LNG flash steam recovery method and system

Abstract

The present invention provides an LNG flash steam recovery method and system, the LNG flash steam recovery system comprises an LNG storage tank, a refrigeration cycle flow path and a recovery flow path; the refrigeration cycle flow path comprises a first compressor, a first heat exchanger, a second heat exchanger, a third heat exchanger, a fourth heat exchanger, a fifth heat exchanger, and a sixth heat exchanger, a first-stage expander, a second-stage expander, a control valve, a low-pressure pipeline and a high-pressure pipeline; the recovery flow path comprises a CH 4 Distillation tower, N 2 Condensation tower, H 2 Condensation tower, I-stage cryogenic adsorber, II-stage cryogenic adsorber, He collection pipe, first gas pipeline, second gas pipeline, third gas pipeline and fourth gas pipeline. In the present invention, the LNG flash steam generated in the LNG storage tank enters the recovery flow path and is cooled step by step through the refrigeration cycle flow path, and then can be successively cooled in CH 4 Distillation tower, N 2 Condensation tower, H 2 High-purity CH is separated from the condensation tower. 4 、N 2 , H 2 , and finally obtain He with high recovery rate and high purity.

Description

Technical Field

[0001] The invention relates to LNG flash steam processing, and in particular to an LNG flash steam recovery method and system. Background Art

[0002] Helium has become one of the important gases indispensable for the development of national defense, military industry and high technology due to its special properties such as extremely low boiling point, density, strong chemical and radioactive inertness. It plays an irreplaceable role in national defense, industry, science and technology fields such as aerospace, nuclear weapons, submarines, saturation diving operations, nuclear magnetic resonance, semiconductors, mobile phones, LCD screens, optical fibers, and large scientific facilities.

[0003] The content of helium in air is only 5ppm, and it mainly exists in natural gas, so the production of helium comes almost entirely from natural gas.

[0004] At present, in order to facilitate storage and transportation, natural gas is usually mined by cryogenic methods to obtain LNG. In the production process of LNG, flash steam, or BOG, will be generated in storage tanks and loading stations. Under normal pressure, the liquefaction temperatures of methane, nitrogen, hydrogen, and helium are -162°C, -196°C, -253°C, and 268.65°C, respectively. Under tank pressure, helium, hydrogen, and nitrogen will evaporate from LNG. In addition, due to the heat exchange between the tank wall and the external environment, some methane will also be vaporized. In order to reduce energy consumption, the LNG production process will have a special recovery process to recover BOG gas. The BOG gas is first compressed to high pressure ( Figure 1 ), and then part of it is used as the regeneration gas of the molecular sieve adsorption tower, and part of it enters the cold box to be re-liquefied into LNG. After multiple cycles, the helium and nitrogen in BOG are continuously concentrated, and the final helium content can be as high as 3%, which is fully worth the industrial development of purified helium.

[0005] With the rapid development and widespread application of the LNG industry, the number of LNG plants in China is increasing, and the amount of BOG waste gas generated in the plants is also increasing. Therefore, the use of new processes to extract helium from BOG in LNG production is a good way to economically extract helium from natural gas that is suitable for my country's national conditions.

[0006] In addition, for LNG plants where the nitrogen molar fraction in the raw gas exceeds 1%, the BOG gas generated in the storage tanks and loading stations re-enters the process of recovering LNG, which easily leads to the accumulation of nitrogen content in the system. The higher the nitrogen content in natural gas, the more difficult it is to liquefy natural gas, and the higher the power consumption of the liquefaction process. Therefore, when separating and purifying helium from BOG, the nitrogen in BOG must also be separated. Summary of the invention

[0007] The embodiment of the present invention relates to an LNG flash steam recovery system, which can comprehensively recover helium, methane and nitrogen from LNG flash steam, has high recovery efficiency and high recovery purity, adopts a simple refrigeration cycle system, and is easy to operate and maintain, thereby solving the problems of difficult gas separation, low recovery efficiency and low purity in BOG waste gas treatment in the prior art.

