Nitrogen and helium capturing system for liquefied natural gas boil-off gas

Abstract

The utility model relates to a liquefied natural gas boil-off gas nitrogen stripping and helium capturing system which can improve the helium recovery efficiency and comprises a recovery tower, a rectifying tower, a crude helium tower and a nitrogen circulating cooling device. A gas inlet of the recovery tower is communicated with the storage tank, a first tower top reflux cooler is arranged in the recovery tower, a gas phase outlet of the recovery tower is connected with a gas phase inlet of the rectifying tower, and a liquid phase outlet at the tower bottom of the recovery tower is communicated with the storage tank; a second tower top reflux cooler is arranged in the rectifying tower, a reboiler is arranged at the bottom, and a gas phase outlet of the rectifying tower is communicated with a gas phase inlet of the crude helium tower; a third tower top reflux cooler is arranged in the crude helium tower, a liquid phase outlet of the crude helium tower is communicated with an inlet of the third tower top reflux cooler, and liquid nitrogen flowing out of the crude helium tower can flow to the third tower top reflux cooler to serve as a cold source; and the nitrogen circulating cooling device is used for providing liquid nitrogen as a refrigerant for the first tower top reflux cooler and the second tower top reflux cooler and recovering nitrogen generated by vaporization of the liquid nitrogen, and providing nitrogen for the reboiler and recovering nitrogen.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of liquefied natural gas storage tank evaporation gas recovery, in particular to a liquefied natural gas evaporation gas nitrogen extraction and helium capture system. BACKGROUND

[0002] Liquefied natural gas (LNG) ships generally use atmospheric low-temperature storage in atmospheric storage tanks with cold insulation measures. Atmospheric storage tanks will inevitably be affected by factors such as atmospheric pressure fluctuations, external atmospheric temperature, and low-speed operation or normal operation of the low-temperature submersible pump in the storage tank, causing the internal pressure of the storage tank to rise. The root cause of the pressure rise is the generation of evaporation gas in the storage tank. After the pressure of the storage tank rises, this part of the BOG (Boiled off Gas) evaporation gas will be discharged to maintain the normal operating pressure of the storage tank.

[0003] In actual operation, this part of BOG gas usually has the following characteristics: 1. The flow is considerable, accounting for about 8% to 16% of the raw gas flow (normal 8%, maximum 16% considering the generation and normal evaporation during LNG unloading). 2. BOG (Boiled off Gas) contains methane, nitrogen, and helium. 3. The component is lighter than pure methane, the nitrogen content is high, and the temperature of the BOG after liquefaction will be lower, possibly ranging from -165℃ to -175℃, lower than the design temperature of the storage tank -165℃. 4. High helium content. The dew point temperature of methane at atmospheric pressure is -163℃, the dew point temperature of nitrogen at atmospheric pressure is -196℃, helium is a rare gas with high added value, and the dew point temperature at atmospheric pressure is -253℃. The nitrogen content in BOG (Boiled off Gas) is about 3v% to 16v%, and the helium content is about 0.2v% to 24v%. It is very important to extract as much helium as possible from BOG (Boiled off Gas).

[0004] The treatment of this part of BOG gas usually has the following treatment methods:

[0005] 1) Use BOG compressor to compress and increase pressure and temperature, and then send it to the gas pipeline network as city gas or plant gas. Because BOG (Boiled off Gas) only contains nitrogen and methane, it is a clean fuel. The process is simple and the equipment is less, but for high-nitrogen BOG (Boiled off Gas), the calorific value is reduced. Moreover, the large amount of cold energy carried by BOG is consumed in the compression process of the compressor, which is not utilized, causing waste. Moreover, it has limitations for areas that are not convenient for long-distance pipeline transportation.

[0006] 2) Recondensation of BOG. After the BOG is extracted, it is pressurized by the BOG (Boiled off Gas) compressor. The 0.7 MPag LNG cryogenic liquid from the storage tank and the 0.72 MPag BOG gas from the BOG compressor are directly contacted in the condenser. After the mass transfer and heat transfer, the BOG is condensed into LNG in the BOG condenser, and then pressurized and exported. For high-nitrogen BOG (Boiled off Gas) re-liquefaction, the nitrogen component in the system accumulates, exists in LNG (Liquefied Natural Gas), and more BOG (Boiled off Gas) is formed in the tank car during the unloading process. If this part of the BOG returns to the BOG main pipe to form a poor circulation, it may increase the risk of overpressure of the LNG (Liquefied Natural Gas) storage tank.

[0007] 3) BOG pressurization-liquefaction. After compression by the BOG (Boiled off Gas) high and low pressure compressors, the BOG is liquefied in the cold box using mixed refrigerant. In the cold box, the mixed refrigerant exchanges heat with the BOG gas at room temperature. For low-nitrogen BOG (Boiled off Gas), it is a high-efficiency recovery method. For high-nitrogen BOG (Boiled off Gas) re-liquefaction, the nitrogen component in the system accumulates, exists in LNG (Liquefied Natural Gas), and more BOG (Boiled off Gas) is formed in the tank car during the unloading process. If this part of the BOG returns to the BOG main pipe to form a poor circulation, it may increase the risk of overpressure of the LNG (Liquefied Natural Gas) storage tank. Moreover, the normal operation of the BOG compressor has the problems of long cold start time before starting, inconvenience of quick full-load operation, pressure fluctuation of the BOG (Boiled off Gas) pipe network system, even overpressure venting to the flare, causing resource waste and unnecessary carbon emission and environmental protection problems.

