A system for liquefying high nitrogen and helium-containing natural gas and extracting crude helium and nitrogen

Abstract

The invention discloses a high-nitrogen and high-helium natural gas liquefaction and crude helium and nitrogen extraction system, which belongs to the technical field of extraction systems and comprises a crude helium condenser, wherein the crude helium condenser is respectively connected with a second liquid nitrogen throttle valve, a liquid nitrogen supercooler, a crude helium separator and a demethanizer condensation separator, wherein the crude helium separator is respectively connected with a liquid nitrogen supercooler and a first liquid nitrogen throttle valve, wherein the other end of the first liquid nitrogen throttle valve is connected with a flash steam separator, wherein the flash steam separator is connected with a liquid nitrogen supercooler, wherein the liquid nitrogen supercooler is connected with a liquid nitrogen evaporation pressure control valve, wherein the other end of the liquid nitrogen evaporation pressure control valve is connected with a demethanizer condenser, wherein the natural gas is less emitted, the helium extraction efficiency is high, and the nitrogen in the natural gas is extracted to produce liquid nitrogen and nitrogen products, thereby achieving good economic benefits.

Description

Technical Field

[0001] The invention relates to an extraction system, in particular to a system for liquefying high-nitrogen and helium-containing natural gas and extracting crude helium and nitrogen, belonging to the technical field of extraction systems. Background Art

[0002] Helium is a kind of inert gas and an important strategic material. As a protective gas and ultra-low temperature refrigerant, it has very important uses in aerospace, national defense, semiconductor production, nuclear magnetic resonance and gas leak detection. Helium mainly exists in natural gas, and extracting helium from natural gas is the main industrial source of helium. The helium content in my country's natural gas is small, and the cost of extracting helium from natural gas alone is high. Liquefied natural gas is a clean energy. With the rise of domestic natural gas liquefaction equipment, the implementation of LNG and crude helium extraction co-production makes helium extraction economically feasible; for natural gas with low nitrogen content, crude helium can be extracted from LNG flash gas after natural gas liquefaction, but in the existing technology, there is a lot of natural gas emission during extraction, the efficiency of helium extraction is low, and it is impossible to extract nitrogen from natural gas to produce liquid nitrogen and nitrogen products, resulting in energy waste, and it is impossible to achieve recycling. Therefore, a high nitrogen and helium-containing natural gas liquefaction and crude helium and nitrogen extraction system is designed to optimize the above problems. Summary of the invention

[0003] The main purpose of the present invention is to provide a system for liquefying high nitrogen and helium-containing natural gas and extracting crude helium and nitrogen to solve the above problems.

[0004] The purpose of the present invention can be achieved by adopting the following technical solutions:

[0005] A high nitrogen and helium-containing natural gas liquefaction and crude helium and nitrogen extraction system, comprising a crude helium condenser, the crude helium condenser is respectively connected to a second liquid nitrogen throttle valve, a liquid nitrogen subcooler, a crude helium separator and a demethanizer condensation separator, the crude helium separator is respectively connected to a liquid nitrogen subcooler and a first liquid nitrogen throttle valve, the other end of the first liquid nitrogen throttle valve is connected to a flash steam separator, the flash steam separator is connected to a liquid nitrogen subcooler, the liquid nitrogen subcooler is connected to a liquid nitrogen evaporation pressure control valve, the other end of the liquid nitrogen evaporation pressure control valve is connected to a demethanizer condenser, a demethanizer is installed on one side of the demethanizer condenser, a demethanizer is installed on the other side of the demethanizer, the demethanizer is connected to the demethanizer condenser, the demethanizer condensation separator is respectively connected to the demethanizer and the demethanizer condenser, the demethanizer condenser is connected to a circulating nitrogen throttle valve, and the other end of the circulating nitrogen throttle valve is respectively connected to the second liquid nitrogen throttle valve, The valve is connected to the liquid nitrogen subcooler, the liquid nitrogen subcooler is connected to the natural gas subcooling heat exchanger, the natural gas subcooling heat exchanger is respectively connected to the mixed refrigerant three-stage throttle valve and the natural gas low-temperature throttle valve, the other end of the natural gas low-temperature throttle valve is connected to the natural gas denitrification tower, a denitrification tower reboiler is installed on one side of the natural gas denitrification tower, the denitrification tower reboiler is connected to the mixed refrigerant two-stage throttle valve, the natural gas subcooling heat exchanger and the natural gas liquefaction heat exchanger, the natural gas denitrification tower is also connected to the demethanizer, the demethanizer reboiler is connected to the natural gas subcooling heat exchanger and the natural gas liquefaction heat exchanger, the mixed refrigerant two-stage throttle valve is respectively connected to the natural gas liquefaction heat exchanger and the natural gas subcooling heat exchanger, the natural gas denitrification tower is connected to the natural gas high-temperature throttle valve, the other end of the natural gas high-temperature throttle valve is connected to the natural gas liquefaction heat exchanger, the natural gas liquefaction heat exchanger is connected to the heavy hydrocarbon separator, and the heavy hydrocarbon separator is connected to the natural gas high-temperature throttle valve.

