System and method for helium extraction from lean helium natural gas with co-production of multiple products

Abstract

The application discloses a system and method for extracting helium from lean-helium natural gas and producing multiple products. The system comprises a primary refrigeration device, a primary low-temperature separator, a pre-denitrogenation tower, a demethanizer, a secondary refrigeration device, a helium extraction tower and a denitrogenation tower. The system and method of the application separate nitrogen, methane, ethane and propane in order from low to high according to the boiling points of the components, separate nitrogen and methane by using the pre-denitrogenation tower, concentrate the helium concentration in the overhead gas by about 30 times, and control the carbon dioxide content in the overhead gas to be lower than 50 ppm; and separate nitrogen and helium by using low-temperature rectification. The system and method realize the economic and effective recovery of helium content of 200-3000 ppm in natural gas, and the recovery rates of ethane and helium can both reach more than 99 mol%. Meanwhile, LNG, liquefied petroleum gas and light hydrocarbons are produced as by-products, and the low-temperature nitrogen gas produced as a by-product can provide cold energy at a temperature of about -184 DEG C, thereby greatly improving the economic benefits.

Description

Technical Field

[0001] This invention relates to the field of cryogenic deep processing technology for natural gas, specifically to a system and method for extracting helium from lean helium natural gas and co-producing multiple products. Background Technology

[0002] Helium is a colorless, odorless, rare inert gas with wide applications in high-tech fields such as clinical medicine, national defense, aerospace, nuclear industry, deep-sea diving, cryogenic superconductivity, and high-precision welding. It is a crucial and scarce strategic resource related to national security and the development of high-tech industries. Helium is a monatomic gas and cannot be synthesized through chemical reactions. While helium is widely distributed on Earth in trace amounts, extracting it from helium-containing or helium-rich natural gas reservoirs remains the only industrial method for helium production. When the helium content exceeds 0.3%, helium in natural gas reservoirs has significant economic value; therefore, currently, the world's industrially usable helium resources are primarily found in helium-rich natural gas reservoirs.

[0003] Cryogenic processes are the most widely used and mature separation technology in the field of helium extraction from natural gas. They typically consist of natural gas pretreatment and purification, cryogenic distillation to extract crude helium, and helium refining. Existing methods for recovering helium components from natural gas require deep cryogenic processes to remove carbon dioxide, ensuring that dry ice does not form under low temperatures and clog refrigeration units and other equipment, leading to secondary dehydration. This operation involves high investment and energy consumption. Multi-stage combined refrigeration is also lengthy, involves high investment, high operating costs, and is complex. Therefore, current technologies cannot economically and effectively recover helium components from helium-poor natural gas. Summary of the Invention

[0004] The purpose of this invention is to overcome the problem that existing technologies cannot economically and effectively recover helium components from lean helium natural gas, especially from natural gas with a helium content below 3000 ppm. This invention provides a system and method for helium extraction from lean helium natural gas and co-production of multiple products. This system and method can recover helium components from natural gas with a helium content as low as 1000 ppm, or even as low as 200 ppm. The theoretical recovery rate of helium and ethane can reach over 99 mol%, while simultaneously producing byproducts such as LNG, liquefied petroleum gas, and light hydrocarbons, significantly reducing energy consumption and improving economic efficiency.

[0005] To achieve the above objectives, a first aspect of the present invention provides a system for helium extraction from lean helium natural gas and co-production of multiple products. This system includes: a primary refrigeration unit, a primary cryogenic separator, a pre-denitrification tower, a demethanizer tower, a secondary refrigeration unit, a helium extraction tower, and a denitrification tower; wherein...

[0006] The feed inlet of the first-stage refrigeration unit is connected to the raw material natural gas pipeline, the discharge outlet of the first-stage refrigeration unit is connected to the feed inlet of the first-stage cryogenic separator, the bottom liquid phase outlet of the first-stage cryogenic separator is connected to the demethanizing tower, and the top gas phase outlet of the first-stage cryogenic separator is sequentially connected to the pre-denitrification reboiler, the first-stage refrigeration unit, and the pre-denitrification tower.

[0007] The bottom liquid phase outlet of the pre-denitrification tower is sequentially connected to the flash tank and the demethanizing tower; the top gas phase outlet of the pre-denitrification tower is sequentially connected to the pre-denitrification condenser and the pre-denitrification reflux tank; the bottom liquid phase outlet of the pre-denitrification reflux tank is connected to the pre-denitrification tower; the top gas phase outlet of the pre-denitrification reflux tank is sequentially connected to the helium extraction tower reboiler, the secondary refrigeration unit, and the helium extraction tower.

[0008] The gas phase outlet at the top of the demethanizer is connected in sequence to the primary refrigeration unit and the lean natural gas pipeline, and the liquid phase outlet at the bottom of the demethanizer is connected to the ethane mixed hydrocarbon processing unit.

[0009] The gas phase outlet at the top of the helium extraction tower is connected in sequence to the secondary refrigeration unit and the crude helium pipeline; the liquid phase outlet at the bottom of the helium extraction tower is connected to the denitrification tower.

[0010] The top gas phase outlet of the denitrification tower is connected in sequence to the denitrification condenser and the denitrification reflux tank; the bottom liquid phase outlet of the denitrification tower is connected in sequence to the secondary refrigeration unit and the LNG product pipeline.