[0008] 4) BOG compression and rectification for nitrogen extraction and two-stage flash for helium extraction. The BOG (Boiled off Gas) evaporated from the liquefied natural gas atmospheric storage tank is all pressurized by a compressor and then cooled by a refrigerant to a certain temperature before entering the rectification tower for component separation. The nitrogen gas at the top of the rectification tower has a relatively high concentration, and the helium gas has a relatively low concentration. The liquefied natural gas (LNG) at the bottom of the rectification tower is the bottom product. The nitrogen gas and helium gas at the top of the rectification tower are cooled by a refrigerant to a certain temperature to form a gas-liquid two-phase mixture, which is then separated by a separator for one-stage flash separation. The crude helium gas is at the top of the separator, and the liquid nitrogen is at the bottom. This method has relatively high energy consumption of the BOG compressor and relatively high investment. The nitrogen concentration in the obtained crude helium gas is relatively high, which affects the consumption and investment of the next process of extracting pure helium gas. Moreover, the recovery rate of helium is relatively low. Content of the utility model

[0009] Therefore, it is necessary to provide a liquefied natural gas evaporation gas nitrogen extraction and helium capture system with high recovery rate and no cyclic accumulation for the high-nitrogen BOG gas generated in the liquefied natural gas storage tank.

[0010] A liquefied natural gas evaporation gas nitrogen extraction and helium capture system, comprising: a recovery tower, a rectification tower, a crude helium tower, and a nitrogen circulation cooling device; an air inlet of the recovery tower is connected with a storage tank through a first pipe; a first overhead reflux cooler is arranged in the recovery tower; a gas phase outlet at the top of the recovery tower is connected with a gas phase inlet of the rectification tower through a second pipe; and a liquid phase outlet at the bottom of the recovery tower is connected with the storage tank through a third pipe.

[0011] A second overhead reflux cooler is arranged in the rectification tower, and a reboiler is arranged at the bottom of the rectification tower; a gas phase outlet at the top of the rectification tower is connected with a gas phase inlet of the crude helium tower;

[0012] A third overhead reflux cooler is arranged in the crude helium tower; a liquid phase outlet of the crude helium tower is connected with an inlet of the third overhead reflux cooler through a pipeline; and liquid nitrogen flowing out of the crude helium tower can flow to the third overhead reflux cooler as a cold source.

[0013] The nitrogen circulation cooling device is used to provide liquid nitrogen as a coolant to the first overhead reflux cooler and the second overhead reflux cooler, recover nitrogen gas generated by vaporization of the liquid nitrogen, and provide nitrogen gas to the reboiler and recover the nitrogen gas.

[0014] In some embodiments, the nitrogen circulation cooling device comprises a multi-stream heat exchanger.

[0015] The multi-stream heat exchanger is connected with the inlet of the first overhead reflux cooler through a first nitrogen pipeline, liquid nitrogen from the multi-stream heat exchanger can enter the first overhead reflux cooler from the first nitrogen pipeline, and the multi-stream heat exchanger is connected with the outlet of the first overhead reflux cooler through a second nitrogen pipeline, nitrogen gas from the first overhead reflux cooler can enter the multi-stream heat exchanger from the second nitrogen pipeline;

[0016] The multi-stream heat exchanger is connected with the inlet of the second overhead reflux cooler through an eighteenth nitrogen pipeline, liquid nitrogen from the multi-stream heat exchanger can enter the second overhead reflux cooler from the eighteenth nitrogen pipeline, and the multi-stream heat exchanger is connected with the outlet of the second overhead reflux cooler through a nineteenth nitrogen pipeline, nitrogen gas from the second overhead reflux cooler can enter the multi-stream heat exchanger from the nineteenth nitrogen pipeline;

[0017] The multi-stream heat exchanger is connected with the inlet of the reboiler through a twentieth nitrogen pipeline;

[0018] The nitrogen gas from the first overhead reflux cooler and the nitrogen gas from the second overhead reflux cooler enter the multi-stream heat exchanger after being reheated, and then enter the twentieth nitrogen pipeline.

[0019] In some embodiments, a liquid phase outlet at the bottom of the rectification tower is connected to the multi-stream heat exchanger through a fourth pipeline, and liquefied natural gas from the rectification tower is supercooled by the multi-stream heat exchanger and then enters the storage tank.

[0020] In some embodiments, the nitrogen circulation cooling device further comprises a first compressor, a nitrogen expander and a gas-liquid separator;

[0021] The outlet of the first compressor is connected with the multi-stream heat exchanger through a sixth nitrogen pipeline, and the first compressor is used for inputting normal-temperature low-pressure nitrogen gas and pressurizing the normal-temperature low-pressure nitrogen gas to output normal-temperature high-pressure nitrogen gas;

[0022] The high-pressure nitrogen gas in the multi-stream heat exchanger has a first flow path and a second flow path, and the multi-stream heat exchanger divides the low-temperature high-pressure nitrogen gas obtained by cooling the normal-temperature high-pressure nitrogen gas from the sixth nitrogen pipeline into two parts, one part flows into the first flow path, and the other part flows into the second flow path;

[0023] The outlet of the first flow path is connected with the inlet of the nitrogen expander through a twelfth nitrogen pipeline, and the outlet of the nitrogen expander is connected with the gas-liquid separator through a fifteenth nitrogen pipeline; the nitrogen expander is used for cooling and decompressing the low-temperature high-pressure nitrogen gas from the twelfth nitrogen pipeline and outputting to the fifteenth nitrogen pipeline;

[0024] The multi-stream heat exchanger can cool and liquefy the high-pressure and low-temperature nitrogen gas in the second flow path, so that the outlet of the second flow path can flow out liquid nitrogen, and the outlet of the second flow path is communicated with the gas-liquid separator in sequence through the seventh nitrogen pipeline and the eighth nitrogen pipeline.

[0025] The top gas outlet of the gas-liquid separator is connected with the multi-stream heat exchanger through the ninth nitrogen pipeline, and the liquid outlet at the bottom of the gas-liquid separator is connected with the first nitrogen pipeline and the eighteenth nitrogen pipeline through the seventeenth nitrogen pipeline.

[0026] In some embodiments, the nitrogen circulation cooling device further comprises a second compressor, the multi-stream heat exchanger is connected with the inlet of the second compressor through the third nitrogen pipeline, the outlet of the second compressor is connected with the inlet of the fifth nitrogen pipeline through the fourth nitrogen pipeline; the second compressor is used for pressurizing the normal-temperature and low-pressure nitrogen gas from the third nitrogen pipeline and outputting to the fourth nitrogen pipeline.

