Marine liquefied natural gas flash steam liquefaction system and method

Abstract

The invention relates to the technical field of LNG transportation and storage, and discloses a marine liquefied natural gas flash steam liquefaction system which comprises an LNG storage device, a BOG cold compression device, a BOG condenser and a BOG reliquefaction device. Flash steam generated by the LNG storage device is firstly shunted to the BOG reliquefaction device, is pressurized by the flash steam compression mechanism, then enters the subsequent heat exchanger to be subjected to deep cold exchange with a mixed working medium and is liquefied into LNG again to flow back to the storage device, the whole process is smooth in linkage and free of redundant links, and efficient recycling of the flash steam is ensured. A gradual change type screw rod structure and a gap adjusting function in a flash steam compression link can be adapted to complex working conditions such as air inlet pressure and flow fluctuation, and the influence of a marine bumpy environment on equipment operation is reduced; through the collaborative design of lubricating oil circulation and flash steam cooling, the system can still keep a stable and reliable operation state under complex offshore conditions, and efficient and energy-saving liquefaction treatment of flash steam is achieved.

Description

Technical Field

[0001] This invention relates to the field of LNG transportation and storage technology, specifically to a marine liquefied natural gas flash liquefaction system and method. Background Technology

[0002] With the steady increase in liquefied natural gas (LNG) energy consumption, the LNG transportation industry has gradually emerged. LNG is typically liquefied and stored in LNG storage tanks at 0.1 MPa and -162°C. During LNG transportation, due to external heat intrusion and other factors, the LNG in the storage tank vaporizes, generating a large amount of blow-off gas (BOG), causing the pressure inside the tank to rise rapidly. To ensure the safe operation of the LNG storage tank system, BOG gas needs to be discharged to maintain the pressure inside the tank within the allowable range. However, directly discharging BOG gas results in a significant waste of resources. Therefore, a device for recovering and reusing BOG gas is needed to improve resource utilization.

[0003] Existing BOG reliquefaction units often use twin-screw compressors to compress and boost BOG, but this requires frequent maintenance and replacement of the male and female screw rotors, resulting in long downtime and affecting the recovery and liquefaction of BOG.

[0004] Therefore, we provide a marine liquefied natural gas flash liquefaction system and method to solve the above problems. Summary of the Invention

[0005] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a marine liquefied natural gas flash vapor liquefaction system and method, which has the advantages of stable flash vapor compression and high liquefaction recovery efficiency. It solves the problem that the flash vapor compression process requires frequent maintenance and replacement of the male and female screw rotors, resulting in long equipment downtime and affecting the recovery and liquefaction of flash vapor.

[0006] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: A marine liquefied natural gas flash vapor liquefaction system includes an LNG storage unit, a BOG cold compression unit, a BOG condenser, and a BOG reliquefaction unit; the flash vapor generated by the LNG storage unit is processed by the BOG reliquefaction unit and returned to the LNG storage unit. The BOG reliquefaction unit includes a flash vapor compression mechanism, a mixed working fluid storage device, and a heat exchanger. The flash vapor compression mechanism includes an inlet chamber, an adjustment chamber, a compression chamber, a cooling and guiding gas chamber, and a separation oil chamber. The compression chamber is rotatably equipped with a female screw and a male screw for compressing flash vapor. The adjustment chamber is equipped with a hydraulic oil chamber that drives the piston plate of the male screw to move axially, so that the male screw can be axially adjusted relative to the female screw. The groove diameter of the helical tooth groove of the female screw is set as a gradient groove, and the helical teeth of the male screw are set as gradient teeth; The cooling guide gas chamber is equipped with a cooling assembly connected to the male screw drive. The cooling assembly includes a return oil pipe that communicates with the separation oil chamber and the compression chamber. The return oil pipe is equipped with multiple cooling fins for cooling flash vapor.

