficiency, the following embodiments are optimized to overcome the defects in the prior art.

[0031] Example 1

[0032] like Figure 1 As shown, this embodiment provides a hydrogen liquefaction device for LNG precooling and nitrogen circulation refrigeration, including a gaseous hydrogen flow channel and a plurality of heat exchangers spaced apart along the conveying direction in the gaseous hydrogen flow channel. A liquid hydrogen storage device 13 is connected after the final heat exchanger 7. At least the first-stage heat exchanger 3 is connected to an LNG precooling pipe 15 for precooling the gaseous hydrogen entering the first-stage heat exchanger 3. At least the first-stage and second-stage heat exchangers 4 are connected to a nitrogen cooling pipeline, which sequentially connects to multiple heat exchangers to form a circulation pipeline.

[0033] Preferably, in this embodiment, the raw material hydrogen gas is transported into the first-stage heat exchanger 3 via the raw material pipe 20, and a five-stage heat exchanger is used for heat exchange. After LNG is introduced into the first-stage heat exchanger 3 via the LNG precooling pipe 15, the LNG releases its cooling capacity and vaporizes into natural gas, which is then discharged through the natural gas pipeline 22.

[0034] The hydrogen liquefaction apparatus disclosed in this embodiment utilizes a multi-stage heat exchanger for step-by-step heat exchange. During the heat exchange process, the conversion between ortho-hydrogen and para-hydrogen also occurs, improving the stability of liquid hydrogen. Simultaneously, a portion of the gaseous hydrogen is expanded to provide cooling, and the flash vapor of the liquid hydrogen is used to provide cooling to promote hydrogen cooling and liquefaction. Finally, the expanded gaseous hydrogen and hydrogen flash vapor are reheated, compressed, and cooled, and then used as raw material hydrogen in subsequent liquefaction cycles, thus avoiding hydrogen waste. The liquefaction of gaseous hydrogen using the above apparatus is not only simple to operate, but also has a simple process, low cost, and simple device structure.

[0035] During the cooling process of gaseous hydrogen, the conversion from orthohydrogen to parahydrogen occurs at multiple points. This conversion can be facilitated by the coordination of devices, and the specific scheme is not limited to one particular method. This embodiment optimizes and adopts one feasible option: at least at the first-stage heat exchanger 3, the second-stage heat exchanger 4, and the tertiary tube heat exchanger, an orthohydrogen-parahydrogen converter is installed and connected to a gaseous hydrogen channel. The gaseous hydrogen channel guides the gaseous hydrogen into the orthohydrogen-parahydrogen converter for conversion, and then guides the gaseous hydrogen back to the corresponding heat exchanger for heat exchange again. When this scheme is adopted, the heat released during the conversion of orthohydrogen to parahydrogen causes the temperature of the gaseous hydrogen to rise, so it is guided back to the heat exchanger for further cooling.

[0036] Preferably, a first intermediate hydrogen converter 8, a second intermediate hydrogen converter 9, and a third intermediate hydrogen converter 10 are respectively installed at the primary heat exchanger 3, the secondary heat exchanger 4, and the tertiary tube heat exchanger.

[0037] During continuous cooling, the expansion of some gaseous hydrogen provides cooling, which in turn promotes hydrogen liquefaction. This can be achieved through various methods and is not limited to a single approach. This embodiment optimizes the process and adopts one feasible option: Turbine expanders are installed at least at the third-stage heat exchanger 5, the fourth-stage heat exchanger 6, and the final-stage heat exchanger 7. A branch hydrogen refrigerant pipeline is connected to the gaseous hydrogen flow channel and then to the turbine expander. The turbine expander is connected to the hydrogen expansion pipeline and several heat exchangers. The hydrogen expansion pipeline is connected to the refrigerant compressor 1 and the hydrogen cooler 2 to generate supplementary gaseous hydrogen feedstock. With this approach, the gaseous hydrogen in the hydrogen expansion pipeline, after providing cooling, experiences a temperature rise. Through the action of the refrigerant compressor 1 and the hydrogen cooler 2, it is converted back to the temperature and pressure values ​​of the feedstock hydrogen and mixed with it before entering the liquefaction unit.

