A BOG dynamic balance processing system for offshore vessels and onshore liquid cargo membrane tanks

Abstract

The present invention relates to a BOG dynamic balance processing system for an offshore ship and an onshore liquid cargo membrane tank. The system includes a first membrane tank and a second membrane tank; the first membrane tank and the second membrane tank are connected; it further includes a BOG cooling and pressure regulating mechanism; it further includes a liquid cargo processing mechanism; the BOG cooling and pressure regulating mechanism is connected to the second membrane tank; the liquid cargo processing mechanism is respectively connected to the first membrane tank and the second membrane tank; the BOG cooling and pressure regulating mechanism is connected to the liquid cargo processing mechanism so that the liquid cargo from the first membrane tank exchanges heat with the BOG from the second membrane tank. The first membrane tank is a ship membrane tank and the second membrane tank is an onshore liquid cargo membrane tank; or the second membrane tank is a ship membrane tank and the first membrane tank is an onshore liquid cargo membrane tank. Compared with the prior art, the present invention can effectively solve the problem that the onshore liquid cargo membrane tank (or ship membrane tank) has an increased temperature 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 particularly to a BOG dynamic balance treatment system for offshore ships and onshore liquid cargo membrane tanks. Background Art

[0002] Liquefied Natural Gas (LNG) has always been the preferred energy for oil substitution with its advantages of being green, environmentally friendly, and efficient, and has become one of the fastest-growing energy industries globally. The application and development of LNG have attracted 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 responsible for storage 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, BOG generated by the absorption of heat by LNG in other equipment and pipelines in the LNG station will also eventually return to the LNG storage tank, and 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 offshore ship's LNG storage tank into the onshore LNG storage tank through pipelines. However, due to reasons such as sunlight 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 the ship, BOG may also be generated in the tank due to the loss of cold from the surface of the LNG storage tank, then it is necessary to reduce the temperature and tank pressure in the ship's 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. After mixing with the LNG in the LNG storage tank, the temperature of the LNG in the LNG storage tank is reduced 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 land LNG storage tanks to be applicable to the liquid cargo transportation process of LNG and the like between the LNG storage tanks of marine vessels and land 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 dynamic balance processing system for marine vessels and land liquid cargo membrane tanks. Before unloading the LNG in the marine vessel membrane tank (or land liquid cargo membrane tank) to the land liquid cargo membrane tank (or vessel membrane tank), by utilizing the cold energy of the LNG in the vessel membrane tank (or land liquid cargo membrane tank) to process the BOG of the LNG in the land liquid cargo membrane tank (or vessel membrane tank), enabling the land 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 land liquid cargo membrane tank (or vessel membrane tank), etc., which can effectively solve the problem that the temperature of the land liquid cargo membrane tank (or vessel membrane tank) rises due to reasons such as sunlight exposure, the BOG generated by liquid cargo such as LNG increases, and the tank pressure rises, affecting 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 dynamic balance processing system for marine vessels and land liquid cargo membrane tanks. The system includes a first membrane tank and a second membrane tank; the first membrane tank and the second membrane tank are connected by pipelines; the system further includes a BOG cooling and pressure regulating mechanism for cooling and regulating the pressure of the BOG in the second membrane tank; the system further includes a liquid cargo processing mechanism for subcooling the liquid cargo in the first membrane tank; the BOG cooling and pressure regulating mechanism is connected to the second membrane tank through a pipeline; the liquid cargo processing mechanism is respectively connected to the first membrane tank and the second membrane 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 membrane tank exchanges heat with the BOG from the second membrane tank.

[0010] 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.

[0011] 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.

[0012] 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.

[0013] Further, the BOG temperature reduction and pressure regulation 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.

[0014] Further, 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 is provided on the pipeline between the outlet of the low-temperature heat exchanger and the second thin-film tank (the pressure regulation is achieved through the pressure regulating valve of the pressure regulating valve, mainly to reduce the fluid pressure to prevent damage to the atmospheric thin-film storage tank).

[0015] Further, 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.

[0016] Further, 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.

[0017] Further, the subcooling unit includes a subcooler.

[0018] 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 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.

[0019] Furthermore, the outlet of the liquid cargo pump is connected to the other inlet of the low-temperature heat exchanger through a pipeline, so that the liquid cargo from the first thin-film tank exchanges heat with the high-temperature BOG from the second thin-film tank; the other outlet of the low-temperature 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.

