BOG circulation treatment method for filling process of marine vessels and land liquid cargo membrane tanks

Abstract

The present invention relates to a BOG circulation processing method for the filling process of marine ships and onshore liquid cargo membrane tanks. The method includes the following steps: after initially cooling the temperature at the top inside the second membrane tank, further cool the second membrane tank; then spray subcooled liquid cargo on the second membrane tank, and connect the second membrane tank with the first membrane tank to achieve gas-liquid pressure balance, and then carry out the filling process: convey the liquid cargo in the first membrane tank into the second membrane tank through a liquid cargo pump and a liquid-phase connection hose. Compared with the prior art, the present invention can effectively solve the problem that the temperature of onshore liquid cargo membrane tanks (or ship membrane tanks) rises due to reasons such as sunlight exposure, resulting in an increase in BOG generated by liquid cargo such as LNG, and thus the tank pressure rises, affecting the storage of compressed cryogenic liquefied gases such as LNG.

Description

Technical Field

[0001] The present invention relates to the technical field of BOG treatment for LNG membrane tanks, and in particular to a BOG circulation treatment method for the filling process of marine vessels and onshore liquid cargo membrane tanks. Background Art

[0002] Liquefied Natural Gas (LNG) has always been the preferred energy source for oil substitution due to its green, environmental, and efficient advantages, and has become one of the fastest-growing energy industries globally. The application and development of LNG have received increasing attention from all parties, and the social demand for clean energy has grown rapidly.

[0003] LNG usually needs to rely on transportation equipment, such as marine equipment like ships, to achieve transportation. The main components of an LNG receiving terminal include terminal unloading, LNG storage, process treatment, and external transportation. Among these, the LNG storage tank that undertakes the storage task has the longest construction period, the most advanced technology, and the most difficulties during the engineering construction process, and has always been managed as the critical path of the entire project.

[0004] LNG has an extremely low temperature, reaching as low as below -160°C. During storage, LNG continuously absorbs heat from the environment and evaporates flash gas (Boil Off Gas, BOG), which is stored in the LNG storage tank. At the same time, the BOG generated by the heat absorption of LNG in other equipment and pipelines of the LNG station will also eventually return to the LNG storage tank. The pressure in the LNG storage tank gradually increases as the BOG increases.

[0005] After the LNG ship arrives at the LNG receiving terminal, it is necessary to send liquid cargo such as LNG in the marine vessel LNG storage tank into the onshore LNG storage tank through pipelines. However, due to reasons such as solar exposure, the temperature of the onshore LNG storage tank rises, the BOG generated by liquid cargo such as LNG increases, and the tank pressure rises, which affects the storage of compressed cryogenic liquefied gases such as LNG. Therefore, it is necessary to promptly treat the BOG to reduce the temperature and tank pressure in the onshore LNG storage tank. In some cases, for example, during the storage and transportation of LNG by ships, BOG may also be generated in the tank due to the loss of cold on the surface of the LNG storage tank, then it is necessary to reduce the temperature and tank pressure in the marine vessel LNG storage tank.

[0006] CN119665136A discloses an LNG storage tank BOG liquefaction recovery system and its control method. When it is necessary to recover the BOG in the LNG storage tank, the BOG transported from the LNG storage tank is cooled and liquefied by a refrigerator and then returned to the LNG storage tank to realize the recovery of the BOG gas in the LNG storage tank. During the BOG recovery process, when it is necessary to maintain the subcooling degree of the LNG storage tank, the LNG transported from the LNG storage tank is cooled by a refrigerator, and the cooled LNG is then returned to the LNG storage tank and mixed with the LNG in the LNG storage tank to reduce the temperature of the LNG in the LNG storage tank to maintain the subcooling degree of the LNG storage tank. The system in CN119665136A is essentially a control process for a single LNG storage tank. Therefore, there is an urgent need for a processing system that can achieve the dynamic balance between the LNG storage tanks of marine vessels and onshore LNG storage tanks to be applicable to the liquid cargo transportation process such as LNG between the LNG storage tanks of marine vessels and onshore LNG storage tanks. Summary of the Invention

[0007] The purpose of the present invention is to overcome the defects existing in the above-mentioned prior art and provide a BOG circulation treatment method for the filling process of marine vessels and onshore liquid cargo membrane tanks. Before unloading the marine vessel membrane tank (or onshore liquid cargo membrane tank) to the onshore liquid cargo membrane tank (or vessel membrane tank), the BOG of the LNG in the onshore liquid cargo membrane tank (or vessel membrane tank) is processed by utilizing the cold energy of the LNG in the vessel membrane tank (or onshore liquid cargo membrane tank), enabling the onshore liquid cargo membrane tank (or vessel membrane tank) to self-circulate and cool down, double-tank circulate to recover BOG, reduce the tank pressure of the onshore liquid cargo membrane tank (or vessel membrane tank), etc., which can effectively solve the problem that the temperature of the onshore liquid cargo membrane tank (or vessel membrane tank) rises due to reasons such as sunlight exposure, resulting in an increase in BOG generated by liquid cargo such as LNG and an increase in tank pressure, which affects the storage of compressed cryogenic liquefied gases such as LNG.

