Liquid hydrogen hydrogenation station BOG recycling system and method thereof

Abstract

The application discloses a kind of liquid hydrogen hydrogenation station BOG recycling system, it is related to liquid hydrogen hydrogenation technical field, including liquid hydrogen storage tank, liquid hydrogen pump, liquid hydrogen tank car, liquid nitrogen tank, gas-liquid separator, condenser, metal hydride hydrogen storage tank, water tank, inlet buffer tank, hydrogen compressor, outlet buffer tank, hydrogenation machine, hydrogen storage bottle group, BOG booster pipeline, liquid hydrogen filling pipeline, circulating pipeline and hydrogen recovery pipeline, the low-temperature hydrogen gas of the system using liquid hydrogen storage tank storage is used to liquefy nitrogen generated by precooling, realize the circulation of liquid nitrogen, also utilize metal hydride hydrogen storage tank to separate nitrogen and hydrogen generated by precooling, simultaneously hydrogen after releasing cold quantity and hydrogen generated by precooling are transported to hydrogen compressor, are pressurized by hydrogen compressor, enter gas storage bottle group storage or hydrogenation for hydrogen energy automobile, improve the utilization efficiency of hydrogen gas, realize BOG zero emission, save energy.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of liquid hydrogen hydrogenation technology, and particularly relates to a liquid hydrogen hydrogenation station BOG recycling system and method thereof. BACKGROUND

[0002] According to the storage state of hydrogen in the station, the hydrogenation station can be divided into two types of gas hydrogen hydrogenation station and liquid hydrogen hydrogenation station, wherein the liquid hydrogen hydrogenation station has obvious advantages in energy density, floor area, transportation efficiency, safety risk and the like compared with the gas hydrogen hydrogenation station, and is regarded as the mainstream development direction of the future hydrogenation station in China.

[0003] Due to the low-temperature characteristics of liquid hydrogen, a certain amount of evaporated hydrogen (BOG) will inevitably be generated in the operation of the liquid hydrogen hydrogenation station. The main sources of the BOG are two aspects: one is that due to the fact that the temperature of liquid hydrogen is much lower than the ambient temperature, external heat will be transferred into the container through the container wall during the storage process, causing the vaporization of liquid hydrogen, generating BOG, leading to the increase of the pressure in the container, and the BOG needs to be discharged to avoid the liquid hydrogen storage tank bearing too high pressure; the other is the loss of liquid hydrogen tank car and liquid hydrogen pipeline and other equipment during pre-cooling and filling process. If the BOG is discharged into the atmosphere through a centralized diffusion system, not only there will be certain safety hazards, but also the atmospheric environment will be polluted, and a large amount of valuable hydrogen resources will be wasted, which seriously reduces the economy of the liquid hydrogen hydrogenation station; and if the BOG is recycled and liquefied, it needs to be cooled in multiple steps, and the temperature thereof needs to be lowered to 20K, in which process, sufficient cold energy needs to be provided, and the energy consumption is also uneconomical. Therefore, a liquid hydrogen hydrogenation station BOG recycling system and method thereof are provided. SUMMARY

[0004] The present application aims at solving the problems in the prior art, and provides a liquid hydrogen hydrogenation station BOG recycling system and method thereof.

[0005] A liquid hydrogen hydrogenation station BOG recycling system comprises a liquid hydrogen storage tank, a liquid hydrogen pump, a liquid hydrogen tank car, a liquid nitrogen tank, a gas-liquid separator, a condenser, a metal hydride hydrogen storage tank, a water tank, an inlet buffer tank, a hydrogen compressor, an outlet buffer tank, a hydrogenation machine, a hydrogen storage bottle group, a BOG pressurizing pipeline, a liquid hydrogen filling pipeline, a circulating pipeline and a hydrogen recovery pipeline.

[0006] The BOG pressurizing pipeline is sequentially connected with the liquid hydrogen storage tank, a first stop valve, the condenser, the inlet buffer tank, the hydrogen compressor and the outlet buffer tank, and the outlet of the outlet buffer tank is connected with the hydrogenation machine and the hydrogen storage bottle group through the second stop valve and the third stop valve respectively.

[0007] The liquid hydrogen filling pipeline is sequentially connected with the liquid hydrogen storage tank, a first liquid hydrogen stop valve, the liquid hydrogen pump, a second liquid hydrogen stop valve and the liquid hydrogen tank car.