[0038] Preferably, a first turbine expander unit 11, a second turbine expander unit 12, and a third turbine expander unit 14 are respectively installed at the third-stage heat exchanger 5, the fourth-stage heat exchanger 6, and the final-stage heat exchanger 7. The inlet and outlet of the first turbine expander unit 11 are connected to the first hydrogen refrigerant line 23 and the first hydrogen expansion line 24, respectively, and the inlet and outlet of the second turbine expander unit 12 are connected to the second hydrogen refrigerant line 25 and the second hydrogen expansion line 26, respectively.

[0039] Preferably, in this embodiment, cooling water is used as the medium for the hydrogen cooler 2.

[0040] In this embodiment, a portion of flash vapor is generated in the liquid hydrogen storage device. The cooling capacity of this flash vapor can also be used for the liquefaction of gaseous hydrogen. The specific method is not limited to one particular method. This embodiment optimizes and adopts one feasible option: the liquid hydrogen storage device is equipped with a flash vapor pipeline that is sequentially connected to several heat exchangers, and the flash vapor pipeline extends to the refrigerant compressor 1 and the hydrogen cooler 2 to generate supplementary gaseous hydrogen feedstock. With this scheme, the flash vapor pipeline can provide cooling capacity to some heat exchangers or all heat exchangers; after the flash vapor provides cooling capacity, the temperature rises and it is converted into gaseous hydrogen. Through the action of the refrigerant compressor 1 and the hydrogen cooler 2, the temperature and pressure values ​​of the feedstock hydrogen can be readjusted.

[0041] Nitrogen circulation cooling can provide cooling to heat exchangers, promoting the conversion of gaseous hydrogen to liquid hydrogen. The cooling method of nitrogen circulation cooling is not limited to a single approach; this embodiment optimizes and adopts one feasible option: the nitrogen cooling pipeline passes through the corresponding connected heat exchangers twice, and the nitrogen cooling pipeline connects the nitrogen intake tank 16, the nitrogen compressor 17, and the nitrogen cooler 18. With this scheme, the nitrogen cooling pipeline can continuously enter multiple heat exchangers and, after adjustment, re-enter multiple heat exchangers, thereby maximizing the cooling capacity and promoting the conversion of gaseous hydrogen to liquid hydrogen.

[0042] Preferably, in this embodiment, the nitrogen cooler 18 uses cooling water as the cooling medium.

[0043] To enhance the cooling effect of nitrogen, the nitrogen cooling pipeline is optimized. This embodiment provides one feasible option: a throttling valve 19 is installed on the nitrogen cooling pipeline. With this solution, the nitrogen cooling pipeline is throttled via the throttling valve 19, which promotes liquid nitrogen subcooling and provides cooling.

[0044] After gaseous hydrogen is converted into liquid hydrogen, it can be transported externally as a liquid hydrogen product: the liquid hydrogen storage device is equipped with a product transport pipeline 21.

[0045] Example 2

[0046] The hydrogen liquefaction apparatus disclosed in Embodiment 1 above is further described below, along with a method for hydrogen liquefaction.

[0047] A method for hydrogen liquefaction using LNG precooling and nitrogen cycle refrigeration, employing the hydrogen liquefaction apparatus described in Example 1 above, includes:

[0048] After the raw hydrogen is mixed with the circulating hydrogen, it is pre-cooled at the first heat exchanger 3, and then enters several heat exchangers in sequence for heat exchange and cooling. The temperature decreases in sequence and it is finally liquefied and stored and transported.

[0049] After hydrogen is output from several of the heat exchangers, it passes through a positive and negative hydrogen converter to convert a portion of the positive hydrogen into negative hydrogen. After releasing heat and heating up, it returns to the heat exchanger to cool down.

[0050] After hydrogen is output from several heat exchangers, a portion of the hydrogen is diverted to the turbine expander for cooling, and then flows through several heat exchangers via the hydrogen expansion pipeline to provide cooling capacity. Finally, the hydrogen is compressed and cooled to become circulating hydrogen.

[0051] Hydrogen is output from the final heat exchanger 7 and liquefied by the turbine expander before entering the liquid hydrogen storage device. The flash vapor generated at the liquid hydrogen storage device is guided and transported through the flash vapor pipeline and passes through several heat exchangers to provide cooling. The flash vapor is compressed and cooled before being used as circulating hydrogen.