[0008] The purpose of the present invention can be achieved through the following technical solutions:

[0009] The purpose of the present invention is to provide a BOG circulation treatment method for the filling process of marine vessels and onshore liquid cargo membrane tanks, and the method includes the following steps:

[0010] Perform preliminary cooling of the top temperature inside the second thin-film tank: The BOG in the second thin-film tank is compressed by a compressor and then enters a seawater heat exchanger for cooling. Then the BOG enters a low-temperature heat exchanger for further cooling. After pressure regulation, the BOG is recycled back to the second thin-film tank to reduce the temperature and pressure inside the second thin-film tank. The liquid cargo in the first thin-film tank is supplied by a liquid cargo pump to the low-temperature heat exchanger to exchange heat with the BOG in the low-temperature heat exchanger. The liquid cargo vaporizes and enters the gas-liquid spray cooling tank to contact and cool with the liquid cargo sprayed from the first thin-film tank loaded by the liquid cargo pump. The obtained low-temperature gaseous liquid cargo is boosted in pressure by a compressor and then mixed with the non-vaporized liquid cargo at the bottom of the gas-liquid spray cooling tank and sent into the subcooling unit together to obtain the liquefied liquid cargo. The liquefied liquid cargo is returned to the first thin-film tank;

[0011] Further cooling of the second thin-film tank: The compressor extracts the BOG in the second thin-film tank and supplies it to the subcooling unit. The subcooling unit cools the BOG to a low temperature and then circulates it to the gas-liquid spray cooling tank. The BOG cooled to a low temperature returns to the second thin-film tank, and through gas-phase circulation, the temperature in the second thin-film tank is further reduced to the liquid cargo storage temperature;

[0012] Spray subcooled liquid cargo on the second thin-film tank: The first thin-film tank loads liquid cargo through a liquid cargo pump and enters the gas-liquid spray cooling tank, and then sends the subcooled and vaporized liquid cargo into the subcooling unit. Then the subcooled liquid cargo is sent into the second thin-film tank until the inside of the second thin-film tank reaches a low temperature state. The gas phase is connected to the second thin-film tank through a gas-phase connection hose to communicate with the first thin-film tank to achieve gas-liquid pressure balance;

[0013] Perform the filling process: The liquid cargo in the first thin-film tank is transported into the second thin-film tank through a liquid cargo pump and a liquid-phase connection hose.

[0014] Further, the method is implemented by a BOG circulation processing system for the filling process of a ship's liquid cargo thin-film tank.

[0015] Further, the system includes a first thin-film tank and a second thin-film tank; the first thin-film tank and the second thin-film tank are connected by pipelines; the system further includes a BOG cooling and pressure regulating mechanism for cooling and pressure regulating the BOG in the second thin-film tank; the system further includes a liquid cargo processing mechanism for subcooling the liquid cargo in the first thin-film tank; the BOG cooling and pressure regulating mechanism is connected to the second thin-film tank through a pipeline; the liquid cargo processing mechanism is respectively connected to the first thin-film tank and the second thin-film tank through pipelines; the BOG cooling and pressure regulating mechanism is connected to the liquid cargo processing mechanism through a pipeline so that the liquid cargo from the first thin-film tank exchanges heat with the BOG from the second thin-film tank.

[0016] Further, the first thin-film tank and the second thin-film tank are connected by a gas-phase connection hose; the first thin-film tank and the second thin-film tank are connected by a liquid-phase connection hose.

[0017] Optionally, when using the cold energy of the liquid cargo in the ship's thin-film tank to handle the BOG of the liquid cargo in the onshore liquid cargo thin-film tank, the first thin-film tank is the ship's thin-film tank, and the second thin-film tank is the onshore liquid cargo thin-film tank.

[0018] Optionally, when using the cold energy of the liquid cargo in the onshore liquid cargo thin-film tank to handle the BOG of the liquid cargo in the ship's thin-film tank, the second thin-film tank is the ship's thin-film tank, and the first thin-film tank is the onshore liquid cargo thin-film tank.

[0019] Furthermore, the liquid cargo treatment mechanism includes a heat exchange component and a compressor; the suction port end of the compressor is connected to the second thin-film tank through a pipeline; the discharge port end of the compressor is connected to the inlet of the heat exchange component through a pipeline; the outlet of the heat exchange component is connected to the second thin-film tank through a pipeline.