[0011] A second aspect of the present invention provides a method for helium extraction from lean helium natural gas and co-production of multiple products, the method comprising:

[0012] The raw natural gas is subjected to a first-stage refrigeration and a first-stage cryogenic separation to obtain a first liquid phase and a first gas phase. The first gas phase is then subjected to pre-denitrification treatment to obtain a second liquid phase and a second gas phase. The second gas phase includes nitrogen, hydrogen and helium, and the carbon dioxide content in the second gas phase does not exceed 50 ppm.

[0013] The first and second liquid phases are subjected to demethanization treatment to obtain methane and light hydrocarbons, and then ethane and propane are separated from the light hydrocarbons.

[0014] The second gas phase is subjected to secondary refrigeration and then helium extraction to obtain a third gas phase and a third liquid phase. In the third gas phase, the concentration of helium is above 60 mol% and the content of nitrogen is below 15 mol%.

[0015] The third liquid phase is subjected to denitrification treatment to obtain LNG product, wherein the nitrogen content in the LNG product does not exceed 1 mol%.

[0016] The intended technical effects achieved by the present invention through the above technical solution are as follows:

[0017] 1) The system and method for helium extraction and multi-product co-production from lean helium natural gas provided by this invention involves first-stage refrigeration of the raw natural gas, followed by sequential distillation removal of nitrogen, methane, ethane, and propane in order of increasing boiling point. First, a pre-denitrification tower separates light components such as nitrogen, hydrogen, and helium, concentrating the helium concentration in the overhead gas (helium feed gas) by approximately 30 times while controlling the carbon dioxide content to no more than 50 ppm. Second, a demethanizer tower achieves efficient separation of methane from light hydrocarbons such as ethane, a deethaner tower achieves efficient separation of ethane from light hydrocarbons such as propane, and a depropanizer tower achieves efficient separation of propane from other light hydrocarbons. Then, a second-stage refrigeration unit further refrigerates the helium feed gas, and a helium extraction tower uses ultra-low temperature distillation to separate nitrogen from helium, achieving a helium concentration of over 60 mol% in the crude helium. Finally, a denitrification tower removes nitrogen from the LNG at the bottom of the helium extraction tower to meet the requirement that the nitrogen content of LNG products should not exceed 1%.

[0018] 2) The system and method of the present invention can economically and effectively recover helium components from natural gas with a helium content of less than 3000 ppm. The recovery rate of ethane and helium can both reach more than 99 mol%. At the same time, by-products include LNG, liquefied petroleum gas and light hydrocarbons. The by-product low-temperature nitrogen can provide cooling at a temperature of about -184°C, which can greatly improve economic efficiency. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a system for helium extraction from lean helium natural gas and the co-production of multiple products, provided by one embodiment of the present invention.

[0020] Explanation of reference numerals in the attached figures

[0021] 1-Raw material natural gas pipeline; 2-Return lean natural gas pipeline; 3-Export lean natural gas pipeline

[0022] 4-First-class gaseous refrigerant at room temperature; 5-First-class liquid refrigerant at room temperature; 6-First-class low-pressure refrigerant at room temperature.

[0023] 9-First-stage cryogenic separator; 11-First-stage refrigeration unit; 13-JT valve

[0024] 20 - Pre-denitrification reboiler; 21 - Reboiler feed inlet; 22 - Reboiler discharge outlet.

[0025] 26-Pre-denitrification tower; 29-Pre-denitrification reflux tank; 32-Pre-denitrification tower condenser

[0026] 35-Flash tank; 42-Ethane mixed hydrocarbon processing unit; 43-Hot feed gas return pipe

[0027] 45-Hot feed gas inlet pipe; 46-Demethanizer reboiler; 51-Demethanizer tower

[0028] 53 - Reboiler outlet; 54 - Reboiler return outlet; 60 - Side stream outlet.

[0029] 61-Side return port; 66-Raw helium pipeline; 68-Flash nitrogen pipeline

[0030] 69 - Secondary low-pressure ambient temperature refrigerant; 70 - Secondary gaseous ambient temperature refrigerant; 71 - Secondary liquid ambient temperature refrigerant.

[0031] 72-Secondary Refrigeration Unit; 74-Built-in Condenser; 75-Helium Extraction Tower

[0032] 78 - Reboiler outlet; 79 - Reboiler inlet; 81 - Helium stripping tower reboiler

[0033] 88-Denitrification reflux tank; 91-LNG product pipeline; 94-Denitrification tower condenser

[0034] 98 - Denitrification tower; 100 - Reboiler outlet; 101 - Reboiler inlet.

[0035] 103-Denitrification Tower Reboiler Detailed Implementation

[0036] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0037] In this invention, helium-poor natural gas refers to natural gas reservoirs with a helium content of 200-3000 ppm (0.02-0.3 mol%).

[0038] The first aspect of this invention provides a system for helium extraction from lean helium natural gas and co-production of multiple products, such as... Figure 1 As shown, the system includes: a primary refrigeration unit 11, a primary cryogenic separator 9, a pre-denitrification tower 26, a demethanizer tower 51, a secondary refrigeration unit 72, a helium stripping tower 75, and a denitrification tower 98; wherein,

[0039] The inlet of the primary refrigeration unit 11 is connected to the raw material natural gas pipeline 1, the outlet of the primary refrigeration unit 11 is connected to the inlet of the primary cryogenic separator 9, the bottom liquid phase outlet of the primary cryogenic separator 9 is connected to the demethanizing tower 51, and the top gas phase outlet of the primary cryogenic separator 9 is sequentially connected to the pre-denitrification reboiler 20, the primary refrigeration unit 11, and the pre-denitrification tower 26.