[0008] The circulation pipeline is connected with a liquid hydrogen tank truck, a fourth stop valve, a fifth stop valve, a metal hydride hydrogen storage tank, a condenser, a gas-liquid separator, a liquid nitrogen tank in sequence, and is connected with a liquid hydrogen filling pipeline through a sixth stop valve, and the connection between the circulation pipeline and the liquid hydrogen filling pipeline is located between the first liquid hydrogen stop valve and the liquid hydrogen pump;

[0009] The circulation pipeline and the hydrogen recovery pipeline are connected through the metal hydride hydrogen storage tank, the hydrogen recovery pipeline is connected with the BOG booster pipeline, and the connection is located between the condenser and the inlet buffer tank;

[0010] The hydrogen collection pipeline is connected with the BOG booster pipeline, a seventh stop valve is arranged on the hydrogen collection pipeline, and the connection between the hydrogen collection pipeline and the BOG booster pipeline is located between the first stop valve and the condenser.

[0011] Preferably, the gas phase outlet of the gas-liquid separator is connected with a reflux pipeline, and the reflux pipeline is connected with the inlet of the condenser on the circulation pipeline through a ninth stop valve.

[0012] Preferably, the inlet of the metal hydride hydrogen storage tank is connected with the circulation pipeline, the outlet of the metal hydride hydrogen storage tank is divided into two branches, one branch is connected with the hydrogen recovery pipeline through an eighth stop valve, and the other branch is connected with the inlet of the condenser.

[0013] Preferably, the water tank is connected with the metal hydride hydrogen storage tank through an eleventh stop valve, a jump pipeline is connected between the outlet of the metal hydride hydrogen storage tank and the inlet of the fifth stop valve, and a tenth stop valve is arranged on the jump pipeline.

[0014] Preferably, the liquid hydrogen storage tank, the liquid nitrogen tank, the metal hydride hydrogen storage tank, the water tank, the hydrogen storage bottle group, the liquid hydrogen filling pipeline and the circulation pipeline are externally provided with heat insulation materials.

[0015] Preferably, the condenser adopts a low-temperature plate-fin heat exchanger.

[0016] Preferably, the hydrogen compressor adopts a diaphragm compressor, and the liquid hydrogen pump adopts a liquid hydrogen centrifugal pump.

[0017] Preferably, the hydrogen storage bottle group is provided with multiple groups, which are respectively used for storing high-pressure 70MPa, medium-pressure 35MPa and low-pressure 25MPa hydrogen.

[0018] A BOG recycling method of a liquid hydrogen refueling station, based on the recycling system, comprises the following steps:

[0019] S1, start-up stage: open the first stop valve, open the second stop valve and the third stop valve respectively, start the hydrogen compressor, the low-temperature hydrogen gas from the liquid hydrogen storage tank enters the BOG booster pipeline, releases cold energy in the condenser, and then enters the hydrogen compressor booster through the inlet buffer tank. After boosting, part of the high-pressure hydrogen gas passes through the second stop valve to the hydrogen dispenser for hydrogen energy vehicles, and the other part passes through the third stop valve to the hydrogen storage bottle group for storage;

[0020] S2, liquid nitrogen precooling stage: open the sixth stop valve, the second liquid hydrogen stop valve, the fourth stop valve, the tenth stop valve and the ninth stop valve, start the gas-liquid separator, the liquid nitrogen in the liquid nitrogen tank enters the liquid hydrogen filling pipeline through the sixth stop valve, and the liquid hydrogen pump and the liquid hydrogen tank truck are preliminarily pre-cooled to convert the liquid nitrogen into nitrogen gas;

[0021] The nitrogen gas enters the condenser in sequence through the fourth stop valve and the tenth stop valve to absorb cold energy and convert into liquid nitrogen, and then enters the gas-liquid separator. Under the action of the gas-liquid separator, the unliquefied nitrogen gas returns to the condenser through the reflux pipeline to absorb cold energy, and the liquid nitrogen enters the liquid nitrogen tank. This process is repeated until the temperature of the liquid hydrogen pump and the liquid hydrogen tank truck drops to the temperature of the liquid nitrogen. At this time, the preliminary precooling stage is completed, and the sixth stop valve and the tenth stop valve are closed.