[0020] Furthermore, a spray cooling pipeline and a spray filling pipeline are sequentially arranged from top to bottom at the top inside the first thin-film tank;

[0021] 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 thin-film tank.

[0022] Furthermore, the liquid cargo is a cryogenic liquid such as liquefied natural gas or liquid ammonia.

[0023] Furthermore, valves are provided on all of the above pipelines.

[0024] Furthermore, the device can utilize 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, enabling the second thin-film tank to cool down by self-circulation, recycling BOG through double-tank (the first thin-film tank and the second thin-film tank) circulation, and reducing the tank pressure of the second thin-film tank.

[0025] Furthermore, the working method of the BOG dynamic balance processing system for marine vessels and onshore liquid cargo thin-film tanks includes the following steps:

[0026] Preliminary cooling of the temperature at the top inside the second thin-film tank:

[0027] The compressor extracts the BOG in the onshore liquid cargo membrane tank, compresses it to obtain compressed gas, then enters the seawater heat exchanger to cool the compressed gas to normal temperature, and then enters the low-temperature heat exchanger to cool the BOG to about -20 to 0 °C. After pressure regulation (0.65 MPa), the BOG is cooled to -80 °C and then recycled back to the onshore liquid cargo membrane tank (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) to further reduce the temperature in the onshore liquid cargo membrane tank 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 supplies the liquid cargo to the low-temperature heat exchanger through the liquid cargo pump to exchange heat with the high-temperature BOG in the onshore liquid cargo membrane tank. The liquid cargo that absorbs heat will vaporize, and the vaporized liquid cargo enters the gas-liquid spray cooling tank and directly contacts with the liquid cargo spray cooling to cool down (the liquid cargo in the gas-liquid spray cooling tank comes from the liquid cargo transported by the liquid cargo pump in the ship's membrane tank and is used to directly exchange heat with the BOG to cool down the BOG; Compressing and boosting the BOG by the compressor will increase the temperature of the compressor). The low-temperature gaseous liquid cargo is boosted to 0.65 MPa by the compressor and then mixed with the unvaporized liquid cargo at the bottom of the gas-liquid spray cooling tank and sent into the subcooling unit together to be cooled to -175 °C to obtain the liquefied liquid cargo, and the liquefied liquid cargo returns to the ship's membrane tank;

[0028] Further cooling of the second membrane tank, reducing the temperature inside the second membrane tank to below -165 degrees to prepare for filling the second membrane tank with the liquid cargo from the first membrane tank:

[0029] The compressor extracts the BOG in the onshore liquid cargo membrane tank and directly supplies it to the subcooling unit. In S1, the subcooling unit cools the BOG temperature to a low temperature (-80 °C) and then circulates to the gas-liquid spray cooling tank for caching and is cooled to a low temperature of -160 °C. The cooled BOG (-160 °C) returns to the onshore liquid cargo membrane tank, and the temperature in the onshore liquid cargo membrane tank is gradually reduced to about -170 °C through continuous gas-phase circulation, completing the cooling inside the onshore liquid cargo membrane tank and reaching a subcooled temperature lower than the liquid cargo storage temperature;

[0030] Spray the subcooled liquid cargo on the second membrane tank:

[0031] Spray a certain amount of subcooled liquid cargo on the second membrane tank to be loaded to make the main shielding layer of the membrane of the second membrane tank adapt to the subcooled liquid cargo;

[0032] First, the first membrane tank loads the liquid cargo into the gas-liquid spray cooling tank through the liquid cargo pump and stores it temporarily. The vaporized liquid cargo after subcooling is sent into the subcooling unit through the circulation pump at the bottom of the gas-liquid spray cooling tank, and then the subcooled liquid cargo is pumped into the second membrane tank and sprayed from the top of the second membrane tank until the inside of the second membrane tank reaches a low temperature state. The gas phase makes the second membrane tank communicate with the first membrane tank through the gas-phase connection hose to achieve gas-liquid pressure balance;

[0033] Carry out the filling process: Transfer the liquid cargo in the first thin-film tank into the second thin-film tank through the liquid cargo pump and the liquid-phase connection hose.