[0006] Preferably, the natural gas liquefaction heat exchanger is connected to a high-pressure mixed refrigerant separator and a mixed refrigerant first-stage throttle valve, the mixed refrigerant first-stage throttle valve is connected to a natural gas precooling heat exchanger, the other end of the mixed refrigerant first-stage throttle valve is connected to the high-pressure mixed refrigerant separator, the high-pressure mixed refrigerant separator is also connected to the natural gas precooling heat exchanger, the natural gas precooling heat exchanger is connected to a first mixed refrigerant compressor, the first mixed refrigerant compressor is connected to a mixed refrigerant inter-stage cooler, the mixed refrigerant inter-stage cooler is connected to a mixed refrigerant inter-stage separator, and the mixed refrigerant inter-stage separator is respectively connected to the mixed refrigerant increasing pump and the second mixed refrigerant compressor.

[0007] Preferably, the second mixed refrigerant compressor is connected to a mixed refrigerant final stage cooler, the mixed refrigerant increasing pump is connected to the mixed refrigerant final stage cooler, the other end of the mixed refrigerant final stage cooler is connected to a mixed refrigerant final stage separator, and the mixed refrigerant final stage separator is connected to the natural gas precooling heat exchanger.

[0008] Preferably, the natural gas precooling heat exchanger is connected to a circulating nitrogen compressor, the natural gas precooling heat exchanger is also connected to a flash steam compressor, and the flash steam compressor is connected to a demethanizer.

[0009] Preferably, the flash steam separator outputs liquid nitrogen and a portion of the liquid nitrogen is input into the crude helium condenser, the natural gas precooling heat exchanger inputs natural gas and outputs heavy hydrocarbons, the circulating nitrogen compressor outputs nitrogen, and the output nitrogen is connected to the natural gas precooling heat exchanger and input into the natural gas precooling heat exchanger.

[0010] Preferably, the natural gas precooling heat exchanger outputs flash steam to the flash steam compressor, and the natural gas precooling heat exchanger outputs mixed refrigerant to the first mixed refrigerant compressor.

[0011] Beneficial technical effects of the present invention:

[0012] The invention provides a system for liquefying high-nitrogen and high-helium natural gas and extracting crude helium and nitrogen. The system has low natural gas emission, high helium extraction efficiency, and can simultaneously extract nitrogen from natural gas to produce liquid nitrogen and nitrogen products, thus achieving good economic benefits.

[0013] Two towers are used to separate light components such as nitrogen and helium from natural gas. First, the natural gas is denitrified to a safe content, and then the methane in the demethanizer is separated. The methane content in light components such as nitrogen and helium can be removed to less than 1ppm, reducing the loss of methane and increasing the output of liquefied natural gas.