[0022] S3, liquid hydrogen precooling stage: open the first liquid hydrogen stop valve, the fifth stop valve and the eleventh stop valve, start the liquid hydrogen pump, the liquid hydrogen in the liquid hydrogen storage tank enters the liquid hydrogen tank truck through the liquid hydrogen filling pipeline to precool it and convert the liquid hydrogen into hydrogen gas;

[0023] The mixed gas generated by precooling enters the metal hydride hydrogen storage tank in sequence through the fourth stop valve and the fifth stop valve, the water tank sends cold water to the metal hydride hydrogen storage tank through the eleventh stop valve to absorb the heat released when the metal hydride hydrogen storage tank stores hydrogen, and then returns to the water tank. The hydrogen gas in the mixed gas is absorbed by the metal hydride hydrogen storage tank, and the nitrogen gas enters the condenser through the circulating pipeline to absorb cold energy, and then enters the gas-liquid separator. The unliquefied nitrogen gas returns to the condenser through the reflux pipeline to absorb cold energy, and the liquid nitrogen enters the liquid nitrogen tank for storage;

[0024] Continue the above process until the gas purity and temperature in the liquid hydrogen tank truck meet the requirements, then stop the gas-liquid separator and the liquid hydrogen pump, close the fifth stop valve and the ninth stop valve, open the eighth stop valve, and the water after absorbing heat enters the metal hydride hydrogen storage tank through the eleventh stop valve to meet the heat absorption requirement when the metal hydride hydrogen storage tank releases hydrogen gas. Hydrogen gas enters the BOG booster pipeline through the hydrogen recovery pipeline, part of the high-pressure hydrogen gas after boosting passes through the second stop valve to the hydrogen dispenser for hydrogen energy vehicles, and the other part passes through the third stop valve to the hydrogen storage bottle group for storage. Continue the above process until there is no hydrogen gas stored in the metal hydride hydrogen storage tank, and close the eighth stop valve and the eleventh stop valve.

[0025] S4, liquid hydrogen filling stage: open the seventh stop valve, start the liquid hydrogen pump, the liquid hydrogen in the liquid hydrogen storage tank enters the liquid hydrogen tank car through the liquid hydrogen filling pipeline, the hydrogen generated by filling enters the BOG booster pipeline through the fourth stop valve and the seventh stop valve, and then is stored after being pressurized by releasing cold energy in the condenser, when the liquid hydrogen in the liquid hydrogen tank car reaches the set liquid level, the filling is completed, then the liquid hydrogen pump is stopped, and the first liquid hydrogen stop valve, the second liquid hydrogen stop valve, the fourth stop valve, the seventh stop valve, the second stop valve and the third stop valve are closed.

[0026] Compared with the prior art, the present application has the advantages that:

[0027] The system of the present application uses the low-temperature hydrogen gas stored in the liquid hydrogen storage tank to liquefy the nitrogen gas generated by precooling, realizes the circulation of liquid nitrogen, and also uses the metal hydride hydrogen storage tank to separate the nitrogen gas and hydrogen gas generated by precooling, while the hydrogen gas after releasing cold energy and the hydrogen gas generated by precooling are transported to the hydrogen compressor for pressurization, and then enter the gas cylinder group for storage or hydrogen refueling for hydrogen energy vehicles, thereby improving the utilization efficiency of hydrogen gas, realizing BOG zero emission, and saving energy. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The figure is a structural schematic diagram of the BOG recycling system of the liquid hydrogen refueling station in the present application.

[0029] In the figure: 1 liquid hydrogen storage tank, 2 liquid hydrogen pump, 3 liquid hydrogen tank car, 4 liquid nitrogen tank, 5 gas-liquid separator, 6 condenser, 7 metal hydride hydrogen storage tank, 8 water tank, 9 inlet buffer tank, 10 hydrogen compressor, 11 outlet buffer tank, 12 hydrogen refueling machine, 13 hydrogen storage cylinder group, 14 first stop valve, 15 first liquid hydrogen stop valve, 16 second liquid hydrogen stop valve, 17 fourth stop valve, 18 fifth stop valve, 19 tenth stop valve, 20 ninth stop valve, 21 sixth stop valve, 22 seventh stop valve, 23 eighth stop valve, 24 eleventh stop valve, 25 second stop valve, 26 third stop valve, 27 BOG booster pipeline, 28 liquid hydrogen filling pipeline, 29 circulation pipeline, 30 hydrogen gas recycling pipeline, 31 backflow pipeline. DETAILED DESCRIPTION

[0030] In order to make the technical means, creative features, purposes and effects achieved by the present application easy to understand, the present application is further described below in combination with specific embodiments.

