BOG recycling system for liquid hydrogen station

Abstract

The utility model belongs to the technical field of liquid hydrogen stations, and particularly relates to a liquid hydrogen station BOG recycling system which comprises a liquid hydrogen tank car, a liquid hydrogen storage tank, a hydrogen liquefying device and a hydrogen recycling device. A gas outlet of the liquid hydrogen storage tank is respectively connected with the hydrogen liquefaction device and the hydrogen recovery device through a BOG gas phase recovery pipeline, and a liquid outlet of the hydrogen liquefaction device is connected with a liquid inlet of the liquid hydrogen storage tank. According to the system and the control scheme, BOG generated in the operation process of the liquid hydrogen filling station is reasonably recovered, complete recovery and efficient storage of BOG hydrogen are achieved, the system and the control scheme are high in automation degree and good in applicability, the on-site operation time of operation personnel is shortened, and the production efficiency is improved. And the overpressure emission or direct emission of hazardous gases such as BOG (boil-off gas) in the transportation process of the liquid hydrogen tank car is reduced.

Description

Technical Field

[0001] The utility model belongs to the technical field of liquid hydrogen stations, and in particular relates to a BOG recovery and utilization system for liquid hydrogen stations. Background Art

[0002] Compared to gaseous hydrogen refueling stations, liquid hydrogen refueling stations offer advantages such as high storage and transportation efficiency, low pressure, and reduced safety risks. They are the mainstream development direction of hydrogen refueling stations in my country. Liquid hydrogen refueling stations generally consist of key modules such as liquid hydrogen storage tanks, liquid hydrogen booster pumps, hydrogen storage containers (tanks or cylinders), hydrogen refueling machines, and control systems.

[0003] Due to the low temperature characteristics of liquid hydrogen, liquid hydrogen refueling stations inevitably produce evaporated hydrogen or flash steam (Boil Off Gas, usually abbreviated as BOG) during operation. The sources of BOG in liquid hydrogen refueling stations mainly include two aspects. First, since the temperature of liquid hydrogen is much lower than the ambient temperature, external heat will be transmitted into the container through the container wall during storage, causing liquid hydrogen to vaporize and produce liquid hydrogen flash steam (BOG), which in turn causes the internal pressure of the container to increase. BOG must be discharged to prevent the liquid hydrogen storage tank from being subjected to excessive pressure; second, there is the evaporation loss of liquid hydrogen tank trucks during loading and unloading, and the evaporation loss of liquid hydrogen tank trucks, liquid hydrogen pipelines and other equipment during pre-operation and official operation.

[0004] Current liquid hydrogen refueling stations primarily discharge this hydrogen into the atmosphere through centralized venting systems, wasting valuable hydrogen resources and significantly reducing the economic viability of these stations. Furthermore, hydrogen has a low explosion limit, so venting large amounts of hydrogen poses a safety hazard. Utility Model Content

[0005] Based on the above defects, the utility model proposes a BOG recovery and utilization system for a liquid hydrogen station, which can reduce the evaporation of liquid hydrogen during the operation of the liquid hydrogen refueling station and effectively recover BOG with good stability and high safety.

[0006] The utility model is achieved through the following technical solutions:

[0007] The utility model provides a BOG recovery and utilization system for a liquid hydrogen station, comprising a liquid hydrogen tank truck, a liquid hydrogen storage tank, a hydrogen liquefaction device and a hydrogen recovery device;

[0008] The liquid hydrogen tank truck is connected to the liquid outlet of the liquid hydrogen storage tank through a liquid hydrogen gas-liquid two-phase loading and unloading pipeline. The gas outlet of the liquid hydrogen storage tank is respectively connected to the hydrogen liquefaction device and the hydrogen recovery device through a BOG gas phase recovery pipeline. The liquid outlet of the hydrogen liquefaction device is connected to the liquid inlet of the liquid hydrogen storage tank.