[0027] The multi-stream heat exchanger is connected with the outlet of the reboiler through the twenty-first nitrogen pipeline, the nitrogen gas from the reboiler can enter the multi-stream heat exchanger through the twenty-first nitrogen pipeline, and then reheat in the multi-stream heat exchanger and enter the third nitrogen pipeline.

[0028] In some embodiments, the multi-stream heat exchanger is connected with the tenth nitrogen pipeline, and is used for outputting normal-temperature and low-pressure nitrogen gas to the tenth nitrogen pipeline.

[0029] The tenth nitrogen pipeline is communicated with the inlet of the first compressor through the fifth nitrogen pipeline; the first compressor is used for pressurizing the normal-temperature and low-pressure nitrogen gas from the fifth nitrogen pipeline to form normal-temperature and high-pressure nitrogen gas, and outputting to the multi-stream heat exchanger through the sixth nitrogen pipeline.

[0030] In some embodiments, the liquefied natural gas boil-off gas extraction nitrogen and helium capture system further comprises an eleventh nitrogen pipeline and a thirteenth nitrogen pipeline, the eleventh nitrogen pipeline is connected with the inlet of the thirteenth nitrogen pipeline, the outlet of the thirteenth nitrogen pipeline is connected with the fifth nitrogen pipeline, and is used for inputting normal-temperature and low-pressure nitrogen gas from the boundary region to the fifth nitrogen pipeline.

[0031] In some embodiments, the liquid phase outlet of the crude helium column is connected with a fifth pipe, and the fifth pipe is communicated with the inlet of the third column top reflux cooler through the twenty-third nitrogen pipeline.

[0032] In some embodiments, the fifth pipe is further communicated with the multi-stream heat exchanger through the twenty-fourth nitrogen pipeline, and the liquid nitrogen from the crude helium column can enter the multi-stream heat exchanger from the twenty-fourth nitrogen pipeline, and is used for providing cold energy to the normal-temperature and high-pressure nitrogen gas from the sixth nitrogen pipeline.

[0033] In some embodiments, a third compressor is further included, the inlet of which is connected to the second pipe, and the outlet of which is connected to the gas phase inlet of the distillation column via a sixth pipe. The third compressor is used to pressurize the gas phase material flowing out of the recovery column.

[0034] In the aforementioned liquefied natural gas (LNG) evaporation gas nitrogen extraction and helium capture system, the high-nitrogen-content boil-off gas (BOG) generated in the storage tank is cooled in the first column top reflux cooler. This liquefies the main components of the BOG into liquid LNG, which is then returned to the storage tank. This prevents nitrogen accumulation in the LNG, reducing the risk of overpressure in the storage tank and improving the safety of LNG carriers. The remaining nitrogen-containing tail gas from the BOG then enters the rectification column and the crude helium column, resulting in crude helium with a high helium concentration and high helium recovery rate. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the composition of the liquefied natural gas vapor gas nitrogen extraction and helium capture system of this application.

[0036] Explanation of reference numerals in the attached figures:

[0037] Recovery column CO1; Distillation column CO2; Crude helium column CO3;

[0038] First column top reflux cooler E01; Second column top reflux cooler E03; Reboiler E04; Third column top reflux cooler E05;

[0039] First tube S01; Second tube S02; Third tube S03; Fourth tube S04; Fifth tube S05; Sixth tube S06; Seventh tube S06; Eighth tube S08; Ninth tube S09;

[0040] Throttling valve JT01; First regulating valve FV01; Second regulating valve LV02; Third regulating valve LV03; First pressure regulating valve FV01; Second pressure regulating valve FV02; ​​Third pressure regulating valve FV02; ​​First exhaust gas pressure valve PV01; Second exhaust gas pressure valve PV02; Third exhaust gas pressure valve PV03;

[0041] Nitrogen cycle cooling device 1; multi-stream heat exchanger E02; first compressor K01; second compressor K02; gas-liquid separator V01; nitrogen expander Ep01;

[0042] First nitrogen line N01; Second nitrogen line N02; Third nitrogen line N03; Fourth nitrogen line N04; Fifth nitrogen line N05; Sixth nitrogen line N06; Seventh nitrogen line N07; Eighth nitrogen line N08; Ninth nitrogen line N09; Tenth nitrogen line N10; Eleventh nitrogen line N11; Twelfth nitrogen line N12; Bypass line N13; Fourteenth nitrogen line N14; Fifteenth nitrogen line N15; Sixteenth nitrogen line N16; Seventeenth nitrogen line N17; Eighteenth nitrogen line N18; Nineteenth nitrogen line N19; Twentieth nitrogen line N20; Twenty-first nitrogen line N21; Twenty-second nitrogen line N22; Twenty-third nitrogen line N23; Twenty-fourth nitrogen line N24; Twenty-fifth nitrogen line N25. Detailed Implementation

[0043] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0044] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application 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, and therefore should not be construed as a limitation of this application.

[0045] 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 at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0046] In the embodiments of this application, "low temperature" and "high temperature" are relative concepts, indicating that the temperature of a high-temperature gas is higher than that of a low-temperature gas, while "normal temperature" is a temperature between low and high temperatures. Similarly, "low pressure" and "high pressure" are relative concepts, with high-pressure gases having higher pressures than low-pressure gases. Therefore, although "low temperature," "high temperature," "normal temperature," "low pressure," and "high pressure" in the embodiments of this application are not limited to specific values, they clearly define the scope of protection when used to describe relative concepts.

[0047] Please refer to Figure 1 One embodiment of this application provides a liquefied natural gas evaporation gas nitrogen extraction and helium capture system, which can be applied to the recovery and treatment of high nitrogen-containing BOG gas from liquefied natural gas ship storage tanks, including: recovery tower CO1, distillation tower CO2, crude helium tower CO3, and nitrogen circulation cooling device 1.

[0048] The gas inlet of the recovery tower C01 is connected to the storage tank through the first pipe S01. The recovery tower C01 is equipped with a first top reflux cooler E01. The gas phase outlet at the top of the recovery tower C01 is connected to the gas phase inlet of the distillation column (C02) through the second pipe S02. The liquid phase outlet at the bottom of the recovery tower C01 is connected to the storage tank through the third pipe S03.