[0040] The bottom liquid phase outlet of the pre-denitrification tower 26 is sequentially connected to the flash tank 35 and the demethanizing tower 51; the top gas phase outlet of the pre-denitrification tower 26 is sequentially connected to the pre-denitrification condenser 32 and the pre-denitrification reflux tank 29; the bottom liquid phase outlet of the pre-denitrification reflux tank 29 is connected to the pre-denitrification tower 26; the top gas phase outlet of the pre-denitrification reflux tank 29 is sequentially connected to the helium extraction tower reboiler 81, the secondary refrigeration unit 72, and the helium extraction tower 75.

[0041] The gas phase outlet at the top of the demethanizer 51 is connected in sequence to the primary refrigeration unit 11 and the lean natural gas pipeline 3, and the liquid phase outlet at the bottom of the demethanizer 51 is connected to the ethane mixed hydrocarbon processing unit 42.

[0042] The gas phase outlet at the top of the helium extraction tower 75 is sequentially connected to the secondary refrigeration unit 72 and the crude helium pipeline 66; the liquid phase outlet at the bottom of the helium extraction tower 75 is connected to the denitrification tower 98.

[0043] The top gas phase outlet of the denitrification tower 98 is sequentially connected to the denitrification condenser 94 and the denitrification reflux tank 88; the bottom liquid phase outlet of the denitrification tower 98 is sequentially connected to the secondary refrigeration unit 72 and the LNG product pipeline 91.

[0044] In this invention, unless otherwise specified, all devices can be selected from those conventional in the art. To further improve efficiency, the primary refrigeration unit 11 can be a quaternary refrigerant refrigeration unit (methane, ethylene, propane, and isopentane); the primary cryogenic separator 9 can be a blade-type high-efficiency separator; the pre-denitrification tower 26 can be a packed distillation tower; the demethanizer tower 51 can be a plate distillation tower; the secondary refrigeration unit 72 can be a quaternary refrigerant refrigeration unit (nitrogen, methane, ethylene, and isopentane); the helium stripping tower 75 can be a packed distillation tower; and the denitrification tower 98 can be a packed distillation tower.

[0045] In some embodiments, the demethanizer 51 includes a side stream outlet 60, a side stream return outlet 61, a reboiler outlet 53, and a reboiler return outlet 54; the side stream outlet 60 and the side stream return outlet 61 are both located in the upper middle part of the demethanizer 51, and the side stream outlet 60 is located above the side stream return outlet 61; the reboiler outlet 53 and the reboiler return outlet 54 are both located in the lower middle part of the demethanizer 51, and the reboiler outlet 53 is located above the reboiler return outlet 54; the demethanizer 51 is connected to the primary refrigeration unit 11 through the side stream outlet 60 and the side stream return outlet 61; the demethanizer 51 is connected to the demethanizer reboiler 46 through the reboiler outlet 53 and the reboiler return outlet 54.

[0046] In some embodiments, the demethanizing reboiler 46 is connected to the hot feed gas inlet pipe 43 and the hot feed gas return pipe 45.

[0047] In some embodiments, the helium extraction tower 75 includes a reboiler outlet 78 and a reboiler inlet 79; both the reboiler outlet 78 and the reboiler inlet 79 are located in the lower middle part of the helium extraction tower 75, and the reboiler outlet 78 is located above the reboiler inlet 79; both the reboiler outlet 78 and the reboiler inlet 79 are connected to the helium extraction reboiler 81.

[0048] In some embodiments, the denitrification tower 98 includes a reboiler outlet 100 and a reboiler inlet 101; both the reboiler outlet 100 and the reboiler inlet 101 are located in the lower middle part of the denitrification tower 98, and the reboiler outlet 100 is located above the reboiler inlet 101; both the reboiler outlet 100 and the reboiler inlet 101 are connected to the denitrification reboiler 103.

[0049] In some embodiments, the top vapor outlet of the flash tank 35 is connected to the demethanizer 51.

[0050] In some embodiments, the bottom liquid phase outlet of the flash tank (35) is connected to the demethanizer (51), and / or the bottom liquid phase outlet of the flash tank 35 is sequentially connected to the denitrification reboiler 103, the pre-denitrification condenser 32 and the demethanizer 51.

[0051] In this invention, the liquid phase outlet of the flash tank can be directly connected to the demethanizing tower, and can be sequentially connected to the denitrification tower reboiler, the pre-denitrification tower condenser, and the demethanizing tower. Two pipelines can also be installed at the liquid phase outlet of the flash tank: one pipeline is directly connected to the demethanizing tower, and the other pipeline is sequentially connected to the denitrification tower reboiler, the pre-denitrification tower condenser, and the demethanizing tower. This allows a portion of the liquid phase in the flash tank to directly enter the demethanizing tower, while the remaining liquid phase enters the demethanizing tower after heat exchange with the denitrification tower reboiler and the pre-denitrification tower condenser.

[0052] In some embodiments, the gas phase outlet of the denitrification reflux tank 88 is sequentially connected to the built-in condenser 74 of the helium extraction tower 75, the secondary refrigeration device 72, and the flash nitrogen pipeline 68; the liquid phase outlet of the denitrification reflux tank 88 is connected to the denitrification tower 98.

