A hydrogen liquefaction system and process based on mixed refrigerant precooling

Abstract

The present invention provides a hydrogen liquefaction system and process based on mixed refrigerant precooling. The hydrogen liquefaction system includes a hydrogen liquefaction pipeline, a precooling cold box module, a normal-parahydrogen conversion module, a supercooling cold box module, a liquid hydrogen storage module, a mixed refrigerant compression module, and a hydrogen refrigerant compression module; wherein: the hydrogen liquefaction pipeline connects the precooling module, the normal-parahydrogen conversion module, the supercooling module, and the liquid hydrogen storage module together in sequence; the mixed refrigerant compression module is connected to the precooling cold box module to provide a mixed refrigerant to the precooling cold box module; the hydrogen refrigerant compression module is connected to the supercooling cold box module to provide a hydrogen refrigerant to the supercooling cold box module. In the hydrogen liquefaction system and hydrogen liquefaction process of the present invention, a mixed refrigerant cycle is used in the precooling section, and a hydrogen refrigeration cycle is used in the supercooling section. The flow rate and pressure of the refrigerant are optimized, which effectively reduces energy consumption, improves the heat exchange characteristics of the liquefaction process, and improves heat exchange efficiency.

Description

Technical Field

[0001] The present invention relates to a hydrogen liquefaction system and process based on mixed refrigerant precooling, belonging to the technical field of hydrogen liquefaction. Background Art

[0002] Excessive use of fossil fuels has led to problems such as environmental pollution and global warming. Replacing fossil fuels with clean, renewable energy is considered a key solution to these problems. Hydrogen, a green and efficient renewable energy source, boasts advantages such as widespread availability, high energy density, and high calorific value. It is considered the most promising clean energy source and will dominate the future energy mix. However, its low volumetric energy density is a major obstacle to long-term storage and long-distance transportation. Hydrogen's volumetric energy density can be increased by liquefying it. Under ambient conditions, the volumetric energy density of liquid hydrogen is 8.5 MJ / L. Furthermore, the volume of liquid hydrogen is 800 times that of hydrogen, increasing its transport efficiency by 6-8 times, making it highly convenient for transportation and long-term storage. However, liquefying hydrogen requires significant energy due to its lower temperature. Under ideal conditions, the specific energy consumption required to liquefy hydrogen is 2.7 kWh / kg. In reality, the specific energy consumption of currently operating hydrogen liquefaction plants worldwide is approximately 13-15 kWh / kg, resulting in low energy efficiency. Therefore, it is urgent to design a more efficient hydrogen liquefaction process. Summary of the Invention

[0003] The present invention aims to provide a hydrogen liquefaction system and process based on mixed refrigerant circulation pre-cooling to address the technical problems of low liquefaction efficiency and high energy consumption in hydrogen liquefaction processes. The hydrogen liquefaction process of the present invention uses a mixed refrigerant circulation to pre-cool the raw hydrogen and a hydrogen refrigerant refrigeration process to subcool the raw hydrogen.

[0004] To achieve the above objectives, the present invention first provides a hydrogen liquefaction system based on mixed refrigerant precooling, which is a hydrogen liquefaction system that uses mixed refrigerant precooling and hydrogen refrigerant expansion cycle subcooling. The hydrogen liquefaction system includes a hydrogen liquefaction pipeline, a precooling cold box module, a normal-para hydrogen conversion module, a subcooling cold box module, a liquid hydrogen storage module, a mixed refrigerant compression module, and a hydrogen refrigerant compression module; wherein:

[0005] The hydrogen liquefaction pipeline sequentially connects the pre-cooling module, the normal-para-hydrogen conversion module, the supercooling module, and the liquid hydrogen storage module;

[0006] The mixed refrigerant compression module is connected to the pre-cooling cold box module and is used to provide the mixed refrigerant to the pre-cooling cold box module;

[0007] The hydrogen refrigerant compression module is connected to the supercooling cold box module and is used to provide hydrogen refrigerant to the supercooling cold box module.

[0008] In the above hydrogen liquefaction system, preferably, the pre-cooling cold box module includes a first-stage heat exchanger, a first-stage two-phase expander, a second-stage heat exchanger and a second-stage two-phase expander;

[0009] The hydrogen liquefaction pipeline is sequentially connected to the first flow channel of the first-stage heat exchanger and the first flow channel of the second-stage heat exchanger;

[0010] The mixed refrigerant compression module is provided with a first outlet branch, a second outlet branch, a first outlet loop, and a second outlet loop, wherein the first outlet branch and the second outlet branch are respectively connected to the inlet of the second flow channel and the inlet of the third flow channel of the first-stage heat exchanger, and the first outlet loop and the second outlet loop are respectively connected to the outlet of the fourth flow channel of the first-stage heat exchanger and the outlet of the third flow channel of the second-stage heat exchanger;

[0011] The outlet of the second flow channel of the first-stage heat exchanger is connected to the inlet of the second flow channel of the second-stage heat exchanger;

[0012] The outlet of the third flow channel of the first-stage heat exchanger is connected to the inlet of the first-stage two-phase expander, and the outlet of the first-stage two-phase expander is connected to the inlet of the fourth flow channel of the first-stage heat exchanger;

[0013] The outlet of the second flow channel of the second-stage heat exchanger is connected to the inlet of the second-stage two-phase expander, and the outlet of the second-stage heat exchanger is connected to the inlet of the third flow channel of the second-stage heat exchanger.

[0014] In the above hydrogen liquefaction system, preferably, the mixed refrigerant compression module includes a first-stage mixed refrigerant compressor, a first-stage mixed refrigerant cooler, a second-stage mixed refrigerant compressor, a second-stage mixed refrigerant cooler, a third-stage mixed refrigerant compressor, a third-stage mixed refrigerant cooler, a first mixed refrigerant mixer, a first mixed refrigerant phase separator, a fourth-stage mixed refrigerant compressor, a first-stage mixed refrigerant pump, a second mixed refrigerant mixer, a fourth-stage mixed refrigerant cooler and a second mixed refrigerant phase separator; wherein:

[0015] The first-stage mixed refrigerant compressor, the first-stage mixed refrigerant cooler, the second-stage mixed refrigerant compressor, and the second-stage mixed refrigerant cooler are connected in sequence, and the inlet of the first-stage mixed refrigerant compressor is connected to the second outlet circuit, and the outlet of the second-stage mixed refrigerant cooler is connected to the inlet of the first mixed refrigerant mixer;

[0016] The third-stage mixed refrigerant compressor and the third-stage mixed refrigerant cooler are connected to each other, and the inlet of the third-stage mixed refrigerant compressor is connected to the first outlet circuit, and the outlet of the third-stage mixed refrigerant cooler is connected to the first mixed refrigerant mixer;

[0017] The outlet of the first mixed refrigerant mixer is connected to the inlet of the first mixed refrigerant phase separator;

[0018] The gas outlet and the liquid outlet of the first mixed refrigerant phase separator are connected to the inlet of the fourth-stage mixed refrigerant compressor and the inlet of the first-stage mixed refrigerant pump respectively;

[0019] The outlet of the fourth-stage mixed refrigerant compressor and the outlet of the first-stage mixed refrigerant pump are respectively connected to the inlet of the second mixed refrigerant mixer;

[0020] The outlet of the second mixed refrigerant mixer is connected to the inlet of the fourth-stage mixed refrigerant cooler;

[0021] The outlet of the fourth-stage mixed refrigerant cooler is connected to the inlet of the second mixed refrigerant phase separator;

[0022] The liquid outlet and the gas outlet of the second mixed refrigerant phase separator are connected to the first outlet branch and the second outlet branch respectively.