[0008] An embodiment of the present invention provides an LNG flash vapor recovery system, comprising an LNG storage tank, a refrigeration cycle flow path and a recovery flow path;

[0009] The refrigeration cycle flow circuit includes a first compressor, a first heat exchanger, a second heat exchanger, a third heat exchanger, a fourth heat exchanger, a fifth heat exchanger, a sixth heat exchanger, a first-stage expander, a second-stage expander, a control valve, a low-pressure pipeline and a high-pressure pipeline, the high-pressure outlet of the first compressor is sequentially connected to the first heat exchanger, the second heat exchanger, the third heat exchanger, the fourth heat exchanger, the first-stage expander, the fifth heat exchanger and the second-stage expander through the high-pressure pipeline, and the low-pressure outlet of the second-stage expander is sequentially connected to the sixth heat exchanger, the fifth heat exchanger, the fourth heat exchanger, the third heat exchanger, the second heat exchanger, the first heat exchanger and the low-pressure inlet of the first compressor through the low-pressure pipeline;

[0010] The recovery flow path includes a CH4 distillation tower, an N2 condensation tower, an H2 condensation tower, a He collection pipe, a stage I cryogenic adsorber, a stage II cryogenic adsorber, a first air guide pipeline, a second air guide pipeline, a third air guide pipeline and a fourth air guide pipeline; the gas outlet of the LNG storage tank is connected to the gas inlet of the CH4 distillation tower along the first air guide pipeline through the second compressor, the first heat exchanger and the second heat exchanger in sequence, the gas outlet of the distillation tower is connected to the third heat exchanger and the gas inlet of the N2 condensation tower in sequence through the second air guide pipeline, the gas outlet of the N2 condensation tower is connected to the stage I cryogenic adsorber, the fourth heat exchanger, the fifth heat exchanger and the H2 condensation tower in sequence through the third air guide pipeline, and the gas outlet of the H2 condensation tower is connected to the sixth heat exchanger, the stage II cryogenic adsorber and the He collection pipe in sequence through the fourth air guide pipeline.

[0011] As one of the embodiments, the recovery flow path further includes a reboiler and a heating branch;

[0012] The air inlet of the heating branch is connected to the air outlet of the first heat exchanger, and the air outlet of the heating branch is connected to the air inlet of the second heat exchanger, and a first regulating valve is arranged between the air outlet of the first heat exchanger and the air inlet of the second heat exchanger, the reboiler is connected in series to the heating branch, and a second regulating valve is arranged on the air inlet pipeline of the heating branch.

[0013] As one of the embodiments, there are two groups of stage I low-temperature adsorbers, and the two groups of stage I low-temperature adsorbers are connected in parallel, and the two groups of stage I low-temperature adsorbers switch to work, one group adsorbs, and the other group regenerates; there are two groups of stage II low-temperature adsorbers, and the two groups of stage II low-temperature adsorbers are connected in parallel, and the two groups of stage II low-temperature adsorbers switch to work, one group adsorbs, and the other group regenerates.

[0014] As one of the embodiments, the He collecting pipe is sequentially connected to the sixth heat exchanger, the fifth heat exchanger, the fourth heat exchanger, the third heat exchanger, the second heat exchanger and the first heat exchanger.

[0015] As one of the embodiments, it also includes a cold box, on which a high-pressure pipeline interface, a low-pressure pipeline interface, a CH4 interface, an N2 interface, an H2 interface, a He collecting pipe interface and a first gas guiding pipeline interface are provided, and the first heat exchanger, the second heat exchanger, the third heat exchanger, the fourth heat exchanger, the fifth heat exchanger, the sixth heat exchanger, the first-stage expander, the second-stage expander, the low-pressure pipeline, the high-pressure pipeline and the recovery flow path are all located in the cold box; and the high-pressure pipeline is connected to the high-pressure outlet of the first compressor through the high-pressure pipeline interface, the low-pressure pipeline is connected to the low-pressure inlet of the first compressor through the low-pressure pipeline interface, the first gas guiding pipeline is connected to the outlet of the second compressor through the first gas guiding pipeline interface, the CH4 interface is connected to the CH4 outlet of the CH4 distillation tower, the N2 interface is connected to the N2 outlet of the N2 condensation tower, the H2 interface is connected to the H2 outlet of the H2 condensation tower, and the He collecting pipe interface is connected to the outlet of the He collecting pipe.

[0016] As one of the embodiments, it also includes a He storage tank, which is connected to the low-pressure inlet of the first compressor, and a control valve is provided on the flow path between the two.