[0034] Furthermore, 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 first thin-film tank and the second thin-film tank body, part of the liquid cargo will also vaporize. To ensure constant temperature and stable BOG, carry out the BOG control of the second thin-film tank:

[0035] The liquid cargo stored in the first thin-film tank is continuously transferred into the second thin-film tank through the liquid cargo pump and the liquid-phase connection hose. The BOG generated by vaporization in the second thin-film tank and the first thin-film tank is pumped away by a compressor (the compression operation is linked with the pressure of the zero thin-film tank to ensure that the tank pressure is in the atmospheric pressure state). The BOG generated by vaporization in the second thin-film tank and the first thin-film tank first enters the gas-liquid spray cooling tank. The BOG is directly cooled by the subcooled liquid cargo of the spray first. The cooled BOG enters the compressor. The BOG compressed to 0.65 MPa 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 re-liquefaction and recovery of the BOG in this process.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1) The present invention provides a BOG dynamic balance processing system for marine ships and onshore liquid cargo thin-film tanks. Before unloading the thin-film tank of a marine ship (or onshore liquid cargo thin-film tank) to the onshore liquid cargo thin-film tank (or ship thin-film tank), by using the cold energy of LNG in the ship thin-film tank (or onshore liquid cargo thin-film tank) to process the BOG of LNG in the onshore liquid cargo thin-film tank (or ship thin-film tank), enabling the onshore liquid cargo thin-film tank (or ship thin-film tank) to cool down by self-circulation, recycle BOG through double-tank circulation, reduce the tank pressure of the onshore liquid cargo thin-film tank (or ship thin-film tank), etc., which can effectively solve the problem that the onshore liquid cargo thin-film tank (or ship thin-film tank) has an increased temperature due to reasons such as sun 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.

[0038] 2) The present invention provides a BOG dynamic balance processing system for marine ships and onshore liquid cargo thin-film tanks. The structure of the entire system is simple and the process operation is simple.

[0039] 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, part of the LNG will vaporize. The present invention provides a BOG dynamic balance processing system for marine ships and onshore liquid cargo thin-film tanks, which can ensure constant temperature and stable BOG during the filling process. Brief Description of the Drawings

[0040] Figure 1 It is a schematic diagram of the overall structure of the BOG dynamic balance processing system for marine ships and onshore liquid cargo membrane tanks in the embodiments of the present invention.

[0041] Figure 2 It is a partial schematic diagram of the BOG dynamic balance processing system for marine ships and onshore liquid cargo membrane tanks in the embodiments of the present invention, to illustrate the BOG cooling and pressure regulating mechanism.

[0042] Figure 3 It is a partial schematic diagram of the BOG dynamic balance processing system for marine ships and onshore liquid cargo membrane tanks in the embodiments of the present invention, to illustrate the liquid cargo processing mechanism and the ship membrane tank.

[0043] Figure 4 It is a partial schematic diagram of the BOG dynamic balance processing system for marine ships and onshore liquid cargo membrane tanks in the embodiments of the present invention, to illustrate the gas-phase connection hose and the liquid-phase connection hose.

[0044] Figure 5 It is a partial schematic diagram of the BOG dynamic balance processing system for marine ships and onshore liquid cargo membrane tanks in the embodiments of the present invention, to illustrate the onshore liquid cargo membrane tank.

[0045] Wherein:

[0046] 1. Ship 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

[0047] The present invention will be described in detail below with reference to 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 described in the technical solution are regarded as common technical features disclosed in the prior art.

[0048] Embodiment 1

[0049] Reference Figures 1 - 5 , the present invention provides a BOG dynamic balance processing system for marine ships and onshore liquid cargo membrane tanks, which can utilize the cold energy of the liquid cargo in the ship membrane tank 1 to process the BOG of the liquid cargo in the onshore liquid cargo membrane tank 10. The system includes a ship membrane tank 1 and an onshore liquid cargo membrane tank 10; the ship membrane tank 1 and the onshore liquid cargo membrane tank 10 are connected through a gas-phase connection hose 8; the ship membrane tank 1 and the onshore liquid cargo membrane tank 10 are connected through a liquid-phase connection hose 9.

