BOG helium concentration device and concentration method

Abstract

The invention provides a BOG helium concentration device and method. The concentration device comprises an LNG cold box and a built-in heat exchanger, and the LNG cold box is used for cooling BOG; the denitrification tower is communicated with the LNG cold box and is used for denitrifying the cooled BOG, methane in the natural gas is changed into mixed gas of liquid, residual helium, nitrogen and hydrogen, and denitrified tail gas is obtained; the helium concentration heat exchanger and the helium concentration tower are sequentially arranged at the downstream of the denitrification tower, and the helium concentration heat exchanger and the helium concentration tower are used for liquefying nitrogen into liquid nitrogen to obtain crude helium; outlets of the helium concentration heat exchanger and the helium concentration tower are communicated with the LNG cold box, and crude helium flows into the LNG cold box. Helium concentration is completed through the denitrification tower, the helium concentration heat exchanger and the helium concentration tower, the economical efficiency of an existing LNG production device is improved, energy is fully utilized, and the cold energy utilization rate is increased.

Description

Technical Field

[0001] The invention relates to the technical field of helium extraction from natural gas (BOG) tail gas, and in particular to a BOG helium enrichment device and enrichment method. Background Art

[0002] Helium plays an irreplaceable role in defense, industry, and technology fields such as aerospace, nuclear weapons, submarines, saturation diving operations, nuclear magnetic resonance, semiconductors, mobile phones, LCD screens, optical fibers, and large scientific facilities due to its special properties such as strong chemical inertness, extremely low boiling point, and very low solubility in the blood.

[0003] Helium exists mainly in natural gas or radioactive ores in nature. In the earth's atmosphere, the concentration of helium is very low, only 1 in 52,000. The helium contained in radioactive minerals on earth is the product of alpha decay. Helium is contained in some natural gas in an amount that is economically worth extracting, up to 7%. In my country's natural gas, helium is about 0.04% to 0.2%, which is not worth economically extracting.

[0004] Therefore, how to provide a BOG helium concentration device and method is a technical problem that those skilled in the art need to solve urgently. Summary of the invention

[0005] The present invention provides a BOG helium enrichment device and enrichment method, which are used to solve the defect of low helium extraction efficiency in the prior art, and to enrich the non-condensable gas helium in the BOG gas of the existing LNG production device, thereby improving the economy of the existing LNG production device.

[0006] The present invention provides a BOG helium enrichment device, comprising: LNG cold box, with a built-in heat exchanger, the LNG cold box is used to cool BOG; A denitrification tower, connected to the LNG cold box, is used to denitrify the cooled BOG, converting the methane in the natural gas into liquid, and leaving a mixed gas of helium, nitrogen and hydrogen to obtain denitrified tail gas; A helium concentration heat exchanger and a helium concentration tower are sequentially arranged downstream of the denitrification tower, and the helium concentration heat exchanger and the helium concentration tower are used to liquefy the nitrogen into liquid nitrogen to obtain crude helium; The outlets of the helium concentration heat exchanger and the helium concentration tower are in communication with the LNG cold box, and the crude helium flows into the LNG cold box.

[0007] A BOG helium concentration device provided according to the present invention also includes a top condenser, which is arranged between the denitrification tower and the helium concentration heat exchanger, and the top condenser is used to condense the remaining methane gas in the denitrification tail gas into a liquid state to completely remove methane.

[0008] A BOG helium concentration device provided by the present invention also includes a heavy hydrocarbon separator, which is connected to the LNG cold box. When the raw gas enters the LNG cold box for cooling, the heavy hydrocarbon separator is used to separate the cooled raw gas, remove heavy hydrocarbon impurities, and obtain cooled gas, and the cooled gas enters the LNG cold box again.

[0009] According to a BOG helium concentration device provided by the present invention, the denitrification tower is connected to the helium concentration heat exchanger, and the LNG formed at the outlet of the denitrification tower passes through the helium concentration heat exchanger and then enters the LNG cold box again.

[0010] According to a BOG helium concentration device provided by the present invention, it also includes an LNG storage tank and a BOG compressor, both of which are connected to the LNG cold box. The LNG storage tank is used to decompress the LNG so that part of the LNG is converted into BOG gas and refluxes to the LNG cold box; the BOG gas is compressed to room temperature by the BOG compressor and then returns to the LNG cold box.