[0017] The embodiment of the present invention also provides a method for recovering LNG flash steam, wherein the LNG flash steam in the LNG storage tank enters a recovery flow path after being compressed;

[0018] The LNG flash steam entering the recovery flow path is sequentially heat exchanged and cooled through multiple heat exchangers on the refrigeration cycle flow path; the recovery flow path is sequentially provided with a CH4 distillation tower, an N2 condensation tower, an H2 condensation tower, and a He collection pipe along the flow direction of the LNG flash steam, and CH4 in the LNG flash steam is separated in the CH4 distillation tower, N2 is separated in the N2 condensation tower, and H2 is separated in the H2 condensation tower, and the remaining He enters the He collection pipe.

[0019] The embodiments of the present invention have at least the following beneficial effects:

[0020] In the recovery system provided by the present invention, the LNG flash steam generated in the LNG storage tank enters the recovery flow path and is gradually cooled down through the refrigeration circulation flow path, so that high-purity CH4, N2, and H2 can be separated in the CH4 distillation tower, N2 condensation tower, and H2 condensation tower in sequence, and the remaining He in the LNG flash steam is collected by a He collection pipe, so that a very high-purity helium product can be obtained. In addition, the recovery rate of CH4, N2, and H2 in the LNG flash steam is also very high. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 Production process for traditional LNG plants;

[0023] Figure 2 A schematic structural diagram of an LNG flash steam recovery system provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] See also Figure 2 An embodiment of the present invention provides an LNG flash steam recovery system, including an LNG storage tank 1, a refrigeration circulation flow path 2 and a recovery flow path 3, wherein the refrigeration circulation flow path 2 is used to generate cold energy and exchange heat with the recovery flow path 3, and the recovery flow path 3 can recover the LNG flash steam generated in the LNG storage tank 1 in sequence.

[0026] Specifically, the refrigeration circulation flow circuit 2 includes a first compressor 21, a first heat exchanger 29, a second heat exchanger 22, a third heat exchanger 23, a fourth heat exchanger 24, a turbine inlet control valve 28, a first expansion machine 25, a fifth heat exchanger 211, a second expansion machine 210, a low-pressure pipeline 26 and a high-pressure pipeline 213. The high-pressure outlet of the first compressor 21 is connected to the first heat exchanger 29, the second heat exchanger 22, the third heat exchanger 23, the fourth heat exchanger 24, the turbine inlet control valve 28, the first expansion machine 25, the fifth heat exchanger 211, and the second expansion machine 210 in sequence through the high-pressure pipeline 213; the low-pressure outlet of the second expansion machine 210 is connected to the sixth heat exchanger 212, the fifth heat exchanger 211, the fourth heat exchanger 24, the third heat exchanger 23, the second heat exchanger 22, the first heat exchanger 29 and the low-pressure inlet of the first compressor 21 in sequence through the low-pressure pipeline 26. The circulating working fluid of the refrigeration circulation circuit 2 can be helium. Specifically, the refrigeration circulation circuit 2 is connected to the He storage tank 4. The helium stored in the He storage tank 4 enters the refrigeration circulation circuit 2, and is compressed by the first compressor 21 to form high-pressure helium, which enters the high-pressure pipeline 213. The helium discharged from the first compressor 21 should usually be deoiled by an oil separator 27, and flows through the first heat exchanger 29, the second heat exchanger 22, the third heat exchanger 23 and the fourth heat exchanger 24 in sequence through the high-pressure pipeline 213. The helium adiabatically expanded to low pressure and low temperature by the first expansion machine 25 enters the fifth heat exchanger 211, and then adiabatically expanded to lower pressure and lower temperature by the second expansion machine 210 enters the low-pressure pipeline 26. The low-pressure and low-temperature helium is then It flows along the low-pressure pipeline 26 in sequence through the sixth heat exchanger 212, the fifth heat exchanger 211, the fourth heat exchanger 24, the third heat exchanger 23, the second heat exchanger 22 and the first heat exchanger 29, and is compressed in the first compressor 21, thereby forming a circulation process of helium. In this process, the heat exchange temperature of the first heat exchanger 29 is higher than the heat exchange temperature of the second heat exchanger 22, the heat exchange temperature of the second heat exchanger 22 is higher than the heat exchange temperature of the third heat exchanger 23, the heat exchange temperature of the third heat exchanger 23 is higher than the heat exchange temperature of the fourth heat exchanger 24, the heat exchange temperature of the fourth heat exchanger 24 is higher than the heat exchange temperature of the fifth heat exchanger 211, and the heat exchange temperature of the fifth heat exchanger 211 is higher than the heat exchange temperature of the sixth heat exchanger 212, that is, multi-stage heat exchange and cooling can be achieved. A regulating valve 28 is provided on the inlet side of the high-pressure pipeline 213 corresponding to the first-stage expansion machine 25, which can adjust the amount of expansion gas entering the first-stage expansion machine 25. A turbine expander can be used for the first-stage expansion machine 25 and the second-stage expansion machine 210. Then, the entire refrigeration cycle flow path 2 is a turbine-reverse Brayton refrigeration cycle. The first-stage expansion machine 25 and the second-stage expansion machine 210 are refrigeration components with high refrigeration efficiency and large refrigeration capacity. The refrigeration cycle system is simple and easy to operate and maintain.