[0007] Preferably, the piston plate of the male screw is slidably connected to the inner wall of the regulating chamber, the regulating chamber is connected to a first oil port and a second oil port, the piston plate divides the regulating chamber into a first oil chamber and a second oil chamber respectively connected to the first oil port and the second oil port, and the piston plate is rotatably connected to the rotating shaft of the male screw in an anti-detachment manner.

[0008] Preferably, the compression chamber and the cooling exhaust chamber are separated by a partition. The partition is provided with an exhaust pipe that communicates with the compression chamber and the separation oil chamber. The flash vapor compressed by the compression chamber passes through the exhaust pipe, passes through the cooling exhaust chamber, and enters the separation oil chamber. The oil filter in the separation oil chamber filters the flash vapor containing oil, so that the oil is retained in the separation oil chamber. The cooling exhaust chamber is connected to an exhaust port.

[0009] Preferably, the shaft of the male screw is rotatably connected to the partition and extends into the cooling guide air chamber. The shaft of the male screw is provided with a linkage head, and a linkage roller is rotatably connected to the oil filter. The linkage roller is provided with a linkage groove that is slidably connected to the linkage head.

[0010] Preferably, the return oil pipe is connected to the bottom of the oil filter and the baffle, and a spiral blade is rotatably connected inside the return oil pipe. The shaft of the spiral blade is connected to the linkage head via a transmission belt.

[0011] Preferably, the ratio of the shaft diameter of the linkage head to the shaft diameter of the helical blade is 3:1.

[0012] Preferably, the side circumferential array of the oil filter has a plurality of first guide plates, second guide plates, and third guide plates; the plurality of first guide plates, second guide plates, and third guide plates are all arranged in an L-shape.

[0013] Preferably, a plurality of first guide plates, second guide plates, and third guide plates are inclinedly arranged on the oil filter and located in the cooling guide air chamber. The air intake chamber is equipped with a motor that drives the female screw to rotate, and the air intake chamber is also equipped with an air inlet that communicates with the compression chamber.

[0014] Preferably, the cooling assembly further includes a cold end plate installed at the bottom of the cooling outlet air chamber, with multiple cooling fins evenly distributed in an array on the cold end plate, and an air duct formed between each pair of adjacent cooling fins. The oil return pipe passes through multiple cooling fins, and the cold end plate is connected to a hot end plate located outside the cooling outlet air chamber via P and N semiconductors. The oil return pipe is connected to the compression chamber via a connecting pipe.

[0015] A method for a marine liquefied natural gas flash liquefaction system includes the following steps: S1. A large amount of BOG gas is generated in the LNG storage unit. The BOG gas enters the pipeline where the BOG cold compression unit and BOG condenser are located from the gas outlet at the top of the LNG storage unit. The BOG gas after diversion enters the BOG reliquefaction unit. S2. The flash vapor is pressurized by the flash vapor compression mechanism, so that the flash vapor can fully exchange cold energy with the mixed working fluid storage device in the refrigerant heat exchanger, so that the flash vapor gas is cooled down, reliquefied to form LNG and returned to the LNG storage device.

[0016] (III) Beneficial Effects Compared with the prior art, the present invention provides a marine liquefied natural gas flash liquefaction system and method, which has the following beneficial effects: 1. The marine liquefied natural gas flash liquefaction system and method, through the setting of the male screw with gradual teeth and the female screw with gradual grooves, makes the airflow smoother and the operation quieter. From the air inlet to the air outlet, the diameter of the gradual groove gradually decreases and the size of the gradual teeth is synchronously adapted, so that the gas volume is gradually compressed. This avoids the abrupt volume change of traditional constant diameter tooth grooves, greatly reduces pressure pulses and airflow eddies during the compression process, and reduces equipment operating noise and vibration. It is suitable for continuous operation scenarios where the stability of ship navigation is not high. Moreover, the continuous compression chamber formed by the gradual structure can reduce the leakage channels of gas between the teeth and improve volumetric efficiency. At the same time, the smooth airflow transition reduces flow loss and makes adiabatic compression more complete.