[0011] The present invention also provides a BOG helium concentration method, comprising: Cooling the BOG by using an LNG cold box to obtain cooled BOG; Denitrification is performed on the cooled BOG by a denitrification tower, so that the methane in the natural gas becomes liquid, and the remaining helium, nitrogen and hydrogen are obtained to obtain denitrified tail gas; The denitrified tail gas is heat exchanged and concentrated through a helium concentration heat exchanger and a helium concentration tower to obtain crude helium; the crude helium flows into the LNG cold box and is then connected to a helium extraction unit.

[0012] A BOG helium enrichment method provided by the present invention comprises: Cooling the BOG by using an LNG cold box to obtain cooled BOG; Denitrification is performed on the cooled BOG by a denitrification tower, so that the methane in the natural gas becomes liquid, and the remaining helium, nitrogen and hydrogen are obtained to obtain denitrified tail gas; The denitrified tail gas is heat exchanged and concentrated through a helium concentration heat exchanger and a helium concentration tower to obtain crude helium; the crude helium flows into the LNG cold box and is then connected to a helium extraction unit.

[0013] A BOG helium enrichment method provided by the present invention further comprises: The raw gas enters the LNG cold box for cooling; The cooled raw gas is separated by a heavy hydrocarbon separator to remove heavy hydrocarbon impurities and obtain cooled gas.

[0014] According to a BOG helium concentration method provided by the present invention, the LNG formed at the outlet of the denitrification tower passes through the helium concentration heat exchanger and then enters the LNG cold box again to obtain the first-stage LNG.

[0015] According to a BOG helium enrichment method provided by the present invention, after obtaining the first-stage LNG, the method further comprises: The first-stage LNG flows from the LNG cold box to the LNG storage tank to achieve decompression, so that part of the liquid LNG becomes BOG gas and flows back to the LNG cold box; and the BOG gas is compressed to room temperature by the BOG compressor and then returns to the LNG cold box to obtain the BOG tail gas.

[0016] The BOG helium enrichment device and enrichment method provided by the present invention cool the BOG tail gas through an LNG cold box, denitrify the cooled BOG tail gas, convert methane in the natural gas into liquid, and obtain a mixed gas of remaining helium, nitrogen and hydrogen to obtain denitrified tail gas; a helium enrichment heat exchanger and a helium enrichment tower liquefy nitrogen into liquid nitrogen to obtain crude helium; and helium enrichment is completed through the denitrification tower, the helium enrichment heat exchanger and the helium enrichment tower, thereby improving the economy of the existing LNG production device, making full use of energy, and improving the utilization rate of cold capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 The figure is a schematic diagram of the structure of the helium enrichment device provided by the present invention.

[0019] Reference numerals: 1. LNG cold box; 2. Heat exchanger; 3. Denitrification tower; 4. Helium concentration heat exchanger; 5. Helium concentration tower; 6. Top condenser; 7. Heavy hydrocarbon separator; 8. LNG storage tank; 9. BOG compressor. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] In the description of the embodiments of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limitations on the embodiments of the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0022] Combine the following Figure 1 The BOG helium concentration device of the present invention includes an LNG cold box 1, a helium concentration tower 5, a denitrification tower 3, a helium concentration heat exchanger 4, and a denitrification tower top condenser 6.

[0023] like Figure 1 As shown, the LNG cold box 1 has a built-in heat exchanger 2, which is an aluminum brazed heat exchanger. The LNG cold box 1 is used to cool the BOG tail gas; the LNG cold box 1 can be filled with pearl sand to keep it cold. The heat exchanger 2 is installed perpendicular to the horizontal plane, that is, vertically installed, and the BOG tail gas enters from the top. The BOG tail gas enters the cold box and automatically recovers the cold energy from the bottom to the top.