[0023] In the above hydrogen liquefaction system, preferably, the subcooling cold box module includes a third-stage heat exchanger, a fourth-stage heat exchanger, a fifth-stage heat exchanger, a sixth-stage heat exchanger, a third-stage two-phase expander, a fourth-stage two-phase expander, a fifth-stage two-phase expander, a sixth-stage two-phase expander, a seventh-stage two-phase expander, a first hydrogen distributor, a second hydrogen distributor and a second-stage hydrogen refrigerant mixer;

[0024] The normal-para hydrogen conversion module includes a first-stage normal-para hydrogen converter, a second-stage normal-para hydrogen converter and a third-stage normal-para hydrogen converter;

[0025] The outlet of the first-stage normal-para hydrogen converter is connected to the inlet of the first flow channel of the third-stage heat exchanger, the outlet of the first flow channel of the third-stage heat exchanger is connected to the inlet of the second-stage normal-para hydrogen converter, the outlet of the second-stage normal-para hydrogen converter is connected to the inlet of the first flow channel of the fourth-stage heat exchanger; the outlet of the first flow channel of the fourth-stage heat exchanger is connected to the inlet of the third-stage normal-para hydrogen converter, and the outlet of the third-stage normal-para hydrogen converter is connected to the inlet of the first flow channel of the fifth-stage heat exchanger;

[0026] The outlet of the second flow channel of the third-stage heat exchanger is connected to the inlet of the fifth-stage two-phase expander, the outlet of the fifth-stage two-phase expander is connected to the inlet of the second hydrogen distributor, the two outlets of the second hydrogen distributor are respectively connected to the inlet of the sixth-stage two-phase expander and the inlet of the third flow channel of the fourth-stage heat exchanger, the outlet of the third flow channel of the fourth-stage heat exchanger is connected to the inlet of the fourth flow channel of the third-stage heat exchanger, the outlet of the fourth flow channel of the third-stage heat exchanger is connected to the inlet of the first flow channel of the sixth-stage heat exchanger, and the outlet of the first flow channel, the outlet of the second flow channel, and the inlet of the third flow channel of the sixth-stage heat exchanger are respectively connected to the hydrogen refrigerant compression module;

[0027] The outlet of the third flow channel of the sixth-stage heat exchanger is connected to the inlet of the first hydrogen distributor, and the two outlets of the first hydrogen distributor are respectively connected to the inlet of the third-stage two-phase expander and the inlet of the second flow channel of the third-stage heat exchanger;

[0028] The outlet of the third-stage two-phase expander is connected to the inlet of the fourth-stage two-phase expander, and the outlet of the fourth-stage two-phase expander is connected to the inlet of the second-stage hydrogen refrigerant mixer;

[0029] The outlet of the second-stage hydrogen refrigerant mixer is connected to the inlet of the third flow channel of the third-stage heat exchanger, and the outlet of the third flow channel of the third-stage heat exchanger is connected to the inlet of the second flow channel of the sixth-stage heat exchanger;

[0030] The outlet of the sixth-stage two-phase expander is connected to the inlet of the second flow channel of the fifth-stage heat exchanger, the outlet of the second flow channel of the fifth-stage heat exchanger is connected to the inlet of the second flow channel of the fourth-stage heat exchanger, and the outlet of the second flow channel of the fourth-stage heat exchanger is connected to the inlet of the second-stage hydrogen refrigerant mixer;

[0031] The outlet of the first flow channel of the fifth-stage heat exchanger is connected to the inlet of the seventh-stage two-phase expander, and the outlet of the seventh-stage two-phase expander is connected to the liquid hydrogen storage module.

[0032] In the above hydrogen liquefaction system, the sixth-stage heat exchanger is used as a heat recovery heat exchanger to pre-cool the hydrogen refrigerant, thereby making full use of the cold energy of the hydrogen refrigeration cycle and avoiding the waste of cold energy to the greatest extent.

[0033] In the above-mentioned hydrogen liquefaction system, preferably, the hydrogen liquefaction pipeline is connected in sequence to the first-stage normal-para-hydrogen converter, the first flow channel of the third-stage heat exchanger, the second-stage normal-para-hydrogen converter, the first flow channel of the fourth-stage heat exchanger, the third-stage normal-para-hydrogen converter, the first flow channel of the fifth-stage heat exchanger, and the seventh-stage two-phase expander.

[0034] In the above hydrogen liquefaction system, preferably, the outlet of the first flow channel of the second-stage heat exchanger is connected to the inlet of the first-stage normal-para hydrogen converter.

[0035] In the above hydrogen liquefaction system, preferably, the hydrogen refrigerant compression module includes a first-stage hydrogen refrigerant compressor, a first-stage hydrogen refrigerant cooler, a first hydrogen refrigerant mixer, a second-stage hydrogen refrigerant compressor, a second-stage hydrogen refrigerant cooler, a third-stage hydrogen refrigerant compressor, a third-stage hydrogen refrigerant cooler, a fourth-stage hydrogen refrigerant compressor, and a fourth-stage hydrogen refrigerant cooler; wherein:

[0036] The outlet of the first-stage hydrogen refrigerant compressor is connected to the inlet of the first-stage hydrogen refrigerant cooler, and the outlet of the first-stage hydrogen refrigerant cooler is connected to the inlet of the first hydrogen refrigerant mixer;

[0037] The outlets and inlets of the first hydrogen refrigerant mixer, the second-stage hydrogen refrigerant compressor, the second-stage hydrogen refrigerant cooler, the third-stage hydrogen refrigerant compressor, the third-stage hydrogen refrigerant cooler, the fourth-stage hydrogen refrigerant compressor and the fourth-stage hydrogen refrigerant cooler are connected in sequence.

[0038] In the above hydrogen liquefaction system, preferably, the inlet of the first hydrogen refrigerant mixer is connected to the outlet of the first flow channel of the sixth-stage heat exchanger;

[0039] The inlet of the first-stage hydrogen refrigerant compressor is connected to the outlet of the second flow channel of the sixth-stage heat exchanger;

[0040] The outlet of the fourth-stage hydrogen refrigerant cooler is connected to the inlet of the third flow channel of the sixth-stage heat exchanger.

[0041] In the above-mentioned hydrogen liquefaction system, preferably, the hydrogen liquefaction pipeline includes a first raw hydrogen pipeline, a second raw hydrogen pipeline, a third raw hydrogen pipeline, a fourth raw hydrogen pipeline, a fifth raw hydrogen pipeline, a sixth raw hydrogen pipeline, a seventh raw hydrogen pipeline, an eighth raw hydrogen pipeline, a ninth raw hydrogen pipeline, and a tenth raw hydrogen pipeline, wherein the first raw hydrogen pipeline, the first flow channel of the first-stage heat exchanger, the second raw hydrogen pipeline, the first flow channel of the second-stage heat exchanger, the third raw hydrogen pipeline, the first-stage normal-para-hydrogen converter, the fourth raw hydrogen pipeline, the first flow channel of the third-stage heat exchanger, the fifth raw hydrogen pipeline, the second-stage normal-para-hydrogen converter, the sixth raw hydrogen pipeline, the first flow channel of the fourth-stage heat exchanger, the seventh raw hydrogen pipeline, the third-stage normal-para-hydrogen converter, the eighth raw hydrogen pipeline, the first flow channel of the fifth-stage heat exchanger, the ninth raw hydrogen pipeline, the seventh-stage two-phase expander, the tenth raw hydrogen pipeline, and the liquid hydrogen storage module are connected in sequence to form a flow channel for the entire process of raw hydrogen from gas to liquid hydrogen.

[0042] The present invention also provides a hydrogen liquefaction process based on mixed refrigerant precooling, wherein the hydrogen liquefaction process is carried out using the above-mentioned hydrogen liquefaction system based on mixed refrigerant precooling;

[0043] The raw hydrogen entering the pre-cooling cold box module is cooled to 80K;

[0044] The raw hydrogen entering the subcooling cold box module is cooled to 20K.

[0045] In the above hydrogen liquefaction process, preferably, the mixed refrigerant in the mixed refrigerant compression module comprises 26.86% methane, 22.23% ethane, 22.45% propane, 13.65% isobutane, 12.85% nitrogen and 1.96% hydrogen, in molar percentage.