[0020] Furthermore, the heat exchange component includes a seawater heat exchanger and a low-temperature heat exchanger; the suction port end of the compressor is connected to the second thin-film tank through a pipeline; the discharge port end of the compressor is connected to the inlet of the seawater heat exchanger through a pipeline; the outlet of the seawater heat exchanger is connected to the inlet of the low-temperature heat exchanger through a pipeline; the outlet of the low-temperature heat exchanger is connected to the second thin-film tank through a pipeline, and a gas pressure regulating valve (the pressure regulation is achieved through the pressure regulating valve, mainly to reduce the fluid pressure to prevent damage to the atmospheric thin-film storage tank) is provided on the pipeline between the outlet of the low-temperature heat exchanger and the second thin-film tank.

[0021] Furthermore, the seawater heat exchanger is a shell-and-tube heat exchanger, a spiral-wound heat exchanger or a plate heat exchanger; the low-temperature heat exchanger is a shell-and-tube heat exchanger, a spiral-wound heat exchanger or a plate heat exchanger.

[0022] Furthermore, the liquid cargo treatment mechanism includes a liquid cargo pump, a subcooling unit, and a gas-liquid spray cooling tank; the inlet of the liquid cargo pump is connected to the first thin-film tank through a pipeline; the outlet of the gas-liquid spray cooling tank is connected to the inlet of the subcooling unit through a pipeline; the outlet of the subcooling unit is connected to the first thin-film tank through a pipeline; the outlet of the subcooling unit is connected to the inlet of the gas-liquid spray cooling tank through a pipeline; the outlet of the gas-liquid spray cooling tank is connected to the second thin-film tank through a pipeline; the outlet of the liquid cargo pump is connected to the inlet of the gas-liquid spray cooling tank through a pipeline; the outlet of the liquid cargo pump is connected to the second thin-film tank through a liquid-phase connection hose.

[0023] Furthermore, the subcooling unit includes a subcooler.

[0024] Furthermore, the outlet of the liquid cargo pump is connected to the heat exchange component through a pipeline; the heat exchange component is connected to the inlet of the gas-liquid spray cooling tank through a pipeline; the discharge port end of the compressor is connected to the inlet of the subcooling unit through a pipeline; the discharge port end of the compressor is connected to the inlet of the gas-liquid spray cooling tank through a pipeline.

[0025] Further, the outlet of the liquid cargo pump is connected to another inlet of the cryogenic heat exchanger through a pipeline, so that the liquid cargo from the first flexible tank exchanges heat with the high-temperature BOG from the second flexible tank; the other outlet of the cryogenic heat exchanger is connected to the inlet of the gas-liquid spray cooling tank through a pipeline; the outlet end of the compressor is connected to the inlet of the subcooling unit through a pipeline; the outlet end of the compressor is connected to the inlet of the gas-liquid spray cooling tank through a pipeline.

[0026] Further, a spray cooling pipeline and a spray filling pipeline are sequentially arranged from top to bottom at the top inside the first flexible tank;

[0027] The heights at which the spray cooling pipeline and the spray filling pipeline are arranged are both higher than the liquid level of the liquid cargo in the first flexible tank.

[0028] Further, the liquid cargo is a cryogenic liquid such as liquefied natural gas (LNG) or liquid ammonia (NH3).

[0029] Further, valves are provided on all the above pipelines.

[0030] Further, the method uses the cold energy of the liquid cargo in the first flexible tank to process the BOG of the liquid cargo in the second flexible tank, enables the second flexible tank to cool down by self-circulation, recycles the BOG through the circulation of the two tanks (the first flexible tank and the second flexible tank), and reduces the tank pressure of the second flexible tank.

[0031] Further, during the filling process, BOG control of the second flexible tank is carried out:

[0032] The liquid cargo stored in the first flexible tank is continuously transported into the second flexible tank through the liquid cargo pump and the liquid-phase connection hose. The BOG gasified in the second flexible tank and the first flexible tank is pumped away by the compressor. The BOG gasified in the second flexible tank and the first flexible tank first enters the gas-liquid spray cooling tank. The BOG is first cooled by the subcooled liquid cargo of the spray. The cooled BOG enters the compressor. The BOG compressed by the compressor is then mixed with the non-vaporized liquid cargo at the bottom of the gas-liquid spray cooling tank and enters the subcooling unit to complete the liquefaction of the BOG, realizing the reliquefaction and recovery of the BOG.

[0033] Further, during the initial cooling process of the top temperature inside the second flexible tank, the BOG in the second flexible tank is compressed by the compressor and then enters the seawater heat exchanger to be cooled to room temperature.

[0034] Further, during the initial cooling process of the top temperature inside the second flexible tank, the BOG enters the cryogenic heat exchanger to be cooled to -20 to 0 °C, and then the BOG is cooled to -80 °C after being regulated to 0.65 MPa. The BOG is circulated back to the second flexible tank to reduce the temperature inside the second flexible tank to -160 °C and the pressure to atmospheric pressure.

[0035] Further, during the initial temperature reduction process at the top inside the second thin-film tank, the unvaporized liquid cargo at the bottom of the gas-liquid spray cooling tank is mixed and fed into the subcooling unit together to be cooled to -170~-160°C to obtain the liquefied liquid cargo, and the liquefied liquid cargo is returned to the first thin-film tank.