[0017] 2. This marine liquefied natural gas flash liquefaction system and method utilizes a design with progressively tapered teeth on the male screw and progressively tapered grooves on the female screw, combined with an axial adjustment structure on the piston plate. This achieves active compensation for tooth clearance, overcoming the drawback of traditional screw compressors where clearance increases after wear. The progressively tapered tooth diameter, combined with axial adjustment, allows the male screw to re-mate with the female screw after wear, precisely offsetting the wear clearance. This improves compression performance and extends the service life of the female and male screws and the entire unit without frequent replacement of core components. Especially in long-term continuous marine BOG reliquefaction, the axial adjustment maintains a reasonable fit clearance between the screw teeth, ensuring stable volumetric efficiency over the long term. It eliminates the need for frequent replacement of worn rotors, reducing the procurement cost of core components and the time cost of downtime for replacement.

[0018] 3. The shipboard liquefied natural gas flash liquefaction system and method achieves dual cooling effects through a cooling assembly linked to a male screw, which cools the flash vapor and circulates the lubricating oil. In terms of flash vapor cooling, after the compressed flash vapor enters the cooling guide chamber through the exhaust pipe, it forms a vortex fluid motion under the guidance of the L-shaped guide plate arranged at an incline on the side of the oil filter, which greatly extends the contact time between the flash vapor and the cooling fins. At the same time, the cooling fins arranged at equal intervals on the cold end plate of the cooling assembly form a dense air channel. When the vortex-shaped flash vapor flows through the air channel, it fully exchanges heat with the low-temperature fins to achieve rapid cooling, providing a pre-guarantee for the deep liquefaction of the subsequent heat exchanger and significantly improving the overall liquefaction efficiency. Regarding the lubrication and protection of the male and female screws, the oil filter first efficiently filters the oil-containing flash vapor, and the separated lubricating oil is stored in the separation oil tank. The shaft of the male screw drives the spiral blades in the oil return pipe to rotate through the transmission action of the linkage head, linkage roller and transmission belt, and circulates the filtered lubricating oil back to the compression chamber to provide continuous lubrication for the male and female screws. Since the oil return pipe runs through the cooling fins, the low temperature pipe wall will simultaneously cool the circulating lubricating oil, forming a cold circulation lubrication effect, avoiding the impact of high temperature oil on the screw working efficiency, effectively reducing component wear, and further ensuring the stable operation of the compression mechanism. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the marine liquefied natural gas flash liquefaction system of the present invention.

[0020] Figure 2 This is a schematic diagram of the flash vapor compression mechanism of the present invention.

[0021] Figure 3 This is a cross-sectional view of the flash vapor compression mechanism of the present invention.

[0022] Figure 4 This is a schematic cross-sectional view of the flash vapor compression mechanism of the present invention from another perspective.

[0023] Figure 5This is a schematic diagram of the male and female screw structures of the present invention.

[0024] Figure 6 This is a schematic diagram of the male screw, the linkage roller, and the spiral blades of the present invention.

[0025] Figure 7 This is a schematic diagram of the oil filter structure of the present invention.

[0026] Figure 8 This is a schematic diagram of the cooling component structure of the present invention.

[0027] In the picture: 1. Flash vapor compression mechanism; 101. Gas outlet; 2. Motor; 201. Air inlet; 3. Regulating compartment; 301. First oil port; 302. Second oil port; 4. Compression chamber; 5. Partition; 501. Exhaust pipe; 6. Cooling and diverting airflow out of the air chamber; 7. Oil filter; 701. Linkage roller; 702. Linkage groove; 703. First guide plate; 704. Second guide plate; 705. Third guide plate; 8. Separate the oil tank; 9. Oil return pipe; 901. Cooling fins; 9011. Air duct; 902. Spiral blades; 903. Cold end plate; 904. Hot end plate; 10. Connecting pipe; 11. Female screw; 1101. Gradient groove; 12. Male screw; 1201. Piston plate; 1202. Gradient teeth; 1203. Linkage head; 13. LNG storage unit; 14. BOG cold compression unit; 15. BOG condenser; 16. BOG reliquefaction unit; 17. Mixed working fluid storage unit; 18. Heat exchanger. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] In the description of this invention, it should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0030] In addition, a fixed connection refers to a connection in which parts or components are fixed and there is no relative movement; a transmission connection refers to a connection in which mechanical motion or torque is transmitted to other working parts through a transmission component; a sliding connection refers to a connection in which two objects are in contact but not fixed and can slide relative to each other; and a rotational connection refers to a connection in which two objects are in contact but not fixed and can rotate relative to each other.

