LNG (Liquefied Natural Gas) precooling and multi-stage cryogenic coupling type hydrogen liquefaction system and working method thereof

Abstract

The invention discloses an LNG pre-cooling and multi-stage cryogenic coupling type hydrogen liquefaction system and a working method of the system.The system comprises a pre-cooling unit and a cryogenic unit, and the pre-cooling unit comprises a hydrogen compression module, a pre-cooler, a first expansion machine and a CO / NHcascade refrigeration system; the precooler is combined with a CO2 / NH3 cascade refrigeration system through cold energy released by LNG gasification to efficiently precool raw material hydrogen compressed by the hydrogen compression module, and the deep cooling unit comprises a refrigerant compression module, a refrigerant flow adjusting module and a plurality of heat exchange modules; compressed refrigerants are provided by the refrigerant compression module, the flow of the refrigerants flowing into the heat exchange modules is adjusted by the refrigerant flow adjusting module, raw material hydrogen is subjected to deep cooling through the heat exchanger, the refrigerant expansion machine and the self-exchange heat exchanger in the heat exchange modules, and multi-stage deep cooling is carried out through different heat exchange modules. According to the system and the method, the LNG cold energy and the CO2 / NH3 cascade refrigeration technology are combined for precooling, flow distribution is optimized, multi-stage cryogenic treatment is achieved, and the hydrogen liquefaction efficiency is improved.

Description

Technical Field

[0001] The invention relates to a hydrogen liquefaction system and a working method thereof, belonging to the technical field of gas liquefaction equipment. Background Art

[0002] Hydrogen is the most promising alternative to fossil fuels due to its high energy density, clean combustion characteristics and renewability. However, the low volume energy density of hydrogen has led to problems such as supply and demand mismatch and high costs during storage, transportation and use, which has become a key factor restricting the industrial development of hydrogen energy. Compared with gaseous hydrogen, liquefied hydrogen has obvious advantages in storage and transportation due to its higher volume energy density.

[0003] The preparation of liquefied hydrogen requires cooling hydrogen to the liquefaction temperature (-253°C). This process involves extremely low temperature technology. Currently, single cycle or multi-stage Brayton cycle is mainly used. However, due to the extremely low liquefaction temperature of hydrogen, the single cryogenic process consumes huge energy in the multi-stage cooling process, resulting in low system operation efficiency. The energy consumption of the hydrogen liquefaction system is usually 10~15kWh / kg, and the energy efficiency is only 20%~30%. Summary of the invention

[0004] In view of the above-mentioned defects of the prior art, the present invention provides an LNG pre-cooling and multi-stage cryogenic coupled hydrogen liquefaction system and a working method, the purpose of which is to improve the efficiency of the liquefaction process and reduce the energy consumption and liquefaction cost of the system.

[0005] The technical solution of the present invention is as follows: an LNG precooling and multi-stage cryogenic coupled hydrogen liquefaction system, comprising a precooling unit, a cryogenic unit and a control module; The precooling unit includes a hydrogen compression module, a precooler, a first expander and a CO 2 / NH 3 Cascade refrigeration system, the hydrogen compression module is used to compress hydrogen and connect to the precooler, the CO 2 / NH 3 The liquid ammonia and LNG of the cascade refrigeration system are connected to the precooler to cool the compressed hydrogen. The liquid ammonia passing through the precooler returns to the CO 2 / NH 3 The cascade refrigeration system circulates, the compressed hydrogen passing through the precooler enters the first expander for expansion and then enters the cryogenic unit, and a first temperature sensor is arranged at the outlet of the first expander; The cryogenic unit includes a refrigerant compression module, a refrigerant flow regulating module and a plurality of heat exchange modules. The refrigerant compression module is provided with a plurality of compressors for compressing the refrigerant, and the refrigerant is a mixture of helium, neon and hydrogen. The refrigerant flow regulating module is used to distribute the refrigerant flow to the heat exchange modules. Each of the heat exchange modules includes a normal para-hydrogen converter, a heat exchanger, a refrigerant expander, a self-exchange heat exchanger and a temperature sensor. The refrigerant distributed by the refrigerant flow regulating module sequentially passes through the self-exchange heat exchanger, the refrigerant expander, the heat exchanger, the self-exchange heat exchanger and then flows back to the refrigerant compression module. The top outlet and the bottom outlet of the normal para-hydrogen converter are mixed and connected to the hydrogen inlet of the heat exchanger. The hydrogen outlet of the heat exchanger is provided with the temperature sensor. The plurality of heat exchange modules are connected in series into a plurality of stages. The inlet of the normal para-hydrogen converter of the heat exchange module of the first stage is connected to the outlet of the first expander, and the inlet of the normal para-hydrogen converter of the heat exchange module of the next stage is connected to the hydrogen outlet of the heat exchange module of the previous stage. The control module is used to control the flow rate of the LNG according to the temperature measured by the first temperature sensor, and is used to control the flow rate of the refrigerant according to the temperature measured by the temperature sensor.