[0049] The distillation column C02 is equipped with a second top reflux cooler E03 and a reboiler E04 at the bottom. The gas phase outlet at the top of the distillation column C02 is connected to the gas phase inlet of the crude helium column C03.

[0050] The crude helium column CO3 is equipped with a third top reflux cooler E05. The liquid phase outlet of the crude helium column CO3 is connected to the inlet of the third top reflux cooler E05 via a pipeline, allowing the liquid nitrogen flowing out of the crude helium column (CO3) to flow to the third top reflux cooler E05 as a cold source. The gas at the top of the crude helium column CO3 can flow to the downstream purification unit for further purification.

[0051] The nitrogen circulation cooling unit 1 is used to supply liquid nitrogen as a refrigerant to the first top reflux cooler E01 and the second top reflux cooler E03, and to recover the nitrogen gas generated by the vaporization of liquid nitrogen. It also supplies nitrogen gas to the reboiler E04 and recovers nitrogen gas. This achieves a closed-loop refrigerant circulation, eliminating the need for an additional cryogenic liquid nitrogen storage tank. It should be noted that the liquid nitrogen and nitrogen gas in the nitrogen circulation cooling unit do not come into contact with the BOG gas in the recovery tower CO1; they only exchange heat.

[0052] In this application, BOG gas from the storage tank enters the recovery tower CO1 through the first pipe S01. Inside the recovery tower CO1, the BOG gas flows upwards and comes into countercurrent contact with the cryogenic liquid coming down from the first tower top reflux cooler E01. Mass and heat transfer occur within the packed tower due to temperature gradients and compositional differences. After heat and mass exchange, the LNG liquid exiting the bottom of the tower returns to the storage tank through the third pipe S03. The remaining nitrogen-containing tail gas in the BOG gas enters the rectification tower CO2 through the second pipe S02 for further separation of the LNG liquid.

[0053] In the aforementioned liquefied natural gas vapor gas nitrogen extraction and helium capture system, the high-nitrogen-content BOG gas generated in the storage tank can be cooled in the first tower top reflux cooler E01, so that the main components in the BOG gas are liquefied into LNG liquid and returned to the storage tank. In this way, the accumulation of nitrogen components in LNG liquid is avoided, thereby reducing the risk of overpressure in the storage tank and improving the safety of liquefied natural gas carriers.

[0054] In addition, the remaining nitrogen-containing tail gas in the BOG gas enters the CO2 distillation column and the CO3 crude helium column successively, resulting in crude helium gas with high helium concentration and high helium recovery rate.

[0055] Furthermore, in the nitrogen cycle cooling unit 1, nitrogen is the sole component of the refrigerant, eliminating the need for mixed refrigerants, multiple refrigerant storage tanks, and a corresponding dehydration system. The refrigeration system is a closed-loop system, eliminating the need for cryogenic liquid nitrogen storage tanks.

[0056] Please refer to Figure 1 The nitrogen circulation cooling device 1 includes a multi-stream heat exchanger E02. The multi-stream heat exchanger E02 is connected to the inlet of the first top-of-tower reflux cooler E01 via a first nitrogen pipeline N01. Liquid nitrogen from the multi-stream heat exchanger E02 can enter the first top-of-tower reflux cooler E01 from the first nitrogen pipeline N01. The multi-stream heat exchanger E02 is connected to the outlet of the first top-of-tower reflux cooler E01 via a second nitrogen pipeline N02. Nitrogen gas from the first top-of-tower reflux cooler E01 can enter the multi-stream heat exchanger E02 from the second nitrogen pipeline N02.

[0057] The multi-stream heat exchanger E02 is connected to the inlet of the second top reflux cooler E03 via the eighteenth nitrogen line N18. Liquid nitrogen from the multi-stream heat exchanger E02 can enter the second top reflux cooler E03 through the eighteenth nitrogen line N18. The multi-stream heat exchanger E02 is connected to the outlet of the second top reflux cooler E03 via the nineteenth nitrogen line N19. Nitrogen from the second top reflux cooler E03 can enter the multi-stream heat exchanger E02 through the nineteenth nitrogen line N19.

[0058] The multi-stream heat exchanger E02 is connected to the inlet of the reboiler E04 via the twentieth nitrogen line N20. Nitrogen from the first top reflux cooler E01 and nitrogen from the second top reflux cooler E03 enter the multi-stream heat exchanger E02 for reheating before entering the twentieth nitrogen line N20.

[0059] Liquid nitrogen from the multi-stream heat exchanger E02 provides refrigerant for the first and second column top reflux coolers E01 and E03. Both E01 and E03 occupy nitrogen channels, where liquid nitrogen flows, transferring its cooling capacity to the corresponding gaseous substances before being converted into nitrogen gas and flowing back to the multi-stream heat exchanger E02. The multi-stream heat exchanger E02 reheats the returning nitrogen gas before it flows to the reboiler E04, serving as a heat source for the reboiler and thus enabling the recycling of nitrogen gas.

[0060] Please refer to Figure 1 In one embodiment, the liquid phase outlet at the bottom of the distillation column CO2 is connected to the multi-stream heat exchanger E02 via the fourth pipe S04. The liquefied natural gas from the distillation column CO2 is subcooled by the multi-stream heat exchanger E02 before entering the storage tank, thereby reducing flash loss.

[0061] Please refer to Figure 1 In one embodiment, the nitrogen cycle cooling device further includes: a first compressor K01, a nitrogen expander Ep01, and a gas-liquid separator V01.

[0062] The multi-flow heat exchanger E02 can simultaneously receive multiple fluids, enabling heat exchange between them. The internal flow paths of the multi-flow heat exchanger E02 can be designed according to requirements. (The principle of the multi-flow heat exchanger itself is existing technology and will not be elaborated here.)