[0009] In a preferred embodiment of the present invention, the hydrogen liquefaction device includes a mixing cooler, a liquid hydrogen cold box and a liquid hydrogen pump. The BOG gas phase recovery pipeline is connected to the mixing cooler through the BOG reliquefaction pipeline. The mixing cooler is connected to the liquid hydrogen cold box. The liquid outlet of the liquid hydrogen cold box is connected to the liquid inlet of the liquid hydrogen storage tank through the liquid hydrogen pump.

[0010] In a preferred embodiment of the present invention, the hydrogen recovery device includes a BOG air-temperature heater, an inlet buffer tank, a hydrogen compressor, an outlet buffer tank, a hydrogen storage bottle group and a hydrogenator. The BOG gas phase recovery pipeline is connected to the BOG air-temperature heater through a BOG booster pipeline, the BOG air-temperature heater is connected to the inlet buffer tank, the inlet buffer tank is connected to the outlet buffer tank through a hydrogen compressor, the outlet buffer tank is connected to the hydrogen storage bottle group through a hydrogen recovery pipeline, and the outlet buffer tank is connected to the hydrogenator through a hydrogen filling pipeline.

[0011] In order to detect the pressure of each device in real time and control the opening and closing of the cut-off valve, the liquid hydrogen station BOG recovery and utilization system also includes a PLC control unit. The liquid hydrogen tank truck, liquid hydrogen storage tank, hydrogen liquefaction device, and hydrogen recovery device are respectively provided with pressure sensors and valves connected to the PLC control unit.

[0012] In order to simultaneously realize the recovery and heat preservation of the BOG gas phase in the liquid hydrogen tank car, the liquid hydrogen gas-liquid two-phase loading and unloading pipeline includes a liquid hydrogen pipeline and a BOG gas phase pipeline. A low-temperature insulation film is provided on the outside of the liquid hydrogen pipeline. The BOG gas phase pipeline is sleeved on the outside of the liquid hydrogen pipeline. A cold insulation layer is provided on the outside of the BOG gas phase pipeline, and a vacuum layer is formed between the BOG gas phase pipeline and the liquid hydrogen pipeline.

[0013] Furthermore, a BOG gas phase branch pipeline 1 is provided between the liquid hydrogen tank truck and the liquid hydrogen gas-liquid two-phase loading and unloading pipeline; a BOG gas phase branch pipeline 2 is provided between the liquid outlet of the liquid hydrogen storage tank and the BOG gas phase recovery pipeline.

[0014] The present invention also provides a BOG recovery and utilization method for a liquid hydrogen station, which uses the above-mentioned BOG recovery and utilization system for a liquid hydrogen station and includes the following steps:

[0015] (1) The pressure of the gas phase space of the liquid hydrogen tank truck is set to 0.2-1.0 MPa, and the pressure gauge control point is 0.2 MPa. When the liquid hydrogen tank truck is loaded, when the pressure gauge is higher than 0.2 MPa, the PLC control unit controls the first shut-off valve to open. At this time, the BOG gas phase in the liquid hydrogen tank truck will be discharged from the BOG gas phase branch line 1, enter the liquid hydrogen gas-liquid two-phase loading and unloading pipeline, and then merge into the BOG gas phase recovery pipeline through the BOG gas phase branch line 2;

[0016] (2) When the internal pressure of the liquid hydrogen storage tank is greater than the set pressure value, the PLC control unit controls the second shut-off valve to open the exhaust, and the BOG gas phase is discharged from the gas outlet of the liquid hydrogen storage tank, passes through the second shut-off valve, enters the BOG gas phase recovery pipeline, and merges with the BOG gas phase in the BOG gas phase branch pipeline 2;