[0014] The extraction of crude helium adopts the method of condensation separation. At the same time, the helium and other components dissolved in liquid nitrogen are throttled and flashed, and then compressed by the flash gas compressor and directly enter the demethanizer for recovery. The process is simplified, the channels of some heat exchangers can be reduced, the helium extraction rate is increased, and the purity of liquid nitrogen and nitrogen is further improved. Among them, liquid nitrogen can be used for helium refining, and nitrogen can be used as nitrogen required by the factory and daily supplement of the mixed refrigerant circulation system;

[0015] A nitrogen circulation refrigeration system is set up to mainly provide cooling capacity for the condenser of the demethanizer and the condensation and separation of helium and nitrogen;

[0016] The liquefaction of natural gas adopts a single mixed refrigerant three-stage throttling refrigeration, in which the secondary and tertiary refrigerants provide heat for the denitrification tower reboiler and the demethanization tower reboiler respectively. The process is relatively simple and the energy consumption is relatively low. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The present invention is a process flow chart of a preferred embodiment of a system for liquefying high-nitrogen and helium-containing natural gas and extracting crude helium and nitrogen according to the present invention.

[0018] In the figure: 1-natural gas precooling heat exchanger, 2-natural gas liquefaction heat exchanger, 3-natural gas subcooling heat exchanger, 4-heavy hydrocarbon separator, 5-natural gas high temperature throttle valve, 6-natural gas low temperature throttle valve, 7-natural gas denitrogenation tower, 8-denitrogenation tower reboiler, 9-demethanizer, 10-demethanizer condenser, 11-demethanizer reboiler, 12-demethanizer condenser separator, 13-crude helium condenser, 14-crude helium separator, 15-first liquid nitrogen throttle valve, 16-flash gas separator, 17-flash gas compressor, 18-circulating nitrogen compressor, 19-liquid nitrogen subcooler, 20-circulating nitrogen throttle valve, 21-liquid nitrogen evaporation pressure control valve, 22-second liquid nitrogen throttle valve, 23-first mixed refrigerant compressor, 24-mixed refrigerant interstage cooler, 25-mixed refrigerant interstage separator, 26-mixed refrigerant booster pump, 27-mixed refrigerant final stage cooler, 28-mixed refrigerant final stage separator, 29-high-pressure mixed refrigerant separator, 30-mixed refrigerant second stage throttle valve, 31-mixed refrigerant third stage throttle valve, 32-mixed refrigerant first stage throttle valve, 33-second mixed refrigerant compressor. DETAILED DESCRIPTION

[0019] In order to make the technical solution of the present invention more clear and specific to those skilled in the art, the present invention is further described in detail below in conjunction with embodiments and drawings, but the implementation manner of the present invention is not limited thereto.

