An LNG device and method integrating natural gas helium extraction, nitrogen removal and BOG reliquefaction

Abstract

This invention discloses an LNG unit and method integrating natural gas helium extraction, denitrification, and BOG reliquefaction. The unit includes a main heat exchanger, a heavy hydrocarbon separator, a denitrification tower, a denitrification tower condenser, a denitrification tower reflux tank, a helium distillation tower, a helium distillation tower condenser, a helium distillation tower reflux tank, a refrigerant cryogenic separator, an LNG storage tank, a BOG heater, a BOG compressor, a helium distillation tower reboiler, a mixed refrigerant compressor system, and a nitrogen compressor system. This solution integrates the mixed refrigerant refrigeration cycle and the nitrogen refrigeration cycle, and through the co-production mode of LNG and crude helium, it significantly reduces the plant's overall energy consumption and improves economic efficiency. Moreover, the unit has outstanding advantages such as strong raw material adaptability, safe and reliable operation, and wide application scenarios, realizing the diversified and efficient utilization of natural gas resources.

Description

Technical Field

[0001] This invention relates to the field of cryogenic liquefaction and separation technology, and in particular to an LNG device and method that integrates natural gas helium extraction, denitrification and BOG reliquefaction. Background Technology

[0002] Helium is an indispensable key strategic resource in high-tech fields such as national defense, aerospace, semiconductors, and medicine, and its stable supply is of great significance to national strategic security. However, my country's natural gas resources are generally characterized by "helium deficiency," with helium content typically below 0.1%. This situation has led to my country's long-term high dependence on imported helium, resulting in a persistently high level of foreign dependence. It is worth noting that flash vapor (BOG) is inevitably generated during the production and storage of LNG (liquefied natural gas). As major components such as methane are liquefied and separated, helium, as a non-condensable gas, naturally accumulates in the BOG, with concentrations reaching several times or even tens of times higher than those of the raw natural gas. This characteristic provides a significant breakthrough for low-cost, large-scale helium extraction.

[0003] Efficient handling of bound gas (BOG) is a key issue for the sustainable development of the LNG industry. During the operation and storage of LNG plants, BOG generation is unavoidable due to factors such as changes in ambient temperature and fluctuations in tank pressure. Directly releasing or simply burning this gas not only wastes valuable energy and causes significant economic losses but also exacerbates greenhouse gas emissions, failing to meet environmental protection requirements. Current industry practices for BOG handling largely focus on reliquefaction and recovery, using specialized equipment to convert it back into liquefied natural gas to maintain stable tank pressure and recover resources. However, these traditional reliquefaction technologies only focus on energy recovery and fail to fully exploit the rare strategic resource of helium enriched in BOG. ​​This results in helium being reintroduced into LNG during the BOG reliquefaction process, causing a hidden loss of this rare resource.

[0004] Existing technologies suffer from significant integration deficiencies in the recovery and processing of by-product resources in the LNG industry. Helium extraction, nitrogen removal, and BOG reliquefaction are often implemented as independent unit operations, lacking systematic coupled optimization design. This results in complex overall processes, large footprints, and high overall energy consumption. From a technological perspective, existing solutions often focus on achieving single functions, with functional modules being isolated and failing to create synergy. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides an LNG device and method integrating natural gas helium extraction, denitrification, and BOG reliquefaction. A cold box includes natural gas denitrification, BOG reliquefaction, and helium extraction equipment. While producing LNG products with a nitrogen content of less than 1%, it increases the liquefaction rate of natural gas and increases helium production. This invention has advantages such as a short process flow, high natural gas liquefaction utilization rate, high helium yield, low energy consumption, and reasonable investment.

[0006] This invention is achieved using the following technical solution: In the first aspect, an LNG unit integrating natural gas helium extraction, denitrification, and BOG reliquefaction is provided. The unit includes a main heat exchanger, a heavy hydrocarbon separator, a denitrification tower, a denitrification tower condenser, a denitrification tower reflux tank, a helium distillation tower, a helium distillation tower condenser, a helium distillation tower reflux tank, a refrigerant cryogenic separator, an LNG storage tank, a BOG heater, a BOG compressor, a helium distillation tower reboiler, a mixed refrigerant compressor system, and a nitrogen compressor system. The main heat exchanger is equipped with a feed gas I channel, a feed gas II channel, a BOG reliquefaction channel, an LNG subcooling channel, a crude helium I channel, a nitrogen-rich I channel, a high-pressure nitrogen I channel, a low-pressure reflux nitrogen I channel, a low-pressure reflux refrigerant I channel, a high-pressure gas phase refrigerant I channel, a high-pressure gas phase refrigerant II channel, a high-pressure liquid phase refrigerant I channel, and a high-pressure liquid phase refrigerant II channel. The denitrification tower condenser is equipped with a nitrogen-rich gas II channel and a low-pressure reflux refrigerant II channel. The helium distillation column condenser is equipped with a low-pressure reflux nitrogen II channel, a crude helium II channel, a liquid nitrogen channel, a nitrogen-rich III channel, and a crude helium III channel.