[0017] (3) The PLC control unit controls the third shut-off valve to open, and the BOG gas phase passes through the BOG gas phase recovery pipeline and then enters the BOG reliquefaction pipeline. The BOG gas phase passes through the mixing cooler, the hydrogen liquefaction cold box, the liquid hydrogen pump, and finally enters the liquid inlet of the liquid hydrogen storage tank, realizing the liquefaction and recovery of the BOG gas phase in the liquid hydrogen tank truck and the liquid hydrogen storage tank;

[0018] (4) The PLC control unit controls the fourth shut-off valve to open. After the BOG gas phase passes through the BOG gas phase recovery pipeline, it enters the BOG boosting pipeline. The BOG gas phase passes through the BOG air temperature heater, the inlet buffer tank, the hydrogen compressor, and the outlet buffer tank in sequence. The outlet pipeline of the outlet buffer tank is divided into two routes. One route of the pressurized BOG gas phase is stored in the hydrogen storage bottle group through the hydrogen recovery pipeline, and the other route is entered into the hydrogenator through the hydrogen filling pipeline to realize BOG recovery.

[0019] The beneficial effects of the utility model are:

[0020] (1) The utility model rationally recovers the BOG gas generated during the operation of the liquid hydrogen filling station, realizes the complete recovery and efficient storage of BOG hydrogen, and the system and control scheme have a high degree of automation and good applicability, which reduces the on-site operation time of operators;

[0021] (2) The utility model reduces the overpressure discharge or direct release of dangerous gases such as BOG during the transportation of liquid hydrogen tank trucks. The introduction of the utility model is of great significance for improving the safety and reliability of liquid hydrogen tank truck transportation, reducing the operating costs of liquid hydrogen refueling stations, and saving energy and reducing emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a structural diagram of the BOG recovery and utilization system of the liquid hydrogen station of the present invention. DETAILED DESCRIPTION

[0023] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more precise definition of the protection scope of the present invention.

[0024] like Figure 1The BOG recovery and utilization system of a liquid hydrogen station shown in the figure includes a liquid hydrogen tank truck 1, a liquid hydrogen storage tank 2, a hydrogen liquefaction device and a hydrogen recovery device, wherein the hydrogen liquefaction device includes a mixing cooler 3, a liquid hydrogen cold box 4 and a liquid hydrogen pump 5, and the hydrogen recovery device includes a BOG air-temperature heater 12, an inlet buffer tank 6, a hydrogen compressor 7, an outlet buffer tank 8, a hydrogen storage bottle group 9 and a hydrogenator 10. In addition, it also includes a PLC control unit 11. The liquid hydrogen tank truck 1, liquid hydrogen storage tank 2, liquid hydrogen pump 5, hydrogen compressor 7, and hydrogen storage bottle group 9 are all provided with corresponding pressure sensors, which are connected to the PLC control unit 11 to detect the pressure value of each device in real time and control the opening and closing of the valves.

[0025] Specifically, the liquid hydrogen tank truck 1 is connected to the liquid outlet 2a of the liquid hydrogen storage tank 2 through the liquid hydrogen gas-liquid two-phase loading and unloading pipeline L1, and the gas outlet 2b of the liquid hydrogen storage tank 2 is respectively connected to the hydrogen liquefaction device and the hydrogen recovery device through the BOG gas phase recovery pipeline L2. A second shut-off valve 2d is provided on the BOG gas phase recovery pipeline L2. A BOG gas phase branch pipeline 1 L11 is provided between the liquid hydrogen tank truck 1 and the liquid hydrogen gas-liquid two-phase loading and unloading pipeline L1. A first shut-off valve 1a is provided on the BOG gas phase branch pipeline 1 L11. A BOG gas phase branch pipeline 2 L12 is provided between the liquid outlet 2a of the liquid hydrogen storage tank 2 and the BOG gas phase recovery pipeline L2.

[0026] Specifically, one of the BOG gas phase recovery pipelines L2 is connected to the mixing cooler 3 via the BOG reliquefaction pipeline L3. A third shut-off valve 3a is provided on the BOG reliquefaction pipeline L3. The mixing cooler 3 is connected to a liquefied hydrogen cold box 4. The liquid outlet of the liquefied hydrogen cold box 4 is connected to the liquid inlet 2c of the liquid hydrogen storage tank 2 via a liquid hydrogen pump 5.