[0020] like Figure 1As shown, a high nitrogen and helium-containing natural gas liquefaction and crude helium and nitrogen extraction system provided in this embodiment includes a crude helium condenser 13, the crude helium condenser 13 is respectively connected to a second liquid nitrogen throttle valve 22, a liquid nitrogen subcooler 19, a crude helium separator 14 and a demethanizer condenser separator 12, the crude helium separator 14 is respectively connected to the liquid nitrogen subcooler 19 and a first liquid nitrogen throttle valve 15, the other end of the first liquid nitrogen throttle valve 15 is connected to a flash steam separator 16, and the flash steam separator 16 is connected to the second liquid nitrogen throttle valve 22, a liquid nitrogen subcooler 19, a crude helium separator 14 and a demethanizer condenser separator 12, and the crude helium separator 14 is respectively connected to the liquid nitrogen subcooler 19 and a first liquid nitrogen throttle valve 15. The steam separator 16 is connected to a liquid nitrogen subcooler 19, the liquid nitrogen subcooler 19 is connected to a liquid nitrogen evaporation pressure control valve 21, the other end of the liquid nitrogen evaporation pressure control valve 21 is connected to a demethanizer condenser 10, a demethanizer 9 is installed on one side of the demethanizer condenser 10, a demethanizer reboiler 11 is installed on the other side of the demethanizer 9, the demethanizer 9 is connected to the demethanizer condenser 10, and the demethanizer condenser separator 12 is connected to the demethanizer 9 and the demethanizer condenser 11 respectively. The tower condenser 10 is connected, the demethanizer condenser 10 is connected with a circulating nitrogen throttle valve 20, and the other end of the circulating nitrogen throttle valve 20 is respectively connected with the second liquid nitrogen throttle valve 22 and the liquid nitrogen subcooler 19, the liquid nitrogen subcooler 19 is connected with a natural gas subcooling heat exchanger 3, the natural gas subcooling heat exchanger 3 is respectively connected with the mixed refrigerant three-stage throttle valve 31 and the natural gas low-temperature throttle valve 6, the other end of the natural gas low-temperature throttle valve 6 is connected with a natural gas denitrification tower 7, a denitrification tower reboiler 8 is installed on one side of the natural gas denitrification tower 7, the denitrification tower reboiler 8 is connected with a mixed refrigerant two-stage throttle valve 30, a natural gas subcooling heat exchanger 3 and a natural gas liquefaction heat exchanger 2, the natural gas denitrification tower 7 is also connected with the demethanizer 9, the demethanizer reboiler 11 is connected with the natural gas subcooling heat exchanger 3 and the natural gas liquefaction heat exchanger 2, the mixed refrigerant two-stage throttle valve 30 is respectively connected with the natural gas liquefaction heat exchanger 2 and the natural gas subcooling heat exchanger 3, the natural gas denitrification tower 7 A natural gas high-temperature throttle valve 5 is connected, the other end of the natural gas high-temperature throttle valve 5 is connected to a natural gas liquefaction heat exchanger 2 , the natural gas liquefaction heat exchanger 2 is connected to a heavy hydrocarbon separator 4 , and the heavy hydrocarbon separator 4 is connected to the natural gas high-temperature throttle valve 5 .

[0021] In the figure: 1-natural gas precooling heat exchanger, 2-natural gas liquefaction heat exchanger, 3-natural gas subcooling heat exchanger, 4-heavy hydrocarbon separator, 5-natural gas high temperature throttle valve, 6-natural gas low temperature throttle valve, 7-natural gas denitrogenation tower, 8-denitrogenation tower reboiler, 9-demethanizer, 10-demethanizer condenser, 11-demethanizer reboiler, 12-demethanizer condenser separator, 13-crude helium condenser, 14-crude helium separator, 15-first liquid nitrogen throttle valve, 16-flash gas separator, 17-flash gas compressor, 18-circulating nitrogen compressor, 19-liquid nitrogen subcooler, 20-circulating nitrogen throttle valve, 21-liquid nitrogen evaporation pressure control valve, 22-second liquid nitrogen throttle valve, 23-first mixed refrigerant compressor, 24-mixed refrigerant interstage cooler, 25-mixed refrigerant interstage separator, 26-mixed refrigerant booster pump, 27-mixed refrigerant final stage cooler, 28-mixed refrigerant final stage separator, 29-high-pressure mixed refrigerant separator, 30-mixed refrigerant second stage throttle valve, 31-mixed refrigerant third stage throttle valve, 32-mixed refrigerant first stage throttle valve, 33-second mixed refrigerant compressor