[0006] Furthermore, the molar percentages of helium, neon and hydrogen in the refrigerant are 75% to 80%, 5% to 10% and 10% to 15%, respectively.

[0007] Furthermore, the heat exchange modules are provided with three, and the hydrogen outlet of the heat exchanger of the last stage of the heat exchange module is connected to the liquid hydrogen storage tank.

[0008] Further, the refrigerant flow regulating module includes a first three-way regulating valve and a second three-way regulating valve, the inlet of the first three-way regulating valve is connected to the refrigerant compression module, one outlet of the first three-way regulating valve is connected to the first-stage heat exchange module, the other outlet of the first three-way regulating valve is connected to the inlet of the second three-way regulating valve, one outlet of the second three-way regulating valve is connected to the second-stage heat exchange module, and the other outlet of the second three-way regulating valve is connected to the third-stage heat exchange module, and the control module is used to control the refrigerant flow rate of the outlets of the first three-way regulating valve and the second three-way regulating valve according to the temperature measured by the temperature sensor.

[0009] Furthermore, the hydrogen compression module comprises at least two hydrogen compressors, the outlet of each hydrogen compressor is connected to a hydrogen cooler, and the outlet of the hydrogen cooler is connected to the inlet of the next hydrogen compressor.

[0010] Furthermore, the refrigerant compression module is provided with a gas-liquid separator, and the refrigerant refluxed from the self-exchange heat exchanger enters the gas-liquid separator, and the gas outlet of the gas-liquid separator is connected to the compressor of the refrigerant compression module.

[0011] Furthermore, the compressors of the refrigerant compression module are connected in series, and a refrigerant cooler is provided at the outlet of each compressor.

[0012] Another technical solution of the present invention is as follows: a working method of the aforementioned LNG precooling and multi-stage cryogenic coupled hydrogen liquefaction system, wherein the control module controls the LNG flow entering the precooler so that the temperature measured by the first temperature sensor is -202~-194℃.

[0013] Furthermore, the control module controls the refrigerant flow entering the first-stage heat exchange module so that the temperature measured by the temperature sensor of the first-stage heat exchange module is -225~-220°C, and the control module controls the refrigerant flow entering the second-stage heat exchange module so that the temperature measured by the temperature sensor of the second-stage heat exchange module is -245~-240°C.

[0014] Furthermore, the control module controls the refrigerant flow rate of the first three-way regulating valve connected to the outlet of the first-stage heat exchange module to be 0.18~0.23, so that the temperature measured by the temperature sensor of the first-stage heat exchange module is -225~-220℃; the control module controls the refrigerant flow rate of the second three-way regulating valve connected to the outlet of the second-stage heat exchange module to be 0.33~0.37, so that the temperature measured by the temperature sensor of the second-stage heat exchange module is -245~-240℃.

[0015] Compared with the prior art, the advantages of the technical solution provided by the present invention are: The present invention utilizes the large amount of cold energy released when LNG is converted into NG in the pre-cooling process, and combines CO 2 / NH 3Cascade refrigeration technology realizes efficient recovery and pre-cooling of cold capacity. At the same time, a mixed refrigerant composed of helium, neon and hydrogen is used in the cryogenic unit, and its flow distribution is optimized to ensure the efficient operation of multi-stage cryogenics. Compared with traditional hydrogen liquefaction technology, this system significantly reduces additional energy consumption and greatly improves energy utilization through the cascade utilization of cold energy and the close combination of pre-cooling unit and cryogenic unit. The use of mixed refrigerants of helium, neon and hydrogen not only broadens the applicable temperature range of refrigerants, but also significantly enhances the operating stability and reliability of the cryogenic system. According to thermodynamic analysis, the system reduces total energy consumption by 14% and improves liquefaction efficiency by 17% under the same liquefaction load. At the same time, optimized system energy management and simplified process flow significantly reduce initial investment costs and operating costs, making the system have significant advantages in both thermodynamic performance and economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a structural schematic diagram of an LNG precooling and multi-stage cryogenic coupled hydrogen liquefaction system according to an embodiment. DETAILED DESCRIPTION

[0017] The present invention is further described below in conjunction with examples. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading this description, various equivalent modifications to this description by those skilled in the art fall within the scope defined by the claims attached to this application.