[0036] Further, during the further temperature reduction process of the second thin-film tank, the subcooling unit reduces the BOG temperature to a low temperature of -160°C.

[0037] Further, during the further temperature reduction process of the second thin-film tank, the temperature in the second thin-film tank is further reduced to the liquid cargo storage temperature of -165~-160°C.

[0038] Further, during the process of spraying subcooled liquid cargo onto the second thin-film tank, the temperature when the inside of the second thin-film tank reaches the low-temperature state is -170°C.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1) The present invention provides a BOG recycling treatment method for the filling process of marine ship and land liquid cargo thin-film tanks. Before unloading the marine ship thin-film tank (or land liquid cargo thin-film tank) to the land liquid cargo thin-film tank (or ship thin-film tank), by using the cold energy of LNG in the ship thin-film tank (or land liquid cargo thin-film tank) to treat the BOG of LNG in the land liquid cargo thin-film tank (or ship thin-film tank), enabling the land liquid cargo thin-film tank (or ship thin-film tank) to self-circulate and cool down, double-tank recycle BOG, reduce the tank pressure of the land liquid cargo thin-film tank (or ship thin-film tank), etc., which can effectively solve the problem that the temperature of the land liquid cargo thin-film tank (or ship thin-film tank) rises due to reasons such as sunlight exposure, and the BOG generated by liquid cargo such as LNG increases, resulting in an increase in tank pressure and affecting the storage of compressed cryogenic liquefied gases such as LNG.

[0041] 2) The present invention provides a BOG recycling treatment method for the filling process of marine ship and land liquid cargo thin-film tanks, and the structure of the system for implementing the method is simple, the process operation of the method is simple, and it is safe and reliable.

[0042] 3) During the filling process, due to reasons such as the friction between LNG and the pipeline, or the heat dissipation of the pipeline temperature, the pipeline cooling process, or the pressure change caused by the heat dissipation of the thin-film tank body temperature, part of the LNG will be vaporized. The present invention provides a BOG recycling treatment method for the filling process of marine ship and land liquid cargo thin-film tanks, which can ensure constant temperature and stable BOG during the filling process. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 is the overall structural schematic diagram of the BOG recycling treatment system for the filling process of the ship liquid cargo thin-film tank in the embodiment of the present invention.

[0044] Figure 2It is a partial schematic diagram of the BOG circulation treatment system for the filling process of the ship's liquid cargo membrane tank in the embodiment of the present invention, to illustrate the BOG cooling and pressure regulating mechanism.

[0045] Figure 3 It is a partial schematic diagram of the BOG circulation treatment system for the filling process of the ship's liquid cargo membrane tank in the embodiment of the present invention, to illustrate the liquid cargo treatment mechanism and the ship's membrane tank.

[0046] Figure 4 It is a partial schematic diagram of the BOG circulation treatment system for the filling process of the ship's liquid cargo membrane tank in the embodiment of the present invention, to illustrate the gas-phase connection hose and the liquid-phase connection hose.

[0047] Figure 5 It is a partial schematic diagram of the BOG circulation treatment system for the filling process of the ship's liquid cargo membrane tank in the embodiment of the present invention, to illustrate the onshore liquid cargo membrane tank.

[0048] Wherein:

[0049] 1. Ship's membrane tank, 2. Liquid cargo pump, 3. Subcooling unit, 4. Gas-liquid spray cooling tank, 5. Seawater heat exchanger, 6. Low-temperature heat exchanger, 7. Compressor, 8. Gas-phase connection hose, 9. Liquid-phase connection hose, 10. Onshore liquid cargo membrane tank, 11. Spray cooling pipeline, 12. Spray filling pipeline. Specific embodiments

[0050] The present invention will be described in detail below in conjunction with specific embodiments. These embodiments are only used to illustrate the present invention and are not used to limit the protection scope of the present invention. Features such as component models, material names, connection structures, and control methods that are not clearly stated in the present technical solution are all regarded as common technical features disclosed in the prior art.

[0051] Embodiment 1

[0052] Reference Figures 1 - 5 , the present invention provides a BOG circulation treatment method for the filling processes of offshore ships and onshore liquid cargo membrane tanks, which can utilize the cold energy of the liquid cargo in the ship's membrane tank 1 to treat the BOG of the liquid cargo in the onshore liquid cargo membrane tank 10, enabling the onshore liquid cargo membrane tank 10 to self-circulate and cool down, the two tanks (the ship's membrane tank 1 and the onshore liquid cargo membrane tank 10) to circulate and recover BOG, and reducing the tank pressure of the onshore liquid cargo membrane tank 10.