[0022] The raw natural gas after being deacidified, dehydrated and demercured passes through the natural gas precooling heat exchanger 1 and the upper part of the natural gas liquefaction heat exchanger 2, and then is connected to the heavy hydrocarbon separator 4. The heavy hydrocarbons at the bottom of the heavy hydrocarbon separator 4 are sequentially stored through the upper part of the natural gas liquefaction heat exchanger 2 and the natural gas precooling heat exchanger 1. The natural gas at the top of the heavy hydrocarbon separator 4 is divided into two streams after passing through the liquefaction heat exchanger 2. One stream is connected to the middle part of the natural gas denitrification tower 7 through the natural gas low-temperature throttle valve 6, and the other stream is sequentially connected to the top of the natural gas denitrification tower 7 through the natural gas subcooling heat exchanger 3 and the natural gas low-temperature throttle valve 6. The bottom of the natural gas denitrification tower 7 is connected to the denitrification tower reboiler 8. The LNG at the bottom of the denitrogenation tower reboiler 8 is sent to the natural gas liquefaction storage device through the natural gas supercooling heat exchanger 3. The top gas of the natural gas denitrogenation tower 7 is connected to the middle of the demethanizer 9 together with the recovered flash gas. The top gas of the demethanizer 9 is connected to the methane tower condenser separator 12 through the denitrogenation tower condenser 10 in turn. The bottom of the methane tower condenser separator 12 is then connected to the top of the demethanizer 9. The bottom of the demethanizer 9 is connected to the evaporator. The natural gas at the bottom of the evaporator is sent to the natural gas liquefaction storage device through the natural gas supercooling heat exchanger. The top of the condenser separator is connected to the crude helium separator through the crude helium condenser. The crude helium at the top of the crude helium separator is sent to the downstream process through the liquid nitrogen supercooler, the natural gas supercooling heat exchanger, the natural gas liquefaction heat exchanger and the natural gas precooling heat exchanger in turn. The bottom of the crude helium separator is connected to the crude helium flash tank through a throttle valve, and the top of the crude helium flash tank is connected to the inlet of the flash gas compressor through a liquid nitrogen subcooler, a natural gas subcooling heat exchanger, a natural gas liquefaction heat exchanger, and a natural gas precooling heat exchanger in turn, and the outlet of the flash gas compressor is connected to the demethanizer. The nitrogen at the outlet of the nitrogen circulation compressor in the nitrogen circulation refrigeration system passes through the natural gas precooling heat exchanger, the natural gas liquefaction heat exchanger, the natural gas subcooling heat exchanger and the liquid nitrogen subcooler in turn, and is divided into two streams, one of which is connected to the demethanizer condenser through a throttle valve, and the other is connected to the crude helium condenser through a throttle valve. The circulating nitrogen coming out of the demethanizer condenser is combined with the circulating nitrogen coming out of the crude helium condenser through a pressure control valve, and then passes through the liquid nitrogen subcooler, the natural gas subcooling heat exchanger, the natural gas liquefaction heat exchanger and the natural gas precooling heat exchanger in turn, and then is connected to the inlet of the nitrogen circulation compressor.In a single mixed refrigerant three-stage throttling refrigeration cycle, the liquid refrigerant of the mixed refrigerant final separator is connected to the primary throttling valve after passing through the natural gas precooling heat exchanger, and the gaseous refrigerant of the mixed refrigerant final separator is connected to the high-pressure refrigerant separator through the natural gas precooling heat exchanger; the liquid mixed refrigerant at the bottom of the high-pressure refrigerant separator is connected to the secondary throttling valve through the natural gas liquefaction heat exchanger and the denitrification tower evaporator in turn; the gaseous refrigerant at the top of the high-pressure refrigerant separator is connected to the third-stage throttling valve through the natural gas liquefaction heat exchanger, the demethanizer reboiler, and the natural gas subcooling heat exchanger in turn, and the mixed refrigerant coming out of the third-stage throttling valve passes through the natural gas subcooling heat exchanger and the mixed refrigerant from the secondary throttling valve. After the refrigerants are combined, they pass through the natural gas liquefaction heat exchanger together, and then merge with the mixed refrigerant from the first-stage throttling valve and pass through the natural gas pre-cooling heat exchanger, and then connected to the inlet of the mixed refrigerant compressor. The outlet of the first stage of the mixed refrigerant compressor is connected to the mixed refrigerant inter-stage separator through the mixed refrigerant inter-stage cooler; the gas refrigerant at the top of the mixed refrigerant inter-stage separator is connected to the inlet of the second stage of the mixed refrigerant compressor, and the liquid refrigerant at the bottom of the mixed refrigerant inter-stage separator is connected to the inlet of the refrigerant booster pump; the liquid refrigerant at the outlet of the refrigerant booster pump and the gaseous refrigerant at the outlet of the second stage of the refrigerant compressor are combined and connected to the mixed refrigerant final-stage separator through the mixed refrigerant final-stage cooler, thereby completing the cycle.