[0053] In this invention, the secondary refrigeration device 72 uses a secondary gaseous ambient temperature refrigerant 70 and a secondary liquid ambient temperature refrigerant 71 for refrigeration, and the denitrification tower condenser 94 uses the secondary refrigeration device 72 and a secondary low-pressure ambient temperature refrigerant 69 for refrigeration.

[0054] Unless otherwise specified, the connection mentioned in this invention refers to a connection through a pipeline, with corresponding valves installed on the pipeline to control the flow and interruption of the fluid.

[0055] A second aspect of the present invention provides a method for extracting helium from lean helium natural gas and co-producing multiple products, the method comprising:

[0056] The raw natural gas is subjected to a first-stage refrigeration and a first-stage cryogenic separation to obtain a first liquid phase and a first gas phase. The first gas phase is then subjected to pre-denitrification treatment to obtain a second liquid phase and a second gas phase. The second gas phase includes nitrogen, hydrogen and helium, and the carbon dioxide content in the second gas phase does not exceed 50 ppm.

[0057] The first and second liquid phases are subjected to demethanization treatment to obtain methane and light hydrocarbons, and then ethane and propane are separated from the light hydrocarbons.

[0058] The second gas phase is subjected to secondary refrigeration and then helium extraction to obtain a third gas phase and a third liquid phase. In the third gas phase, the concentration of helium is above 60 mol% and the content of nitrogen is below 15 mol%.

[0059] The third liquid phase is subjected to denitrification treatment to obtain LNG product, wherein the nitrogen content in the LNG product does not exceed 1 mol%.

[0060] In this invention, ppm refers to the mole fraction of a gas. For example, a helium content of less than 3000 ppm in a natural gas reservoir means that the mole fraction of helium in the natural gas is less than 0.3 mol%, and a carbon dioxide content of no more than 50 ppm means that the mole fraction of carbon dioxide in the second gas phase is 0.005 mol%.

[0061] This invention utilizes a denitrification tower 98 to denitrify and separate LNG from the bottom of a helium extraction tower 75 to meet the requirement that the nitrogen content of LNG products should not exceed 1 mol%.

[0062] In some embodiments, the pressure of the raw material natural gas is 3.5-5 MPa, preferably 4.3 MPa, the temperature is 15-25°C, preferably 20°C, the methane content is 80-98 mol%, preferably 93 mol%, the ethane and above light hydrocarbon content is 2-5.5 mol%, preferably 4.8 mol%, the carbon dioxide content is less than 1.5 mol%, preferably 1 mol%, the nitrogen content is 0.1-5 mol%, preferably 0.7 mol%, and the helium content is 200-3000 ppm, preferably 300-1000 ppm, more preferably 600 ppm.

[0063] The natural gas used as a raw material in this invention also contains trace amounts of hydrogen sulfide.

[0064] In some embodiments, the pre-denitrification treatment is carried out in a pre-denitrification tower 26, and the conditions for the pre-denitrification treatment include: a tower top operating temperature of -85°C to -100°C, preferably -92°C, a tower bottom operating temperature of -75°C to -90°C, preferably -82°C, and an operating pressure of 3-5 MPa, preferably 4.1 MPa.

[0065] In some embodiments, the demethanizing process is carried out in a demethanizing tower 51, and the conditions for the demethanizing process include: a tower top operating temperature of -90°C to -105°C, preferably -98°C, a tower bottom operating temperature of 0-10°C, preferably 4°C, and an operating pressure of 2-3.5 MPa, preferably 2.6 MPa.

[0066] In some embodiments, the helium extraction process is carried out in a helium extraction tower 75, and the conditions for the helium extraction process include: a tower top operating temperature of -170°C to -190°C, preferably -179.5°C, a tower bottom operating temperature of -105°C to -120°C, preferably -112.6°C, and an operating pressure of 1.8-3 MPa, preferably 2.4 MPa.

[0067] In some embodiments, the denitrification treatment is carried out in a denitrification tower 98, and the conditions for the denitrification treatment include: a tower top operating temperature of -150°C to -170°C, preferably -159°C, a tower bottom operating temperature of -100°C to -120°C, preferably -110°C, and an operating pressure of 1-2.5 MPa, preferably 1.8 MPa.

[0068] In some embodiments, the primary refrigerant used for the primary refrigeration includes methane, ethylene, propane, and isopentane, with a molar ratio of 1-6:2-8:1-5:1; the condensation pressure of the primary refrigerant is 2.5-3.5 MPa, preferably 3.1 MPa, and the evaporation pressure is 0.1-0.3 MPa, preferably 0.2 MPa.

[0069] In some embodiments, the secondary refrigerant used for the secondary refrigeration includes nitrogen, methane, ethylene, propane, and isopentane, with a molar ratio of 1-5:1-6:1-8:1; the condensation pressure of the secondary refrigerant is 2.5-3.5 MPa, preferably 3.2 MPa, and the evaporation pressure is 0.2-0.3 MPa, preferably 0.25 MPa.

[0070] According to a particularly preferred embodiment of the present invention, such as Figure 1As shown, the system for helium extraction from lean helium natural gas and co-production of multiple products includes: a primary refrigeration unit 11, a primary cryogenic separator 9, a pre-denitrification tower 26, a demethanizer tower 51, a secondary refrigeration unit 72, a helium extraction tower 75, and a denitrification tower 98; wherein, the inlet of the primary refrigeration unit 11 is connected to the raw material natural gas pipeline 1 for cryogenic treatment of the raw material natural gas to obtain cryogenic natural gas; the outlet of the primary refrigeration unit 11 is connected to the inlet of the primary cryogenic separator 9 for gas-liquid separation of cryogenic natural gas.