[0046] In the above hydrogen liquefaction process, preferably, the pressure of the raw hydrogen is 2100 kPa, the temperature is 25° C., and the flow rate is 3.5 kg / s;

[0047] The compressed and purified raw hydrogen enters the heat exchanger of the pre-cooling cold box module (preferably the first-stage heat exchanger and the second-stage heat exchanger) and is cooled to -193°C. Then, the first hydrogen conversion to ortho-parahydrogen is performed, and the composition is converted into 48.09% parahydrogen + 51.91% orthohydrogen, calculated in molar percentage;

[0048] The raw hydrogen after the first conversion enters the heat exchanger of the subcooling cold box module (preferably the third stage heat exchanger) and is cooled to -221°C, and then undergoes a second hydrogen conversion to ortho-parahydrogen, with the composition converted to 73.38% parahydrogen + 26.62% orthohydrogen, calculated in molar percentage;

[0049] The raw hydrogen after the second conversion enters the heat exchanger of the supercooling cold box module (preferably the fourth stage heat exchanger) and is cooled to -242°C, and then undergoes a third hydrogen conversion to ortho-parahydrogen, with the components converted to 96.48% parahydrogen + 3.52% orthohydrogen, calculated in molar percentage;

[0050] The raw hydrogen after the third conversion enters the heat exchanger of the supercooling cold box module (preferably enters the fifth-stage heat exchanger) to be supercooled to -253°C, and then reduced in pressure to 110-150 kPa before entering the liquefied hydrogen storage tank.

[0051] In the above hydrogen liquefaction process, preferably, the total mass flow rate of the mixed refrigerant provided by the mixed refrigerant compression module is 273254.7 kg / h. The mixed refrigerant is pressurized to 4812.25 kPa and cooled to 25°C, and then subjected to gas-liquid separation to obtain gas-phase refrigerant and liquid-phase refrigerant. The gas-phase refrigerant enters the heat exchanger of the pre-cooling cold box module (preferably the first-stage heat exchanger and the second-stage heat exchanger) and is cooled to -193°C, and then reduced in pressure to 228. 99kPa, returns to the heat exchanger of the pre-cooling cold box module (preferably returns to the second-stage heat exchanger and the first-stage heat exchanger) to provide cold energy; the liquid refrigerant enters the heat exchanger of the pre-cooling cold box module (preferably enters the first-stage heat exchanger) and is cooled to -30°C, then depressurized to 717.96kPa, and returns to the heat exchanger of the pre-cooling cold box module (preferably returns to the first-stage heat exchanger) to provide cold energy; the gaseous refrigerant and the liquid refrigerant after providing cold energy return to the mixed refrigerant compression module;

[0052] The mass flow rate of the hydrogen refrigerant provided by the hydrogen refrigerant compression module is 50770.74 kg / h. The hydrogen refrigerant is pressurized to 3297.08 kPa and cooled to 25°C before entering the heat exchanger of the supercooling cold box module (preferably entering the sixth stage heat exchanger) and being cooled to -167°C. It is then divided into a first hydrogen refrigerant and a second hydrogen refrigerant. The first hydrogen refrigerant enters the heat exchanger of the supercooling cold box module (preferably entering the third stage heat exchanger) and is cooled to -221°C. It is then depressurized to 352.29 kPa and then divided into a third hydrogen refrigerant and a fourth hydrogen refrigerant. Gas refrigerant, the third hydrogen refrigerant enters the heat exchanger of the supercooling cold box module (preferably enters the third-stage heat exchanger and the fourth-stage heat exchanger) to provide cold energy, and then returns to the hydrogen refrigerant compression module, the fourth hydrogen refrigerant is depressurized to 113.63 kPa, and then enters the heat exchanger of the supercooling cold box module (preferably enters the fifth-stage heat exchanger and the fourth-stage heat exchanger) to provide cold energy, and is mixed with the second hydrogen refrigerant depressurized to 113.63 kPa and enters the heat exchanger of the supercooling cold box module (preferably enters the third-stage heat exchanger) to provide cold energy, and then returns to the hydrogen refrigerant compression module.

[0053] The hydrogen liquefaction process of the hydrogen liquefaction system based on mixed refrigerant cycle precooling provided by the present invention may include the following specific steps:

[0054] Hydrogen liquefaction pipeline: The compressed and purified raw hydrogen enters the first-stage heat exchanger of the pre-cooling cycle and the second-stage heat exchanger for pre-cooling, then enters the first-stage normal-para-hydrogen converter for normal-para-hydrogen conversion. It then enters the third-stage heat exchanger for cooling, then enters the second-stage normal-para-hydrogen converter for normal-para-hydrogen conversion. Then, it enters the fourth-stage heat exchanger for cooling, then enters the third-stage normal-para-hydrogen converter for normal-para-hydrogen conversion. Finally, it enters the fifth-stage heat exchanger for further cooling, then enters the seventh-stage two-phase expander for decompression to the liquefied hydrogen storage pressure. The liquid hydrogen released from the seventh-stage two-phase expander after decompression enters the liquid hydrogen storage module.

[0055] Mixed refrigerant cycle: After being pressurized and cooled by the mixed refrigerant compression module, the mixed refrigerant enters the second mixed refrigerant phase separator and is separated into two refrigerants (gas phase refrigerant and liquid phase refrigerant). Among them, one refrigerant (liquid phase refrigerant) enters the first-stage heat exchanger and the first-stage two-phase expander in sequence, and then enters the first-stage heat exchanger again to provide cold energy; the other refrigerant (gas phase refrigerant) passes through the first-stage heat exchanger and the second-stage heat exchanger in sequence to reduce the temperature, enters the second-stage two-phase expander to reduce the pressure, and then passes through the second-stage heat exchanger to provide cold energy; the two refrigerants finally return to the mixed refrigerant compression module to complete the refrigeration cycle;

[0056] Hydrogen refrigerant cycle: The hydrogen refrigerant is pressurized and cooled by the mixed refrigerant compression module, then enters the sixth stage heat exchanger for cooling, then enters the first hydrogen distributor and is divided into two refrigerants (the first hydrogen refrigerant and the second hydrogen refrigerant). One refrigerant (the second hydrogen refrigerant) enters the third stage expander, the fourth stage expander, and then enters the second stage hydrogen mixer for mixing, then enters the third stage heat exchanger and the sixth stage heat exchanger to provide cold energy; the other refrigerant (the first hydrogen refrigerant) enters the third stage heat exchanger for cooling, then enters the After entering the fifth-stage expander, it enters the first-stage hydrogen distributor and is separated into two other refrigerants (the third hydrogen refrigerant and the fourth hydrogen refrigerant). Among them, one refrigerant (the third hydrogen refrigerant) enters the fourth-stage heat exchanger, the third-stage heat exchanger, and the sixth-stage heat exchanger to provide cold energy, and the other refrigerant (the fourth hydrogen refrigerant) enters the sixth-stage expander for pressure reduction and then enters the fifth-stage heat exchanger. The third-stage heat exchanger and the sixth-stage heat exchanger provide cold energy; finally, the two refrigerants return to the hydrogen refrigerant compression module to complete the refrigeration cycle.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] The present invention proposes a hydrogen liquefaction system and hydrogen liquefaction process based on mixed refrigerant cycle precooling. The system uses a highly efficient mixed refrigeration cycle and a hydrogen refrigerant cycle to provide cold energy for liquefying feed hydrogen. The mixed refrigerant cycle is used in the precooling stage, and the hydrogen low-temperature expansion refrigeration cycle is used in the supercooling stage. The refrigerant flow and pressure are optimized, effectively reducing energy consumption, improving the heat exchange characteristics of the liquefaction process, and increasing heat exchange efficiency. Compared with the precooling method using liquid nitrogen (the production of liquid nitrogen requires additional energy consumption), the use of hydrogen refrigerant can save energy.

[0059] The present invention effectively improves the refrigeration efficiency of the refrigeration cycle by dividing each refrigeration cycle into two refrigeration branches; wherein:

[0060] The mixed refrigerant cycle is divided into two branches (e.g., the first outlet branch and the second outlet branch) to provide cooling energy for the pre-cooling cold box (e.g., the first heat exchanger and the second heat exchanger). The refrigerant in each branch is cooled at different pressures, thereby improving the efficiency of the refrigeration cycle. In addition, in order to fully utilize the different condensing pressures (low pressures) of the two branches to reduce the energy consumption of the pre-cooling cycle, different compressor units (e.g., the first-stage mixed refrigerant compressor + the second-stage mixed refrigerant compressor, the third-stage mixed refrigerant compressor) are used to pressurize the low-pressure refrigerant, and a compressor (e.g., the fourth-stage mixed refrigerant compressor) and a pump (e.g., the first-stage mixed refrigerant pump) are used to pressurize the medium-pressure gas-phase refrigerant and the liquid-phase refrigerant to the same evaporation pressure (high pressure of the refrigerant). This structural arrangement not only ensures that the compressor can operate efficiently and safely, but also effectively reduces the energy consumption of the process.