[0023] In this embodiment, the natural gas liquefaction heat exchanger 2 is connected to a high-pressure mixed refrigerant separator 29 and a mixed refrigerant primary throttle valve 32, the mixed refrigerant primary throttle valve 32 is connected to a natural gas precooling heat exchanger 1, the other end of the mixed refrigerant primary throttle valve 32 is connected to the high-pressure mixed refrigerant separator 29, the high-pressure mixed refrigerant separator 29 is also connected to the natural gas precooling heat exchanger 1, the natural gas precooling heat exchanger 1 is connected to a first mixed refrigerant compressor 23, the first mixed refrigerant compressor 23 is connected to a mixed refrigerant inter-stage cooler 24, the mixed refrigerant inter-stage cooler 24 is connected to a mixed refrigerant inter-stage separator 25, and the mixed refrigerant inter-stage separator 25 is respectively connected to a mixed refrigerant increasing pump 26 and a second mixed refrigerant compressor 33.

[0024] In this embodiment, the second mixed refrigerant compressor 33 is connected to the mixed refrigerant final stage cooler 27, the mixed refrigerant increasing pump 26 is connected to the mixed refrigerant final stage cooler 27, the other end of the mixed refrigerant final stage cooler 27 is connected to the mixed refrigerant final stage separator 28, and the mixed refrigerant final stage separator 28 is connected to the natural gas precooling heat exchanger 1.

[0025] In this embodiment, the natural gas precooling heat exchanger 1 is connected to a circulating nitrogen compressor 18 , and the natural gas precooling heat exchanger 1 is also connected to a flash steam compressor 17 , and the flash steam compressor 17 is connected to a demethanizer 9 .

[0026] In this embodiment, the flash steam separator 16 outputs liquid nitrogen and a portion of the liquid nitrogen is input into the crude helium condenser 13, the natural gas precooling heat exchanger 1 inputs natural gas and outputs heavy hydrocarbons, the circulating nitrogen compressor 18 outputs nitrogen, and the output nitrogen is connected to the natural gas precooling heat exchanger 1 and input into the natural gas precooling heat exchanger 1.

[0027] In this embodiment, the natural gas precooling heat exchanger 1 outputs flash steam to the flash steam compressor 17 , and the natural gas precooling heat exchanger 1 outputs mixed refrigerant to the first mixed refrigerant compressor 23 .

[0028] The above are only further embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and concepts of the present invention within the scope disclosed by the present invention, which belong to the protection scope of the present invention.