[0063] The outlet of the first compressor K01 is connected to the multi-stream heat exchanger E02 via the sixth nitrogen pipeline N06. The first compressor K01 is used to introduce low-pressure nitrogen at room temperature and pressurize it to obtain high-pressure nitrogen at room temperature. The high-pressure nitrogen at room temperature enters the multi-stream heat exchanger E02 through the sixth nitrogen pipeline N06.

[0064] The high-pressure nitrogen in the multi-stream heat exchanger E02 has a first flow path and a second flow path. The multi-stream heat exchanger E02 cools the room-temperature high-pressure nitrogen from the sixth nitrogen line N06 to obtain low-temperature high-pressure nitrogen. The low-temperature high-pressure nitrogen is divided into two paths, one part flows into the first flow path and the other part flows into the second flow path.

[0065] The outlet of the first flow path is connected to the inlet of nitrogen expander Ep01 via the twelfth nitrogen line N12. The outlet of nitrogen expander Ep01 is connected to gas-liquid separator V01 via the fifteenth nitrogen line N15. After the low-temperature, high-pressure nitrogen enters the twelfth nitrogen line N12 from the outlet of the first flow path, nitrogen expander Ep01 cools and depressurizes the nitrogen from the twelfth nitrogen line N12 and outputs it to the fifteenth nitrogen line N15, which then enters gas-liquid separator V01. The nitrogen cooled and depressurized by nitrogen expander Ep01 can then be used as a cold source for the nitrogen circulation cooling device.

[0066] The outlet of the second flow path is connected to the gas-liquid separator V01 via the seventh nitrogen line N07 and the eighth nitrogen line N08. During the flow of low-temperature, high-pressure nitrogen in the second flow path, the multi-stream heat exchanger E02 cools and liquefies the nitrogen, allowing liquid nitrogen to flow out of the outlet. The liquid nitrogen exiting the second flow path then enters the gas-liquid separator V01 via the seventh nitrogen line N07 and the eighth nitrogen line N08.

[0067] The top gas outlet of the gas-liquid separator V01 is connected to the multi-stream heat exchanger E02 via the ninth nitrogen line N09. The bottom liquid outlet of the gas-liquid separator V01 is connected to the first nitrogen line N01 and the eighteenth nitrogen line N18 via the seventeenth nitrogen line N17. Then, it is connected to the inlet of the first top reflux cooler E01 via the first nitrogen line N01, and to the second top reflux cooler E02 via the eighteenth nitrogen line N18.

[0068] After gas-liquid separation by gas-liquid separator V01, the nitrogen gas, after being cooled and depressurized by nitrogen expander Ep01, can enter the multi-stream heat exchanger E02 through the ninth nitrogen pipeline N09 to provide cooling capacity; while liquid nitrogen flows from the bottom liquid outlet of gas-liquid separator V01 into the first top reflux cooler E01 and the second top reflux cooler E02 through the first nitrogen pipeline N01 and the eighteenth nitrogen pipeline N18, respectively.

[0069] It is worth noting that when the nitrogen gas, after being cooled and depressurized by the nitrogen expander Ep01, enters the gas-liquid separator V01, it can meet the liquid nitrogen flowing out from the outlet of the second flow path in the gas-liquid separator V01, thereby further cooling the liquid nitrogen and ensuring that the liquid nitrogen has a sufficiently low temperature when it enters the first top reflux cooler E01 and the second top reflux cooler E02.

[0070] In this application, the liquid nitrogen flowing out of the second flow path serves as a cold source with a pressure range of 0.2 MPag to 0.4 MPag. It does not require a cryogenic liquid nitrogen pump to provide pressure. The liquid nitrogen comes from the refrigeration cycle. The first compressor K01 provides sufficient pressure, and the nitrogen expander Ep01 provides the cooling capacity to convert nitrogen into liquid nitrogen.

[0071] Furthermore, since nitrogen is the sole component of the refrigerant, there is no need for mixed refrigerants, multiple refrigerant storage tanks, or associated dehydration systems. The refrigeration system is a closed-loop system, and it is preferable not to configure cryogenic liquid nitrogen storage tanks.

[0072] The outlet fluid of the first compressor K01 is at room temperature, so a corresponding aftercooler is considered, using circulating water for cooling. The high-pressure end of the first compressor K01 is considered to be coaxially connected with the nitrogen expander Ep01, and the power output of the nitrogen expander Ep01 drives the first compressor K01.

[0073] Please refer to Figure 1 In one embodiment, the nitrogen circulation cooling device includes a second compressor K02, a multi-stream heat exchanger E02 connected to the inlet of the second compressor K02 via a third nitrogen line N03, and the second compressor K02 connected to the inlet of a fifth nitrogen line N05 via a fourth nitrogen line N04. The second compressor K02 is used to pressurize the ambient temperature low-pressure nitrogen gas from the third nitrogen line N03 and output it to the fourth nitrogen line N04. The multi-stream heat exchanger E02 is connected to the outlet of the reboiler E04 via a twenty-first nitrogen line N21. Nitrogen gas from the reboiler E04 can enter the multi-stream heat exchanger E02 via the twenty-first nitrogen line N21, and after being reheated in the multi-stream heat exchanger E02 via the twenty-first nitrogen line N21, it enters the third nitrogen line (N03); typically reheated to -110°C.

[0074] The second compressor K02 is used to pressurize the ambient temperature low-pressure nitrogen from the third nitrogen line N03 and output it to the fourth nitrogen line N04. Then, from the fourth nitrogen line N04, it enters the first compressor K01 through the fifth nitrogen line N05 for pressurization. Thus, this part of the ambient temperature low-pressure nitrogen is pressurized and enters the multi-flow heat exchanger E02, which helps to reduce the amount of cooling required for this part of the ambient temperature low-pressure nitrogen to become liquid nitrogen.

[0075] Please refer to Figure 1 In one embodiment, the multi-stream heat exchanger E02 is connected to the tenth nitrogen line N10 and is used to output ambient temperature low-pressure nitrogen to the tenth nitrogen line N10.