[0007] Specifically, the inlet of the raw material gas I channel is connected to the purified raw material gas from the outside, and the outlet is connected to the feed inlet of the heavy hydrocarbon separator. The bottom liquid phase outlet of the heavy hydrocarbon separator is connected to the external heavy hydrocarbon storage pipeline. The top gas phase outlet of the heavy hydrocarbon separator is divided into two parts: one part is connected to the inlet of the raw material gas II channel, and the other part is connected to the feed inlet of the denitrification tower. The outlet of the raw material gas II channel is connected to the feed inlet of the denitrification tower.

[0008] Specifically, the bottom liquid phase outlet of the denitrification tower is connected to the inlet of the LNG subcooling channel, and the outlet of the LNG subcooling channel is connected to the feed inlet of the LNG storage tank; the top gas phase outlet of the LNG storage tank is connected to the inlet of the BOG heater, the outlet of the BOG heater is connected to the inlet of the BOG compressor, the outlet of the BOG compressor is connected to the inlet of the BOG reliquefaction channel, and the outlet of the BOG reliquefaction channel is connected to the feed inlet of the denitrification tower.

[0009] Specifically, the top gas phase outlet of the denitrification tower is connected to the inlet of the nitrogen-rich gas II channel, and the outlet of the nitrogen-rich gas II channel is connected to the feed inlet of the denitrification tower reflux tank; the bottom liquid phase outlet of the denitrification tower reflux tank is connected to the feed inlet of the denitrification tower, and the top gas phase outlet is connected to the feed inlet of the helium distillation tower; the bottom liquid phase outlet of the helium distillation tower is connected to the inlet of the nitrogen-rich gas III channel, the outlet of the nitrogen-rich gas III channel is connected to the inlet of the nitrogen-rich gas I channel, and the outlet of the nitrogen-rich gas I channel is connected to an external nitrogen-rich gas pipeline. The top gas phase outlet of the helium distillation column is connected to the inlet of the crude helium III channel, and the outlet of the crude helium III channel is connected to the feed inlet of the helium distillation column reflux tank; the bottom liquid phase outlet of the helium distillation column reflux tank is connected to the feed inlet of the helium distillation column, and the top gas phase outlet is connected to the inlet of the crude helium II channel; the outlet of the crude helium II channel is connected to the inlet of the crude helium I channel, and the outlet of the crude helium I channel is connected to the external crude helium pipeline.

[0010] Specifically, the outlet of the nitrogen compressor system is connected to the inlet of the high-pressure nitrogen I channel, and the outlet of the high-pressure nitrogen I channel is connected to the inlet of the helium distillation column reboiler; the outlet of the helium distillation column reboiler is connected to the inlet of the liquid nitrogen channel, the outlet of the liquid nitrogen channel is connected to the inlet of the low-pressure reflux nitrogen II channel, and the outlet of the low-pressure reflux nitrogen II channel is connected to the inlet of the low-pressure reflux nitrogen I channel; the outlet of the low-pressure reflux nitrogen I channel is connected to the inlet of the nitrogen compressor system, and the high-pressure mixed refrigerant liquid phase pipeline at the outlet of the mixed refrigerant compressor system is connected to the inlet of the high-pressure liquid phase refrigerant I channel.

[0011] Specifically, the outlet of the high-pressure liquid refrigerant I channel is connected to the inlet of the low-pressure reflux refrigerant I channel; the outlet of the mixed refrigerant compressor system, the high-pressure mixed refrigerant gas phase, is connected to the inlet of the high-pressure gas phase refrigerant I channel, and the outlet of the high-pressure gas phase refrigerant I channel is connected to the inlet of the refrigerant cryogenic separator; the bottom liquid phase outlet of the refrigerant cryogenic separator is connected to the inlet of the high-pressure liquid refrigerant II channel, and the outlet of the high-pressure liquid refrigerant II channel is connected to the inlet of the low-pressure reflux refrigerant I channel; the top gas phase outlet of the refrigerant cryogenic separator is connected to the inlet of the high-pressure gas phase refrigerant II channel, and the outlet of the high-pressure gas phase refrigerant II channel is divided into two parts, one part being connected to the inlet of the low-pressure reflux refrigerant I channel, and the other part being connected to the inlet of the low-pressure reflux refrigerant II channel; the outlet of the low-pressure reflux refrigerant II channel is connected to the inlet of the low-pressure reflux refrigerant I channel, and the outlet of the low-pressure reflux refrigerant I channel is connected to the inlet of the mixed refrigerant compressor system.