[0031] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0032] This embodiment provides a marine liquefied natural gas flash liquefaction system and method, which has the following technical features.

[0033] Please see Figures 1 to 8 A marine liquefied natural gas flash vapor liquefaction system includes an LNG storage unit 13, a BOG cold compression unit 14, a BOG condenser 15, and a BOG reliquefaction unit 16; the flash vapor generated by the LNG storage unit 13 is processed by the BOG reliquefaction unit 16 and returned to the LNG storage unit 13. The BOG reliquefaction unit 16 includes a flash vapor compression mechanism 1, a mixed working fluid storage device 17, and a heat exchanger 18. The flash vapor compression mechanism 1 includes an air inlet chamber, an adjustment chamber 3, a compression chamber 4, a cooling and guiding air outlet chamber 6, and a separation oil chamber 8. The compression chamber 4 is rotatably equipped with a female screw 11 and a male screw 12 for compressing flash vapor. The adjustment chamber 3 is equipped with a hydraulic oil chamber that drives the piston plate 1201 of the male screw 12 to move axially, so that the male screw 12 can be axially adjusted relative to the female screw 11. The groove diameter of the helical tooth groove of the female screw 11 is set as a gradient groove 1101, and the helical tooth of the male screw 12 is set as a gradient tooth 1202. The cooling guide gas chamber 6 is equipped with a cooling assembly that is drivenly connected to the male screw 12. The cooling assembly includes a return oil pipe 9 that is connected to the separation oil chamber 8 and the compression chamber 4. The return oil pipe 9 is equipped with a plurality of cooling fins 901 for cooling flash vapor.

[0034] The piston plate 1201 of the male screw 12 is slidably connected to the inner wall of the regulating chamber 3. The regulating chamber 3 is connected to the first oil port 301 and the second oil port 302. The piston plate 1201 divides the regulating chamber 3 into a first oil chamber and a second oil chamber that are respectively connected to the first oil port 301 and the second oil port 302. The piston plate 1201 is rotatably connected to the rotating shaft of the male screw 12 in an anti-detachment manner.

[0035] The compression chamber 4 and the cooling exhaust chamber 6 are separated by a partition 5. The partition 5 is equipped with an exhaust pipe 501 that connects to the compression chamber 4 and the separation oil chamber 8. The flash vapor compressed by the compression chamber 4 passes through the exhaust pipe 501, passes through the cooling exhaust chamber 6, and enters the separation oil chamber 8. The oil filter 7 of the separation oil chamber 8 filters the flash vapor containing oil, so that the oil is retained in the separation oil chamber 8. The cooling exhaust chamber 6 is connected to an exhaust port 101.

[0036] The rotating shaft of the male screw 12 is rotatably connected to the partition plate 5 and extends into the cooling guide air chamber 6. The rotating shaft of the male screw 12 is provided with a linkage head 1203. A linkage roller 701 is rotatably connected to the oil filter 7. A linkage groove 702 is opened on the linkage roller 701 and is slidably connected to the linkage head 1203.

[0037] The return oil pipe 9 is connected to the bottom of the oil filter 7 and the baffle 5. A spiral blade 902 is rotatably connected inside the return oil pipe 9. The shaft of the spiral blade 902 is connected to the linkage roller 701 via a transmission belt.