[0027] Specifically, the other route of the BOG gas phase recovery pipeline L2 is connected to the BOG air-temperature heater 12 through the BOG boosting pipeline L4, and a fourth shut-off valve 4a is provided on the BOG boosting pipeline L4. The BOG air-temperature heater 12 is connected to the inlet buffer tank 6, and the inlet buffer tank 6 is connected to the outlet buffer tank 8 through the hydrogen compressor 7. The outlet buffer tank 8 is connected to the hydrogen storage bottle group 9 through the hydrogen recovery pipeline L5, and a fifth shut-off valve L5 is provided on the hydrogen recovery pipeline L5. The outlet buffer tank 8 is connected to the hydrogenator 10 through the hydrogen filling pipeline L6, and a sixth shut-off valve 6a is provided on the hydrogen filling pipeline L6.

[0028] The BOG recovery and utilization system of the liquid hydrogen station of the present invention includes six pipelines, namely the liquid hydrogen gas-liquid two-phase loading and unloading pipeline L1, the BOG gas phase recovery pipeline L2, the BOG reliquefaction pipeline L3, the BOG boosting pipeline L4, the hydrogen recovery pipeline L5, and the hydrogen filling pipeline L6; each of the six pipelines is equipped with a shut-off valve 1a, 2d, 3a, 4a, 5a, and 6a, and all pipelines and equipment in the system need to be insulated.

[0029] In the present invention, the pressure take-off point of the liquid hydrogen tank truck 1 is the pressure of the gas phase space in the liquid hydrogen tank truck. The BOG pressure is usually between 0.2 and 1.0 MPa, and the pressure gauge control point is 0.2 MPa. When the liquid hydrogen tank truck 1 is loaded, when the pressure gauge is higher than 0.2 MPa, the PLC control unit 11 controls the first shut-off valve 1a to open. At this time, the BOG in the liquid hydrogen tank truck will be discharged from the BOG gas phase branch pipeline 1 L11, enter the liquid hydrogen gas-liquid two-phase loading and unloading pipeline L1, and then pass through the BOG gas phase branch pipeline 2 L12 to merge into the BOG gas phase recovery pipeline L2; when the internal pressure of the liquid hydrogen storage tank 2 is greater than the set pressure value, the second shut-off valve 2d is automatically opened to exhaust.

[0030] The inner tube of the liquid hydrogen / gas-liquid dual-phase loading and unloading pipeline L1 of the present invention is a liquid hydrogen pipeline, which directly contacts cryogenic liquid hydrogen. A cryogenic insulation film is provided on the exterior of the liquid hydrogen pipeline, which is then provided with a vacuum layer formed by physical evacuation. A BOG gas phase pipeline is provided on the exterior of the vacuum layer, which is provided with a cold insulation layer. Both the liquid hydrogen pipeline and the BOG gas phase pipeline are made of cryogenic stainless steel pipes. The liquid hydrogen pipeline is located at the innermost portion of the liquid hydrogen / gas-liquid dual-phase loading and unloading pipeline, minimizing the cold loss of the cryogenic liquid hydrogen. The vacuum layer isolates the cryogenic liquid hydrogen from heat conduction and convection from the outside world, reducing the amount of BOG generated. The BOG gas phase pipeline is concentrically wrapped around the outer periphery of the vacuum layer, serving as a BOG return path generated during liquid hydrogen refueling. The pipe is also made of cryogenic stainless steel, fully utilizing the residual cold of the returning BOG to insulate the internal liquid hydrogen pipeline. The cold insulation layer is located at the outermost portion, in direct contact with the external environment, primarily isolating the pipeline from external heat conduction and water vapor intrusion.