[0061] The hydrogen refrigerant cycle is also divided into multiple sub-circuits to provide cold energy for the subcooling cold box (such as the third heat exchanger, the fourth heat exchanger, and the fifth heat exchanger); as with the mixed refrigerant cycle, each sub-refrigeration circuit operates at a different pressure level; if the hydrogen refrigeration cycle uses multiple circuits, and each circuit continuously provides cold energy for multiple heat exchangers, it will cause some heat exchangers to have a large temperature difference, which will not only waste cold energy, but also lead to lower heat exchange efficiency of the heat exchanger, and also cause a high degree of mutual influence between the heat exchangers; each heat exchanger in the present invention is connected to a refrigerant circuit, which minimizes the degree of mutual influence between the heat exchangers. Therefore, by adjusting the refrigerant flow and pressure connected to each heat exchanger, cold energy matching the heat flow can be provided, thereby effectively reducing the temperature difference of the heat exchanger;

[0062] At the same time, the mixed refrigerant cycle and the hydrogen refrigerant cycle of the present invention operate independently, which simplifies the process structure, avoids the mutual influence between the two refrigerant cycles, and facilitates the subsequent optimization of the refrigerant flow and pressure of each refrigeration cycle;

[0063] The technical solution of the present invention involves measures such as mixed refrigerant pre-cooling, two branches of mixed refrigerant dual pressure, compressor unit configuration, multiple sub-circuits of the supercooling cycle, multi-stage normal-parahydrogen conversion, mixed refrigerant component control, and refrigeration process parameter control. These measures are not simply superimposed but coordinated with each other to form an organic whole. As a result, the liquefaction process of the present invention has the advantages of low energy consumption and high liquefaction rate, and the parahydrogen concentration in the product liquid hydrogen is ≥95%. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 Schematic diagram of a hydrogen liquefaction system based on mixed refrigerant precooling provided in Example 1.

[0065] Figure 2a-2h This is the THCC curve of the subcooling heat exchanger.

[0066] Description of main figures:

[0067] C1 First stage mixed refrigerant compressor C5 First stage hydrogen refrigerant compressor

[0068] E1 First stage mixed refrigerant cooler E5 First stage hydrogen refrigerant cooler

[0069] C2 Second stage mixed refrigerant compressor C6 Second stage hydrogen refrigerant compressor

[0070] E2 Second stage mixed refrigerant cooler E6 Second stage hydrogen refrigerant cooler

[0071] C3 third stage mixed refrigerant compressorC7 third stage hydrogen refrigerant compressor

[0072] E3 third stage mixed refrigerant cooler E7 third stage hydrogen refrigerant cooler

[0073] C4 4th stage mixed refrigerant compressor C8 4th stage hydrogen refrigerant compressor

[0074] P1 First stage mixed refrigerant pump E8 Fourth stage hydrogen refrigerant cooler

[0075] E2 4th stage mixed refrigerant cooler HX6 6th stage heat exchanger

[0076] M1 First mixed refrigerant mixer T1 First hydrogen distributor

[0077] S1 First mixed refrigerant phase separator EX3 Third stage expander

[0078] M2 Second mixed refrigerant mixer EX4 Fourth stage expander

[0079] S2 Second mixed refrigerant phase separator M3 First hydrogen refrigerant mixer

[0080] HX1 First stage heat exchanger M4 Second stage hydrogen refrigerant mixer

[0081] EX1 first stage expander HX3 third stage heat exchanger

[0082] HX2 second stage heat exchanger EX5 fifth stage expander

[0083] EX2 Second stage expander T2 Second hydrogen distributor

[0084] R1 First stage normal and secondary hydrogen converter EX6 Sixth stage expander

[0085] R2 Second stage normal-parahydrogen converter HX4 Fourth stage heat exchanger

[0086] R3 third stage normal and para hydrogen converter HX5 fifth stage heat exchanger

[0087] EX7 seventh stage expander tank liquid hydrogen storage tank

[0088] 1. First raw hydrogen pipeline 2. Second raw hydrogen pipeline 3. Third raw hydrogen pipeline

[0089] 4 Fourth raw hydrogen pipeline 5 Fifth raw hydrogen pipeline 6 Sixth raw hydrogen pipeline

[0090] 7 Seventh raw hydrogen pipeline 8 Eighth raw hydrogen pipeline 9 Ninth raw hydrogen pipeline

[0091] 10. Tenth raw material hydrogen pipeline 11, 13-14, 16-17, 19-21, 23-59 pipeline

[0092] 12 First outlet branch 18 Second outlet branch 15 First outlet loop 22 Second exit circuit DETAILED DESCRIPTION

[0093] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be understood as limiting the scope of implementation of the present invention.

[0094] Example 1

[0095] This embodiment provides a hydrogen liquefaction system based on mixed refrigerant circulation precooling, which is composed of Figure 1 As shown, the hydrogen liquefaction system includes:

[0096] Hydrogen liquefaction pipeline, pre-cooling cold box module, normal-para-hydrogen conversion module, supercooling cold box module, liquid hydrogen storage module, mixed refrigerant compression module, hydrogen refrigerant compression module; Among them:

[0097] The hydrogen liquefaction pipeline is used to pre-cool the raw hydrogen to 80K and supercool it to 20K, and includes a first raw hydrogen pipeline 1, a second raw hydrogen pipeline 2, a third raw hydrogen pipeline 3, a fourth raw hydrogen pipeline 4, a fifth raw hydrogen pipeline 5, a sixth raw hydrogen pipeline 6, a seventh raw hydrogen pipeline 7, an eighth raw hydrogen pipeline 8, a ninth raw hydrogen pipeline 9, and a tenth raw hydrogen pipeline 10;

[0098] The pre-cooling cold box module includes a first-stage heat exchanger HX1, a first-stage two-phase expander EX1, a second-stage heat exchanger HX2 and a second-stage two-phase expander EX2;

[0099] The normal-para hydrogen conversion module includes a first-stage normal-para hydrogen converter R1, a second-stage normal-para hydrogen converter R2 and a third-stage normal-para hydrogen converter R3;

[0100] The subcooling cold box module is used to subcool the raw hydrogen to 20K, which includes a third-stage heat exchanger HX3, a fourth-stage heat exchanger HX4, a fifth-stage heat exchanger HX5, a sixth-stage heat exchanger HX6, a third-stage two-phase expander EX3, a fourth-stage two-phase expander EX4, a fifth-stage two-phase expander EX5, a sixth-stage two-phase expander EX6, a seventh-stage two-phase expander EX7, a first hydrogen distributor T1, a second hydrogen distributor T2 and a second-stage hydrogen refrigerant mixer M4;

[0101] The liquid hydrogen storage module is a liquid hydrogen storage tank;

[0102] The mixed refrigerant compression module is used to transport the mixed refrigerant to the pre-cooling cold box module to provide cold energy, which includes a first-stage mixed refrigerant compressor C1, a first-stage mixed refrigerant cooler E1, a second-stage mixed refrigerant compressor C2, a second-stage mixed refrigerant cooler E2, a third-stage mixed refrigerant compressor C3, a third-stage mixed refrigerant cooler E3, a first mixed refrigerant mixer M1, a first mixed refrigerant phase separator S1, a fourth-stage mixed refrigerant compressor C4, a first-stage mixed refrigerant pump P1, a second mixed refrigerant mixer M2, a fourth-stage mixed refrigerant cooler E4 and a second mixed refrigerant phase separator S2;