[0012] Specifically, the denitrification tower and the helium distillation tower are packed towers or plate towers; the reboiler of the helium distillation tower can be built-in or external.

[0013] Specifically, the pipeline between the top gas phase outlet of the heavy hydrocarbon separator and the feed inlet of the denitrification tower is equipped with a regulating valve a for regulating the bottom temperature of the denitrification tower; the pipeline at the outlet of the raw material gas II channel is equipped with a regulating valve b; the inlet pipeline of the low-pressure reflux refrigerant II channel is equipped with a regulating valve c; the top gas phase outlet pipeline of the denitrification tower reflux tank is equipped with a regulating valve d for regulating the top pressure of the denitrification tower; and the outlet pipeline of the LNG subcooling channel is equipped with a regulating valve e for regulating the liquid level at the bottom of the denitrification tower. The bottom liquid phase outlet pipeline of the helium distillation column is equipped with a regulating valve f for adjusting the liquid level at the bottom of the helium distillation column; the top gas phase outlet pipeline of the helium distillation column reflux tank is equipped with a regulating valve g for adjusting the pressure at the top of the helium distillation column; a regulating valve h is installed between the liquid nitrogen channel outlet and the low-pressure reflux nitrogen II channel inlet for controlling the outlet temperature of the crude helium III channel. A regulating valve i is installed on the pipeline between the outlet of the high-pressure gaseous refrigerant II channel and the inlet of the low-pressure reflux refrigerant I channel; a regulating valve j is installed on the pipeline between the outlet of the high-pressure liquid refrigerant II channel and the inlet of the low-pressure reflux refrigerant I channel; a regulating valve k is installed on the pipeline between the outlet of the high-pressure liquid refrigerant I channel and the inlet of the low-pressure reflux refrigerant I channel; a regulating valve l is installed on the outlet pipeline of the BOG reliquefaction channel; a regulating valve m is installed on the top gaseous outlet pipeline of the LNG storage tank to control the top pressure of the LNG storage tank; and a regulating valve n is installed on the pipeline between the inlet and outlet of the helium distillation tower reboiler to control the liquid temperature at the bottom of the helium distillation tower.

[0014] On the other hand, a method for LNG integrating helium extraction, denitrification, and BOG reliquefaction of natural gas includes pretreatment and further helium extraction, denitrification, and BOG reliquefaction, wherein the pretreatment specifically includes the following steps: Step S1: Purified natural gas containing nitrogen and helium enters the feed gas I channel, where it is cooled to -70~-60℃ by the reflux cold stream. Some of the heavy components condense and enter the heavy hydrocarbon separator for gas-liquid separation. The liquid at the bottom is sent outside the boundary as a heavy hydrocarbon product, while the gas phase at the top re-enters the feed gas II channel and is cooled to -145~-130℃ by the cold stream. It is then sent to the middle of the denitrification tower for distillation separation. The LNG from the bottom of the denitrification tower is sent to the LNG subcooling channel of the main heat exchanger for subcooling to -162℃, and then sent to the LNG storage tank for storage through regulating valve e. Step S2: The low-temperature nitrogen-rich gas at the top outlet of the denitrification tower enters the nitrogen-rich gas II channel and is cooled to -155~-163℃. The methane component is condensed again and then enters the denitrification tower reflux tank for gas-liquid separation. The liquid at the bottom of the tank returns to the top feed port of the denitrification tower for reflux. The nitrogen-rich gas at the top of the denitrification tower reflux tank is depressurized by regulating valve d and then sent to the middle of the helium distillation tower for distillation. Step S3: Inside the helium distillation column, rising helium gas and downstream nitrogen-rich liquid come into contact and transfer heat and mass on the surface of the structured packing. The nitrogen-rich liquid obtained at the bottom of the helium distillation column is depressurized by regulating valve f and sent to the nitrogen-rich gas III channel of the helium distillation column condenser to provide cooling for the condensation reflux of the helium distillation column. Then it enters the nitrogen-rich gas I channel and is reheated to room temperature by the hot flow before being sent out of the boundary area as fuel gas. Step S4: The low-temperature helium-rich gas at the top outlet of the helium distillation column is cooled to -182~-175℃ in the crude helium III channel of the helium distillation column condenser. The methane component and part of the nitrogen component are condensed and enter the helium distillation column reflux tank for gas-liquid separation. The liquid at the bottom of the tank returns to the feed inlet at the top of the helium distillation column for reflux. The crude helium gas at the top of the reflux tank is introduced into the crude helium II channel through the regulating valve g for cold recovery. It is then introduced into the crude helium I channel to be reheated to room temperature and sent out of the boundary as crude helium product.