[0027] The recovery flow path 3 includes a CH4 distillation tower 31, an N2 condensation tower 32, an H2 condensation tower 33, a He collection pipe 34, a first gas guide pipeline 35, a second gas guide pipeline 36, a third gas guide pipeline 37 and a fourth gas guide pipeline 322. The gas outlet of the LNG storage tank 1 is connected to the gas inlet of the CH4 distillation tower 31 through the second compressor 11 and the first gas guide pipeline 35 in sequence, the gas outlet of the CH4 distillation tower 31 is connected to the gas inlet of the N2 condensation tower 32 through the second gas guide pipeline 36, the gas outlet of the N2 condensation tower 32 is connected to the gas inlet of the H2 condensation tower 33 through the third gas guide pipeline 37, and the gas outlet of the H2 condensation tower 33 is connected to the He collection pipe 34 through the fourth gas guide pipeline 322. The LNG flash steam volatilized in the LNG storage tank 1 is reheated to room temperature and then pressurized by the second compressor 11, and then deoiled by an oil separator 12. The deoiled LNG flash steam enters the CH4 distillation tower 31, the N2 condensation tower 32, the I-stage cryogenic adsorber 316, the H2 condensation tower 33, the II-stage cryogenic adsorber 320, and the He collection pipe 34 in sequence. Of course, in this process, the temperature should be gradually reduced through the refrigeration circulation flow path 2, so that CH4, N2, and H2 in the LNG flash steam can be separated in sequence. 2， High-purity He is obtained. Of course, the separated CH4, N2, and He can be collected by the refrigeration circulation flow path 2 to recycle the cold energy, and the separated H2 can be led to the flare vent pipe.

[0028] Specifically, the LNG flash steam in the first gas pipeline 35 is cooled by heat exchange through the first heat exchanger 29 and the second heat exchanger 22. The cooled LNG flash steam enters the distillation tower 31 for distillation. Specifically, a condenser 38 is arranged at the top of the distillation tower 31. The cooling capacity of the condenser 38 can be provided by liquid nitrogen or a separate nitrogen refrigerator, so that the CH4 in the LNG flash steam can be separated in liquid form to the bottom of the CH4 distillation tower 31, and the remaining N2, He and H2 in the LNG flash steam are discharged from the top. The purity of the liquid CH4 collected by the distillation tower 31 reaches more than 99%.