[0024] The denitrification tower 3 is connected to the LNG cold box 1, and is used to denitrify the cooled BOG tail gas, so that the methane in the natural gas becomes liquid, and the remaining helium, nitrogen and hydrogen are mixed to obtain the denitrified tail gas; the helium concentration heat exchanger 4 and the helium concentration tower 5 are sequentially arranged downstream of the denitrification tower 3, and the helium concentration heat exchanger 4 and the helium concentration tower 5 are used to liquefy nitrogen into liquid nitrogen to obtain crude helium; The outlets of the helium concentration heat exchanger 4 and the helium concentration tower 5 are connected to the LNG cold box 1 , and the crude helium flows into the LNG cold box 1 .

[0025] like Figure 1 As shown, the working process of the helium enrichment device provided by the present invention is as follows: BOG tail gas enters the LNG cold box 1 and is cooled by the built-in aluminum brazing heat exchanger. The cooled BOG tail gas enters the denitrification tower 3 for denitrification treatment to obtain denitrified tail gas, and the denitrified tail gas enters the helium enrichment heat exchanger 4 for preliminary liquefaction of nitrogen, and then enters the nitrogen enrichment tower 5 for further purification to obtain crude helium. The crude helium flows out from the outlet of the helium enrichment tower 5 and re-enters the LNG cold box for connection to the helium extraction unit.

[0026] The helium concentration device provided by the present invention concentrates the non-condensable gas helium in the BOG gas of the existing LNG production device, thereby improving the economy of the existing LNG production device, making full use of energy, and improving the utilization rate of cold capacity.

[0027] In a feasible embodiment of the present invention, a tower top condenser 6 is further included, which is arranged between the denitrification tower 3 and the helium concentration heat exchanger 4. The tower top condenser 6 is used to condense the remaining methane gas in the denitrification tail gas into a liquid state to completely remove methane. By removing methane, the purity of the raw materials in the subsequent helium concentration process can be further improved, thereby ensuring that the final crude helium or higher-level helium products have higher quality. In addition, condensing methane can also recover part of the cold energy, which helps to maintain the energy balance of the entire system and may reduce additional cooling requirements.

[0028] In the above embodiment, a part of BOG enters the top condenser 6 to condense the gas phase at the top of the denitrification tower; the other part of BOG enters the middle of the denitrification tower. The helium-containing tail gas obtained at the top of the denitrification tower enters the top condenser 6 for cooling, and then enters the denitrification tower reflux tank to reflux the liquid phase to the denitrification tower 3. The gas phase enters the top condenser 6 for cooling, and then enters the helium concentration heat exchanger 4 for cooling, and then enters the top of the helium concentration tower 5. Liquid nitrogen is obtained at the bottom of the helium concentration tower 5. The crude helium obtained at the top enters the helium concentration heat exchanger 4 again for reheating, and then enters the plate-fin heat exchanger for reheating to room temperature to obtain crude helium with a concentration of 80%.

[0029] In a feasible embodiment of the present invention, a heavy hydrocarbon separator 7 is further included, which is connected to the LNG cold box 1. When the raw gas enters the LNG cold box 1 for cooling, the heavy hydrocarbon separator 7 is used to separate the cooled raw gas, remove heavy hydrocarbon impurities, and obtain cooled gas, and the cooled gas enters the LNG cold box 1 again. The denitrification tower 3 is connected to the helium concentration heat exchanger 4, and the LNG formed at the outlet of the denitrification tower enters the LNG cold box 1 again after passing through the helium concentration heat exchanger 4.

[0030] In the above embodiment, the cooled raw gas enters the heavy hydrocarbon separator 7, and the natural gas at the top of the heavy hydrocarbon separator 7 is divided into two paths. One part enters the LNG cold box 1, and is gradually cooled, condensed and supercooled in the process of flowing to the bottom until it is liquefied to -140°C, and then enters the middle part of the denitrification tower 3 after throttling and reducing the pressure through the flow regulating valve (JT valve) and flows from top to bottom; the other part of the natural gas enters the bottom of the denitrification tower 3 after throttling and reducing the pressure through the flow regulating valve as stripping gas to strip the LNG and remove nitrogen from the LNG.