[0015] Specifically, the further helium extraction, denitrification, and BOG reliquefaction include: Step S5: The BOG from the LNG storage tank is first heated to room temperature by the BOG heater, then sent to the BOG compressor for pressurization to 0.6~1.0 MPa, and then introduced into the BOG reliquefaction channel to be cooled to -162~-155℃. It then enters the top feed inlet of the denitrification tower for distillation and separation to recover methane and helium. Step S6: The high-pressure liquid refrigerant from the mixed refrigerant compressor system is subcooled to -30~-70℃ in the high-pressure liquid refrigerant I channel of the main heat exchanger. After being throttled and depressurized by regulating valve k, it enters the inlet of the low-pressure return refrigerant I channel. The high-pressure gaseous refrigerant from the mixed refrigerant compressor system is cooled to -30~-70℃ in the high-pressure gaseous refrigerant I channel of the main heat exchanger and then enters the refrigerant cryogenic separator for gas-liquid separation. The liquid separated at the bottom enters the high-pressure liquid refrigerant II channel, is subcooled to -130~-80℃, and then throttled and depressurized by regulating valve j before entering the inlet of the low-pressure return refrigerant I channel. The liquid from the top of the refrigerant cryogenic separator... The high-pressure gaseous refrigerant enters the high-pressure gaseous refrigerant II channel and is cooled and condensed to -165~-160℃. It is divided into two parts. Most of it is throttled and depressurized by regulating valve i and then enters the inlet of the low-pressure reflux refrigerant I channel. A small part is throttled and depressurized by regulating valve c and then enters the low-pressure reflux refrigerant II channel. This provides a cold source for the separation of methane at the top of the denitrification tower. The refrigerant exits the low-pressure reflux refrigerant II channel and returns to the inlet of the low-pressure reflux refrigerant I channel. The mixed refrigerant entering the low-pressure reflux refrigerant I channel absorbs heat and evaporates. After evaporating into gas and being reheated to room temperature, it exits the main heat exchanger and then returns to the mixed refrigerant compressor system to complete the mixed refrigerant refrigeration cycle. Step S7: High-pressure nitrogen from the nitrogen compression system is cooled to approximately -155~-145℃ in the high-pressure nitrogen I channel, and then enters the reboiler of the helium distillation column as a heat source for the helium distillation column. The helium content in the nitrogen-rich liquid is controlled to be ≤50ppm. After being cooled by the liquid in the bottom of the helium distillation column, it is reintroduced into the liquid nitrogen channel for subcooling to -180℃. After being throttled and depressurized by the regulating valve h, it enters the low-pressure reflux nitrogen II channel to provide cooling for the helium distillation of the helium in the helium distillation column. Then it returns to the low-pressure reflux nitrogen I channel to be reheated to room temperature before exiting the main heat exchanger and then returning to the inlet of the nitrogen compression system to complete the nitrogen refrigeration cycle.

[0016] The beneficial effects of this invention are as follows: (1) High process integration, excellent resource utilization and investment economy: This solution integrates three core functions—natural gas helium extraction, BOG reliquefaction, and denitrification—through a single cold box, achieving multi-unit collaborative operation. The raw gas is first distilled in a denitrification tower to remove light components such as nitrogen and helium, ensuring that the nitrogen content of the LNG product meets the standards. At the same time, the nitrogen-enriched gas at the top of the denitrification tower achieves preliminary enrichment of helium components. After enrichment, the gas enters the helium distillation tower for further separation to obtain crude helium products. The BOG generated by the LNG storage tank is pressurized and returned to the cold box for reliquefaction, and then sent back to the denitrification tower for distillation. This integrated design significantly shortens the process flow, reduces the equipment footprint, lowers the overall investment cost, and significantly improves the methane liquefaction rate and helium recovery efficiency, achieving cascade utilization of resources.