[0018] Please combine Figure 1 As shown, the LNG precooling and multi-stage cryogenic coupled hydrogen liquefaction system of this embodiment includes a precooling unit, a cryogenic unit and a control module.

[0019] The precooling unit includes a hydrogen compression module, a precooler, a first expander and a CO 2 / NH 3 Cascade refrigeration system. In the hydrogen compression module, the raw hydrogen is connected to the inlet of the first hydrogen cooler 102 through a pipeline via the first hydrogen compressor 101, and the outlet of the first hydrogen cooler 102 is connected to the second hydrogen cooler 104 through a pipeline via the second hydrogen compressor 103. The outlet of the second hydrogen cooler 104 is connected to the hydrogen inlet a1 of the precooler 105, and the hydrogen outlet a2 of the precooler 105 is connected to the first expander 106. A first temperature sensor 119 is provided at the outlet of the first expander 106. After the flow rate of LNG is adjusted by the flow control valve 107, it is connected to the LNG inlet a3 of the precooler 105, and the NG outlet a4 of the precooler 105 is connected to the subsequent processing device through a pipeline.

[0020] CO 2 / NH 3 NH in cascade refrigeration system 3The compressor 201 outlet passes through the NH 3 Cooler 202 is connected to NH 3 Inlet g1, NH from evaporative condenser 203 3 The outlet g2 is connected to the NH of the precooler 105 through the pipeline via the second throttle valve 204. 3 Inlet a5, NH of precooler 105 3 The outlet a6 is connected to NH via a pipeline. 3 The compressor 201 completes the cycle. The CO in the evaporating condenser 203 2 The outlet g4 is connected to the CO 2 Compressor 205 inlet, CO 2 The outlet of the compressor 205 is connected to the inlet of the second expander 207 through a pipeline via the condenser 206, and the outlet of the second expander 207 is connected to the inlet g3 of the evaporative condenser 203 through a pipeline to complete the cycle.

[0021] The cryogenic unit includes a refrigerant compression module, a refrigerant flow regulating module and three heat exchange modules. The top outlet of the gas-liquid separator 315 in the refrigerant compression module is connected to the first compressor 301 through a pipeline, the outlet of the first compressor 301 is connected to the inlet of the second compressor 303 through a pipeline via the first cooler 302, the outlet of the second compressor 303 is connected to the inlet of the third compressor 305 through a pipeline via the second cooler 304, and the outlet of the third compressor 305 is connected to the refrigerant flow regulating module through a pipeline via the third cooler 306.

[0022] The refrigerant flow regulating module includes a first three-way regulating valve 307 and a second three-way regulating valve 310. The outlet of the third cooler 306 is connected to the inlet e1 of the first three-way regulating valve 307 and then divided into two paths, one of which flows out through the outlet e2 of the first three-way regulating valve 307, and the other of which flows out through the outlet e3 of the first three-way regulating valve 307 and then connected to the inlet g1 of the second three-way regulating valve 310 and then divided into two paths, one of which flows out through the outlet g2 of the second three-way regulating valve 310, and the other of which flows out through the outlet g3 of the second three-way regulating valve 310.