[0071] The bottom liquid phase outlet of the primary cryogenic separator 9 is connected to the demethanizing tower 51. The top gas phase outlet of the primary cryogenic separator 9 is sequentially connected to the pre-denitrification reboiler 20, the primary refrigeration unit 11, and the pre-denitrification tower 26. The gas at the top of the primary cryogenic separator 9 passes through a pipeline via the pre-denitrification reboiler 20 and the primary refrigeration unit 11 before entering the pre-denitrification tower 26.

[0072] The pre-denitrification tower 26 includes a reboiler outlet 22 and a reboiler inlet 21. The material coming out of the reboiler outlet 22 passes through the pre-denitrification reboiler 20 and then enters the pre-denitrification tower 26 through the reboiler inlet 21. The gas at the top of the primary low-temperature separator 9 exchanges heat with the material coming out of the reboiler outlet 22 in the pre-denitrification reboiler 20.

[0073] The return lean natural gas pipeline 2 is connected in sequence to the primary refrigeration unit 11 and the demethanizer 51; the top gas phase outlet of the demethanizer 51 is connected in sequence to the primary refrigeration unit 11 and the external lean natural gas pipeline 3; the top gas phase outlet of the demethanizer 51 is also connected in sequence to the pre-denitrification tower condenser 32 and the pre-denitrification tower 26.

[0074] The bottom liquid outlet of the pre-denitrification tower 26 is connected to the flash tank 35 via a pipeline; the top gas outlet of the flash tank 35 is connected to the demethanizing tower 51 via a pipeline; the bottom liquid outlet of the flash tank 35 is connected to the demethanizing tower 51; and / or, the liquid outlet of the flash tank 35 is connected in sequence to the dedenitrification tower reboiler 103, the pre-denitrification tower condenser 32, and the demethanizing tower 51 via pipelines.

[0075] The gas phase outlet at the top of the pre-denitrification tower 26 is connected in sequence to the pre-denitrification condenser 32 and the pre-denitrification reflux tank 29 via pipelines. The liquid phase outlet of the pre-denitrification reflux tank 29 is connected to the pre-denitrification tower 26 via a pipeline; the gas phase outlet of the pre-denitrification reflux tank 29 is connected in sequence to the helium extraction tower reboiler 81, the secondary refrigeration unit 72, and the helium extraction tower 75 via pipelines.

[0076] The bottom gas phase outlet of the demethanizer 51 is connected to the primary refrigeration unit 11 and the external lean natural gas pipeline 3 in sequence through a pipeline, and the top liquid phase outlet of the demethanizer 51 is connected to the ethane mixed hydrocarbon processing unit 42 through a pipeline.

[0077] The demethanizing tower 51 is connected to the primary refrigeration unit 11 through the side outlet 60 and the side return outlet 61; the demethanizing tower 51 is connected to the demethanizing reboiler 46 through the reboiler outlet 53 and the reboiler return outlet 54.

[0078] The demethanizing reboiler 46 is connected to the hot feed gas inlet pipe 43 and the hot feed gas return pipe 45 via pipes.

[0079] The top gas phase outlet of the helium extraction tower 75 is connected in sequence to the secondary refrigeration unit 72 and the crude helium pipeline 66 via pipelines; the bottom liquid phase outlet of the helium extraction tower 75 is connected to the denitrification tower 98 via pipelines. The helium extraction tower 75 is connected to the helium extraction reboiler 81 via the reboiler material outlet 78 and the reboiler material inlet 79.

[0080] The top gas phase outlet of the denitrification tower 98 is connected in sequence to the denitrification condenser 94 and the denitrification reflux tank 88 via pipelines; the gas phase outlet of the denitrification reflux tank 88 is connected in sequence to the built-in condenser 74 of the helium extraction tower 75, the secondary refrigeration unit 72, and the flash nitrogen pipeline 68 via pipelines; the liquid phase outlet of the denitrification reflux tank 88 is connected to the denitrification tower 98 via pipelines; the bottom liquid phase outlet of the denitrification tower 98 is connected in sequence to the secondary refrigeration unit 72 and the LNG product pipeline 91 via pipelines.

[0081] The denitrification tower 98 is connected to the denitrification reboiler 103 through the reboiler material outlet 100 and the reboiler material inlet 101.

[0082] The primary refrigeration unit 11 uses primary gaseous refrigerant 4 and primary liquid refrigerant 5 for refrigeration. The primary gaseous refrigerant 4 and primary liquid refrigerant 5 enter the primary refrigeration unit 11, and after heat exchange, they refrigerate the material entering the primary refrigeration unit 11. After passing through JT valve 13, refrigeration continues, and then primary low-pressure refrigerant 6 is discharged.

[0083] The secondary refrigeration unit 72 uses secondary low-pressure ambient temperature refrigerant 69, secondary gaseous ambient temperature refrigerant 70, and secondary liquid ambient temperature refrigerant 71 for refrigeration. The secondary gaseous ambient temperature refrigerant 70 and the secondary liquid ambient temperature refrigerant 71 are connected sequentially to the secondary refrigeration unit 72 and the denitrification tower condenser 94 via pipelines. The denitrification tower condenser 94 is also connected sequentially to the secondary refrigeration unit 72 and the secondary low-pressure ambient temperature refrigerant 69 via pipelines.