[0050] The system further includes a BOG cooling and pressure regulating mechanism, which is used for cooling and pressure regulating the BOG in the onshore liquid cargo membrane tank 10; the BOG cooling and pressure regulating mechanism includes a seawater heat exchanger 5, a cryogenic 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 cryogenic heat exchanger 6 through a pipeline; the outlet of the cryogenic 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 cryogenic heat exchanger 6 and the onshore liquid cargo membrane tank 10; the other inlet of the seawater heat exchanger 5 is connected to a seawater inlet pipeline; the other outlet of the seawater heat exchanger 5 is connected to a seawater outlet pipeline.

[0051] The system further includes a liquid cargo processing mechanism, which is used for subcooling the liquid cargo in the ship membrane tank 1; 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 ship membrane tank 1 through a pipeline; the outlet of the liquid cargo pump 2 is connected to the other inlet of the cryogenic heat exchanger 6 through a pipeline, so that the liquid cargo from the ship membrane tank 1 exchanges heat with the high-temperature BOG from the onshore liquid cargo membrane tank 10; the other outlet of the cryogenic 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 subcooling unit 3 through a pipeline; the discharge port end of the compressor 7 is connected to the inlet of the subcooling unit 3 through a pipeline; the outlet of the subcooling unit 3 is connected to the ship membrane tank 1 through a pipeline; the outlet of the subcooling 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 discharge port end of the compressor 7 is connected to the inlet of the gas-liquid spray cooling tank 4 through a pipeline.

[0052] A spray cooling pipeline 11 and a spray filling pipeline 12 are sequentially arranged from top to bottom at the top inside the ship membrane tank 1; the heights of the spray cooling pipeline 11 and the spray filling pipeline 12 are both higher than the liquid level of the liquid cargo in the ship membrane tank 1.

[0053] The seawater heat exchanger 5 can be a shell-and-tube heat exchanger, a spiral-wound heat exchanger, or a plate heat exchanger; the cryogenic heat exchanger 6 can be a shell-and-tube heat exchanger, a spiral-wound heat exchanger, or a plate heat exchanger.

[0054] The subcooling unit 3 includes a subcooler.

[0055] The liquid cargo is a cryogenic liquid such as liquefied natural gas (LNG) or liquid ammonia (NH3).

[0056] A circulation pump is provided at the bottom of the gas-liquid spray cooling tank 4.

[0057] Embodiment 2

[0058] This embodiment provides a working method for the BOG dynamic balance processing system of the offshore ship and the onshore liquid cargo thin-film tank in Embodiment 1, and the liquid cargo is LNG. The method includes the following steps:

[0059] S1. Preliminary cooling of the temperature at the top inside the onshore liquid cargo thin-film tank 10:

[0060] The compressor 7 extracts the BOG in the onshore liquid cargo thin-film tank 10 for compression to obtain compressed gas, and then enters the seawater heat exchanger 5 to cool the compressed gas to normal temperature. Then it enters the low-temperature heat exchanger 6 to cool 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 thin-film 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 and enter the atmospheric thin-film tank) to further reduce the temperature inside the onshore liquid cargo thin-film tank 10 to -160 °C and the pressure to atmospheric pressure to prepare for the next step of reducing the temperature to a lower level; The ship thin-film 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 thin-film 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 thin-film 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 fed 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 thin-film tank 1;

[0061] S2. Further cooling of the onshore liquid cargo thin-film tank 10, reducing the temperature inside the onshore liquid cargo thin-film tank 10 below -170 °C to prepare for filling the onshore liquid cargo thin-film tank 10 with the liquid cargo from the ship thin-film tank 1:

[0062] The compressor 7 extracts the BOG in the onshore liquid cargo thin-film tank 10 and directly supplies it to the subcooling unit 3. In S1, the subcooling unit 3 cools 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 a low temperature of -160 °C. The BOG cooled to a low temperature (-160 °C) returns to the onshore liquid cargo thin-film tank 10, and the temperature inside the onshore liquid cargo thin-film tank 10 is gradually reduced to about -170 °C through continuous gas-phase circulation, completing the cooling inside the onshore liquid cargo thin-film tank 10 and reaching a subcooled temperature lower than the liquid cargo storage temperature;

[0063] S3. Supercooled liquid cargo is sprayed onto the onshore liquid cargo membrane tank 10:

[0064] A certain amount of supercooled liquid cargo (the re-liquefaction device can supercool the liquid cargo pumped by the liquid cargo pump to -170°C for spraying to reduce the temperature) is sprayed onto the onshore liquid cargo membrane tank 10 to be loaded, so that the film main shielding layer of the onshore liquid cargo membrane tank 10 adapts to the supercooled liquid cargo;

[0065] First, the liquid cargo in the ship's membrane tank 1 is loaded into the gas-liquid spray cooling tank 4 through the liquid cargo pump 2 and temporarily stored. Then, it is sent into the supercooling unit 3 through the circulation pump at the bottom of the gas-liquid spray cooling tank 4 to supercool the liquid cargo (the sprayed liquid cargo is not in the gas phase, and the low-temperature BOG can be pre-cooled to -160°C by circulation. The sprayed liquid cargo is the low-temperature -170°C supercooled liquid cargo 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 supercooled to -170°C, the liquid cargo at -165°C is filled. Among them, -170°C is the supercooling temperature, and -165°C is the normal liquid cargo temperature. Supercooling is to leave a margin of 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;

[0066] S4. Carry out 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.

[0067] Furthermore, 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, including the following process:

[0068] The liquid cargo stored in the ship's thin-film tank 1 is continuously transported into the onshore liquid cargo thin-film tank 10 through the liquid cargo pump 2 and the liquid-phase connection hose 9. The BOG gasified in the onshore liquid cargo thin-film tank 10 and the ship's thin-film tank 1 is evacuated by the compressor 7 (the compression operation is linked to the pressure of the thin-film tank to be filled to ensure that the tank pressure is in the normal pressure state). (When there is no excess BOG generated normally, there is not much gasification. The ship's thin-film tank 1 and the onshore liquid cargo thin-film tank 10 achieve pressure balance through natural gas-phase flow. When additional BOG is generated, it will cause the pressure to rise, and the compressor 7 needs to be started. The BOG gasified in the onshore liquid cargo thin-film tank 10 and the ship's thin-film tank 1 first enters the gas-liquid spray cooling tank 4. The BOG is directly cooled by the supercooled liquid cargo sprayed (the liquid cargo is from a small amount of liquid cargo diverted by the liquid cargo pump 2 during the filling process). The cooled BOG enters the compressor 7. The BOG compressed to 0.65 MPa by the compressor 7 is then mixed with the non-gasified 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 (after that, the liquefied BOG is sent into the ship's thin-film tank 1 and / or the onshore liquid cargo thin-film tank 10), realizing the reliquefaction and recovery of the BOG in this process.)

[0069] 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 skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A BOG dynamic balance processing system for an offshore ship and an onshore liquid cargo membrane tank, characterized in that 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; The system further includes a BOG cooling and pressure regulating mechanism, which is used for cooling and pressure regulating the BOG in the second thin-film tank; The system further includes a liquid cargo processing mechanism, which is used 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 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; 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.

2. The BOG dynamic balance processing system for an offshore ship and an onshore liquid cargo membrane tank according to claim 1, characterized in that, The first thin-film tank and the second thin-film tank are connected by a gas-phase connection hose (8); The first thin-film tank and the second thin-film tank are connected by a liquid-phase connection hose (9).

3. A BOG dynamic balance processing system for an offshore ship and an onshore liquid cargo membrane tank according to claim 1, characterized in that, The first thin-film tank is a ship thin-film tank (1); The second thin-film tank is a land liquid cargo thin-film tank (10).

4. The BOG dynamic balance processing system for an offshore ship and an onshore liquid cargo membrane tank according to claim 1, characterized in that, The second thin-film tank is a ship thin-film tank (1); The first thin-film tank is a land liquid cargo thin-film tank (10).

5. A BOG dynamic balance processing system for an offshore ship and a land liquid cargo membrane tank according to claim 1, characterized in that, 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 dynamic balance processing system for an offshore ship and an onshore liquid cargo membrane tank according to claim 1, wherein, At the top inside the first thin-film tank, a spray cooling pipeline (11) and a spray filling pipeline (12) are arranged from top to bottom in sequence; The heights of the spray cooling pipeline (11) and the spray filling pipeline (12) are both higher than the liquid level of the liquid cargo in the first thin-film tank.

7. A BOG dynamic balance processing system for an offshore ship and an onshore liquid cargo membrane tank according to claim 1, characterized in that, The liquid cargo is liquefied natural gas or liquid ammonia.

Images