[0029] In a preferred embodiment, a reboiler 39 is provided at the bottom of the distillation tower 31, and the cold energy of CH4 can be recovered through the reboiler 39. Specifically, the recovery flow path 3 also includes a heating branch 310, and the LNG flash steam in the first air guide pipeline 35 first enters the first heat exchanger 29 for heat exchange and cooling, and then enters the second heat exchanger 22 for heat exchange and cooling, and enters the distillation tower 31 through a regulating valve 312; the air inlet and the air outlet of the heating branch 310 are both connected to the first air guide pipeline 35, and the above-mentioned reboiler 39 is connected in series to the heating branch 310, specifically, the air inlet of the heating branch 310 is connected to the air outlet of the first heat exchanger 29, and the air outlet of the heating branch 310 is connected to the first air guide pipeline 35, and the flow path between the second heat exchanger 22 and the first heat exchanger 29, and a first regulating valve 311 is arranged on the flow path, and a second regulating valve 312 is arranged on the heating branch 310, and the second regulating valve 312 is located on the flow path between the air inlet of the heating branch 310 and the reboiler 39. In this embodiment, a part of the LNG flash steam after heat exchange in the first heat exchanger 29 can continue to enter the CH4 distillation tower 31 along the first gas pipeline 35, and a part of it can enter the heating branch 310. The LNG flash steam entering the heating branch 310 exchanges heat with the liquid CH4 in the CH4 distillation tower 31 at the reboiler 39, and the evaporation latent heat of the liquid CH4 in the reboiler can be used to precool the LNG flash steam in the heating branch 310. The LNG flash steam continues to enter the first gas pipeline 35 along the heating branch 310. And by adjusting the opening of the first regulating valve 311 and the second regulating valve 312, the flow of the corresponding flow path can be controlled to achieve the purpose of controlling the heating amount of the reboiler 39. In addition, the CH4 separated in the CH4 distillation tower 31 is first throttled and expanded by a throttling valve 313, and then sequentially passes through the second heat exchanger 22 and the first heat exchanger 29 to recover cold energy, and is finally collected by the LNG liquefaction system.

[0030] Furthermore, the mixed gas (N2, He and H2 remaining in the LNG flash steam) discharged from the top of the CH4 distillation tower 31 is connected to the air inlet of the N2 condensation tower 32 through the second gas pipeline 36, that is, the mixed gas is introduced into the N2 condensation tower 32 to separate the N2. Of course, a throttle valve 314 should be provided on the second gas pipeline 36 to control the pressure. The mixed gas in the second gas pipeline 36 first passes through the third heat exchanger 23 for heat exchange and temperature reduction to 65K, so that the mixed gas becomes a gas-liquid two-phase mixture, wherein the liquid is liquid N2, which is separated after entering the N2 condensation tower 32, and its purity can also reach more than 99%, and the remaining mixed gas is discharged from the top of the N2 condensation tower 32. The separated liquid N2 is also expanded through a throttle valve 315 and then passes through the third heat exchanger 23, the second heat exchanger 22 and the first heat exchanger 29 in sequence to recover cold energy, and can provide cold energy to the condenser in the distillation tower 31.

[0031] Furthermore, the mixed gas discharged from the N2 condensation tower 32 enters the third gas guide pipe 37, and after heat exchange and cooling in the fourth heat exchanger 24 and the fifth heat exchanger 211, it can enter the H2 condensation tower 33 to separate H2. However, since the mixed gas discharged from the N2 condensation tower 32 usually contains trace nitrogen, a first-stage cryogenic adsorber 316 is connected in series on the third gas guide pipe 37, and the adsorption temperature is 65K, and the trace nitrogen can be adsorbed and removed by the first-stage cryogenic adsorber 316. In the preferred embodiment, there are two groups of first-stage cryogenic adsorbers 316, and the two groups of first-stage cryogenic adsorbers 316 are connected in parallel, and the two groups switch to work. When one group of first-stage cryogenic adsorbers 316 adsorbs and removes trace nitrogen, the other group of first-stage cryogenic adsorbers 316 is regenerated. In this way, the mixed gas entering the fourth heat exchanger 24 is mainly He and a small amount of H2. The bottoms of the two groups of I-stage cryogenic adsorbers 316 are connected to a flow path for discharging the regeneration purge gas to the flare vent pipe, and a regulating valve 317 is also provided in the flow path.

[0032] In order to completely separate H2 to obtain high-purity He, the secondary expander 210 connected in series on the low-pressure pipeline 26 can reduce the temperature to 15K. The He collection pipe 34 is sequentially connected to the sixth heat exchanger 212, the fifth heat exchanger 211, the fourth heat exchanger 24, the third heat exchanger 23, the second heat exchanger 22, and the first heat exchanger 29. The high-purity and low-temperature He in the He collection pipe 34 is sequentially collected by the sixth heat exchanger 212, the fifth heat exchanger 211, the fourth heat exchanger 24, the third heat exchanger 23, the second heat exchanger 22, and the first heat exchanger 29 to recover the cold. In this way, the mixed gas in the third gas pipeline 37 can be cooled to 20K by heat exchange in the fifth heat exchanger 211 to form a gas-liquid two-phase mixture, and then enter the H2 condensation tower 33 through a regulating valve 318, and most of the liquid hydrogen is separated in the H2 condensation tower 33. When the liquid hydrogen level in the H2 condensation tower 33 reaches a certain value, it will be discharged to the flare vent pipe through a regulating valve 319.