[0031] In a feasible embodiment of the present invention, an LNG storage tank 8 and a BOG compressor 9 are also included, both of which are connected to the LNG cold box 1. The LNG storage tank 8 is used to reduce the pressure of LNG so that part of the LNG becomes BOG gas and flows back to the LNG cold box 1; the BOG gas is compressed to room temperature by the BOG compressor and then returns to the LNG cold box 1. The top of the denitrification tower 3 will obtain nitrogen-containing tail gas, and part of the LNG flowing out from the bottom of the denitrification tower 3 enters the reboiler of the helium concentration tower 5 and then merges into the LNG main pipe again, enters the LNG cold box 1 for cooling, and then enters the LNG storage tank 8. There is a decompression process in the LNG storage tank. Due to the reduction in pressure, part of the liquid phase will become a gas phase, that is, LNG becomes BOG. ​​BOG enters the LNG cold box 1 and recovers cold energy from bottom to top. After leaving the cold box, it enters the BOG compressor 9 for pressurization. The pressurized BOG re-enters the LNG cold box 1 for step-by-step cooling and condensation. Part of the BOG enters the top condenser 6 to condense the gas phase at the top of the denitrification tower; the other part of the BOG enters the middle of the denitrification tower.

[0032] A second aspect of the present invention provides a method for enriching BOG helium, comprising: S1. Cooling the BOG tail gas through the LNG cold box 1 to obtain cooled BOG tail gas.

[0033] The LNG cold box 1 has a built-in heat exchanger 2, which is an aluminum brazed heat exchanger. The LNG cold box 1 is used to cool the BOG tail gas; the LNG cold box 1 can be filled with pearl sand to keep it cold. The heat exchanger 2 is installed vertically on a horizontal plane, and the BOG tail gas enters from the top. The BOG tail gas enters the cold box and automatically recovers cold energy from bottom to top.

[0034] S2. The cooled BOG tail gas is denitrified by a denitrification tower 3, and the methane in the natural gas becomes liquid, and the remaining helium, nitrogen and hydrogen are obtained to obtain denitrified tail gas.

[0035] S3, the denitrified tail gas is heat exchanged and concentrated through the helium concentration heat exchanger 4 and the helium concentration tower 5 to obtain crude helium; the crude helium flows into the LNG cold box and is then connected to the helium extraction unit.

[0036] In the helium enrichment method provided by the present invention, BOG tail gas enters the LNG cold box 1 and is cooled by the built-in aluminum brazing heat exchanger. The cooled BOG tail gas enters the denitrification tower 3 for denitrification to obtain denitrified tail gas, and the denitrified tail gas enters the helium enrichment heat exchanger 4 for preliminary liquefaction of nitrogen, and then enters the nitrogen enrichment tower 5 for further purification to obtain crude helium. The crude helium flows out from the outlet of the helium enrichment tower 5 and re-enters the LNG cold box for connecting the helium extraction unit.

[0037] In a feasible embodiment of the present invention, before step S3, the remaining methane gas in the denitrification tail gas is condensed into a liquid state by a tower top condenser 6 to completely remove methane. By removing methane, the purity of the raw material in the subsequent helium concentration process can be further improved, thereby ensuring that the final crude helium or higher-level helium product has a higher quality. In addition, condensing methane can also recover part of the cold energy, which helps to maintain the energy balance of the entire system and may reduce the need for additional cooling.

[0038] In the above embodiment, a part of BOG enters the top condenser 6 to condense the gas phase at the top of the denitrification tower; the other part of BOG enters the middle of the denitrification tower. The helium-containing tail gas obtained at the top of the denitrification tower enters the top condenser 6 for cooling, and then enters the denitrification tower reflux tank to reflux the liquid phase to the denitrification tower 3. The gas phase enters the top condenser 6 for cooling, and then enters the helium concentration heat exchanger 4 for cooling, and then enters the top of the helium concentration tower 5. Liquid nitrogen is obtained at the bottom of the helium concentration tower 5. The crude helium obtained at the top enters the helium concentration heat exchanger 4 for reheating again, and then enters the plate-fin heat exchanger for reheating to room temperature to obtain crude helium with a concentration of 80%.

[0039] In a feasible embodiment of the present invention, before step S1, the method further includes: The raw gas enters the LNG cold box 1 for cooling; the cooled raw gas is separated by the heavy hydrocarbon separator 7 to remove heavy hydrocarbon impurities to obtain cooled gas.