[0053] In this embodiment, the liquid cargo is LNG, and the method includes the following steps:

[0054] S1. Preliminary cooling of the temperature at the top inside the onshore liquid cargo membrane tank 10:

[0055] The compressor 7 extracts the BOG in the onshore liquid cargo membrane tank 10 for compression to obtain compressed gas, which then enters the seawater heat exchanger 5 to reduce the compressed gas to normal temperature, and then enters the low-temperature heat exchanger 6 to reduce the BOG to about -20 to 0 °C. After pressure regulation (0.65 MPa), the BOG is cooled to -80 °C and recycled back to the onshore liquid cargo membrane tank 10 (pressure regulation is to reduce the pressure of the fluid in the pipeline. The BOG in the tank needs to be pressurized by the compressor and then cooled to a low temperature to be liquefied, and then reduced to a low pressure before entering the atmospheric pressure membrane tank), and then the temperature in the onshore liquid cargo membrane tank 10 is reduced to -160 °C and the pressure to atmospheric pressure to prepare for the next step of reducing to a lower temperature; The ship's membrane tank 1 supplies the liquid cargo to the low-temperature heat exchanger 6 through the liquid cargo pump 2 to exchange heat with the high-temperature BOG in the onshore liquid cargo membrane tank 10. The liquid cargo that absorbs heat will vaporize, and the vaporized liquid cargo enters the gas-liquid spray cooling tank 4 to directly contact the liquid cargo spray cooling for temperature reduction (the liquid cargo in the gas-liquid spray cooling tank 4 comes from the liquid cargo transported by the liquid cargo pump 2 in the ship's membrane tank 1 and is used to directly exchange heat with the BOG to cool and reduce the temperature of the BOG; the compression and pressure increase of the BOG by the compressor 7 will cause the temperature of the compressor 7 to rise). The low-temperature gaseous liquid cargo is pressurized to 0.65 MPa by the compressor 7 and then mixed with the unvaporized liquid cargo at the bottom of the gas-liquid spray cooling tank 4 and sent into the subcooling unit 3 to be cooled to -175 °C together to obtain the liquefied liquid cargo, and the liquefied liquid cargo returns to the ship's membrane tank 1;

[0056] S2. Further cooling of the onshore liquid cargo membrane tank 10, reducing the temperature inside the onshore liquid cargo membrane tank 10 to below -170 °C to prepare for filling the onshore liquid cargo membrane tank 10 with the liquid cargo from the ship's membrane tank 1:

[0057] The compressor 7 extracts the BOG in the onshore liquid cargo membrane tank 10 and directly supplies it to the subcooling unit 3. In S1, the subcooling unit 3 reduces the temperature of the BOG to a low temperature (-80 °C) and then circulates to the gas-liquid spray cooling tank 4 for caching and is cooled to -160 °C. The BOG cooled to a low temperature (-160 °C) returns to the onshore liquid cargo membrane tank 10, and the temperature in the onshore liquid cargo membrane tank 10 is gradually reduced to about -170 °C through continuous gas-phase circulation, completing the cooling inside the onshore liquid cargo membrane tank 10 and reaching a subcooled temperature lower than the liquid cargo storage temperature;

[0058] S3. Spraying subcooled liquid cargo on the onshore liquid cargo membrane tank 10:

[0059] Spray a certain amount of subcooled liquid cargo (the re-liquefaction device can subcool the liquid cargo transported by the liquid cargo pump to -170 °C for spraying to reduce the temperature) on the onshore liquid cargo membrane tank 10 to be loaded, so that the main shielding layer of the membrane of the onshore liquid cargo membrane tank 10 can adapt to the subcooled liquid cargo;

[0060] First, the liquid cargo in the ship's membrane tank 1 is loaded into the gas-liquid spray cooling tank 4 for temporary storage through the liquid cargo pump 2, and then sent to the subcooling unit 3 through the circulation pump at the bottom of the gas-liquid spray cooling tank 4 to subcool the liquid cargo (the sprayed liquid cargo is not in the gas phase, and the low-temperature BOG can be recycled and precooled to -160°C. The sprayed liquid cargo is at -170°C for subcooling before filling). Then, the liquid cargo pump 2 sends the liquid cargo into the onshore liquid cargo membrane tank 10, and sprays it from the top of the onshore liquid cargo membrane tank 10 until the inside of the onshore liquid cargo membrane tank 10 reaches a low temperature state (after the inside of the onshore liquid cargo membrane tank 10 is subcooled to -170°C, liquid cargo at -165°C is filled. Among them, -170°C is the subcooling temperature, and -165°C is the normal liquid cargo temperature. Subcooling is to leave a margin temperature for the liquid cargo. The normal tank body will also heat up during filling and rise to -165°C, and the tank body may rise to a temperature higher than -165°C). The gas phase makes the onshore liquid cargo membrane tank 10 communicate with the ship's membrane tank 1 through the gas-phase connection hose 8 to achieve gas-liquid pressure balance;

[0061] S4. Perform the filling process: The liquid cargo in the ship's membrane tank 1 is transported into the onshore liquid cargo membrane tank 10 through the liquid cargo pump 2 and the liquid-phase connection hose 9.