[0023] The three heat exchange modules are sequentially connected in series. Specifically, the first heat exchange module includes the first normal para-hydrogen converter 108, the first normal para-hydrogen mixer 109, the first heat exchanger 110, the first refrigerant expander 309, and the first self-exchange heat exchanger 308. The inlet of the first normal para-hydrogen converter 108 is connected to the outlet of the first expander 106, and the top outlet and the bottom outlet of the first normal para-hydrogen converter 108 are mixed through the first normal para-hydrogen mixer 109 through a pipeline and connected to the inlet b1 of the first heat exchanger 110. The outlet e2 of the first three-way regulating valve 307 is connected to the inlet f1 of the first self-exchange heat exchanger 308 through a pipeline, the outlet f2 of the first self-exchange heat exchanger 308 is connected to the refrigerant inlet b3 of the first heat exchanger 110 through a pipeline via the first refrigerant expander 309, the refrigerant outlet b4 of the first heat exchanger 110 is connected to the inlet f3 of the first self-exchange heat exchanger 308 through a pipeline, and the outlet f4 of the first self-exchange heat exchanger 308 is connected to the inlet of the gas-liquid separator 315 through the first check valve 316. The refrigerant exchanges heat with hydrogen in the first heat exchanger 110, and the refrigerant flowing into the first refrigerant expander 309 and the refrigerant flowing out of the first heat exchanger 110 after completing the heat exchange are heat exchanged in the first self-exchange heat exchanger 308. Hydrogen flows out from the outlet b2 of the first heat exchanger 110, and the second temperature sensor 120 is set at the outlet b2 of the first heat exchanger 110.

[0024] The second heat exchange module includes a second normal para-hydrogen converter 111, a second normal para-hydrogen mixer 112, a second heat exchanger 113, a second refrigerant expander 312, and a second self-exchange heat exchanger 311. The inlet of the second normal para-hydrogen converter 111 is connected to the outlet b2 of the first heat exchanger 110, and the top outlet and the bottom outlet of the second normal para-hydrogen converter 111 are mixed through the second normal para-hydrogen mixer 112 through a pipeline and connected to the inlet c1 of the second heat exchanger 113. The outlet g2 of the second three-way regulating valve 310 is connected to the inlet h1 of the second self-exchange heat exchanger 311 through a pipeline, the outlet h2 of the second self-exchange heat exchanger 311 is connected to the refrigerant inlet c3 of the second heat exchanger 113 through a pipeline via the second refrigerant expander 312, the refrigerant outlet c4 of the second heat exchanger 113 is connected to the inlet h3 of the second self-exchange heat exchanger 311 through a pipeline, and the outlet h4 of the second self-exchange heat exchanger 311 is connected to the inlet of the gas-liquid separator 315 through the second one-way valve 317. The refrigerant exchanges heat with hydrogen in the second heat exchanger 113, and the refrigerant flowing into the second refrigerant expander 312 and the refrigerant flowing out of the second heat exchanger 113 after completing the heat exchange are heat exchanged in the second self-exchange heat exchanger 311. Hydrogen flows out from the outlet c2 of the second heat exchanger 113, and the outlet c2 of the second heat exchanger 113 is provided with a third temperature sensor 121.

[0025] The third heat exchange module includes a third normal para-hydrogen converter 114, a third normal para-hydrogen mixer 115, a third heat exchanger 116, a third refrigerant expander 314, and a third self-exchange heat exchanger 313. The inlet of the third normal para-hydrogen converter 114 is connected to the outlet c2 of the second heat exchanger 113, and the top outlet and the bottom outlet of the third normal para-hydrogen converter 114 are mixed through the third normal para-hydrogen mixer 113 through a pipeline and connected to the inlet d1 of the third heat exchanger 116. The outlet g3 of the second three-way regulating valve 310 is connected to the inlet i1 of the third self-exchange heat exchanger 313 through a pipeline, the outlet i2 of the third self-exchange heat exchanger 313 is connected to the refrigerant inlet d3 of the third heat exchanger 116 through a pipeline via the third refrigerant expander 314, the refrigerant outlet d4 of the third heat exchanger 116 is connected to the inlet i3 of the third self-exchange heat exchanger 313 through a pipeline, and the outlet i4 of the third self-exchange heat exchanger 313 is connected to the inlet of the gas-liquid separator 315 through the third one-way valve 318. The refrigerant exchanges heat with hydrogen in the third heat exchanger 116, and the refrigerant flowing into the third refrigerant expander 314 and the refrigerant flowing out of the third heat exchanger 116 after completing the heat exchange are heat exchanged in the third self-exchange heat exchanger 313. Hydrogen flows out from the outlet d2 of the third heat exchanger 116, and after being throttled and reduced in pressure by the first throttle valve 117, the outlet d2 of the third heat exchanger 116 is passed into the liquid hydrogen storage tank 118 to be supplied to users.