[0040] When the raw gas enters the LNG cold box 1 for cooling, the heavy hydrocarbon separator 7 is used to separate the cooled raw gas, remove heavy hydrocarbon impurities, and obtain cooled gas, and the cooled gas enters the LNG cold box 1 again. The denitrification tower 3 is connected to the helium concentration heat exchanger 4, and the LNG formed at the outlet of the denitrification tower passes through the helium concentration heat exchanger 4 and enters the LNG cold box 1 again. The LNG formed through the outlet of the denitrification tower 3 passes through the helium concentration heat exchanger 4 and enters the LNG cold box 1 again to obtain the first stage LNG.

[0041] In the above embodiment, the cooled raw gas enters the heavy hydrocarbon separator 7, and the natural gas at the top of the heavy hydrocarbon separator 7 is divided into two paths. One part enters the LNG cold box 1, and is gradually cooled, condensed and supercooled in the process of flowing to the bottom until it is liquefied to -140°C, and then enters the middle part of the denitrification tower 3 after throttling and reducing the pressure through the flow regulating valve (JT valve) and flows from top to bottom; the other part of the natural gas enters the bottom of the denitrification tower 3 after throttling and reducing the pressure through the flow regulating valve as stripping gas to strip the LNG and remove nitrogen from the LNG.

[0042] In a feasible embodiment of the present invention, after obtaining the first-stage LNG, the method further comprises: In the first stage, LNG flows from the LNG cold box 1 to the LNG storage tank 8 to achieve decompression, so that part of the liquid LNG is converted into BOG gas and flows back to the LNG cold box 1; and the BOG gas is compressed to room temperature by the BOG compressor 9 and then returns to the LNG cold box 1 to obtain BOG tail gas.

[0043] Nitrogen-containing tail gas will be obtained at the top of the denitrification tower 3. Part of the LNG flowing out from the bottom of the denitrification tower 3 enters the reboiler of the helium concentration tower 5 and then enters the LNG main pipe again, enters the LNG cold box 1 for cooling, and then enters the LNG storage tank 8. There is a decompression process in the LNG storage tank. Due to the pressure reduction, part of the liquid phase will become the gas phase, that is, LNG becomes BOG. ​​BOG enters the LNG cold box 1 to recover cold energy from bottom to top. After leaving the cold box, it enters the BOG compressor 9 for pressurization. The pressurized BOG re-enters the LNG cold box 1 for step-by-step cooling and condensation. Part of the BOG enters the top condenser 6 to condense the gas phase at the top of the denitrification tower; the other part of the BOG enters the middle of the denitrification tower.

[0044] In the helium enrichment method provided by the present invention, the raw gas (natural gas) enters the LNG cold box 1, and the heat exchanger is an aluminum brazing heat exchanger. After being cooled by the LNG cold box 1, the raw gas enters the heavy hydrocarbon separator 7, and the gas at the top of the heavy hydrocarbon separator 7 enters the LNG cold box 1 again, and then enters the denitrification tower 3 through the regulating valve.

[0045] The liquid phase coming out of the bottom of the denitrification tower 3 is LNG, which enters the helium concentration heat exchanger 2, then returns to the LNG cold box 1 and enters the LNG storage tank 8. There is a decompression process in the LNG storage tank 8. Due to the reduction in pressure, part of the liquid will turn into flash steam, i.e. BOG, and then enter the LNG cold box 1 to room temperature, then enter the BOG compressor for pressurization, and then enter the LNG cold box 1.

[0046] Then it enters the denitrification tower 3, and the components are methane, helium, nitrogen and hydrogen. In the denitrification tower 3, most of the methane will change from liquid to gaseous phase, and the remaining helium, nitrogen, hydrogen and part of the methane will enter the top condenser 6, and then enter the helium concentration heat exchanger 4. In the helium concentration heat exchanger 4 and the helium concentration tower 5, in the helium concentration tower 5, the nitrogen will change from gaseous to liquid, which is called liquid nitrogen. The remaining gas is a mixture of helium and hydrogen, so as to obtain the required helium, which will be sent to the corresponding helium extraction unit.