[0062] The method of this embodiment is implemented based on a BOG circulation processing system for the filling process of the ship's liquid cargo membrane tank. The system includes a ship's membrane tank 1 and an onshore liquid cargo membrane tank 10; the ship's membrane tank 1 and the onshore liquid cargo membrane tank 10 are connected through a gas-phase connection hose 8; the ship's membrane tank 1 and the onshore liquid cargo membrane tank 10 are connected through a liquid-phase connection hose 9.

[0063] The system further includes a BOG cooling and pressure regulating mechanism for cooling and regulating the pressure of the BOG in the onshore liquid cargo membrane tank 10; the BOG cooling and pressure regulating mechanism includes a seawater heat exchanger 5, a low-temperature heat exchanger 6, and a compressor 7; the suction port end of the compressor 7 is connected to the onshore liquid cargo membrane tank 10 through a pipeline; the discharge port end of the compressor 7 is connected to the inlet of the seawater heat exchanger 5 through a pipeline; the outlet of the seawater heat exchanger 5 is connected to the inlet of the low-temperature heat exchanger 6 through a pipeline; the outlet of the low-temperature heat exchanger 6 is connected to the onshore liquid cargo membrane tank 10 through a pipeline, and a gas pressure regulating valve is provided on the pipeline between the outlet of the low-temperature heat exchanger 6 and the onshore liquid cargo membrane tank 10; the other inlet of the seawater heat exchanger 5 is connected to the seawater inlet pipeline; the other outlet of the seawater heat exchanger 5 is connected to the seawater outlet pipeline.

[0064] The system further includes a liquid cargo processing mechanism for supercooling the liquid cargo in the ship's membrane tank 1. The liquid cargo processing mechanism includes a liquid cargo pump 2, a supercooling unit 3, and a gas-liquid spray cooling tank 4. The inlet of the liquid cargo pump 2 is connected to the ship's membrane tank 1 through a pipeline. The outlet of the liquid cargo pump 2 is connected to another inlet of the low-temperature heat exchanger 6 through a pipeline so that the liquid cargo from the ship's membrane tank 1 exchanges heat with the high-temperature BOG from the onshore liquid cargo membrane tank 10. The other outlet of the low-temperature heat exchanger 6 is connected to the inlet of the gas-liquid spray cooling tank 4 through a pipeline. The outlet of the gas-liquid spray cooling tank 4 is connected to the inlet of the supercooling unit 3 through a pipeline. The outlet end of the compressor 7 is connected to the inlet of the supercooling unit 3 through a pipeline. The outlet of the supercooling unit 3 is connected to the ship's membrane tank 1 through a pipeline. The outlet of the supercooling unit 3 is connected to the inlet of the gas-liquid spray cooling tank 4 through a pipeline. The outlet of the gas-liquid spray cooling tank 4 is connected to the onshore liquid cargo membrane tank 10 through a pipeline. The outlet of the liquid cargo pump 2 is connected to the inlet of the gas-liquid spray cooling tank 4 through a pipeline. The outlet of the liquid cargo pump 2 is connected to the onshore liquid cargo membrane tank 10 through a liquid-phase connection hose 9. The outlet end of the compressor 7 is connected to the inlet of the gas-liquid spray cooling tank 4 through a pipeline.

[0065] Inside the top of the ship's membrane tank 1, a spray cooling pipeline 11 and a spray filling pipeline 12 are successively arranged from top to bottom. The heights at which the spray cooling pipeline 11 and the spray filling pipeline 12 are arranged are both higher than the liquid level of the liquid cargo in the ship's membrane tank 1.

[0066] The seawater heat exchanger 5 can be a shell-and-tube heat exchanger, a wound-tube heat exchanger, or a plate heat exchanger. The low-temperature heat exchanger 6 can be a shell-and-tube heat exchanger, a wound-tube heat exchanger, or a plate heat exchanger.

[0067] The supercooling unit 3 includes a subcooler.

[0068] A circulation pump is provided at the bottom of the gas-liquid spray cooling tank 4.

[0069] Embodiment 2

[0070] Reference Figures 1 - 5 , the present invention provides a BOG circulation processing method for the filling process of an offshore ship and an onshore liquid cargo membrane tank. On the basis of Embodiment 1, the following steps are further included:

[0071] During the filling process, due to reasons such as the friction between the liquid cargo and the pipeline, or the heat dissipation of the pipeline temperature, the pipeline cooling process, or the pressure change caused by the heat dissipation of the tank bodies of the ship's membrane tank 1 and the onshore liquid cargo membrane tank 10, part of the liquid cargo will also vaporize. To ensure constant temperature and stable BOG, the BOG control of the onshore liquid cargo membrane tank 10 is carried out. The BOG control of the onshore liquid cargo membrane tank 10 includes the following process:

[0072] The liquid cargo stored in the ship's membrane tank 1 is continuously pumped through the liquid cargo pump 2 and the liquid-phase connection hose 9 into the onshore liquid cargo membrane tank 10. The BOG generated by vaporization in the onshore liquid cargo membrane tank 10 and the ship's membrane tank 1 is removed by the compressor 7 (the compression operation is linked with the pressure of zero membrane tanks to ensure that the tank pressure is in the atmospheric pressure state). The BOG generated by vaporization in the onshore liquid cargo membrane tank 10 and the ship's membrane tank 1 first enters the gas-liquid spray cooling tank 4. The BOG is directly cooled by the supercooled liquid cargo of the spray first, and the cooled BOG enters the compressor 7. The BOG compressed to 0.65 MPa by the compressor 7 is mixed with the unvaporized liquid cargo at the bottom of the gas-liquid spray cooling tank 4 and enters the subcooling unit 3 to complete the liquefaction of the BOG, realizing the reliquefaction and recovery of the BOG in this process.

[0073] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. It is obvious that those who are familiar with the technology in this field can easily make various modifications to these embodiments and apply the general principles described here to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art according to the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A method for BOG cycle treatment during the filling process of marine ships and onshore liquid cargo membrane tanks, characterized in that, The method includes the following steps: Preliminary cooling of the top temperature inside the second thin-film tank: The BOG in the second thin-film tank is compressed by a compressor (7), then enters a seawater heat exchanger (5) for cooling, then enters a low-temperature heat exchanger (6) for cooling, and after pressure regulation, the BOG is recycled back to the second thin-film tank to reduce the temperature and pressure inside the second thin-film tank. The liquid cargo in the first thin-film tank is supplied to the low-temperature heat exchanger (6) by a liquid cargo pump (2) to exchange heat with the BOG in the low-temperature heat exchanger (6). The liquid cargo is vaporized and enters a gas-liquid spray cooling tank (4) to contact and cool with the liquid cargo sprayed from the first thin-film tank loaded by the liquid cargo pump (2). The obtained low-temperature gaseous liquid cargo is boosted by a compressor (7) and then mixed with the non-vaporized liquid cargo at the bottom of the gas-liquid spray cooling tank (4) and fed into a subcooling unit (3) to obtain the liquefied liquid cargo, and the liquefied liquid cargo returns to the first thin-film tank; Further cooling of the second thin-film tank: The compressor (7) extracts the BOG in the second thin-film tank and supplies it to the subcooling unit (3). The subcooling unit (3) cools the BOG to a low temperature and then circulates it to the gas-liquid spray cooling tank (4). The BOG cooled to a low temperature returns to the second thin-film tank, and through gas-phase circulation, the temperature in the second thin-film tank is further reduced to the liquid cargo storage temperature; Spraying subcooled liquid cargo on the second thin-film tank: The first thin-film tank loads liquid cargo through a liquid cargo pump (2) and enters the gas-liquid spray cooling tank (4), and then sends the subcooled and vaporized liquid cargo into the subcooling unit (3). Then, the subcooled liquid cargo is sent into the second thin-film tank until the inside of the second thin-film tank reaches a low-temperature state. The gas phase makes the second thin-film tank communicate with the first thin-film tank through a gas-phase connection hose (8) to achieve gas-liquid pressure balance; Carrying out the filling process: The liquid cargo in the first thin-film tank is transported into the second thin-film tank through a liquid cargo pump (2) and a liquid-phase connection hose (9).

2. The BOG circulation treatment method for the filling process of marine ships and onshore liquid cargo membrane tanks according to claim 1, wherein, The method is implemented by a BOG circulation processing system for the filling process of a ship's liquid cargo thin-film tank; The BOG circulation processing system for the filling process of a ship's liquid cargo thin-film tank includes a first thin-film tank and a second thin-film tank; the first thin-film tank and the second thin-film tank are connected; the system further includes a BOG cooling and pressure regulating mechanism for cooling and regulating the BOG in the second thin-film tank; the system further includes a liquid cargo processing mechanism for subcooling the liquid cargo in the first thin-film tank; the BOG cooling and pressure regulating mechanism is connected to the second thin-film tank; the liquid cargo processing mechanism is respectively connected to the first thin-film tank and the second thin-film tank; the BOG cooling and pressure regulating mechanism is connected to the liquid cargo processing mechanism so that the liquid cargo from the first thin-film tank exchanges heat with the BOG from the second thin-film tank; the first thin-film tank and the second thin-film tank are connected through a gas-phase connection hose (8); the first thin-film tank and the second thin-film tank are connected through a liquid-phase connection hose (9).

3. The BOG recycling treatment method for the filling process of the offshore ship and the onshore liquid cargo membrane tank according to claim 2, characterized in that, The first thin-film tank is a ship thin-film tank (1) and the second thin-film tank is a land liquid cargo thin-film tank (10); Or, the second thin-film tank is a ship thin-film tank (1) and the first thin-film tank is a land liquid cargo thin-film tank (10).