Claims

1. A system for liquefying high nitrogen and helium-containing natural gas and extracting crude helium and nitrogen, characterized by: The invention comprises a crude helium condenser (13), wherein the crude helium condenser (13) is respectively connected to a second liquid nitrogen throttle valve (22), a liquid nitrogen subcooler (19), a crude helium separator (14) and a demethanizer condenser separator (12), wherein the crude helium separator (14) is respectively connected to the liquid nitrogen subcooler (19) and a first liquid nitrogen throttle valve (15), wherein the other end of the first liquid nitrogen throttle valve (15) is connected to a flash steam separator (16), wherein the flash steam separator (16) is connected to the liquid nitrogen subcooler (19), wherein the liquid nitrogen subcooler (19) is connected to a liquid nitrogen evaporation pressure control valve (21), and wherein the liquid nitrogen evaporation pressure control valve (21) is connected to the liquid nitrogen evaporation pressure control valve (21). The other end of the valve (21) is connected to a demethanizer condenser (10), a demethanizer (9) is installed on one side of the demethanizer condenser (10), a demethanizer reboiler (11) is installed on the other side of the demethanizer (9), the demethanizer (9) is connected to the demethanizer condenser (10), the demethanizer condensation separator (12) is respectively connected to the demethanizer (9) and the demethanizer condenser (10), the demethanizer condensation separator (12) is respectively connected to the demethanizer (9) and the demethanizer condenser (10), the demethanizer condenser (10) is connected to a circulating nitrogen throttle valve (20), and the other end of the circulating nitrogen throttle valve (20) is respectively connected to the second liquid nitrogen throttle valve (22). The liquid nitrogen subcooler (19) is connected to a natural gas subcooling heat exchanger (3), the natural gas subcooling heat exchanger (3) is respectively connected to a mixed refrigerant three-stage throttle valve (31) and a natural gas low-temperature throttle valve (6), the other end of the natural gas low-temperature throttle valve (6) is connected to a natural gas denitrification tower (7), a denitrification tower reboiler (8) is installed on one side of the natural gas denitrification tower (7), the denitrification tower reboiler (8) is connected to a mixed refrigerant two-stage throttle valve (30), the natural gas subcooling heat exchanger (3) and a natural gas liquefaction heat exchanger (2), the natural gas denitrification tower (7) is also connected to the The demethanizer (9) is connected to the demethanizer reboiler (11) and the natural gas subcooling heat exchanger (3) and the natural gas liquefaction heat exchanger (2). The mixed refrigerant second-stage throttle valve (30) is respectively connected to the natural gas liquefaction heat exchanger (2) and the natural gas subcooling heat exchanger (3). The natural gas denitrification tower (7) is connected to the natural gas high-temperature throttle valve (5). The other end of the natural gas high-temperature throttle valve (5) is connected to the natural gas liquefaction heat exchanger (2). The natural gas liquefaction heat exchanger (2) is connected to the heavy hydrocarbon separator (4), and the heavy hydrocarbon separator (4) is connected to the natural gas high-temperature throttle valve (5). The natural gas liquefaction heat exchanger (2) is connected to a high-pressure mixed refrigerant separator (29) and a mixed refrigerant primary throttle valve (32); the mixed refrigerant primary throttle valve (32) is connected to a natural gas precooling heat exchanger (1); the other end of the mixed refrigerant primary throttle valve (32) is connected to the high-pressure mixed refrigerant separator (29); the high-pressure mixed refrigerant separator (29) is also connected to the natural gas precooling heat exchanger (1); the natural gas precooling heat exchanger (1) is connected to a first mixed refrigerant compressor (23); the first mixed refrigerant compressor (23) is connected to a mixed refrigerant interstage cooler (24); the mixed refrigerant interstage cooler (24) is connected to a mixed refrigerant interstage separator (25); the mixed refrigerant interstage separator (25) is respectively connected to a mixed refrigerant increasing pump (26) and a second mixed refrigerant compressor (33); The second mixed refrigerant compressor (33) is connected to a mixed refrigerant final stage cooler (27), the mixed refrigerant increasing pump (26) is connected to the mixed refrigerant final stage cooler (27), the other end of the mixed refrigerant final stage cooler (27) is connected to a mixed refrigerant final stage separator (28), and the mixed refrigerant final stage separator (28) is connected to the natural gas precooling heat exchanger (1); The natural gas precooling heat exchanger (1) is connected to a circulating nitrogen compressor (18), the natural gas precooling heat exchanger (1) is also connected to a flash steam compressor (17), and the flash steam compressor (17) is connected to a demethanizer (9); the bottom of the demethanizer (9) is connected to an evaporator, and the natural gas at the bottom of the evaporator is sent to a natural gas liquefaction storage device through a natural gas subcooling heat exchanger.

2. A system for liquefying high nitrogen and helium-containing natural gas and extracting crude helium and nitrogen according to claim 1, characterized in that: The flash steam separator (16) outputs liquid nitrogen and a portion of the liquid nitrogen is input into the crude helium condenser (13); the natural gas precooling heat exchanger (1) inputs natural gas and outputs heavy hydrocarbons; the circulating nitrogen compressor (18) outputs nitrogen, and the output nitrogen is connected to the natural gas precooling heat exchanger (1) and input into the natural gas precooling heat exchanger (1).

3. A system for liquefying high nitrogen and helium-containing natural gas and extracting crude helium and nitrogen according to claim 2, characterized in that: The natural gas precooling heat exchanger (1) outputs flash steam to the flash steam compressor (17), and the natural gas precooling heat exchanger (1) outputs mixed refrigerant to the first mixed refrigerant compressor (23).

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