[0031] The BOG recycling method of the liquid hydrogen station of the present utility model specifically includes:

[0032] The pressure of the gas phase space of the liquid hydrogen tank truck 1 is set to 0.2-1.0 MPa, and the pressure gauge control point is 0.2 MPa. When the liquid hydrogen tank truck 1 is loaded, when the pressure gauge exceeds 0.2 MPa, the PLC control unit 11 controls the first shut-off valve 1a to open. At this time, the BOG gas phase in the liquid hydrogen tank truck 1 will be discharged from the BOG gas phase branch line 1 L11, enter the liquid hydrogen gas-liquid two-phase loading and unloading pipeline L1, and then pass through the BOG gas phase branch line 2 L12 to merge into the BOG gas phase recovery pipeline L2;

[0033] When the internal pressure of the liquid hydrogen storage tank 2 is greater than the set pressure value, the PLC control unit 11 controls the second shut-off valve 2d to open and exhaust. The BOG gas phase is discharged from the gas outlet 2b of the liquid hydrogen storage tank 2, passes through the second shut-off valve 2d, enters the BOG gas phase recovery pipeline L2, and merges with the BOG in the BOG gas phase branch pipeline L12. In this embodiment, the opening range of the second shut-off valve 2d is 0.2MPa to 1.0MPa.

[0034] This utility model provides two BOG recovery and utilization solutions:

[0035] The PLC control unit 11 controls the third shut-off valve 3a to open. After passing through the BOG gas phase recovery line L2, the BOG enters the BOG reliquefaction line L3. In the BOG reliquefaction line L3, the line is connected to the mixing cooler 3, the hydrogen liquefaction cold box 4, and the liquid hydrogen pump 5 in sequence, and finally connected to the liquid inlet 2c of the liquid hydrogen storage tank 2, realizing the liquefaction and recovery of the BOG gas phase in the liquid hydrogen tank truck 1 and the liquid hydrogen storage tank 2.

[0036] In the above scheme, BOG undergoes two-stage cooling, including a mixing cooler 3 and a hydrogen liquefaction cold box 4. The mixing cooler 3 uses an insulated cold box to stabilize the BOG temperature. The cold source in the hydrogen liquefaction cold box 4 is a low-temperature refrigerator or a hydrogen liquefaction turbine unit. After entering the hydrogen liquefaction cold box 4, the BOG absorbs cold energy and turns into liquid hydrogen. The liquid hydrogen pump 5 is a reciprocating high-pressure liquid hydrogen pump. Under the action of the liquid hydrogen pump 5, the liquid hydrogen enters the liquid hydrogen storage tank 2 through the liquid inlet 2c, thereby recovering the BOG.

[0037] The PLC control unit 11 controls the fourth shut-off valve 4a to open. After passing through the BOG gas phase recovery pipeline L2, the BOG enters the BOG pressurizing pipeline L4. In the BOG pressurizing pipeline L4, the pipeline is connected to the BOG air-temperature heater 12, the inlet buffer tank 6, the hydrogen compressor 7, and the outlet buffer tank 8 in sequence, and the BOG is pressurized to 70MPa, 35MPa, and 20MPa. The outlet pipe of the outlet buffer tank 8 is divided into two routes, one of which is connected to the hydrogen storage bottle group 9, and the other is connected to the hydrogenator 10. The pressurized BOG is stored in the hydrogen storage bottle group 9 through the hydrogen recovery pipeline L5 and enters the hydrogenator 10 through the hydrogen filling pipeline L6 to achieve BOG recovery.

[0038] In the above scheme, the hydrogen compressor 7 is a diaphragm compressor. According to the specifications, buffer tanks are set before and after the hydrogen compressor 7. The speed of BOG entering the buffer tank is reduced, which can stabilize the pressure, thereby reducing the vibration of the compressor, reducing power consumption, and preventing the connection parts from loosening. There are multiple groups of hydrogen storage bottle groups 9, and each hydrogen storage bottle group 9 is provided with multiple hydrogen storage bottles, which are used to store high-pressure 70MPa, medium-pressure 35MPa, and low-pressure 25MPa hydrogen respectively.