[0038] The ratio of the shaft diameter of the linkage roller 701 to the shaft diameter of the spiral blade 902 is 3:1.

[0039] The side circumferential array of the oil filter 7 has multiple first guide plates 703, second guide plates 704, and third guide plates 705; all of the multiple first guide plates 703, second guide plates 704, and third guide plates 705 are arranged in an L-shape.

[0040] Multiple first guide plates 703, second guide plates 704, and third guide plates 705 are inclinedly arranged on the oil filter 7 and located in the cooling guide air chamber 6. The air intake chamber is equipped with a motor 2 that drives the female screw 11 to rotate, and the air intake chamber is also equipped with an air inlet 201 that communicates with the compression chamber 4.

[0041] The cooling assembly also includes a cold end plate 903 installed at the bottom of the cooling exhaust chamber 6. Multiple cooling fins 901 are evenly distributed in an array on the cold end plate 903. An air duct 9011 is formed between each pair of adjacent cooling fins 901. The oil return pipe 9 passes through multiple cooling fins 901. The cold end plate 903 is connected to a hot end plate 904 located outside the cooling exhaust chamber 6 via P and N semiconductors. The oil return pipe 9 is connected to the compression chamber 4 via a connecting pipe 10.

[0042] A method for a marine liquefied natural gas flash liquefaction system includes the following steps: S1. A large amount of BOG gas is generated in the LNG storage unit 13. The BOG gas enters the pipeline where the BOG cold compression unit 14 and BOG condenser 15 are located from the gas outlet at the top of the LNG storage unit 13. The BOG gas after diversion enters the BOG reliquefaction unit 16. S2. The flash vapor is pressurized by the flash vapor compression mechanism 1, so that the flash vapor can fully exchange cold energy with the mixed working fluid storage device 17 in the refrigerant heat exchanger 18, so that the flash vapor gas is cooled down, reliquefied to form LNG and returned to the LNG storage device 13.

[0043] Working principle: Under the influence of external heat, a large amount of BOG gas is generated inside the LNG storage unit 13, such as... Figure 1 As shown, BOG gas enters the pressurized delivery pipeline containing the BOG compression unit 14 and BOG condenser 15 from the top outlet of the LNG storage unit 13. The diverted BOG gas then enters the BOG reliquefaction unit 16. In the flash vapor compression mechanism 1 and the multi-stage regenerative heat exchanger, the BOG gas fully exchanges heat with the mixed working fluid storage device 17 in the refrigerant heat exchanger 18, causing the BOG gas to cool down and reliquefy to form LNG. After being diverted, the BOG gas enters the BOG reliquefaction unit 16 and first enters the flash vapor compression mechanism 1 for pressurization. During this process, the motor 2 drives the female screw 11 and the male screw 12 to rotate, so that the compression chamber 4 compresses the flash vapor. The compressed flash vapor enters the separation oil chamber 8 through the exhaust pipe 501. The flash vapor containing oil is filtered and separated by the oil filter 7, so that the oil is retained in the separation oil chamber 8. The filtered flash vapor is guided by the L-shaped first guide plate 703, second guide plate 704 and third guide plate 705 inclined on the oil filter 7, and forms a vortex fluid motion in the cooling guide gas chamber 6. Meanwhile, the controller controls the operation of P and N semiconductors in the cooling assembly. According to the Peltier effect, the cooling fins 901 and oil return pipe 9 on the cold end plate 903 are in a low temperature state. When the vortex flash vapor fluid formed in the cooling guide chamber 6 flows through the air duct 9011, it is cooled by the cooling fins 901 and then discharged to the subsequent heat exchanger process through the outlet 101, thereby increasing the cooling rate of the flash vapor and thus improving the efficiency of flash vapor reliquefaction into LNG. At the same time, the linkage head 1203 of the male screw 12 drives the spiral blade 902 to rotate through the linkage roller 701, so that the spiral blade 902 transports the oil in the separation oil tank 8 back to the compression tank 4 to supply the female screw 11 and the male screw 12 for lubrication. During this process, the pipe wall of the return oil pipe 9 at low temperature cools the oil transported in the tank, so that the oil circulating into the compression tank 4 is effectively cooled, which plays a cold circulation treatment effect on the lubricating oil of the female screw 11 and the male screw 12, ensuring the working efficiency of the female screw 11 and the male screw 12. When the helical teeth of the female screw 11 and the male screw 12 wear, oil injection / extraction operations are performed at the first oil port 301 and the second oil port 302. This causes the piston plate 1201 to drive the male screw 12 to perform axial displacement adjustment within the compression chamber 4, thereby adjusting and compensating for the fit clearance between the helical teeth of the male screw 12 and the helical teeth of the female screw 11. This eliminates the need for equipment shutdown and cumbersome disassembly and replacement of parts, ensuring equipment operating efficiency and the service life of parts.