[0031] REFERENCE Figure 1As shown, a liquid hydrogen hydrogenation station BOG recycling system includes a liquid hydrogen storage tank 1, a liquid hydrogen pump 2, a liquid hydrogen tank car 3, a liquid nitrogen tank 4, a gas-liquid separator 5, a condenser 6, a metal hydride hydrogen storage tank 7, a water tank 8, an inlet buffer tank 9, a hydrogen compressor 10, an outlet buffer tank 11, a hydrogenation machine 12, a hydrogen storage bottle group 13, a BOG booster pipeline 27, a liquid hydrogen filling pipeline 28, a circulation pipeline 29 and a hydrogen recovery pipeline 30.

[0032] The BOG booster pipeline 27 is connected with the liquid hydrogen storage tank 1, the first stop valve 14, the condenser 6, the inlet buffer tank 9, the hydrogen compressor 10 and the outlet buffer tank 11 in sequence, and is used for pressurizing the low-temperature hydrogen in the liquid hydrogen storage tank 1 after releasing cold energy in the condenser 6, and the outlet of the outlet buffer tank 11 is connected with the hydrogenation machine 12 and the hydrogen storage bottle group 13 through the second stop valve 25 and the third stop valve 26 respectively, and the BOG booster pipeline 27 is used for pressurizing the low-temperature hydrogen in the liquid hydrogen storage tank 1 after releasing cold energy in the condenser 6, and the pressurized hydrogen is sent to the hydrogen storage bottle group 13 or the hydrogenation machine 12.

[0033] The liquid hydrogen filling pipeline 28 is connected with the liquid hydrogen storage tank 1, the first liquid hydrogen stop valve 15, the liquid hydrogen pump 2, the second liquid hydrogen stop valve 16 and the liquid hydrogen tank car 3 in sequence, and is used for conveying liquid hydrogen from the liquid hydrogen storage tank 1 to the liquid hydrogen tank car 3.

[0034] The circulation pipeline 29 is connected with the liquid hydrogen tank car 3, the fourth stop valve 17, the fifth stop valve 18, the metal hydride hydrogen storage tank 7, the condenser 6, the gas-liquid separator 5 and the liquid nitrogen tank 4 in sequence, and is connected with the liquid hydrogen filling pipeline 28 through the sixth stop valve 21, so as to realize the circulation liquefaction of nitrogen, and the connection position of the circulation pipeline 29 and the liquid hydrogen filling pipeline 28 is between the first liquid hydrogen stop valve 15 and the liquid hydrogen pump 2.

[0035] The circulation pipeline 29 and the hydrogen recovery pipeline 30 are connected through the metal hydride hydrogen storage tank 7, the hydrogen recovery pipeline 30 is connected with the BOG booster pipeline 27, and the connection position is between the condenser 6 and the inlet buffer tank 9, so that the hydrogen enters the BOG booster pipeline 27 through the hydrogen recovery pipeline 30 for pressurization, and the pressurized hydrogen is sent to the hydrogen storage bottle group 13 or the hydrogenation machine 12.

[0036] The hydrogen gas collection pipeline is connected with the BOG booster pipeline 27 at the pipeline connection position of the circulation pipeline 29 and the inlet of the fifth stop valve 18, the seventh stop valve 22 is arranged on the hydrogen gas collection pipeline, and the connection position of the hydrogen gas collection pipeline and the BOG booster pipeline 27 is between the first stop valve 14 and the condenser 6.

[0037] In the embodiment, the gas phase outlet of the gas-liquid separator 5 is connected with a reflux pipeline 31, the reflux pipeline is connected with the inlet of the condenser 6 on the circulation pipeline 29 through the ninth stop valve 20, and the secondary circulation of the unliquefied nitrogen gas is realized.

[0038] In the embodiment, the inlet of the metal hydride hydrogen storage tank 7 is connected with the circulation pipeline 29, the outlet of the metal hydride hydrogen storage tank 7 is divided into two branches, one branch is connected with the hydrogen recovery pipeline 30 through the eighth stop valve 23, the hydrogen generated in the precooling is recovered, and the other branch is connected with the inlet of the condenser 6, so that the nitrogen gas is de-liquefied, and the nitrogen gas and the hydrogen gas are separated from the two branches.