[0033] The mixed gas discharged from the H2 condensation tower 33 is He and trace hydrogen. The mixed gas first passes through the sixth heat exchanger 212 for heat exchange and cooling, and then enters the II-level cryogenic adsorber 320. The adsorption temperature of the II-level cryogenic adsorber 320 is 15K, which can adsorb and remove trace hydrogen in the mixed gas. Finally, the high-purity and low-temperature He enters the He collection pipe 34. Among them, there are two groups of II-level cryogenic adsorbers 320, and the two groups of II-level cryogenic adsorbers 320 are connected in parallel. The two groups switch to work. When one group of II-level cryogenic adsorbers 320 adsorbs and removes trace hydrogen, the other group of II-level cryogenic adsorbers 320 regenerates. Of course, the two groups of II-level cryogenic adsorbers 320 are also provided with a flow path for the regeneration purge gas to be discharged to the flare vent pipe, and a regulating valve 321 is provided on the flow path.

[0034] In a preferred embodiment, the recovery system further comprises a cold box 5, which is a relatively sealed box structure, and most of the above structures are arranged in the cold box 5. Specifically, the first heat exchanger 29, the second heat exchanger 22, the third heat exchanger 23, the fourth heat exchanger 24, the fifth heat exchanger 211, the sixth heat exchanger 212, the first-stage expander 25, the second-stage expander 210, the low-pressure pipeline 26, the high-pressure pipeline 213 and the recovery flow path 3 are all located in the cold box 5. Correspondingly, the cold box 5 is provided with a high-pressure pipeline 213 interface, a low-pressure pipeline 26 interface, a CH4 interface, a N2 interface, a H2 interface, and a H e collecting pipe 34 interface and the first air guide pipe 35 interface, the high pressure pipe 213 is connected to the high pressure outlet of the first compressor 21 through the high pressure pipe 213 interface, the low pressure pipe 26 is connected to the low pressure inlet of the first compressor 21 through the low pressure pipe 26 interface, the first air guide pipe 35 is connected to the outlet of the second compressor 11 through the first air guide pipe 35 interface, the CH4 interface is connected to the CH4 outlet of the CH4 distillation tower 31, the N2 interface is connected to the N2 outlet of the N2 condensation tower 32, the H2 interface is connected to the H2 outlet of the H2 condensation tower 33, and the He collecting pipe 34 interface is connected to the outlet of the He collecting pipe 34. Therefore, except for the compressor and the storage tank, most of the structures of the recovery system are integrated into the cold box 5. When it is necessary to collect the gas separated from the LNG flash steam, it only needs to be connected to the corresponding interface, which is very convenient. At the same time, the cold box 5 protects the above structures.

[0035] The embodiment of the present invention also provides a LNG flash steam recovery method. By adopting the above-mentioned recovery system, CH4, N2, H2, and He in the LNG flash steam volatilized in the LNG storage tank 1 can be effectively recovered, and not only the recovery rate is very high, but also the purity is very high.