[0047] In the description of the embodiments of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

[0048] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "mode", "specific mode", or "some modes" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or mode are included in at least one embodiment or mode of the embodiment of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or mode. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or modes in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or modes described in this specification and the features of the different embodiments or modes, without contradiction.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A BOG helium concentration device, characterized in that: include: An LNG cold box (1) has a heat exchanger (2) built in it, and the LNG cold box (1) is used to cool BOG tail gas; A denitrification tower (3) is connected to the LNG cold box (1) and is used to denitrify the cooled BOG tail gas, converting the methane in the natural gas into liquid and leaving a mixed gas of helium, nitrogen and hydrogen to obtain denitrified tail gas; A helium concentration heat exchanger (4) and a helium concentration tower (5) are sequentially arranged downstream of the denitrification tower (3); the helium concentration heat exchanger (4) and the helium concentration tower (5) are used to liquefy the nitrogen into liquid nitrogen to obtain crude helium; the outlets of the helium concentration heat exchanger (4) and the helium concentration tower (5) are connected to the LNG cold box (1), and the crude helium flows into the LNG cold box (1).

2. The BOG helium concentration device according to claim 1, characterized in that: It also includes a tower top condenser (6) disposed between the denitrification tower (3) and the helium concentration heat exchanger (4), the tower top condenser (6) being used to condense the remaining methane gas in the denitrification tail gas into a liquid state, so as to completely remove the methane.

3. The BOG helium concentration device according to claim 1, characterized in that: It also includes a heavy hydrocarbon separator (7) which is in communication with the LNG cold box (1). When the raw gas enters the LNG cold box (1) for cooling, the heavy hydrocarbon separator (7) is used to separate the cooled raw gas and remove heavy hydrocarbon impurities to obtain cooled gas. The cooled gas then enters the LNG cold box (1) again.

4. The BOG helium concentration device according to claim 3, characterized in that: The denitrification tower (3) is connected to the helium concentration heat exchanger (4), and the LNG formed at the outlet of the denitrification tower passes through the helium concentration heat exchanger (4) and then enters the LNG cold box (1) again.

5. The BOG helium concentration device according to claim 4, characterized in that: It also includes an LNG storage tank (8) and a BOG compressor (9), both of which are connected to the LNG cold box (1). The LNG storage tank (8) is used to reduce the pressure of LNG so that part of the LNG is converted into BOG gas and flows back to the LNG cold box (1); the BOG gas is compressed to room temperature by the BOG compressor and then returns to the LNG cold box (1).

6. A method for enriching BOG helium, characterized in that: include: Cooling the BOG by means of an LNG cold box (1) to obtain cooled BOG; Denitrogenating the cooled BOG through a denitrogenation tower (3), whereby the methane in the natural gas becomes liquid, and remaining helium, nitrogen and hydrogen are obtained to obtain denitrogenated tail gas; The denitrified tail gas is heat exchanged and concentrated by a helium concentration heat exchanger (4) and a helium concentration tower (5) to obtain crude helium; the crude helium flows into the LNG cold box and is then connected to a helium extraction unit.

7. The BOG helium concentration method according to claim 6, characterized in that: Before the denitrification tail gas is subjected to heat exchange and concentration through the helium concentration heat exchanger (4) and the helium concentration tower (5), the method further comprises condensing the remaining methane gas in the denitrification tail gas into liquid.

8. The BOG helium concentration method according to claim 7, characterized in that: Also includes: The raw gas enters the LNG cold box (1) for cooling; The cooled raw gas is separated by a heavy hydrocarbon separator (7) to remove heavy hydrocarbon impurities, thereby obtaining cooled gas.

9. The BOG helium concentration method according to claim 8, characterized in that: The LNG formed at the outlet of the denitrification tower (3) passes through the helium concentration heat exchanger (4) and then enters the LNG cold box (1) again to obtain the first-stage LNG.

10. The BOG helium concentration method according to claim 9, characterized in that: After obtaining the first phase of LNG, it also includes: The first-stage LNG flows from the LNG cold box (1) to the LNG storage tank (8) to achieve decompression, so that part of the liquid phase LNG is converted into BOG gas and flows back to the LNG cold box (1); and the BOG gas is compressed to room temperature by the BOG compressor (9) and then returns to the LNG cold box (1), thereby obtaining BOG tail gas.

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