[0039] In the embodiment, the water tank 8 is connected with the metal hydride hydrogen storage tank 7 through the eleventh stop valve 24, when the metal hydride hydrogen storage tank 7 absorbs hydrogen, the water tank 8 passes the cold water into the metal hydride hydrogen storage tank 7 through the eleventh stop valve 24 to absorb heat, when the hydrogen is released, the water after absorbing heat is used to meet the heat absorption requirement of the metal hydride hydrogen storage tank 7, the pipeline at the outlet of the metal hydride hydrogen storage tank 7 and the pipeline at the inlet of the fifth stop valve 18 are connected with a jump pipeline, and the tenth stop valve 19 is arranged on the jump pipeline.

[0040] In the embodiment, the liquid hydrogen is used as an extremely low temperature liquid, and the heat preservation management in the storage and transportation process is very important, in order to keep the low temperature state of the liquid hydrogen in the transportation process and reduce the heat loss, the liquid hydrogen storage tank 1, the liquid nitrogen tank 4, the metal hydride hydrogen storage tank 7, the water tank 8, the hydrogen storage bottle group 13, the liquid hydrogen filling pipeline 28 and the circulation pipeline 29 are all externally provided with heat insulation materials, and the heat loss is effectively prevented.

[0041] In the embodiment, the condenser 6 adopts a low temperature plate-fin heat exchanger, the low temperature plate-fin heat exchanger is small in size and light in weight, the compact structure makes the heat exchange surface area large, and the heat exchange efficiency can be effectively improved.

[0042] In the embodiment, the hydrogen compressor 10 adopts a diaphragm compressor, the diaphragm compressor can realize a high compression ratio, has good sealing performance, is suitable for applications with high gas purity requirements, and the liquid hydrogen pump 2 adopts a liquid hydrogen centrifugal pump.

[0043] In the embodiment, the hydrogen storage bottle group 13 is provided with multiple groups and is respectively used for storing hydrogen gas with high pressure 70MPa, medium pressure 35MPa and low pressure 25MPa.

[0044] The application also provides a liquid hydrogen hydrogenation station BOG recycling method, which is based on the recycling system and includes the following steps.

[0045] S1, start-up stage: open the first stop valve 14, open the second stop valve 25 and the third stop valve 26 respectively, start the hydrogen compressor 10, the low-temperature hydrogen gas from the liquid hydrogen storage tank 1 enters the BOG booster pipeline 27, releases cold energy in the condenser 6, and then enters the hydrogen compressor 10 for boosting through the inlet buffer tank 9, after boosting, part of the high-pressure hydrogen gas is sent to the hydrogen filling machine 12 for hydrogen filling of hydrogen energy vehicles through the second stop valve 25, and the other part is sent to the hydrogen storage bottle group 13 for storage through the third stop valve 26;

[0046] S2, liquid nitrogen precooling stage: open the sixth stop valve 21, the second liquid hydrogen stop valve 16, the fourth stop valve 17, the tenth stop valve 19 and the ninth stop valve 20, start the gas-liquid separator 5, the liquid nitrogen in the liquid nitrogen tank 4 enters the liquid hydrogen filling pipeline 28 through the sixth stop valve 21 to preliminarily precool the liquid hydrogen pump 2 and the liquid hydrogen tank truck 3, so that the liquid nitrogen is converted into nitrogen gas;

[0047] The nitrogen gas enters the condenser to be converted into liquid nitrogen in sequence through the fourth stop valve 17 and the tenth stop valve 19, and then enters the gas-liquid separator 5, under the action of the gas-liquid separator 5, the nitrogen gas that is not liquefied returns to the condenser 6 through the reflux pipeline 31 to absorb cold energy, and the liquid nitrogen enters the liquid nitrogen tank 4, the process is repeated in a cycle until the temperature of the liquid hydrogen pump 2 and the liquid hydrogen tank truck 3 drops to the temperature of the liquid nitrogen, at this time, the preliminary precooling stage is completed, and the sixth stop valve 21 and the tenth stop valve 19 are closed;