[0044] In summary, the marine LNG flash vapor liquefaction system and method optimizes the flash vapor compression process and maintains a reasonable clearance between the screw teeth through axial adjustment, avoiding the widening of the clearance due to wear. This ensures stable volumetric efficiency over the long term and reduces energy waste caused by gas leakage. The energy-saving effect is particularly significant in long-term continuous operation scenarios (such as LNG BOG processing). The gradually changing tooth diameter can adapt to the gas volume changes in different compression stages, making the airflow transition during intake, compression, and exhaust processes smoother and reducing pressure pulses and vibrations.

[0045] When fluctuations in operating conditions (such as inlet pressure and gas flow) cause uneven stress on the screw teeth and localized wear, the clearance can be flexibly adjusted through axial adjustment to avoid problems such as jamming and abnormal noise caused by excessively large or small local clearances. This allows the equipment to operate stably under complex operating conditions without the need for frequent replacement of worn rotors, reducing the procurement cost of core components and the time cost of downtime for replacement. Especially for large screw compressors (such as marine BOG processing units), where rotor replacement costs are high and cycles are long, this design can significantly reduce maintenance pressure. Axial adjustment is simple to operate, requiring no complicated disassembly procedures, and clearance adjustment can be completed online or quickly, further reducing maintenance workload and downtime losses.

[0046] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0047] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A marine liquefied natural gas flash liquefaction system, characterized in that, It includes an LNG storage unit (13), a BOG cold compression unit (14), a BOG condenser (15), and a BOG reliquefaction unit (16); the flash vapor generated by the LNG storage unit (13) is processed by the BOG reliquefaction unit (16) and returned to the LNG storage unit (13); The BOG reliquefaction unit (16) includes a flash vapor compression mechanism (1), a mixed working fluid storage device (17), and a heat exchanger (18). The flash vapor compression mechanism (1) includes an air inlet chamber, a regulating chamber (3), a compression chamber (4), a cooling guide gas chamber (6), and a separation oil chamber (8). The compression chamber (4) is rotatably equipped with a female screw (11) and a male screw (12) for compressing flash vapor. The regulating chamber (3) is equipped with a hydraulic oil chamber that drives the piston plate (1201) of the male screw (12) to move axially, so that the male screw (12) can be axially adjusted relative to the female screw (11). The groove diameter of the helical tooth groove of the female screw (11) is set as a gradient groove (1101), and the helical tooth of the male screw (12) is set as a gradient tooth (1202). The cooling guide gas chamber (6) is equipped with a cooling assembly that is connected to the male screw (12) for transmission. The cooling assembly includes an oil return pipe (9) that is connected to the separation oil chamber (8) and the compression chamber (4). The oil return pipe (9) is equipped with multiple cooling fins (901) for cooling flash vapor.

2. The marine liquefied natural gas flash liquefaction system according to claim 1, characterized in that, The piston plate (1201) of the male screw (12) is slidably connected to the inner wall of the regulating chamber (3). The regulating chamber (3) is connected to a first oil port (301) and a second oil port (302). The piston plate (1201) divides the regulating chamber (3) into a first oil chamber and a second oil chamber that are respectively connected to the first oil port (301) and the second oil port (302). The piston plate (1201) is rotatably connected to the rotating shaft of the male screw (12) in an anti-detachment manner.