[0026] The first temperature sensor 119, the second temperature sensor 120 and the third temperature sensor 121 are all electrically connected to the input of the control module (not shown in the figure) through wires, and the output of the control module is connected to the flow control valve 107, the first three-way control valve 307 and the second three-way control valve 310 through wires. The control module can use a controller with computing capabilities in the prior art, such as a single-chip microcomputer, a PLC, etc. The control module controls the opening of the flow control valve 107 according to the temperature measured by the first temperature sensor 119 to adjust the flow of LNG, controls the refrigerant flow rate of the outlet e2 of the first three-way control valve 307 according to the temperature measured by the second temperature sensor 120, and controls the refrigerant flow rate of the outlet g2 of the second three-way control valve 310 according to the temperature measured by the third temperature sensor 121.

[0027] The working method of the LNG precooling and multi-stage cryogenic coupled hydrogen liquefaction system is as follows: the refrigerant is a mixture of helium, neon and hydrogen with molar percentages of 75% to 80%, 5% to 10% and 10% to 15% respectively, and the mixed refrigerant has good compressibility, heat exchange and low power consumption. In this embodiment, a refrigerant with a molar percentage of helium of 80%, a molar percentage of neon of 6% and a molar percentage of hydrogen of 14% is selected.

[0028] The raw hydrogen is compressed by the first hydrogen compressor 101, cooled by the second hydrogen cooler 102, compressed again by the second hydrogen compressor 103, and further cooled by the second hydrogen cooler 104, completing the two-stage compression and cooling process, and compressing the raw hydrogen to a pressure of not less than 10 MPa high-pressure hydrogen by water cooling; the high-pressure hydrogen enters the precooler 105, absorbs the cold provided by the LNG gasification and cascade refrigeration system, and enters the first expander 106 for expansion and cooling after completing the initial cooling. The control module flow control valve 107 adjusts the opening, and the valve opening of the flow control valve 107 is in direct proportion to the temperature at the outlet of the first expander 106. When the hydrogen temperature at the outlet of the first expander 106 is too high, it means that the precooling unit has insufficient cold capacity. At this time, the valve opening of the flow control valve 107 is adjusted to increase the flow of LNG and increase the cooling capacity. Based on the raw hydrogen flow rate of 3.45 kg / s, the LNG flow rate is controlled at 9.7~10 kg / s, so that the temperature at the outlet of the first expander 106 is between -202℃ and -194℃, and the raw hydrogen expanded and cooled by the first expander 106 enters the cryogenic unit.

[0029] In the precooling unit, the LNG in the precooler 105 is gasified during the conversion to NG and releases a large amount of cold energy, which is used to cool the raw hydrogen. Part of the additional cold energy is provided by NH 3 / CO 2 Cascade refrigeration system provides. High temperature grade CO 2 CO in refrigeration systems 2 The high-pressure CO discharged from the compressor 205 2 The gas, after releasing heat in the condenser 206 and expanding and cooling in the second expander 207, enters the evaporative condenser 203 as the low-temperature NH 3 Cold source of refrigeration system, NH 3 High temperature NH discharged from compressor 201 3 , via NH 3 The cooler 202 and the evaporative condenser 203 reduce the temperature to form liquid ammonia, which is then throttled and depressurized by the second throttle valve 204 to provide low-temperature liquid ammonia for the precooler.

[0030] In the cryogenic unit, the raw hydrogen after expansion and cooling in the first expander 106 enters the first normal-parahydrogen converter 108 for conversion of normal hydrogen into parahydrogen, and enters the first normal-parahydrogen mixer 109 after mixing, and enters the first heat exchanger 110, and is cooled by the low-temperature mixed refrigerant to reach the set temperature of -220°C~-225°C, completing the first stage of cryogenic cooling; then enters the second normal-parahydrogen converter 111 and the second normal-parahydrogen mixer 112, completing the further conversion and mixing of normal hydrogen into parahydrogen; and then enters the second heat exchanger 113, after being cooled by the low-temperature mixed refrigerant, it reaches the set temperature of -240℃~-245℃, completing the second-stage deep cooling; after passing through the third normal-para-hydrogen converter 114 and the third normal-para-hydrogen mixer 115, it enters the third heat exchanger 116, is further cooled, and completes the third-stage deep cooling; after three consecutive conversions, the raw hydrogen at the outlet of the third normal-para-hydrogen mixer 115 is 96.2% para-hydrogen + 3.8% normal hydrogen, and is throttled and depressurized by the first throttle valve 117 to complete the fourth-stage deep cooling, the temperature drops to 20K, and the pressure drops to 130 kPa, realizing the conversion of gaseous hydrogen into liquid hydrogen, and stored in the liquid hydrogen storage tank 118 for users.