[0052] Nitrogen refrigeration circulation pipelines were formed at several heat exchangers to cool the hydrogen flowing through them.

[0053] During the staged cooling process, the heat exchange cooling rate of hydrogen can be achieved using various methods and is not limited to a single one. This embodiment optimizes and adopts one feasible option: hydrogen is cooled to -150℃ to -155℃ via the first-stage heat exchanger 3, to -190℃ via the second-stage heat exchanger 4, to -200℃ to -220℃ via the third-stage heat exchanger 5, to -228℃ to -248℃ via the fourth-stage heat exchanger 6, and then liquefied and subcooled to -253℃ via the final-stage heat exchanger 7. The pressure of the raw hydrogen is greater than or equal to 1.4 MPa, and the pressure output from the final-stage heat exchanger 7 is 15 kPa to 120 kPa. With this scheme, each heat exchanger can reduce the temperature of gaseous hydrogen to the set range, making it easier to achieve, while ensuring the stability of liquid hydrogen, thus simplifying the processing technology.

[0054] When using nitrogen for refrigeration, various schemes can be adopted for nitrogen delivery control. This embodiment optimizes and adopts one feasible option: nitrogen is pressurized to 2.3MPa~3MPa, sequentially enters several heat exchangers for liquefaction and subcooling, and then re-enters the heat exchangers for cooling after being throttled and subcooled by throttling valve 19. The reheated nitrogen is then delivered for cooling and enters the next cycle. With this scheme, nitrogen circulates for refrigeration in the circulation pipeline.

[0055] When the above plan is implemented, the following effects can be achieved:

[0056] (1) The hydrogen liquefaction unit is suitable for large-scale hydrogen liquefaction production. Based on the characteristics of hydrogen liquefaction, hydrogen precooling adopts LNG precooling and nitrogen cycle refrigeration, and the circulating hydrogen refrigeration system is subcooled. The cooling capacity of hydrogen precooling is supplied through LNG and liquid nitrogen respectively, reducing the energy consumption provided by the hydrogen cycle refrigeration. The raw material hydrogen is converted by a three-stage ortho-parahydrogen converter, and the parahydrogen content in the liquid hydrogen is ≥95%.

[0057] (2) By setting up two-stage hydrogen expansion and liquid hydrogen turbine expansion to recover pressure energy, and by adding hydrogen flash vapor generated during liquid hydrogen production due to the JT effect (isoenthalpic expansion) to the heat exchange network, energy consumption is further reduced. Therefore, the above-mentioned hydrogen liquefaction equipment has the advantages of high conversion rate of ortho- and para-hydrogen, high hydrogen liquefaction efficiency, and low energy consumption.

[0058] The above are the embodiments listed in this example. However, this example is not limited to the optional embodiments described above. Those skilled in the art can arbitrarily combine the above methods to obtain other various embodiments. Anyone can derive other various forms of embodiments under the guidance of this example. The above specific embodiments should not be construed as limiting the scope of protection of this example. The scope of protection of this example should be defined in the claims.

Claims

1. A device for hydrogen liquefaction using LNG precooling and nitrogen cycle refrigeration, characterized in that: It includes a gaseous hydrogen flow channel and several heat exchangers spaced apart along the transport direction in the gaseous hydrogen flow channel. The final heat exchanger (7) is connected to a liquid hydrogen storage device. At least the first heat exchanger (3) is connected to an LNG precooling pipe (15) and used to precool the gaseous hydrogen entering the first heat exchanger (3). At least the first and second heat exchangers (4) are connected to a nitrogen cooling pipeline. The nitrogen cooling pipeline is connected to multiple heat exchangers in sequence to form a circulation pipeline.

2. The apparatus for hydrogen liquefaction using LNG precooling and nitrogen cycle refrigeration according to claim 1, characterized in that: At least at the primary heat exchanger (3), secondary heat exchanger (4) and tertiary tube heat exchanger, a secondary hydrogen converter is installed and connected to a gas hydrogen channel. The gas hydrogen channel guides the gas hydrogen into the secondary hydrogen converter for conversion and then guides the gas hydrogen back to the corresponding heat exchanger for heat exchange again.