4. The BOG recycling treatment method for the filling process of an offshore ship and an onshore liquid cargo membrane tank according to claim 2, wherein The BOG cooling and pressure regulating mechanism includes a heat exchange component and a compressor (7); the suction port end of the compressor (7) is connected to the second thin film tank; the discharge port end of the compressor (7) is connected to the inlet of the heat exchange component; the outlet of the heat exchange component is connected to the second thin film tank; the heat exchange component includes a seawater heat exchanger (5) and a low-temperature heat exchanger (6); the suction port end of the compressor (7) is connected to the second thin film tank; the discharge port end of the compressor (7) is connected to the inlet of the seawater heat exchanger (5); the outlet of the seawater heat exchanger (5) is connected to the inlet of the low-temperature heat exchanger (6); the outlet of the low-temperature heat exchanger (6) is connected to the second thin film tank.

5. The BOG recycling treatment method for the filling process of the marine ship and the onshore liquid cargo membrane tank according to claim 4, wherein The liquid cargo processing mechanism includes a liquid cargo pump (2), a subcooling unit (3), and a gas-liquid spray cooling tank (4); the inlet of the liquid cargo pump (2) is connected to the first thin film tank; the outlet of the gas-liquid spray cooling tank (4) is connected to the inlet of the subcooling unit (3); the outlet of the subcooling unit (3) is connected to the first thin film tank; the outlet of the subcooling unit (3) is connected to the inlet of the gas-liquid spray cooling tank (4); the outlet of the gas-liquid spray cooling tank (4) is connected to the second thin film tank; the outlet of the liquid cargo pump (2) is connected to the inlet of the gas-liquid spray cooling tank (4); the outlet of the liquid cargo pump (2) is connected to the second thin film tank; the outlet of the liquid cargo pump (2) is connected to the heat exchange component; the heat exchange component is connected to the inlet of the gas-liquid spray cooling tank (4); the discharge port end of the compressor (7) is connected to the inlet of the subcooling unit (3); the discharge port end of the compressor (7) is connected to the inlet of the gas-liquid spray cooling tank (4).

6. The BOG recycling treatment method for the filling process of the offshore ship and the onshore liquid cargo membrane tank according to claim 1, wherein The liquid cargo is liquefied natural gas or liquid ammonia; The method utilizes the cold energy of the liquid cargo in the first thin film tank to process the BOG of the liquid cargo in the second thin film tank.

7. The BOG recycling treatment method for the filling process of the offshore ship and the onshore liquid cargo membrane tank according to claim 1, wherein During the filling process, BOG control of the second thin film tank is carried out: The liquid cargo stored in the first thin film tank is continuously transported into the second thin film tank through the liquid cargo pump (2) and the liquid-phase connection hose (9). The BOG gasified in the second thin film tank and the first thin film tank is pumped away by the compressor (7). The BOG gasified in the second thin film tank and the first thin film tank first enters the gas-liquid spray cooling tank (4). The BOG is first cooled by the sprayed subcooled liquid cargo. The cooled BOG enters the compressor (7). The BOG compressed by the compressor (7) is then mixed with the unvaporized liquid cargo at the bottom of the gas-liquid spray cooling tank (4) and enters the subcooling unit (3) to complete the liquefaction of the BOG, realizing the reliquefaction and recovery of the BOG.

8. The BOG recycling treatment method for the filling process of the offshore ship and the onshore liquid cargo membrane tank according to claim 1, characterized in that, During the initial temperature reduction process of the top inner temperature of the second thin film tank, the BOG in the second thin film tank is compressed by the compressor (7) and then enters the seawater heat exchanger (5) to be cooled to room temperature; During the initial temperature reduction process of the top inner temperature of the second thin film tank, the BOG enters the low-temperature heat exchanger (6) to be cooled to -20 to 0 °C, and then the BOG is cooled to -80 °C after being regulated to 0.65 MPa. The BOG is circulated back to the second thin film tank to reduce the temperature in the second thin film tank to -160 °C and the pressure to atmospheric pressure; During the initial temperature reduction process at the top inside the second thin-film tank, the unvaporized liquid cargo at the bottom of the gas-liquid spray cooling tank (4) is mixed and fed into the subcooling unit (3) together, and then cooled down to -170~-160 °C to obtain the liquefied liquid cargo, and the liquefied liquid cargo is returned to the first thin-film tank.

9. The BOG recycling processing method for the filling process of the marine ship and the onshore liquid cargo membrane tank according to claim 1, wherein During the further temperature reduction process of the second thin-film tank, the subcooling unit (3) reduces the BOG temperature to the low temperature of -160 °C; During the further temperature reduction process of the second thin-film tank, the temperature inside the second thin-film tank is further reduced to the liquid cargo storage temperature of -165~-160 °C.

10. The method for BOG cycle treatment during the filling process of the marine ship and the onshore liquid cargo membrane tank according to claim 1, characterized in that, During the process of spraying the subcooled liquid cargo on the second thin-film tank, the temperature when the inside of the second thin-film tank reaches the low-temperature state is -170 °C.

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