[0103] The hydrogen refrigerant compression module is used to transport hydrogen refrigerant to the subcooling cold box module to provide cold energy, which includes a first-stage hydrogen refrigerant compressor C5, a first-stage hydrogen refrigerant cooler E5, a first hydrogen refrigerant mixer M3, a second-stage hydrogen refrigerant compressor C6, a second-stage hydrogen refrigerant cooler E6, a third-stage hydrogen refrigerant compressor C7, a third-stage hydrogen refrigerant cooler E7, a fourth-stage hydrogen refrigerant compressor C8 and a fourth-stage hydrogen refrigerant cooler E8;

[0104] Wherein: the first raw hydrogen pipeline 1 is connected to the inlet of the first flow channel of the first-stage heat exchanger HX1 for inputting raw hydrogen, the outlet of the first flow channel of the first-stage heat exchanger HX1 is connected to the inlet of the first flow channel of the second-stage heat exchanger HX2 through the second raw hydrogen pipeline 2, the outlet of the first flow channel of the second-stage heat exchanger HX2 is connected to the inlet of the first-stage normal-para-hydrogen converter R1 through the third raw hydrogen pipeline 3, the outlet of the first-stage normal-para-hydrogen converter R1 is connected to the inlet of the first flow channel of the third-stage heat exchanger HX3 through the fourth raw hydrogen pipeline 4, and the outlet of the first flow channel of the third-stage heat exchanger HX3 is connected to the second-stage normal-para-hydrogen converter R2 through the fifth raw hydrogen pipeline 5 The outlet of the second-stage normal-para-hydrogen converter R2 is connected to the inlet of the first flow channel of the fourth-stage heat exchanger HX4 through the sixth raw hydrogen pipeline 6, the outlet of the first flow channel of the fourth-stage heat exchanger HX4 is connected to the inlet of the third-stage normal-para-hydrogen converter R3 through the seventh raw hydrogen pipeline 7, the outlet of the third-stage normal-para-hydrogen converter R3 is connected to the inlet of the first flow channel of the fifth-stage heat exchanger HX5 through the eighth raw hydrogen pipeline 8, the outlet of the first flow channel of the fifth-stage heat exchanger HX5 is connected to the inlet of the seventh-stage two-phase expander EX7 through the ninth raw hydrogen pipeline 9, and the outlet of the seventh-stage two-phase expander EX7 is connected to the hydrogen storage tank Tank through the tenth raw hydrogen pipeline 10;

[0105] The mixed refrigerant compression module is provided with a first outlet branch 12, a second outlet branch 18, a first outlet circuit 15, and a second outlet circuit 22. The first outlet branch 12 and the second outlet branch 18 are respectively connected to the inlet of the second flow channel and the inlet of the third flow channel of the first-stage heat exchanger HX1. The first outlet circuit 15 and the second outlet circuit 22 are respectively connected to the outlet of the fourth flow channel of the first-stage heat exchanger HX1 and the outlet of the third flow channel of the second-stage heat exchanger HX2.

[0106] The first-stage mixed refrigerant compressor C1, the first-stage mixed refrigerant cooler E1, the second-stage mixed refrigerant compressor C2, and the second-stage mixed refrigerant cooler E2 are connected in sequence through pipelines 23, 24, and 25. The outlet of the second-stage mixed refrigerant cooler E2 is connected to the inlet of the first mixed refrigerant mixer M1 through pipeline 26. The third-stage mixed refrigerant compressor C3 is connected to the third-stage mixed refrigerant cooler E3 through pipeline 16. The outlet of the third-stage mixed refrigerant cooler E3 is connected to the inlet of the first mixed refrigerant mixer M1.

[0107] The outlet of the first mixed refrigerant mixer M1 is connected to the inlet of the first mixed refrigerant phase separator S1 via pipeline 27; the gas outlet and liquid outlet of the first mixed refrigerant phase separator S1 are connected to the inlet of the fourth-stage mixed refrigerant compressor C4 and the inlet of the first-stage mixed refrigerant pump P1 via pipelines 28 and 30 respectively; the outlet of the fourth-stage mixed refrigerant compressor C4 and the outlet of the first-stage mixed refrigerant pump P1 are connected to the inlet of the second mixed refrigerant mixer M2 via pipelines 29 and 31 respectively;

[0108] The outlet of the second mixed refrigerant mixer M2 is connected to the inlet of the fourth-stage mixed refrigerant cooler E4 via a pipeline 32; the outlet of the fourth-stage mixed refrigerant cooler E4 is connected to the inlet of the second mixed refrigerant phase separator S2 via a pipeline 11; the liquid outlet and gas outlet of the second mixed refrigerant phase separator S2 are connected to the first outlet branch 12 and the second outlet branch 18, respectively; the inlet of the third-stage mixed refrigerant compressor C3 is connected to the first outlet circuit 15, and the inlet of the first-stage mixed refrigerant compressor C1 is connected to the second outlet circuit 22;

[0109] The second outlet branch 18 is connected to the inlet of the second flow channel of the first-stage heat exchanger HX1. The outlet of the second flow channel of the first-stage heat exchanger HX1 is connected to the inlet of the second flow channel of the second-stage heat exchanger HX2 via a pipeline 19. The outlet of the second flow channel of the second-stage heat exchanger HX2 is connected to the inlet of the second-stage two-phase expander EX2 via a pipeline 20. The outlet of the second-stage two-phase expander EX2 is connected to the inlet of the fourth flow channel of the second-stage heat exchanger HX2 via a pipeline 21.

[0110] The first outlet branch 12 is connected to the inlet of the third flow channel of the first-stage heat exchanger HX1. The outlet of the third flow channel of the first-stage heat exchanger HX1 is connected to the inlet of the first-stage two-phase expander EX1 through a pipeline 13. The outlet of the first-stage two-phase expander EX1 is connected to the inlet of the fourth flow channel of the first-stage heat exchanger HX1 through a pipeline 14.

[0111] The outlet of the second flow channel of the third-stage heat exchanger HX3 is connected to the inlet of the fifth-stage two-phase expander EX5 through a pipeline 49. The outlet of the fifth-stage two-phase expander EX5 is connected to the inlet of the second hydrogen distributor T2 through a pipeline 50. The two outlets of the second hydrogen distributor T2 are connected to the inlet of the third flow channel of the fourth-stage heat exchanger HX4 and the inlet of the sixth-stage two-phase expander EX6 through pipelines 51 and 52, respectively. The outlet of the third flow channel of the fourth-stage heat exchanger HX4 is connected to the inlet of the fourth flow channel of the third-stage heat exchanger HX3 through a pipeline 57. The outlet of the fourth flow channel of the third-stage heat exchanger HX3 is connected to the inlet of the first flow channel of the sixth-stage heat exchanger HX6 through a pipeline 59.

[0112] The outlet of the third flow channel of the sixth-stage heat exchanger HX6 is connected to the inlet of the first hydrogen distributor T1 via pipeline 44. The two outlets of the first hydrogen distributor T1 are connected to the inlet of the third-stage two-phase expander EX3 and the inlet of the second flow channel of the third-stage heat exchanger HX3 via pipelines 45 and 48 respectively.

[0113] The outlet of the third-stage two-phase expander EX3 is connected to the inlet of the fourth-stage two-phase expander EX4 via a pipeline 46, and the outlet of the fourth-stage two-phase expander EX4 is connected to the inlet of the second-stage hydrogen refrigerant mixer M4 via a pipeline 47;

[0114] The outlet of the sixth-stage two-phase expander EX6 is connected to the inlet of the second flow channel of the fifth-stage heat exchanger HX5 via a pipeline 53. The outlet of the second flow channel of the fifth-stage heat exchanger HX5 is connected to the inlet of the second flow channel of the fourth-stage heat exchanger HX4 via a pipeline 54. The outlet of the second flow channel of the fourth-stage heat exchanger HX4 is connected to the inlet of the second-stage hydrogen refrigerant mixer M4 via a pipeline 55.