3. The apparatus for hydrogen liquefaction using LNG precooling and nitrogen cycle refrigeration according to claim 1, characterized in that: Turbine expanders are provided at least at the third-stage heat exchanger (5), the fourth-stage heat exchanger (6), and the final-stage heat exchanger (7). A branch hydrogen refrigerant pipeline is connected to the hydrogen flow channel and to the turbine expander. The turbine expander is connected to the hydrogen expansion pipeline and to several heat exchangers. The hydrogen expansion pipeline is connected to the refrigerant compressor (1) and the hydrogen cooler (2) to generate supplementary gaseous hydrogen feedstock.

4. The apparatus for hydrogen liquefaction using LNG precooling and nitrogen cycle refrigeration according to claim 1, characterized in that: The liquid hydrogen storage device is equipped with a flash vapor pipeline connected in sequence to several heat exchangers, and the flash vapor pipeline extends to the refrigerant compressor (1) and the hydrogen cooler (2) to generate supplementary gaseous hydrogen feedstock.

5. The apparatus for hydrogen liquefaction using LNG precooling and nitrogen cycle refrigeration according to claim 1, characterized in that: The nitrogen cooling pipeline passes through the corresponding heat exchanger twice, and the nitrogen cooling pipeline connects the nitrogen intake tank (16), the nitrogen compressor (17) and the nitrogen cooler (18).

6. The apparatus for hydrogen liquefaction using LNG precooling and nitrogen cycle refrigeration according to claim 1 or 5, characterized in that: A throttle valve (19) is installed on the nitrogen cooling pipeline.

7. The apparatus for hydrogen liquefaction using LNG precooling and nitrogen cycle refrigeration according to claim 1, characterized in that: The liquid hydrogen storage device is equipped with a product delivery pipeline (21).

8. A method for hydrogen liquefaction using LNG precooling and nitrogen cycle refrigeration, employing the apparatus according to any one of claims 1 to 7, characterized in that, include: After the raw hydrogen is mixed with the circulating hydrogen, it is pre-cooled at the first heat exchanger (3) and then enters several heat exchangers in sequence for heat exchange and cooling. The temperature decreases in sequence and is finally liquefied and stored and transported. After hydrogen is output from several of the heat exchangers, it passes through a positive and negative hydrogen converter to convert a portion of the positive hydrogen into negative hydrogen. After releasing heat and heating up, it returns to the heat exchanger to cool down. After hydrogen is output from several heat exchangers, a portion of the hydrogen is diverted to the turbine expander for cooling, and then flows through several heat exchangers via the hydrogen expansion pipeline to provide cooling capacity. Finally, the hydrogen is compressed and cooled to become circulating hydrogen. Hydrogen is output from the final heat exchanger (7) and liquefied by the turbine expander before entering the liquid hydrogen storage device. The flash vapor generated at the liquid hydrogen storage device is guided and transported through the flash vapor pipeline and passes through several heat exchangers to provide cooling. The flash vapor is compressed and cooled before being used as circulating hydrogen. Nitrogen refrigeration circulation pipelines were formed at several heat exchangers to cool the hydrogen flowing through them.

9. The method for hydrogen liquefaction using LNG precooling and nitrogen cycle refrigeration according to claim 8, characterized in that: Hydrogen is cooled to -150℃ to -155℃ by the first-stage heat exchanger (3), to -190℃ by the second-stage heat exchanger (4), to -200℃ to -220℃ by the third-stage heat exchanger (5), to -228℃ to -248℃ by the fourth-stage heat exchanger (6), and then liquefied and subcooled to -253℃ by the final-stage heat exchanger (7). The pressure of the raw hydrogen is greater than or equal to 1.4MPa, and the pressure after output from the final-stage heat exchanger (7) is 115KPa to 120KPa.

10. The method for hydrogen liquefaction using LNG precooling and nitrogen cycle refrigeration according to claim 8, characterized in that: Nitrogen gas is pressurized to 2.3MPa to 3MPa and enters several heat exchangers in sequence for liquefaction and subcooling. After being throttled and subcooled by a throttling valve (19), it re-enters the heat exchanger for cooling. The reheated nitrogen gas is then transported for cooling and enters the next cycle.

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