[0084] In this invention, the refrigerant components in the primary gaseous refrigerant 4, the primary liquid refrigerant 5, and the primary low-pressure refrigerant 6 are the same, only the temperature and heat exchange pressure differ. This refrigerant is a primary refrigerant, comprising methane, ethylene, propane, and isopentane in a molar ratio of 1-6:2-8:1-5:1; the condensation pressure of the primary refrigerant is 2.5-3.5 MPa, and the evaporation pressure is 0.1-0.3 MPa.

[0085] In this invention, the refrigerant components in the secondary low-pressure ambient temperature refrigerant 69, the secondary gaseous ambient temperature refrigerant 70, and the secondary liquid ambient temperature refrigerant 71 are the same; they are all secondary refrigerants, only differing in temperature and heat exchange pressure. This refrigerant is a secondary refrigerant, comprising nitrogen, methane, ethylene, and isopentane in a molar ratio of 1-5:1-6:1-8:1; the condensation pressure of the secondary refrigerant is 2.5-3.5 MPa, and the evaporation pressure is 0.2-0.3 MPa.

[0086] According to a particularly preferred embodiment of the present invention, by means of the foregoing... Figure 1 The system shown illustrates a method for helium extraction from lean helium natural gas and co-production of multiple products, comprising the following steps:

[0087] S1. The raw natural gas is sequentially passed through a primary refrigeration unit 11 and a primary cryogenic separator 9 for primary refrigeration and cryogenic separation to obtain a first liquid phase and a first gas phase; wherein, the pressure of the raw natural gas is 3.5-5 MPa, preferably 4.3 MPa, the temperature is 15-25℃, preferably 20℃, the methane content is 80-98 mol%, preferably 93 mol%, the ethane and above light hydrocarbon component content is 2-5.5 mol%, preferably 4.8 mol%, and the carbon dioxide content is less than 1.5 mol%, preferably... The refrigerant has a concentration of 1 mol%, a nitrogen content of 0.1-5 mol%, preferably 0.7 mol%, and a helium content of 200-3000 ppm, preferably 300-1000 ppm, more preferably 600 ppm; the primary refrigerant used for the primary refrigeration includes methane, ethylene, propane, and isopentane, with a molar ratio of 1-6:2-8:1-5:1; the condensation pressure of the primary refrigerant is 2.5-3.5 MPa, preferably 3.1 MPa, and the evaporation pressure is 0.1-0.3 MPa, preferably 0.2 MPa;

[0088] S2. The first gas phase is sequentially passed through the pre-denitrification reboiler 20 and the first-stage refrigeration unit 11 into the pre-denitrification tower 26 for pre-denitrification treatment to obtain a second liquid phase and a second gas phase; wherein, the second gas phase includes nitrogen, hydrogen and helium, and the carbon dioxide content in the second gas phase does not exceed 50 ppm; the conditions for the pre-denitrification treatment include: the tower top operating temperature is -85℃ to -100℃, preferably -92℃, the tower bottom operating temperature is -75℃ to -90℃, preferably -82℃, and the operating pressure is 3-5 MPa, preferably 4.1 MPa;

[0089] The vapor phase at the top of the pre-denitrification tower 26 enters the pre-denitrification reflux tank 29 via the pre-denitrification condenser 32; the liquid phase of the pre-denitrification reflux tank 29 is connected to the pre-denitrification tower 26 via a pipeline; the vapor phase of the pre-denitrification reflux tank 29 is connected to the helium extraction tower 75 via the helium extraction reboiler 81 and the secondary refrigeration unit 72; the pre-denitrification tower 26 is connected to the pre-denitrification reboiler 20 via the reboiler outlet 22 and the reboiler inlet 21;

[0090] S3. The first liquid phase and the second liquid phase are subjected to demethanization treatment in demethanizing tower 51 to obtain methane and light hydrocarbons, and then ethane and propane are separated from the light hydrocarbons; wherein, the conditions for the demethanization treatment include: the tower top operating temperature is -90℃ to -105℃, preferably -98℃, the tower bottom operating temperature is 0-10℃, preferably 4℃, and the operating pressure is 2-3.5MPa, preferably 2.6MPa;

[0091] The second liquid phase at the bottom of the pre-denitrification tower 26 is connected to the flash tank 35 via a pipeline; the gas phase of the flash tank 35 is connected to the demethanizer 51 via a pipeline; a portion of the liquid phase of the flash tank 35 is connected to the demethanizer 51 via the dedenitrification tower reboiler 103 and the pre-denitrification tower condenser 32, and the remaining liquid phase of the flash tank 35 is directly connected to the demethanizer 51; the gas phase of the demethanizer 51 is connected to the lean natural gas pipeline 3 via the primary refrigeration unit 11, and the liquid phase of the demethanizer 51 is connected to the ethane mixed hydrocarbon processing unit 42 via a pipeline, through which ethane and propane are obtained.

[0092] The demethanizer 51 is connected to the first-stage refrigeration unit 11 via the side outlet 60 and the side inlet 61; the demethanizer 51 is connected to the demethanizer reboiler 46 via the reboiler outlet 53 and the reboiler inlet 54; the demethanizer reboiler 46 is connected in sequence to the hot feed gas inlet pipe 45 and the hot feed gas return pipe 43.