[0076] The multi-stream heat exchanger E02 uses the cooling energy provided by nitrogen gas after it has been cooled and depressurized by the nitrogen expander Ep01 to cool the room-temperature high-pressure nitrogen gas from the sixth nitrogen line N06 to form liquid nitrogen. After releasing the cooling energy, the nitrogen gas will heat up, and the heated room-temperature low-pressure nitrogen gas can then be output to the tenth nitrogen line N10.

[0077] The tenth nitrogen line N10 is connected to the inlet of the first compressor K01 via the fifth nitrogen line N05. Thus, the ambient temperature, low-pressure nitrogen gas from the tenth nitrogen line N10 can be pressurized by the first compressor K01 to become ambient temperature, high-pressure nitrogen gas, which then enters the sixth nitrogen line N06 and then the multi-stream heat exchanger E02. In this way, the ambient temperature, low-pressure nitrogen gas output from the multi-stream heat exchanger E02 can be returned to the multi-stream heat exchanger E02 for recycling.

[0078] The multi-stream heat exchanger E02 uses the cooling energy provided by nitrogen gas cooled and depressurized from nitrogen expander Ep01 to cool the room-temperature high-pressure nitrogen gas from the sixth nitrogen line N06 to form liquid nitrogen. After releasing the cooling energy, the nitrogen gas will heat up. Some of the heated room-temperature low-pressure nitrogen gas can be output to the tenth nitrogen line N10; and some room-temperature low-pressure nitrogen gas can be output to the third nitrogen line N03.

[0079] Please refer to Figure 1 In one embodiment, the liquefied natural gas vapor gas nitrogen extraction and helium capture system further includes an eleventh nitrogen pipeline N11 and a thirteenth nitrogen pipeline N13. The inlets of the eleventh nitrogen pipeline N11 and the thirteenth nitrogen pipeline N13 are connected, and the outlet of the thirteenth nitrogen pipeline (N13) is connected to the fifth nitrogen pipeline (N05), for introducing ambient temperature, low-pressure nitrogen from the boundary area into the fifth nitrogen pipeline N05. Thus, the nitrogen lost by the system can be replenished to the nitrogen circulation cooling device through the eleventh nitrogen pipeline N11. The pressure of the nitrogen entering the eleventh nitrogen pipeline N11 from the boundary area is approximately 0.3~0.5 MPa, and the temperature is ambient temperature.

[0080] Please refer to Figure 1 In one embodiment, the liquid phase outlet of the crude helium tower CO3 is connected to a fifth pipe S05, which is connected to the inlet of the third top reflux cooler E05 via the sixteenth nitrogen line N16. The fifth pipe S05 is also connected to the multi-stream heat exchanger E02 via the twenty-fourth nitrogen line N24. Liquid nitrogen from the crude helium tower CO3 can enter the multi-stream heat exchanger E02 through the twenty-fourth nitrogen line N24 to provide cooling for the ambient temperature, high-pressure nitrogen gas from the sixth nitrogen line N06. Therefore, a portion of the liquid nitrogen at the bottom of the crude helium tower CO3 provides cooling for the third top reflux cooler E05, and another portion provides cooling for the multi-stream heat exchanger E02.

[0081] The outlet of the third top reflux cooler E05 is connected to the multi-stream heat exchanger E02 via the twenty-second nitrogen pipeline N22. The nitrogen gas after the liquid nitrogen from the third top reflux cooler E05 is vaporized enters the multi-stream heat exchanger E02 for reheating, and then enters the third nitrogen pipeline N03 for recycling.

[0082] Liquid nitrogen from the crude helium tower CO3 is vaporized in the multi-stream heat exchanger E02 and can be vented through the 25th nitrogen pipeline N25.

[0083] Please refer to Figure 1 In one embodiment, a third compressor K03 is also included. The inlet of the third compressor K03 is connected to the second pipe S02, and the outlet of the third compressor K03 is connected to the gas phase inlet of the distillation column CO2 through the sixth pipe S06. The third compressor K03 is used to pressurize the gas phase material flowing out of the recovery column (CO1).

[0084] Please refer to Figure 1 In one embodiment, a first regulating valve FV01 is provided on the third pipe S03 to regulate the pressure of LNG entering the storage tank. A second regulating valve LV02 is provided on the fourth pipe S04 to regulate the bottom liquid level of the second distillation column (CO2). A third regulating valve LV03 is provided on the fourth pipe S05 to regulate the bottom liquid level of the third crude argon column (CO3).

[0085] The seventh nitrogen pipeline N07 is equipped with a throttle valve JT01. The liquid nitrogen can be depressurized through the throttle valve JT01 and then output to the gas-liquid separator V01 via the eighth nitrogen pipeline N08.

[0086] The first nitrogen line N01 is equipped with a first pressure regulating valve FV01 to regulate the flow rate of liquid nitrogen entering the first column top reflux cooler E01. The twenty-third nitrogen line N23 is equipped with a second pressure regulating valve FV02 to regulate the flow rate of nitrogen gas entering the third column top reflux cooler E05. The eighteenth nitrogen line N18 is equipped with a third pressure regulating valve FV03 to regulate the flow rate of liquid nitrogen entering the second column top reflux cooler E03. The twelfth nitrogen line N12 is equipped with a first tail gas pressure valve PV01 to regulate the pressure of nitrogen gas entering the expander (Ep01). The second line S02 is equipped with a second tail gas pressure valve PV02 to regulate the pressure of nitrogen-containing tail gas entering the third compressor (K03). The sixth line S06 is equipped with a third tail gas pressure valve PV03 to stabilize the pressure of crude helium output.

[0087] Unless otherwise specified, all percentages of gases mentioned in this application refer to volume fractions.

[0088] In this application, the high-nitrogen BOG gas from the storage tank refers to BOG with a nitrogen content of 3% to 16%, a helium content of 0.2% to 24%, a temperature of -150℃ to -155℃, and a pressure of 110 kPa to 120 kPa. The methane content in the liquid after BOG recovery and liquefaction is approximately 99.3%, with a recovery rate as high as 99.9%.

[0089] When BOG enters the recovery tower C01, it is under a slightly positive pressure, with a pressure range of 110~120 kPa. After passing through the recovery system, the pressure drop is less than 5 kPa. The gas pressure at the top of the recovery tower C01 is between 105~115 kPa, and the pressure is maintained at a slightly positive pressure. It is preferable not to install a BOG compressor at the inlet of the recovery tower C01.