[0039] Finally, it should be noted that while the embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to the specific embodiments described above, which are merely illustrative and non-restrictive. It will be apparent to those skilled in the art that other variations or modifications may be made without departing from the spirit and scope of the present invention and the claims, and all such variations and modifications are within the scope of protection of the present invention.

Claims

1. A BOG recovery and utilization system for a liquid hydrogen station, characterized by: Including liquid hydrogen tank trucks, liquid hydrogen storage tanks, hydrogen liquefaction equipment and hydrogen recovery equipment; The liquid hydrogen tank truck is connected to the liquid outlet of the liquid hydrogen storage tank through a liquid hydrogen gas-liquid two-phase loading and unloading pipeline. The gas outlet of the liquid hydrogen storage tank is respectively connected to the hydrogen liquefaction device and the hydrogen recovery device through a BOG gas phase recovery pipeline. The liquid outlet of the hydrogen liquefaction device is connected to the liquid inlet of the liquid hydrogen storage tank.

2. The BOG recovery and utilization system for liquid hydrogen stations according to claim 1, characterized in that: The hydrogen liquefaction device includes a mixing cooler, a liquid hydrogen cold box and a liquid hydrogen pump. The BOG gas phase recovery pipeline is connected to the mixing cooler through a BOG reliquefaction pipeline. The mixing cooler is connected to the liquid hydrogen cold box. The liquid outlet of the liquid hydrogen cold box is connected to the liquid inlet of the liquid hydrogen storage tank through a liquid hydrogen pump.

3. The BOG recovery and utilization system for liquid hydrogen stations according to claim 2, characterized in that: The hydrogen recovery device includes a BOG air-temperature heater, an inlet buffer tank, a hydrogen compressor, an outlet buffer tank, a hydrogen storage bottle group and a hydrogenator. The BOG gas phase recovery pipeline is connected to the BOG air-temperature heater through a BOG booster pipeline. The BOG air-temperature heater is connected to the inlet buffer tank. The inlet buffer tank is connected to the outlet buffer tank through a hydrogen compressor. The outlet buffer tank is connected to the hydrogen storage bottle group through a hydrogen recovery pipeline. The outlet buffer tank is connected to the hydrogenator through a hydrogen filling pipeline.

4. The BOG recovery and utilization system for liquid hydrogen stations according to claim 3, characterized in that: The BOG recovery and utilization system of the liquid hydrogen station also includes a PLC control unit. The liquid hydrogen tank truck, liquid hydrogen storage tank, hydrogen liquefaction device, and hydrogen recovery device are respectively provided with pressure sensors and valves connected to the PLC control unit.

5. The BOG recovery and utilization system for liquid hydrogen stations according to claim 4, characterized in that: The liquid hydrogen and gas-liquid two-phase loading and unloading pipeline includes a liquid hydrogen pipeline and a BOG gas phase pipeline. A low-temperature insulation film is provided on the outside of the liquid hydrogen pipeline. The BOG gas phase pipeline is sleeved outside the liquid hydrogen pipeline. A cold insulation layer is provided on the outside of the BOG gas phase pipeline. A vacuum layer is formed between the BOG gas phase pipeline and the liquid hydrogen pipeline.

6. The BOG recovery and utilization system for liquid hydrogen stations according to claim 5, characterized in that: A BOG gas phase branch pipeline 1 is provided between the liquid hydrogen tank truck and the liquid hydrogen gas-liquid two-phase loading and unloading pipeline.

7. The BOG recovery and utilization system for liquid hydrogen stations according to claim 6, characterized in that: A second BOG gas phase branch pipeline is provided between the liquid outlet of the liquid hydrogen storage tank and the BOG gas phase recovery pipeline.

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