[0036] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. LNG flash steam recovery system, including LNG storage tank, characterized by: It includes a refrigeration cycle flow path and a recovery flow path; The refrigeration cycle flow circuit includes a first compressor, a first heat exchanger, a second heat exchanger, a third heat exchanger, a fourth heat exchanger, a fifth heat exchanger, a sixth heat exchanger, a first-stage expander, a second-stage expander, a control valve, a low-pressure pipeline and a high-pressure pipeline, the high-pressure outlet of the first compressor is sequentially connected to the first heat exchanger, the second heat exchanger, the third heat exchanger, the fourth heat exchanger, the first-stage expander, the fifth heat exchanger and the second-stage expander through the high-pressure pipeline, and the low-pressure outlet of the second-stage expander is sequentially connected to the sixth heat exchanger, the fifth heat exchanger, the fourth heat exchanger, the third heat exchanger, the second heat exchanger, the first heat exchanger and the low-pressure inlet of the first compressor through the low-pressure pipeline; The recovery flow path includes a CH4 distillation tower, an N2 condensation tower, an H2 condensation tower, a He collection pipe, a level I cryogenic adsorber, a level II cryogenic adsorber, a first air guide pipeline, a second air guide pipeline, a third air guide pipeline, and a fourth air guide pipeline; the gas outlet of the LNG storage tank is connected to the gas inlet of the CH4 distillation tower through the second compressor, the first heat exchanger, and the second heat exchanger in sequence along the first air guide pipeline, the gas outlet of the CH4 distillation tower is connected to the third heat exchanger and the gas inlet of the N2 condensation tower in sequence through the second air guide pipeline, the gas outlet of the N2 condensation tower is connected to the level I cryogenic adsorber, the fourth heat exchanger, the fifth heat exchanger, and the H2 condensation tower in sequence through the third air guide pipeline, and the gas outlet of the H2 condensation tower is connected to the sixth heat exchanger, the level II cryogenic adsorber, and the He collection pipe in sequence through the fourth air guide pipeline; The recovery flow path also includes a reboiler and a heating branch; The air inlet of the heating branch is connected to the air outlet of the first heat exchanger, the air outlet of the heating branch is connected to the air inlet of the second heat exchanger, and a first regulating valve is provided between the air outlet of the first heat exchanger and the air inlet of the second heat exchanger, the reboiler is connected in series to the heating branch, and a second regulating valve is provided on the air inlet pipeline of the heating branch; The He collecting pipe is sequentially connected to the sixth heat exchanger, the fifth heat exchanger, the fourth heat exchanger, the third heat exchanger, the second heat exchanger and the first heat exchanger.

2. The LNG flash vapor recovery system according to claim 1, characterized in that: There are two groups of stage I low-temperature adsorbers, and the two groups of stage I low-temperature adsorbers are connected in parallel. The two groups of stage I low-temperature adsorbers switch to work, one group adsorbs and the other group regenerates; there are two groups of stage II low-temperature adsorbers, and the two groups of stage II low-temperature adsorbers are connected in parallel. The two groups of stage II low-temperature adsorbers switch to work, one group adsorbs and the other group regenerates.

3. The LNG flash vapor recovery system according to claim 1, characterized in that: It also includes a cold box, on which a high-pressure pipeline interface, a low-pressure pipeline interface, a CH4 interface, an N2 interface, an H2 interface, a He collecting pipe interface and a first gas guiding pipeline interface are provided, and the first heat exchanger, the second heat exchanger, the third heat exchanger, the fourth heat exchanger, the fifth heat exchanger, the sixth heat exchanger, the first-stage expander, the second-stage expander, the low-pressure pipeline, the high-pressure pipeline and the recovery flow path are all located in the cold box; and the high-pressure pipeline is connected to the high-pressure outlet of the first compressor through the high-pressure pipeline interface, the low-pressure pipeline is connected to the low-pressure inlet of the first compressor through the low-pressure pipeline interface, the first gas guiding pipeline is connected to the outlet of the second compressor through the first gas guiding pipeline interface, the CH4 interface is connected to the CH4 outlet of the CH4 distillation tower, the N2 interface is connected to the N2 outlet of the N2 condensation tower, the H2 interface is connected to the H2 outlet of the H2 condensation tower, and the He collecting pipe interface is connected to the outlet of the He collecting pipe.

4. The LNG flash vapor recovery system according to claim 1, characterized in that: It also includes a He storage tank, which is connected to the low-pressure inlet of the first compressor, and a control valve is provided on the flow path between the two.

5. An LNG flash steam recovery method, the method being applied to the LNG flash steam recovery system according to any one of claims 1 to 4, characterized in that: The LNG flash steam in the LNG storage tank enters the recovery flow path after being compressed; The LNG flash steam entering the recovery flow path is sequentially heat exchanged and cooled through multiple heat exchangers on the refrigeration circulation flow path; the recovery flow path is sequentially provided with a CH4 distillation tower, an N2 condensation tower, a stage I cryogenic adsorber, an H2 condensation tower, a stage II cryogenic adsorber, and a He collection pipe along the flow direction of the LNG flash steam, and CH4 in the LNG flash steam is separated in the CH4 distillation tower, N2 is separated in the N2 condensation tower, and H2 is separated in the H2 condensation tower, and the remaining He enters the He collection pipe.

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