[0090] After BOG is recycled and liquefied, the LNG concentration is controlled at 99.3% V%, and the temperature is controlled at -162℃ to -163℃, which is higher than the design temperature of -165℃, so it can be directly returned to the storage tank.

[0091] The gas at the top of the recovery tower C01 is pressurized by the third compressor K03; the pressure range after pressurization is 0.6~0.8MPa, and this part of the compressed gas accounts for about 25% of the total BOG gas volume.

[0092] The gas pipeline S02, which exits from the first tower top reflux cooler E01, is then compressed by the third compressor K03 to a pressure of 0.7 MPa, and the temperature is approximately -75℃.

[0093] The gas exiting from the top of the CO2 distillation column has an N2 concentration of approximately 98%, with the remainder being helium. The temperature is approximately -173°C. The gas then enters the downstream crude helium column CO3 via the seventh tube S07.

[0094] This application sets up a distillation column CO2 and a crude helium column CO3, resulting in a high helium concentration in the crude helium gas, with a recovery rate of 98-99.5% and a helium concentration range of 78-82%.

[0095] In one embodiment,

[0096] The BOG evaporated from the top of the storage tank at a pressure of 115 kPa enters the first pipeline S01 at a pressure of 113 kPa and a temperature of -153°C. Its composition is methane (CH4): 85.8%, N2: 14.0%, and He: 0.2%. It enters the bottom of the recovery tower C01. The gas flows upward and comes into countercurrent contact with the low-temperature liquid coming down from the first tower top reflux cooler E01. Mass and heat transfer occur in the packed tower by relying on the temperature gradient, and heat and mass are exchanged.

[0097] The third pipe S03 at the bottom of the recovery tower C01 contains 99.3% methane at a temperature of -163.2℃. This portion of methane accounts for approximately 75% of the total BOG and is returned to the storage tank as liquefied natural gas (LNG).

[0098] The gas exiting the first column top reflux cooler E01 accounts for approximately 25% of the total BOG, with a nitrogen content of 55% V, a He content of 1% V, and the remainder being methane. Its temperature is approximately -172°C. After being compressed to 0.7 MPa by the third compressor K03, its temperature drops to -75°C before entering the distillation column CO2.

[0099] The gas exiting from the top of the CO2 distillation column contains no methane, has a nitrogen content of 98% V%, a he content of 2% V%, and a temperature of approximately -174.5℃. The liquid exiting from the bottom of the CO2 distillation column is methane, with a temperature of approximately -133℃. It is then subcooled to approximately -160℃ by the multi-stream heat exchanger E02 and returned to the storage tank.

[0100] The tail gas from the top of the CO2 distillation column enters the crude helium column CO3. The gas temperature at the top of the crude helium column CO3 is approximately -194℃, with a nitrogen content of 18-20%. The helium content is 80-82% V%. The liquid exiting from the bottom of the crude helium column CO3 is high-purity liquid nitrogen, with a temperature of approximately -175℃.

[0101] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0102] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0103] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0104] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0105] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A liquefied natural gas evaporation gas nitrogen extraction and helium capture system, characterized in that, include: Recovery tower (C01), distillation tower (C02), crude helium tower (C03), nitrogen circulation cooling device (1); The gas inlet of the recovery tower (C01) is connected to the storage tank through the first pipe (S01). The recovery tower (C01) is equipped with a first top reflux cooler (E01). The gas phase outlet at the top of the recovery tower (C01) is connected to the gas phase inlet of the distillation tower (C02) through the second pipe (S02). The liquid phase outlet at the bottom of the recovery tower (C01) is connected to the storage tank through the third pipe (S03). The distillation column (CO2) is equipped with a second top reflux cooler (E03) and a bottom reboiler (E04). The gas phase outlet at the top of the distillation column (CO2) is connected to the gas phase inlet of the crude helium column (CO3). The crude helium tower (CO3) is equipped with a third top reflux cooler (E05). The liquid phase outlet of the crude helium tower (CO3) is connected to the inlet of the third top reflux cooler (E05) through a pipeline. The liquid nitrogen flowing out of the crude helium tower (CO3) can flow to the third top reflux cooler (E05) as a cold source. The nitrogen circulation cooling device (1) is used to supply liquid nitrogen as a refrigerant to the first top reflux cooler (E01) and the second top reflux cooler (E03) and to recover the nitrogen generated by the vaporization of the liquid nitrogen, and to supply nitrogen to the reboiler (E04) and to recover the nitrogen.

2. The liquefied natural gas vapor gas nitrogen extraction and helium capture system according to claim 1, characterized in that, The nitrogen cycle cooling device (1) includes a multi-stream heat exchanger (E02). The multi-stream heat exchanger (E02) is connected to the inlet of the first top reflux cooler (E01) via a first nitrogen line (N01). Liquid nitrogen from the multi-stream heat exchanger (E02) can enter the first top reflux cooler (E01) via the first nitrogen line (N01). The multi-stream heat exchanger (E02) is connected to the outlet of the first top reflux cooler (E01) via a second nitrogen line (N02). Nitrogen from the first top reflux cooler (E01) can enter the multi-stream heat exchanger (E02) via the second nitrogen line (N02). The multi-stream heat exchanger (E02) is connected to the inlet of the second top reflux cooler (E03) via the eighteenth nitrogen line (N18). Liquid nitrogen from the multi-stream heat exchanger (E02) can enter the second top reflux cooler (E03) through the eighteenth nitrogen line (N18). The multi-stream heat exchanger (E02) is connected to the outlet of the second top reflux cooler (E03) via the nineteenth nitrogen line (N19). Nitrogen from the second top reflux cooler (E03) can enter the multi-stream heat exchanger (E02) through the nineteenth nitrogen line (N19). The multi-stream heat exchanger (E02) is connected to the inlet of the reboiler (E04) via the twentieth nitrogen line (N20); Nitrogen from the first top reflux cooler (E01) and nitrogen from the second top reflux cooler (E03) are reheated in the multi-stream heat exchanger (E02) and then enter the second nitrogen pipeline (N20).