[0031] The mixed refrigerant gas at the top outlet of the gas-liquid separator 315 in the refrigerant compression module is compressed by three-stage water cooling of the first compressor 301, the first cooler 302, the second compressor 303, the second cooler 304, the third compressor 305 and the third cooler 306, and the pressure rises to 1000 kPa, and enters the first three-way regulating valve 307 to adjust the flow rate. In this embodiment, the refrigerant flow rate of the outlet e2 of the first three-way regulating valve 307 is 0.18~0.23 calculated based on the raw hydrogen flow rate of 3.45 kg / s; the refrigerant flowing out of the outlet e2 of the first three-way regulating valve 307 flows into the first self-exchange heat exchanger 308 to release heat, and then expands and cools down through the first refrigerant expander 309, enters the first heat exchanger 110, completes the first-stage deep cooling of the raw hydrogen, and flows back to the first self-exchange heat exchanger 308; the refrigerant flowing out of the outlet e3 of the first three-way regulating valve 307 is adjusted by the second three-way regulating valve 310. In this embodiment, the refrigerant flow rate is calculated based on the raw hydrogen flow rate of 3.45 Calculated at kg / s, the refrigerant flow rate of the outlet g2 of the second three-way regulating valve 310 is between 0.33 and 0.37. The refrigerant flowing out of the outlet g2 of the second three-way regulating valve 310 flows into the second self-exchange heat exchanger 311 to release heat, and then expands and cools through the second refrigerant expander 312, enters the second heat exchanger 113, completes the second-stage deep cooling of the raw hydrogen, and flows back to the second self-exchange heat exchanger 311; the refrigerant flowing out of the outlet g3 of the second three-way regulating valve 310 flows into the third self-exchange heat exchanger 313 to release heat, and then expands and cools through the third refrigerant expansion machine 314, enters the third heat exchanger 116, completes the third-stage deep cooling of the raw hydrogen, and flows back to the third self-exchange heat exchanger 313. The return refrigerant of the first self-exchange heat exchanger 308 enters the gas-liquid separator 315 through the first one-way valve 316, the return refrigerant of the second self-exchange heat exchanger 311 enters the gas-liquid separator 315 through the second one-way valve 317, and the return refrigerant of the third self-exchange heat exchanger 313 enters the gas-liquid separator 315 through the third one-way valve 318.

Claims

1. An LNG precooling and multi-stage cryogenic coupled hydrogen liquefaction system, characterized in that: It includes a pre-cooling unit, a deep cooling unit and a control module; The precooling unit includes a hydrogen compression module, a precooler, a first expander and a CO2 / NH3 cascade refrigeration system. The hydrogen compression module is used to compress hydrogen and is connected to the precooler. Liquid ammonia and LNG of the CO2 / NH3 cascade refrigeration system are connected to the precooler to cool the compressed hydrogen. The liquid ammonia passing through the precooler returns to the CO2 / NH3 cascade refrigeration system for circulation. The compressed hydrogen passing through the precooler enters the first expander for expansion and then enters the cryogenic unit. A first temperature sensor is arranged at the outlet of the first expander. The cryogenic unit includes a refrigerant compression module, a refrigerant flow regulating module and a plurality of heat exchange modules. The refrigerant compression module is provided with a plurality of compressors for compressing the refrigerant, and the refrigerant is a mixture of helium, neon and hydrogen. The refrigerant flow regulating module is used to distribute the refrigerant flow to the heat exchange modules. Each of the heat exchange modules includes a normal para-hydrogen converter, a heat exchanger, a refrigerant expander, a self-exchange heat exchanger and a temperature sensor. The refrigerant distributed by the refrigerant flow regulating module sequentially passes through the self-exchange heat exchanger, the refrigerant expander, the heat exchanger, the self-exchange heat exchanger and then flows back to the refrigerant compression module. The top outlet and the bottom outlet of the normal para-hydrogen converter are mixed and connected to the hydrogen inlet of the heat exchanger. The hydrogen outlet of the heat exchanger is provided with the temperature sensor. The plurality of heat exchange modules are connected in series into a plurality of stages. The inlet of the normal para-hydrogen converter of the heat exchange module of the first stage is connected to the outlet of the first expander, and the inlet of the normal para-hydrogen converter of the heat exchange module of the next stage is connected to the hydrogen outlet of the heat exchange module of the previous stage. The control module is used to control the flow rate of the LNG according to the temperature measured by the first temperature sensor, and is used to control the flow rate of the refrigerant according to the temperature measured by the temperature sensor.