3. A marine liquefied natural gas flash liquefaction system according to claim 2, characterized in that, The compression chamber (4) and the cooling exhaust chamber (6) are separated by a partition (5). The partition (5) is provided with an exhaust pipe (501) that communicates with the compression chamber (4) and the separation oil chamber (8). The flash vapor compressed by the compression chamber (4) passes through the exhaust pipe (501) and enters the separation oil chamber (8) after passing through the cooling exhaust chamber (6). The oil filter (7) of the separation oil chamber (8) filters the flash vapor containing oil, so that the oil is retained in the separation oil chamber (8). The cooling exhaust chamber (6) is connected to an exhaust port (101).

4. A marine liquefied natural gas flash liquefaction system according to claim 3, characterized in that, The shaft of the male screw (12) is rotatably connected to the partition plate (5) and extends into the cooling guide air chamber (6). The shaft of the male screw (12) is provided with a linkage head (1203). A linkage roller (701) is rotatably connected to the oil filter (7). A linkage groove (702) is opened on the linkage roller (701) and is slidably connected to the linkage head (1203).

5. A marine liquefied natural gas flash liquefaction system according to claim 4, characterized in that, The return oil pipe (9) is connected to the bottom of the oil filter (7) and the baffle (5). A spiral blade (902) is rotatably connected inside the return oil pipe (9). The rotating shaft of the spiral blade (902) is connected to the linkage roller (701) via a transmission belt.

6. A marine liquefied natural gas flash liquefaction system according to claim 5, characterized in that, The ratio of the shaft diameter of the linkage roller (701) to the shaft diameter of the spiral blade (902) is 3:

1.

7. A marine liquefied natural gas flash liquefaction system according to claim 4, characterized in that, The oil filter (7) has a side circumferential array with multiple first guide plates (703), second guide plates (704), and third guide plates (705); the multiple first guide plates (703), second guide plates (704), and third guide plates (705) are all arranged in an L-shape.

8. A marine liquefied natural gas flash liquefaction system according to claim 7, characterized in that, Multiple first guide plates (703), second guide plates (704), and third guide plates (705) are inclinedly arranged on the oil filter (7) and located in the cooling guide air chamber (6). The air chamber is equipped with a motor (2) that drives the female screw (11) to rotate. The air chamber is also equipped with an air inlet (201) that communicates with the compression chamber (4).

9. A marine liquefied natural gas flash liquefaction system according to claim 8, characterized in that, The cooling assembly also includes a cold end plate (903) installed at the bottom of the cooling exhaust chamber (6), multiple cooling fins (901) are evenly distributed on the cold end plate (903), and an air duct (9011) is formed between each two adjacent cooling fins (901). The oil return pipe (9) passes through multiple cooling fins (901). The cold end plate (903) is connected to a hot end plate (904) located outside the cooling exhaust chamber (6) through P and N semiconductors. The oil return pipe (9) is connected to the compression chamber (4) through a connecting pipe (10).

10. A method for a marine liquefied natural gas flash liquefaction system, applied to the marine liquefied natural gas flash liquefaction system according to any one of claims 1-9, characterized in that, Includes the following steps: S1. A large amount of BOG gas is generated in the LNG storage unit (13). The BOG gas enters the pipeline where the BOG cold compression unit (14) and BOG condenser (15) are located from the gas outlet at the top of the LNG storage unit (13). The BOG gas after diversion enters the BOG reliquefaction unit (16). S2. The flash vapor is pressurized by the flash vapor compression mechanism (1) so that the flash vapor can fully exchange cold energy with the mixed working fluid storage device (17) in the refrigerant heat exchanger (18), so that the flash vapor gas is cooled down, reliquefied to form LNG and returned to the LNG storage device (13).

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