3. The liquefied natural gas vapor gas nitrogen extraction and helium capture system according to claim 2, characterized in that, The liquid phase outlet at the bottom of the distillation column (CO2) is connected to the multi-stream heat exchanger (E02) via a fourth pipe (S04). The liquefied natural gas from the distillation column (CO2) is subcooled by the multi-stream heat exchanger (E02) before entering the storage tank.

4. The liquefied natural gas vapor gas nitrogen extraction and helium capture system according to claim 2, characterized in that, The nitrogen cycle cooling device also includes: a first compressor (K01), a nitrogen expander (Ep01), and a gas-liquid separator (V01). The outlet of the first compressor (K01) is connected to the multi-flow heat exchanger (E02) through the sixth nitrogen pipeline (N06). The first compressor (K01) is used to introduce ambient temperature low-pressure nitrogen and pressurize the ambient temperature low-pressure nitrogen to output ambient temperature high-pressure nitrogen. The high-pressure nitrogen in the multi-stream heat exchanger (E02) has a first flow path and a second flow path. The low-temperature high-pressure nitrogen obtained by cooling the room-temperature high-pressure nitrogen from the sixth nitrogen pipeline (N06) in the multi-stream heat exchanger (E02) is divided into two paths, one part flows into the first flow path and the other part flows into the second flow path. The outlet of the first flow path is connected to the inlet of the nitrogen expander (Ep01) via the twelfth nitrogen line (N12), and the outlet of the nitrogen expander (Ep01) is connected to the gas-liquid separator (V01) via the fifteenth nitrogen line (N15). The nitrogen expander (Ep01) is used to cool and depressurize the low-temperature, high-pressure nitrogen from the twelfth nitrogen line (N12) and output it to the fifteenth nitrogen line (N15). The multi-stream heat exchanger (E02) can cool and liquefy the low-temperature, high-pressure nitrogen gas in the second flow path so that liquid nitrogen can flow out of the outlet of the second flow path. The outlet of the second flow path is connected to the gas-liquid separator (V01) in sequence through the seventh nitrogen pipeline (N07) and the eighth nitrogen pipeline (N08). The top gas outlet of the gas-liquid separator (V01) is connected to the multi-stream heat exchanger (E02) via the ninth nitrogen line (N09), and the bottom liquid outlet of the gas-liquid separator (V01) is connected to the first nitrogen line (N01) and the eighteenth nitrogen line (N18) via the seventeenth nitrogen line (N17).

5. The liquefied natural gas vapor gas nitrogen extraction and helium capture system according to claim 4, characterized in that, The nitrogen circulation cooling device further includes a second compressor (K02). The multi-stream heat exchanger (E02) is connected to the inlet of the second compressor (K02) via a third nitrogen pipeline (N03). The outlet of the second compressor (K02) is connected to the inlet of a fifth nitrogen pipeline (N05) via a fourth nitrogen pipeline (N04). The second compressor (K02) is used to pressurize the ambient temperature low-pressure nitrogen gas from the third nitrogen pipeline (N03) and then output it to the fourth nitrogen pipeline (N04). The multi-stream heat exchanger (E02) is connected to the outlet of the reboiler (E04) via the twenty-first nitrogen line (N21). Nitrogen gas from the reboiler (E04) can enter the multi-stream heat exchanger (E02) via the twenty-first nitrogen line (N21) and enter the third nitrogen line (N03) after being reheated in the multi-stream heat exchanger (E02).

6. The liquefied natural gas evaporation gas nitrogen extraction and helium capture system according to claim 3, characterized in that, The multi-stream heat exchanger (E02) is connected to the tenth nitrogen pipeline (N10) and is used to output ambient temperature low-pressure nitrogen gas to the tenth nitrogen pipeline (N10); The tenth nitrogen line (N10) is connected to the inlet of the first compressor (K01) via the fifth nitrogen line (N05); the first compressor (K01) is used to pressurize the ambient temperature low-pressure nitrogen from the fifth nitrogen line (N05) to form ambient temperature high-pressure nitrogen, and output it to the multi-stream heat exchanger (E02) via the sixth nitrogen line (N06).

7. The liquefied natural gas vapor gas nitrogen extraction and helium capture system according to claim 6, characterized in that, The liquefied natural gas vapor gas nitrogen extraction and helium capture system further includes an eleventh nitrogen pipeline (N11) and a thirteenth nitrogen pipeline (N13). The inlet of the eleventh nitrogen pipeline (N11) is connected to the inlet of the thirteenth nitrogen pipeline (N13), and the outlet of the thirteenth nitrogen pipeline (N13) is connected to the fifth nitrogen pipeline (N05) for introducing ambient temperature low-pressure nitrogen gas from the boundary area into the fifth nitrogen pipeline (N05).

8. The liquefied natural gas vapor gas nitrogen extraction and helium capture system according to claim 4, characterized in that, The liquid phase outlet of the crude helium tower (CO3) is connected to a fifth pipe (S05), which is connected to the inlet of the third tower top reflux cooler (E05) via the twenty-third nitrogen pipeline (N23).

9. The liquefied natural gas vapor gas nitrogen extraction and helium capture system according to claim 8, characterized in that, The fifth pipe (S05) is also connected to the multi-stream heat exchanger (E02) via the twenty-fourth nitrogen line (N24). Liquid nitrogen from the crude helium tower (CO3) can enter the multi-stream heat exchanger (E02) from the twenty-fourth nitrogen line (N24) to provide cooling for the ambient temperature high-pressure nitrogen from the sixth nitrogen line (N06).

10. The liquefied natural gas vapor gas nitrogen extraction and helium capture system according to claim 1, characterized in that, It also includes a third compressor (K03), the inlet of which is connected to the second pipe (S02), and the outlet of which is connected to the gas phase inlet of the distillation column (C02) through the sixth pipe (S06). The third compressor (K03) is used to pressurize the gas phase material flowing out of the recovery column (C01).

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