[0048] S3, liquid hydrogen precooling stage: open the first liquid hydrogen stop valve 15, the fifth stop valve 18 and the eleventh stop valve 24, start the liquid hydrogen pump 2, the liquid hydrogen in the liquid hydrogen storage tank 1 enters the liquid hydrogen tank truck 3 through the liquid hydrogen filling pipeline 28 to precool it, so that the liquid hydrogen is converted into hydrogen gas;

[0049] The mixed gas generated by precooling enters the metal hydride hydrogen storage tank 7 in sequence through the fourth stop valve 17 and the fifth stop valve 18, the water tank 8 sends cold water to the metal hydride hydrogen storage tank 7 through the eleventh stop valve 24 to absorb the heat released when the metal hydride hydrogen storage tank 7 stores hydrogen, and then returns to the water tank, the hydrogen gas in the mixed gas is absorbed by the metal hydride hydrogen storage tank 7, and the nitrogen gas enters the condenser 6 to absorb cold energy through the circulation pipeline 29, and then enters the gas-liquid separator 5, the nitrogen gas that is not liquefied returns to the condenser 6 through the reflux pipeline 31 to absorb cold energy, and the liquid nitrogen enters the liquid nitrogen tank 4 for storage;

[0050] The above process is continued until the gas purity and temperature in the liquid hydrogen tank truck 3 meet the requirements, then the gas-liquid separator 5, the liquid hydrogen pump 2 are stopped, the fifth stop valve 18 and the ninth stop valve 20 are closed, the eighth stop valve 23 is opened, the water after absorbing heat enters the metal hydride hydrogen storage tank 7 through the eleventh stop valve 24, the heat absorption requirement of the metal hydride hydrogen storage tank 7 when releasing hydrogen is met, the hydrogen enters the BOG booster pipeline 27 through the hydrogen recovery pipeline 30, after being boosted, part of the high-pressure hydrogen is sent to the hydrogen filling machine 12 for hydrogen energy automobile hydrogenation through the second stop valve 25, and the other part is sent to the hydrogen storage bottle group 13 for storage through the third stop valve 26, the above process is continued until there is no hydrogen stored in the metal hydride hydrogen storage tank 7, and the eighth stop valve 23 and the eleventh stop valve 24 are closed.

[0051] S4, liquid hydrogen filling stage: the seventh stop valve 22 is opened, the liquid hydrogen pump 2 is started, the liquid hydrogen in the liquid hydrogen storage tank 1 enters the liquid hydrogen tank truck 3 through the liquid hydrogen filling pipeline 28, the hydrogen generated by filling enters the BOG booster pipeline through the fourth stop valve 17 and the seventh stop valve 22, and then is boosted and stored after releasing cold energy in the condenser 6, when the liquid hydrogen in the liquid hydrogen tank truck 3 reaches the set liquid level, the filling is completed at this time, then the liquid hydrogen pump 2 is stopped, and the first liquid hydrogen stop valve 15, the second liquid hydrogen stop valve 16, the fourth stop valve 17, the seventh stop valve 22, the second stop valve 25 and the third stop valve 26 are closed.

[0052] In summary, the BOG recycling system provided by the application uses low-temperature BOG to liquefy the nitrogen generated in the precooling process, realizes the circulation of nitrogen, and uses the metal hydride hydrogen storage tank 7 to separate the nitrogen and hydrogen generated in the precooling process, while the hydrogen is transported to the hydrogen compressor 10, boosted by the hydrogen compressor 10, and stored in the gas storage bottle group 13 or used for hydrogen energy automobile hydrogenation, thereby improving the utilization efficiency of hydrogen

[0053] From the common general knowledge, the application can be realized by other embodiments without departing from the spirit or essential characteristics thereof. Therefore, the above disclosed embodiments are only examples in all aspects, and are not the only ones. All changes within the scope of the application or within the scope equivalent to the application are included in the application.