[0115] The outlet of the second-stage hydrogen refrigerant mixer M4 is connected to the inlet of the third flow channel of the third-stage heat exchanger HX3 via a pipeline 56, and the outlet of the third flow channel of the third-stage heat exchanger HX3 is connected to the inlet of the second flow channel of the sixth-stage heat exchanger HX6 via a pipeline 58;

[0116] The outlet of the first flow channel of the sixth-stage heat exchanger HX6 is connected to the inlet of the first hydrogen refrigerant mixer M3 via pipeline 33; the outlet of the second flow channel of the sixth-stage heat exchanger HX6 is connected to the inlet of the first-stage hydrogen refrigerant compressor C5 via pipeline 34; the outlet of the first-stage hydrogen refrigerant compressor C5 is connected to the inlet of the first-stage hydrogen refrigerant cooler E5 via pipeline 35, and the outlet of the first-stage hydrogen refrigerant cooler E5 is connected to the inlet of the first hydrogen refrigerant mixer M3 via pipeline 36;

[0117] The first hydrogen refrigerant mixer M3, the second-stage hydrogen refrigerant compressor C6, the second-stage hydrogen refrigerant cooler E6, the third-stage hydrogen refrigerant compressor C7, the third-stage hydrogen refrigerant cooler E7, the fourth-stage hydrogen refrigerant compressor C8, and the fourth-stage hydrogen refrigerant cooler E8 are connected in sequence through pipelines 37, 38, 39, 40, 41, and 42; the outlet of the fourth-stage hydrogen refrigerant cooler E8 is connected to the inlet of the third flow channel of the sixth-stage heat exchanger HX6 through pipeline 43;

[0118] exist Figure 1 In the figure, the flow channels of the first-stage heat exchanger HX1 to the fifth-stage heat exchanger HX5 are named in order from bottom to top, that is, the flow channel at the bottom is the first flow channel, and the flow channels of the sixth-stage heat exchanger HX6 are named in order from left to right, that is, the flow channel on the far left is the first flow channel.

[0119] Example 2

[0120] This embodiment provides a hydrogen liquefaction process, which is carried out using the hydrogen liquefaction system of Example 1, wherein the pressure of the raw hydrogen is 2100 kPa, the temperature is 25° C., and the flow rate is 3.5 kg / s.

[0121] The specific steps of hydrogen liquefaction are as follows:

[0122] Pre-cooling section: The mixed refrigerant includes 26.86% methane, 22.23% ethane, 22.45% propane, 13.65% isobutane, 12.85% nitrogen and 1.96% hydrogen in molar percentage. The total mass flow rate of the refrigerant is 273254.7 kg / h. The mixed refrigerant is increased to 4812.25 kPa and cooled to 25°C before entering the second mixed refrigerant phase separator S2 for gas-liquid separation.

[0123] After separation, the gaseous refrigerant enters the first-stage heat exchanger HX1 and the second-stage heat exchanger HX2 sequentially through the second outlet branch 18, where it is cooled to -193°C. It then enters the second-stage two-phase expander EX2 via line 20, where its pressure is reduced to 228.99 kPa. It then returns to the second-stage heat exchanger HX2 via line 21 for sufficient heat exchange with the heat source. Finally, it enters the compression unit via the second outlet circuit 22, completing the cycle. The liquid refrigerant from S2 flows through the first outlet branch 12 into the first-stage heat exchanger HX1, where it is cooled to -30°C. It then passes through the first-stage two-phase expander EX1 via line 13, where its pressure is reduced to 717.96 kPa. It then returns to the first-stage heat exchanger HX1 via line 14, providing cooling energy for cooling the feed hydrogen and refrigerant. Finally, the low-pressure, high-temperature refrigerant enters the compression unit via the first outlet circuit 15, completing the cycle.

[0124] Subcooling section: The hydrogen refrigerant has a mass flow rate of 50,770.74 kg / h. The hydrogen refrigerant is first pressurized to 3,297.08 kPa and cooled to 25°C before entering the sixth-stage heat exchanger HX6, where it is cooled to -167°C by the reflux hydrogen refrigerant. Subsequently, the hydrogen refrigerant is split into two refrigerant streams, the first hydrogen refrigerant and the second hydrogen refrigerant, via pipeline 44 in the first hydrogen distributor T1. These streams operate in different refrigeration branches. In the first refrigeration branch, the second hydrogen refrigerant enters the third-stage two-phase expander EX3 and the fourth-stage two-phase expander EX4 through pipeline 45 in sequence, and its pressure is reduced to 113.63 kPa. Subsequently, the second hydrogen refrigerant enters the first hydrogen refrigerant mixer M4 through pipeline 47 and mixes with another fourth hydrogen refrigerant from pipeline 55, and then enters the third-stage heat exchanger HX3 to provide cold energy. In the other refrigeration branch, the first hydrogen refrigerant enters the third-stage heat exchanger HX3 through pipeline 48 and is cooled to -221°C. Then, the first hydrogen refrigerant enters through pipeline 49. The pressure of the fifth-stage two-phase expander EX5 drops to 352.29 kPa. Subsequently, the first hydrogen refrigerant enters the second hydrogen distributor T2 through pipeline 50 and is divided into two refrigerants, namely the third hydrogen refrigerant and the fourth hydrogen refrigerant. Among them, the third refrigerant directly flows into the fourth-stage heat exchanger HX4 through pipeline 51 to provide cooling energy. The fourth hydrogen refrigerant enters the sixth-stage two-phase expander EX6 through pipeline 52 to reduce its pressure to 113.63 kPa and then enters the fifth-stage heat exchanger HX5, the fourth-stage heat exchanger HX4, the third-stage heat exchanger HX3 and the sixth-stage heat exchanger HX6 in sequence to provide cooling energy.

[0125] The compressed and purified raw hydrogen 1 is pre-cooled to -193°C through the first-stage heat exchanger HX1 and the second-stage heat exchanger HX2, and then passes through the first-stage normal-para-hydrogen converter R1 for the first hydrogen to normal-para-hydrogen conversion to a composition of 48.09% para-hydrogen and 51.91% ortho-hydrogen by mole percentage. The raw hydrogen 4 after the first conversion passes through the third-stage heat exchanger HX3 and is cooled to -221°C. It then enters the second-stage normal-para-hydrogen converter R2 for the second hydrogen to normal-para-hydrogen conversion to a composition of 73.38% para-hydrogen by mole percentage. After the second conversion, the raw hydrogen 6 enters the fourth-stage heat exchanger HX4 and is cooled to -242°C before entering the third-stage normal-para-hydrogen converter R3 for the third hydrogen-para-hydrogen conversion until the components become 96.48% para-hydrogen and 3.52% ortho-hydrogen by mole percentage; finally, the raw hydrogen 8 is supercooled to -253°C through the fifth-stage heat exchanger HX5 and enters the seventh-stage two-phase expander EX7 to reduce the pressure to 110 kPa before entering the liquefied hydrogen storage tank Tank.

[0126] HYSYS software simulations show that the energy consumption of this hydrogen liquefaction system, based on mixed refrigerant cycle pre-cooling, is 5.96 kWh / kg. After passing through the three-stage n-parahydrogen converter (first-stage n-parahydrogen converter R1, second-stage n-parahydrogen converter R2, and third-stage n-parahydrogen converter R3), the molar percentage of parahydrogen in the liquid hydrogen is 96.48%, achieving a liquefaction rate of 100%.

[0127] To demonstrate the high heat exchange efficiency of the subcooling heat exchanger of the present invention, the present invention evaluated its key design parameters. These parameters include the minimum heat transfer temperature difference (MITA) and the logarithmic mean temperature difference (LMTD). Under the constraints, the smaller the MITA and LMTD values, the higher the heat exchange efficiency. Table 1 shows the design parameters of the subcooling heat exchangers of the present invention and CN 216204684 U.

[0128] Table 1 MITA and LMTD of subcooling heat exchanger

[0129]

[0130] As can be seen from Table 1, the MITA and LMTD of the subcooling heat exchanger of the present invention are smaller than those of the subcooling heat exchanger in CN 216204684 U, especially the LMTD, which indicates that the subcooling heat exchanger of the present invention has higher heat exchange efficiency.