2. The LNG precooling and multi-stage cryogenic coupled hydrogen liquefaction system according to claim 1 is characterized in that: The molar percentages of helium, neon and hydrogen in the refrigerant are 75% to 80%, 5% to 10% and 10% to 15% respectively.

3. The LNG precooling and multi-stage cryogenic coupled hydrogen liquefaction system according to claim 1 or 2, characterized in that: The heat exchange modules are provided with three, and the hydrogen outlet of the heat exchanger of the last stage of the heat exchange module is connected to the liquid hydrogen storage tank.

4. The LNG precooling and multi-stage cryogenic coupled hydrogen liquefaction system according to claim 3 is characterized in that: The refrigerant flow regulating module includes a first three-way regulating valve and a second three-way regulating valve, wherein the inlet of the first three-way regulating valve is connected to the refrigerant compression module, an outlet of the first three-way regulating valve is connected to the first-stage heat exchange module, another outlet of the first three-way regulating valve is connected to the inlet of the second three-way regulating valve, one outlet of the second three-way regulating valve is connected to the second-stage heat exchange module, and another outlet of the second three-way regulating valve is connected to the third-stage heat exchange module, and the control module is used to control the refrigerant flow rate of the outlets of the first three-way regulating valve and the second three-way regulating valve according to the temperature measured by the temperature sensor.

5. The LNG precooling and multi-stage cryogenic coupled hydrogen liquefaction system according to claim 1, characterized in that: The hydrogen compression module comprises at least two hydrogen compressors, the outlet of each hydrogen compressor is connected to a hydrogen cooler, and the outlet of the hydrogen cooler is connected to the inlet of the next hydrogen compressor.

6. The LNG precooling and multi-stage cryogenic coupled hydrogen liquefaction system according to claim 1, characterized in that: The refrigerant compression module is provided with a gas-liquid separator, and the refrigerant returning from the self-exchange heat exchanger enters the gas-liquid separator, and the gas outlet of the gas-liquid separator is connected to the compressor of the refrigerant compression module.

7. The LNG precooling and multi-stage cryogenic coupled hydrogen liquefaction system according to claim 1, characterized in that: The compressors of the refrigerant compression module are connected in series, and a refrigerant cooler is provided at the outlet of each compressor.

8. A method for operating the LNG precooling and multi-stage cryogenic coupled hydrogen liquefaction system according to any one of claims 1 to 7, characterized in that: The control module controls the LNG flow entering the precooler so that the temperature measured by the first temperature sensor is -202~-194℃.

9. A method for operating the LNG precooling and multi-stage cryogenic coupled hydrogen liquefaction system as claimed in claim 3, characterized in that: The control module controls the LNG flow entering the precooler so that the temperature measured by the first temperature sensor is -202~-194℃, the control module controls the refrigerant flow entering the first-stage heat exchange module so that the temperature measured by the temperature sensor of the first-stage heat exchange module is -225~-220℃, and the control module controls the refrigerant flow entering the second-stage heat exchange module so that the temperature measured by the temperature sensor of the second-stage heat exchange module is -245~-240℃.

10. A method for operating the LNG precooling and multi-stage cryogenic coupled hydrogen liquefaction system as claimed in claim 4, characterized in that: The control module controls the LNG flow entering the precooler so that the temperature measured by the first temperature sensor is -202~-194℃; the control module controls the refrigerant flow rate of the first three-way regulating valve connected to the outlet of the first-stage heat exchange module to be 0.18~0.23, so that the temperature measured by the temperature sensor of the first-stage heat exchange module is -225~-220℃; the control module controls the refrigerant flow rate of the second three-way regulating valve connected to the outlet of the second-stage heat exchange module to be 0.33~0.37, so that the temperature measured by the temperature sensor of the second-stage heat exchange module is -245~-240℃.

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