Claims

1. A liquid hydrogen filling station BOG recycling system, characterized in that: The system comprises a liquid hydrogen storage tank (1), a liquid hydrogen pump (2), a liquid hydrogen tank truck (3), a liquid nitrogen tank (4), a gas-liquid separator (5), a condenser (6), a metal hydride hydrogen storage tank (7), a water tank (8), an inlet buffer tank (9), a hydrogen compressor (10), an outlet buffer tank (11), a hydrogen filling machine (12), a hydrogen storage bottle group (13), a BOG booster pipeline (27), a liquid hydrogen filling pipeline (28), a circulation pipeline (29) and a hydrogen recovery pipeline (30). The BOG booster pipeline (27) is sequentially connected with the liquid hydrogen storage tank (1), a first stop valve (14), the condenser (6), the inlet buffer tank (9), the hydrogen compressor (10) and the outlet buffer tank (11), and the outlet of the outlet buffer tank (11) is connected with the hydrogen filling machine (12) and the hydrogen storage bottle group (13) through a second stop valve (25) and a third stop valve (26) respectively. The liquid hydrogen filling pipeline (28) is sequentially connected with the liquid hydrogen storage tank (1), a first liquid hydrogen stop valve (15), the liquid hydrogen pump (2), a second liquid hydrogen stop valve (16) and the liquid hydrogen tank truck (3). The circulation pipeline (29) is sequentially connected with the liquid hydrogen tank truck (3), a fourth stop valve (17), a fifth stop valve (18), the metal hydride hydrogen storage tank (7), the condenser (6), the gas-liquid separator (5) and the liquid nitrogen tank (4), and is connected with the liquid hydrogen filling pipeline (28) through a sixth stop valve (21), and the connection position of the circulation pipeline (29) and the liquid hydrogen filling pipeline (28) is between the first liquid hydrogen stop valve (15) and the liquid hydrogen pump (2). The circulation pipeline (29) and the hydrogen recovery pipeline (30) are connected through the metal hydride hydrogen storage tank (7), the hydrogen recovery pipeline (30) is connected with the BOG booster pipeline (27), and the connection position is between the condenser (6) and the inlet buffer tank (9). A hydrogen collection pipeline is connected with the BOG booster pipeline (27) at the inlet of the fifth stop valve (18) on the circulation pipeline (29), a seventh stop valve (22) is arranged on the hydrogen collection pipeline, and the connection position of the hydrogen collection pipeline and the BOG booster pipeline (27) is between the first stop valve (14) and the condenser (6). A reflux pipeline (31) is connected with the gas phase outlet of the gas-liquid separator (5), and the reflux pipeline is connected with the inlet of the condenser (6) on the circulation pipeline (29) through a ninth stop valve (20). The inlet of the metal hydride hydrogen storage tank (7) is connected with the circulation pipeline (29), the outlet of the metal hydride hydrogen storage tank (7) is divided into two branches, one branch is connected with the hydrogen recovery pipeline (30) through an eighth stop valve (23), and the other branch is connected with the inlet of the condenser (6). The water tank (8) is connected with the metal hydride hydrogen storage tank (7) through an eleventh stop valve (24), a jump pipeline is connected between the outlet pipeline of the metal hydride hydrogen storage tank (7) and the inlet pipeline of the fifth stop valve (18), and a tenth stop valve (19) is arranged on the jump pipeline.

2. A liquid hydrogen filling station BOG recycling system according to claim 1, characterized in that: The liquid hydrogen storage tank (1), the liquid nitrogen tank (4), the metal hydride hydrogen storage tank (7), the water tank (8), the hydrogen storage bottle group (13), the liquid hydrogen filling pipeline (28) and the circulating pipeline (29) are externally provided with heat insulation materials.

3. The liquid hydrogen filling station BOG recycling system of claim 1, wherein: The condenser (6) is a low-temperature plate-fin heat exchanger.

4. The liquid hydrogen filling station BOG recycling system of claim 1, wherein: The hydrogen compressor (10) is a diaphragm compressor, and the liquid hydrogen pump (2) is a liquid hydrogen centrifugal pump.

5. The liquid hydrogen filling station BOG recycling system of claim 1, wherein: The hydrogen storage bottle group (13) is provided with multiple groups and is used for storing high-pressure 70MPa, medium-pressure 35MPa and low-pressure 25MPa hydrogen.