[0131] In addition, in order to more clearly illustrate the heat transfer performance of the subcooling heat exchanger of the present invention, the temperature heat flow composite curve (THCC) of the subcooling heat exchanger is given here, as shown in FIG. Figure 2a-2h As shown, Figure 2a 、 Figure 2c 、 Figure 2e 、 Figure 2g is the curve corresponding to the subcooling heat exchanger of the present invention, Figure 2b 、 Figure 2d 、 Figure 2f 、 Figure 2h This is the curve corresponding to the subcooling heat exchanger of CN 216204684 U. THCC reflects the change of the temperature of the hot flow and cold flow relative to the hot flow inside the heat exchanger. Its interval can be used to evaluate the heat exchanger's The smaller the interval of loss, The smaller the loss, the higher the heat transfer efficiency. Figure 2a-2h It can be seen that the interval of the THCC curve of the subcooling heat exchanger of the present invention is smaller than that of CN 216204684 U, which indicates that the heat exchange efficiency of the subcooling heat exchanger of the present invention is better than that of the subcooling heat exchanger of CN 216204684 U, and the heat exchange efficiency of the hydrogen liquefaction system and the hydrogen liquefaction process of the present invention is better than that of CN 216204684 U.

Claims

1. A hydrogen liquefaction system based on mixed refrigerant precooling, characterized in that: The hydrogen liquefaction system includes a hydrogen liquefaction pipeline, a pre-cooling cold box module, a normal-para-hydrogen conversion module, a super-cooling cold box module, a liquid hydrogen storage module, a mixed refrigerant compression module, and a hydrogen refrigerant compression module; wherein: The hydrogen liquefaction pipeline sequentially connects the pre-cooling cold box module, the normal-para hydrogen conversion module, the supercooling cold box module, and the liquid hydrogen storage module; The mixed refrigerant compression module is connected to the pre-cooling cold box module and is used to provide the mixed refrigerant to the pre-cooling cold box module; The hydrogen refrigerant compression module is connected to the subcooling cold box module and is used to provide hydrogen refrigerant to the subcooling cold box module; The subcooling cold box module includes a third-stage heat exchanger (HX3), a fourth-stage heat exchanger (HX4), a fifth-stage heat exchanger (HX5), a sixth-stage heat exchanger (HX6), a third-stage two-phase expander (EX3), a fourth-stage two-phase expander (EX4), a fifth-stage two-phase expander (EX5), a sixth-stage two-phase expander (EX6), a seventh-stage two-phase expander (EX7), a first hydrogen distributor (T1), a second hydrogen distributor (T2) and a second-stage hydrogen refrigerant mixer (M4); The normal-para hydrogen conversion module includes a first-stage normal-para hydrogen converter (R1), a second-stage normal-para hydrogen converter (R2) and a third-stage normal-para hydrogen converter (R3); The outlet of the first-stage normal-para-hydrogen converter (R1) is connected to the inlet of the first flow channel of the third-stage heat exchanger (HX3), the outlet of the first flow channel of the third-stage heat exchanger (HX3) is connected to the inlet of the second-stage normal-para-hydrogen converter (R2), the outlet of the second-stage normal-para-hydrogen converter (R2) is connected to the inlet of the first flow channel of the fourth-stage heat exchanger (HX4); the outlet of the first flow channel of the fourth-stage heat exchanger (HX4) is connected to the inlet of the third-stage normal-para-hydrogen converter (R3), and the outlet of the third-stage normal-para-hydrogen converter (R3) is connected to the inlet of the first flow channel of the fifth-stage heat exchanger (HX5); The outlet of the second flow channel of the third-stage heat exchanger (HX3) is connected to the inlet of the fifth-stage two-phase expander (EX5), the outlet of the fifth-stage two-phase expander (EX5) is connected to the inlet of the second hydrogen distributor (T2), the two outlets of the second hydrogen distributor (T2) are respectively connected to the inlet of the sixth-stage two-phase expander (EX6) and the inlet of the third flow channel of the fourth-stage heat exchanger (HX4), the outlet of the third flow channel of the fourth-stage heat exchanger (HX4) is connected to the inlet of the fourth flow channel of the third-stage heat exchanger (HX3), the outlet of the fourth flow channel of the third-stage heat exchanger (HX3) is connected to the inlet of the first flow channel of the sixth-stage heat exchanger (HX6), and the outlet of the first flow channel, the outlet of the second flow channel, and the inlet of the third flow channel of the sixth-stage heat exchanger (HX6) are respectively connected to the hydrogen refrigerant compression module; The outlet of the third flow channel of the sixth-stage heat exchanger (HX6) is connected to the inlet of the first hydrogen distributor (T1), and the two outlets of the first hydrogen distributor (T1) are respectively connected to the inlet of the third-stage two-phase expander (EX3) and the inlet of the second flow channel of the third-stage heat exchanger (HX3); The outlet of the third-stage two-phase expander (EX3) is connected to the inlet of the fourth-stage two-phase expander (EX4), and the outlet of the fourth-stage two-phase expander (EX4) is connected to the inlet of the second-stage hydrogen refrigerant mixer (M4); The outlet of the second-stage hydrogen refrigerant mixer (M4) is connected to the inlet of the third flow channel of the third-stage heat exchanger (HX3), and the outlet of the third flow channel of the third-stage heat exchanger (HX3) is connected to the inlet of the second flow channel of the sixth-stage heat exchanger (HX6); The outlet of the sixth-stage two-phase expander (EX6) is connected to the inlet of the second flow channel of the fifth-stage heat exchanger (HX5), the outlet of the second flow channel of the fifth-stage heat exchanger (HX5) is connected to the inlet of the second flow channel of the fourth-stage heat exchanger (HX4), and the outlet of the second flow channel of the fourth-stage heat exchanger (HX4) is connected to the inlet of the second-stage hydrogen refrigerant mixer (M4); The outlet of the first flow channel of the fifth-stage heat exchanger (HX5) is connected to the inlet of the seventh-stage two-phase expander (EX7), and the outlet of the seventh-stage two-phase expander (EX7) is connected to the liquid hydrogen storage module; The hydrogen refrigerant compression module includes a first-stage hydrogen refrigerant compressor (C5), a first-stage hydrogen refrigerant cooler (E5), a first hydrogen refrigerant mixer (M3), a second-stage hydrogen refrigerant compressor (C6), a second-stage hydrogen refrigerant cooler (E6), a third-stage hydrogen refrigerant compressor (C7), a third-stage hydrogen refrigerant cooler (E7), a fourth-stage hydrogen refrigerant compressor (C8) and a fourth-stage hydrogen refrigerant cooler (E8); wherein: The outlet of the first-stage hydrogen refrigerant compressor (C5) is connected to the inlet of the first-stage hydrogen refrigerant cooler (E5), and the outlet of the first-stage hydrogen refrigerant cooler (E5) is connected to the inlet of the first hydrogen refrigerant mixer (M3); The outlet and inlet of the first hydrogen refrigerant mixer (M3), the second-stage hydrogen refrigerant compressor (C6), the second-stage hydrogen refrigerant cooler (E6), the third-stage hydrogen refrigerant compressor (C7), the third-stage hydrogen refrigerant cooler (E7), the fourth-stage hydrogen refrigerant compressor (C8) and the fourth-stage hydrogen refrigerant cooler (E8) are connected in sequence; The inlet of the first hydrogen refrigerant mixer (M3) is connected to the outlet of the first flow channel of the sixth-stage heat exchanger (HX6); The inlet of the first-stage hydrogen refrigerant compressor (C5) is connected to the outlet of the second flow channel of the sixth-stage heat exchanger (HX6); The outlet of the fourth-stage hydrogen refrigerant cooler (E8) is connected to the inlet of the third flow channel of the sixth-stage heat exchanger (HX6).