[0093] S4. The second gas phase is subjected to secondary refrigeration, and then helium is extracted through helium extraction tower 75 to obtain a third gas phase and a third liquid phase. In the third gas phase, the concentration of helium is above 60 mol% and the content of nitrogen is below 15 mol%. The helium extraction process is carried out in helium extraction tower 75, and the conditions for the helium extraction process include: the tower top operating temperature is -170℃ to -190℃, preferably -179.5℃, the tower bottom operating temperature is -105℃ to -120℃, preferably -112.6℃, and the operating pressure is 1.8-3 MPa, preferably 2.4 MPa.

[0094] The gas phase of the helium extraction tower 75 is connected to the secondary refrigeration unit 72 and the crude helium pipeline 66 in sequence through pipelines; the liquid phase of the helium extraction tower 75 is connected to the denitrification tower 98 through pipelines; the helium extraction tower 75 is connected to the helium extraction reboiler 81 through the reboiler material outlet 78 and the reboiler material inlet 79.

[0095] S5. The third liquid phase is denitrified by passing it through a denitrification tower 98 to obtain LNG product. The nitrogen content in the LNG product does not exceed 1 mol%. The denitrification conditions include: a tower top operating temperature of -150℃ to -170℃, preferably -159℃; a tower bottom operating temperature of -100℃ to -120℃, preferably -110℃; and an operating pressure of 1-2.5 MPa, preferably 1.8 MPa.

[0096] The gas phase of the denitrification tower 98 is connected to the denitrification condenser 94 and the denitrification reflux tank 88 in sequence via pipelines; the gas phase of the denitrification reflux tank 88 is connected to the built-in condenser 74 of the helium extraction tower 75, the secondary refrigeration unit 72 and the flash nitrogen pipeline 68 in sequence via pipelines; the liquid phase of the denitrification reflux tank 88 is connected to the denitrification tower 98 via pipelines; the liquid phase of the denitrification tower 98 is connected to the secondary refrigeration unit 72 and the LNG product pipeline 91 in sequence via pipelines; and the denitrification tower 98 is connected to the denitrification reboiler 103 via pipelines.

[0097] In summary, the system and method provided by this invention can achieve a helium recovery rate and an ethane recovery rate of over 99 mol%, while producing LNG as a byproduct to improve the project's economic benefits. The byproduct cryogenic nitrogen can provide cooling at a temperature of approximately -184°C. This method is a process system for the efficient recovery of helium from nitrogen-containing lean helium natural gas. It can economically and effectively recover helium components from natural gas with a helium content below 3000 ppm, and even economically and effectively recover helium components from natural gas with a helium content of around 200 ppm. It will play a leading role in the recovery of helium from lean helium natural gas in China and even in the recovery of helium from PetroChina and even in other parts of China.

[0098] This invention extracts helium from natural gas, which is of significant strategic importance for ensuring national helium security. Simultaneously, it also has positive implications for the comprehensive and efficient utilization of natural gas resources and for improving the economic benefits of gas field development.

[0099] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0100] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A system for helium extraction from lean helium natural gas and co-production of multiple products, characterized in that, The system includes: a primary refrigeration unit (11), a primary cryogenic separator (9), a pre-denitrification tower (26), a demethanizer tower (51), a secondary refrigeration unit (72), a helium extraction tower (75), and a denitrification tower (98); among which, The feed inlet of the primary refrigeration unit (11) is connected to the raw material natural gas pipeline (1), the discharge outlet of the primary refrigeration unit (11) is connected to the feed inlet of the primary low-temperature separator (9), the bottom liquid phase outlet of the primary low-temperature separator (9) is connected to the demethanizing tower (51), and the top gas phase outlet of the primary low-temperature separator (9) is sequentially connected to the pre-denitrification reboiler (20), the primary refrigeration unit (11), and the pre-denitrification tower (26). The bottom liquid phase outlet of the pre-denitrification tower (26) is sequentially connected to the flash tank (35) and the demethanizing tower (51), and the top gas phase outlet of the pre-denitrification tower (26) is sequentially connected to the pre-denitrification condenser (32) and the pre-denitrification reflux tank (29). The bottom liquid phase outlet of the pre-denitrification reflux tank (29) is connected to the pre-denitrification tower (26). The top gas phase outlet of the pre-denitrification reflux tank (29) is sequentially connected to the helium extraction tower reboiler (81), the secondary refrigeration unit (72), and the helium extraction tower (75). The top gas phase outlet of the demethanizer (51) is connected in sequence to the first-stage refrigeration unit (11) and the external lean natural gas pipeline (3), and the bottom liquid phase outlet of the demethanizer (51) is connected to the ethane mixed hydrocarbon processing unit (42). The gas phase outlet at the top of the helium extraction tower (75) is connected in sequence to the secondary refrigeration unit (72) and the crude helium pipeline (66); the liquid phase outlet at the bottom of the helium extraction tower (75) is connected to the denitrification tower (98). The top gas phase outlet of the denitrification tower (98) is connected in sequence to the denitrification condenser (94) and the denitrification reflux tank (88); the bottom liquid phase outlet of the denitrification tower (98) is connected in sequence to the secondary refrigeration unit (72) and the LNG product pipeline (91).