6. A method for BOG recycling in a liquid hydrogen refueling station, based on the recycling system according to any one of claims 1-5, characterized in that: The method comprises the following steps: S1, starting stage: open the first stop valve (14), open the second stop valve (25) and the third stop valve (26) respectively, start the hydrogen compressor (10), the low-temperature hydrogen from the liquid hydrogen storage tank (1) enters the BOG booster pipeline (27), releases cold energy in the condenser (6), and then enters the hydrogen compressor (10) through the inlet buffer tank (9) for pressure boosting, and after pressure boosting, part of the high-pressure hydrogen is sent to the hydrogen filling machine (12) for hydrogen filling of hydrogen energy vehicles, and the other part is sent to the hydrogen storage bottle group (13) for storage; S2, liquid nitrogen precooling stage: open the sixth stop valve (21), the second liquid hydrogen stop valve (16), the fourth stop valve (17), the tenth stop valve (19) and the ninth stop valve (20), start the gas-liquid separator (5), the liquid nitrogen in the liquid nitrogen tank (4) enters the liquid hydrogen filling pipeline (28) through the sixth stop valve (21), and the liquid hydrogen pump (2) and the liquid hydrogen tank car (3) are preliminarily precooled, so that the liquid nitrogen is converted into nitrogen gas; The nitrogen gas enters the condenser to absorb cold energy and is converted into liquid nitrogen through the fourth stop valve (17) and the tenth stop valve (19) in sequence, and then enters the gas-liquid separator (5), under the action of the gas-liquid separator (5), the nitrogen gas that is not liquefied returns to the condenser (6) through the reflux pipeline (31) to absorb cold energy, and the liquid nitrogen enters the liquid nitrogen tank (4), and the process is repeated until the temperature of the liquid hydrogen pump (2) and the liquid hydrogen tank car (3) drops to the temperature of the liquid nitrogen, at which time the preliminary precooling stage is completed, and the sixth stop valve (21) and the tenth stop valve (19) are closed; S3, liquid hydrogen precooling stage: open the first liquid hydrogen stop valve (15), the fifth stop valve (18) and the eleventh stop valve (24), start the liquid hydrogen pump (2), the liquid hydrogen in the liquid hydrogen storage tank (1) enters the liquid hydrogen tank car (3) through the liquid hydrogen filling pipeline (28), and is pre-cooled to convert the liquid hydrogen into hydrogen gas; The mixed gas generated by pre-cooling passes through the fourth stop valve (17) and the fifth stop valve (18) into the metal hydride hydrogen storage tank (7) in sequence. The water tank (8) sends cold water to the metal hydride hydrogen storage tank (7) through the eleventh stop valve (24) to absorb the heat released when the metal hydride hydrogen storage tank (7) stores hydrogen, and then returns to the water tank. The hydrogen in the mixed gas is absorbed by the metal hydride hydrogen storage tank (7), and the nitrogen enters the condenser (6) through the circulating pipeline (29) to absorb cold, and then enters the gas-liquid separator (5). The nitrogen that is not liquefied returns to the condenser (6) through the reflux pipeline (31) to absorb cold, and the liquid nitrogen is stored in the liquid nitrogen tank (4); The above process continues until the gas purity and temperature in the liquid hydrogen tank truck (3) meet the requirements, and then the gas-liquid separator (5) and the liquid hydrogen pump (2) are stopped, the fifth stop valve (18) and the ninth stop valve (20) are closed, and the eighth stop valve (23) is opened. The water after absorbing heat enters the metal hydride hydrogen storage tank (7) through the eleventh stop valve (24) to meet the heat absorption requirement when the metal hydride hydrogen storage tank (7) releases hydrogen. The hydrogen enters the BOG booster pipeline (27) through the hydrogen recovery pipeline (30), and after being boosted, part of the high-pressure hydrogen is sent to the hydrogen filling machine (12) for hydrogen filling for hydrogen energy vehicles through the second stop valve (25), and the other part is sent to the hydrogen storage bottle group (13) for storage through the third stop valve (26). The above process continues until there is no hydrogen stored in the metal hydride hydrogen storage tank (7), and the eighth stop valve (23) and the eleventh stop valve (24) are closed. S4, liquid hydrogen filling stage: open the seventh stop valve (22) and start the liquid hydrogen pump (2). The liquid hydrogen in the liquid hydrogen storage tank (1) enters the liquid hydrogen tank truck (3) through the liquid hydrogen filling pipeline (28). The hydrogen generated by filling enters the BOG booster pipeline through the fourth stop valve (17) and the seventh stop valve (22), and then releases cold in the condenser (6) to be stored after being boosted. When the liquid hydrogen in the liquid hydrogen tank truck (3) reaches the set liquid level, the filling is completed, and then the liquid hydrogen pump (2) is stopped, and the first liquid hydrogen stop valve (15), the second liquid hydrogen stop valve (16), the fourth stop valve (17), the seventh stop valve (22), the second stop valve (25), and the third stop valve (26) are closed.

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