2. The hydrogen liquefaction system according to claim 1, characterized in that The pre-cooling cold box module includes a first-stage heat exchanger (HX1), a first-stage two-phase expander (EX1), a second-stage heat exchanger (HX2) and a second-stage two-phase expander (EX2); The hydrogen liquefaction pipeline is sequentially connected to the first flow channel of the first-stage heat exchanger (HX1) and the first flow channel of the second-stage heat exchanger (HX2); The mixed refrigerant compression module is provided with a first outlet branch (12), a second outlet branch (18), a first outlet circuit (15), and a second outlet circuit (22); the first outlet branch (12) and the second outlet branch (18) are respectively connected to the inlet of the second flow channel and the inlet of the third flow channel of the first-stage heat exchanger (HX1); the first outlet circuit (15) and the second outlet circuit (22) are respectively connected to the outlet of the fourth flow channel of the first-stage heat exchanger (HX1) and the outlet of the third flow channel of the second-stage heat exchanger (HX2); The outlet of the second flow channel of the first-stage heat exchanger (HX1) is connected to the inlet of the second flow channel of the second-stage heat exchanger (HX2); The outlet of the third flow channel of the first-stage heat exchanger (HX1) is connected to the inlet of the first-stage two-phase expander (EX1), and the outlet of the first-stage two-phase expander (EX1) is connected to the inlet of the fourth flow channel of the first-stage heat exchanger (HX1); The outlet of the second flow channel of the second-stage heat exchanger (HX2) is connected to the inlet of the second-stage two-phase expander (EX2), and the outlet of the second-stage heat exchanger (HX2) is connected to the inlet of the third flow channel of the second-stage heat exchanger (HX2).

3. The hydrogen liquefaction system according to claim 2, characterized in that The mixed refrigerant compression module includes a first-stage mixed refrigerant compressor (C1), a first-stage mixed refrigerant cooler (E1), a second-stage mixed refrigerant compressor (C2), a second-stage mixed refrigerant cooler (E2), a third-stage mixed refrigerant compressor (C3), a third-stage mixed refrigerant cooler (E3), a first mixed refrigerant mixer (M1), a first mixed refrigerant phase separator (S1), a fourth-stage mixed refrigerant compressor (C4), a first-stage mixed refrigerant pump (P1), a second mixed refrigerant mixer (M2), a fourth-stage mixed refrigerant cooler (E4) and a second mixed refrigerant phase separator (S2); wherein: The first-stage mixed refrigerant compressor (C1), the first-stage mixed refrigerant cooler (E1), the second-stage mixed refrigerant compressor (C2), and the second-stage mixed refrigerant cooler (E2) are connected in sequence, and the inlet of the first-stage mixed refrigerant compressor (C1) is connected to the second outlet circuit (22), and the outlet of the second-stage mixed refrigerant cooler (E2) is connected to the inlet of the first mixed refrigerant mixer (M1); The third-stage mixed refrigerant compressor (C3) and the third-stage mixed refrigerant cooler (E3) are connected to each other, and the inlet of the third-stage mixed refrigerant compressor (C3) is connected to the first outlet circuit (15), and the outlet of the third-stage mixed refrigerant cooler (E3) is connected to the first mixed refrigerant mixer (M1); The outlet of the first mixed refrigerant mixer (M1) is connected to the inlet of the first mixed refrigerant phase separator (S1); The gas outlet and the liquid outlet of the first mixed refrigerant phase separator (S1) are connected to the inlet of the fourth-stage mixed refrigerant compressor (C4) and the inlet of the first-stage mixed refrigerant pump (P1) respectively; The outlet of the fourth-stage mixed refrigerant compressor (C4) and the outlet of the first-stage mixed refrigerant pump (P1) are respectively connected to the inlet of the second mixed refrigerant mixer (M2); The outlet of the second mixed refrigerant mixer (M2) is connected to the inlet of the fourth-stage mixed refrigerant cooler (E4); The outlet of the fourth-stage mixed refrigerant cooler (E4) is connected to the inlet of the second mixed refrigerant phase separator (S2); The liquid outlet and the gas outlet of the second mixed refrigerant phase separator (S2) are connected to the first outlet branch (12) and the second outlet branch (18) respectively.

4. The hydrogen liquefaction system according to claim 2, characterized in that The hydrogen liquefaction pipeline is sequentially connected to the first-stage normal-para-hydrogen converter (R1), the first flow channel of the third-stage heat exchanger (HX3), the second-stage normal-para-hydrogen converter (R2), the first flow channel of the fourth-stage heat exchanger (HX4), the third-stage normal-para-hydrogen converter (R3), the first flow channel of the fifth-stage heat exchanger (HX5), and the seventh-stage two-phase expander (EX7).

5. The hydrogen liquefaction system according to claim 4, wherein: The outlet of the first flow channel of the second-stage heat exchanger (HX2) is connected to the inlet of the first-stage normal-parahydrogen converter (R1).

6. A hydrogen liquefaction process based on mixed refrigerant precooling, characterized in that: The hydrogen liquefaction process is carried out using the hydrogen liquefaction system based on mixed refrigerant precooling according to any one of claims 1 to 5; The raw hydrogen entering the pre-cooling cold box module is cooled to 80K; The raw hydrogen entering the subcooling cold box module is cooled to 20K.

7. The hydrogen liquefaction process according to claim 6, characterized in that: The mixed refrigerant in the mixed refrigerant compression module includes 26.86% methane, 22.23% ethane, 22.45% propane, 13.65% isobutane, 12.85% nitrogen and 1.96% hydrogen, calculated in mole percentages.

8. The hydrogen liquefaction process according to claim 6 or 7, characterized in that: The pressure of the raw hydrogen is 2100 kPa, the temperature is 25°C, and the flow rate is 3.5 kg / s; The compressed and purified raw hydrogen enters the heat exchanger of the pre-cooling cold box module and is cooled to -193°C. It then undergoes the first hydrogen to para-hydrogen conversion, with the components converted to 48.09% para-hydrogen + 51.91% ortho-hydrogen, calculated in molar percentage. The raw hydrogen after the first conversion enters the heat exchanger of the supercooling cold box module and is cooled to -221°C, and then undergoes the second hydrogen conversion from ortho-parahydrogen to hydrogen, with the components converted to 73.38% parahydrogen + 26.62% orthohydrogen, calculated in molar percentage; The raw hydrogen after the second conversion enters the heat exchanger of the supercooling cold box module and is cooled to -242°C, and then undergoes the third hydrogen conversion to ortho-parahydrogen, with the components converted to 96.48% parahydrogen + 3.52% orthohydrogen, calculated in molar percentage; The raw hydrogen after the third conversion enters the heat exchanger of the supercooling cold box module to be supercooled to -253°C, and then the pressure is reduced to 110-150 kPa and enters the liquefied hydrogen storage tank.

9. The hydrogen liquefaction process according to claim 6 or 7, wherein: The total mass flow rate of the mixed refrigerant provided by the mixed refrigerant compression module is 273254.7 kg / h. The mixed refrigerant is pressurized to 4812.25 kPa and cooled to 25°C, and then gas-liquid separation is performed to obtain gas-phase refrigerant and liquid-phase refrigerant, wherein the gas-phase refrigerant enters the heat exchanger of the pre-cooling cold box module and is cooled to -193°C, and then the pressure is reduced to 228.99 kPa, and returns to the heat exchanger of the pre-cooling cold box module to provide cold energy; the liquid-phase refrigerant enters the heat exchanger of the pre-cooling cold box module and is cooled to -30°C, and then the pressure is reduced to 717.96 kPa, and returns to the heat exchanger of the pre-cooling cold box module to provide cold energy; the gas-phase refrigerant and the liquid-phase refrigerant after providing cold energy return to the mixed refrigerant compression module; The mass flow rate of hydrogen refrigerant provided by the hydrogen refrigerant compression module is 50770.74 kg / h. The hydrogen refrigerant is pressurized to 3297.08 kPa and cooled to 25°C before entering the heat exchanger of the subcooling cold box module and being cooled to -167°C. It is then divided into a first hydrogen refrigerant and a second hydrogen refrigerant. The first hydrogen refrigerant enters the heat exchanger of the subcooling cold box module and is cooled to -221°C, then depressurized to 352.29 kPa, and then It is divided into a third hydrogen refrigerant and a fourth hydrogen refrigerant. The third hydrogen refrigerant enters the heat exchanger of the supercooling cold box module to provide cold energy, and then returns to the hydrogen refrigerant compression module. The fourth hydrogen refrigerant is depressurized to 113.63 kPa, and then enters the heat exchanger of the supercooling cold box module to provide cold energy, and is mixed with the second hydrogen refrigerant depressurized to 113.63 kPa and enters the heat exchanger of the supercooling cold box module to provide cold energy, and then returns to the hydrogen refrigerant compression module.

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