2. The system according to claim 1, wherein, The demethanizer (51) includes a side stream outlet (60), a side stream return outlet (61), a reboiler outlet (53), and a reboiler return outlet (54); the side stream outlet (60) and the side stream return outlet (61) are both located in the upper middle part of the demethanizer (51), and the side stream outlet (60) is located above the side stream return outlet (61); the reboiler outlet (53) and the reboiler return outlet (54) are both located in the upper middle part of the demethanizer (51). Located in the lower middle part of the demethanizer (51), and the reboiler outlet (53) is located above the reboiler return outlet (54); the demethanizer (51) is connected to the primary refrigeration unit (11) through the side line outlet (60) and the side line return outlet (61); the demethanizer (51) is connected to the demethanizer reboiler (46) through the reboiler outlet (53) and the reboiler return outlet (54).

3. The system according to claim 1, wherein, The helium extraction tower (75) includes a reboiler outlet (78) and a reboiler inlet (79); both the reboiler outlet (78) and the reboiler inlet (79) are located in the lower middle part of the helium extraction tower (75), and the reboiler outlet (78) is located above the reboiler inlet (79); the helium extraction tower (75) is connected to the helium extraction tower reboiler (81) through the reboiler outlet (78) and the reboiler inlet (79).

4. The system according to claim 1, wherein, The denitrification tower (98) includes a reboiler outlet (100) and a reboiler inlet (101); both the reboiler outlet (100) and the reboiler inlet (101) are located in the lower middle part of the denitrification tower (98), and the reboiler outlet (100) is located above the reboiler inlet (101); the denitrification tower (98) is connected to the denitrification reboiler (103) through the reboiler outlet (100) and the reboiler inlet (101).

5. The system according to claim 4, wherein, The top vapor outlet of the flash tank (35) is connected to the demethanizer (51); The bottom liquid phase outlet of the flash tank (35) is connected to the demethanizer (51), and / or the bottom liquid phase outlet of the flash tank (35) is sequentially connected to the denitrification reboiler (103), the pre-denitrification condenser (32) and the demethanizer (51).

6. The system according to claim 1, wherein, The gas phase outlet of the denitrification reflux tank (88) is sequentially connected to the built-in condenser (74) of the helium extraction tower (75), the secondary refrigeration device (72), and the flash nitrogen pipeline (68); the liquid phase outlet of the denitrification reflux tank (88) is connected to the denitrification tower (98).

7. A method for extracting helium from lean helium natural gas and producing multiple products, characterized in that, The method includes: The raw natural gas is subjected to a first-stage refrigeration and a first-stage cryogenic separation to obtain a first liquid phase and a first gas phase. The first gas phase is then subjected to pre-denitrification treatment to obtain a second liquid phase and a second gas phase. The second gas phase includes nitrogen, hydrogen and helium, and the carbon dioxide content in the second gas phase does not exceed 50 ppm. The first and second liquid phases are subjected to demethanization treatment to obtain methane and light hydrocarbons, and then ethane and propane are separated from the light hydrocarbons. The second gas phase is subjected to secondary refrigeration and then helium extraction to obtain a third gas phase and a third liquid phase. In the third gas phase, the concentration of helium is above 60 mol% and the content of nitrogen is below 15 mol%. The third liquid phase is subjected to denitrification treatment to obtain LNG product, wherein the nitrogen content in the LNG product does not exceed 1 mol%. The conditions for the pre-denitrification treatment include: the tower top operating temperature is -85℃ to -100℃, the tower bottom operating temperature is -75℃ to -90℃, and the operating pressure is 3-5 MPa. The conditions for helium extraction include: a tower top operating temperature of -170°C to -190°C, a tower bottom operating temperature of -105°C to -120°C, and an operating pressure of 1.8-3 MPa. The denitrification treatment conditions include: a tower top operating temperature of -150℃ to -170℃, a tower bottom operating temperature of -100℃ to -120℃, and an operating pressure of 1-2.5MPa.

8. The method according to claim 7, wherein, The raw material natural gas has a pressure of 3.5-5 MPa, a temperature of 15-25℃, a methane content of 80-98 mol%, a ethane and above light hydrocarbon content of 2-5.5 mol%, a carbon dioxide content of less than 1.5 mol%, a nitrogen content of 0.1-5 mol%, and a helium content of 200-3000 ppm.

9. The method according to claim 7, wherein, The conditions for the demethanization process include: a tower top operating temperature of -90°C to -105°C, a tower bottom operating temperature of 0-10°C, and an operating pressure of 2-3.5 MPa.

10. The method according to any one of claims 7-9, wherein, The method is performed in the system described in any one of claims 1-6.

11. The method according to claim 10, wherein, The pre-denitrification treatment is carried out in a pre-denitrification tower (26); and / or, The demethanizing process is carried out in a demethanizing tower (51); and / or, The helium extraction process is carried out in a helium extraction tower (75); and / or, The denitrification process is carried out in a denitrification tower (98).

12. The method according to claim 7, wherein, The primary refrigerant used in the primary refrigeration includes methane, ethylene, propane, and isopentane in a molar ratio of 1-6:2-8:1-5:1; the condensing pressure of the primary refrigerant is 2.5-3.5 MPa, and the evaporating pressure is 0.1-0.3 MPa; and / or, The secondary refrigerant used in the secondary refrigeration includes nitrogen, methane, ethylene, and isopentane, with a molar ratio of 1-5:1-6:1-8:1; the condensation pressure of the secondary refrigerant is 2.5-3.5 MPa, and the evaporation pressure is 0.2-0.3 MPa.

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