[0017] (2) Low energy consumption and high operational flexibility: This scheme adopts a dual-cycle coupling design of mixed refrigerant refrigeration and nitrogen refrigeration to meet different process requirements. The mixed refrigerant refrigeration cycle provides cooling for the natural gas liquefaction and denitrification processes, while the nitrogen refrigeration cycle provides cooling for the helium distillation process. The two refrigeration cycles are relatively independent and can be flexibly adjusted according to production needs. When helium extraction is not required, the helium distillation tower can be stopped, while the LNG liquefaction and BOG reliquefaction systems can still operate normally, avoiding the impact of a single function shutdown on the overall unit and greatly improving the operational flexibility and overall energy efficiency of the unit.

[0018] (3) High helium yield and full recovery of strategic resources: On the one hand, the denitrification tower enables efficient distillation and separation of nitrogen and light components such as helium in LNG, laying the foundation for helium enrichment; on the other hand, the BOG generated by the LNG storage tank is heated and pressurized and returned to the cold box for reliquefaction, and then re-enters the denitrification tower to participate in the separation process, effectively recovering the helium components enriched in the BOG, avoiding the loss of rare strategic resources, and significantly improving the overall helium yield.

[0019] (4) In addition, this device has the advantages of convenient maintenance, reliable operation, safety and reliability, and wide applicability. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the LNG device integrating natural gas helium extraction, denitrification and BOG reliquefaction in an embodiment of the present invention; in: 1-Main heat exchanger, 2-Heavy hydrocarbon separator, 3-Denitrification tower, 4-Denitrification tower condenser, 5-Denitrification tower reflux tank, 6-Helium distillation tower, 7-Helium distillation tower condenser, 8-Helium distillation tower reflux tank, 9-Refrigerant cryogenic separator, 10-LNG storage tank, 11-BOG heater, 12-BOG compressor, 13-Helium distillation tower reboiler, 14-Mixed refrigerant compressor system, 15-Nitrogen compressor system; 2-A, 2-B, and 2-C represent the feed inlet, bottom liquid phase outlet, and top gas phase outlet of the heavy hydrocarbon separator, respectively. 3-A, 3-B, 3-D, and 3-F represent the four feed inlets of the denitrification tower, 3-C represents the top gas phase outlet of the denitrification tower, and 3-E represents the bottom liquid phase outlet of the denitrification tower. 5-A, 5-B, and 5-C represent the feed inlet, top gas phase outlet, and bottom liquid phase outlet of the denitrification tower reflux tank, respectively. 6-A and 6-C represent the two feed inlets of the helium distillation column, 6-B represents the top vapor phase outlet of the helium distillation column, and 6-D represents the bottom liquid phase outlet of the helium distillation column. 8-A, 8-B, and 8-C represent the feed inlet, top vapor outlet, and bottom liquid outlet of the helium distillation column reflux tank, respectively. 9-A, 9-B, and 9-C represent the feed inlet, bottom liquid phase outlet, and top gas phase outlet of the refrigerant cryogenic separator, respectively. 10-A and 10-B represent the LNG storage tank's feed inlet and top vapor phase outlet, respectively. 101-Control valve a, 102-Control valve b, 103-Control valve c, 104-Control valve d, 105-Control valve e, 106-Control valve f, 107-Control valve g, 108-Control valve h, 109-Control valve i, 110-Control valve j, 111-Control valve k, 112-Control valve l, 113-Control valve m, 114-Control valve n; A1 - Feed gas I channel, A2 - Feed gas II channel, A3 - BOG reliquefaction channel, A4 - LNG subcooling channel, A5 - Crude helium I channel, A6 - Nitrogen-rich I channel, A7 - High-pressure nitrogen I channel, A8 - Low-pressure reflux nitrogen I channel, A9 - Low-pressure reflux refrigerant I channel, A10 - High-pressure gas phase refrigerant channel I, A11 - High-pressure gas phase refrigerant channel II, A12 - High-pressure liquid phase refrigerant I channel, A13 - High-pressure liquid phase refrigerant II channel, B1 - Nitrogen-rich II channel, B2 - Low-pressure reflux refrigerant II channel, C1 - Low-pressure reflux nitrogen II channel, C2 - Crude helium II channel, C3 - Liquid nitrogen channel, C4 - Nitrogen-rich III channel, C5 - Crude helium III channel; A9-A, A9-B, and A9-C represent the three inlets of the low-pressure reflux refrigerant channel I. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0023] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0024] The following is in conjunction with the appendix Figure 1 The following describes some embodiments of the present invention in detail. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0025] This invention proposes an LNG device and method integrating natural gas helium extraction, denitrification, and BOG reliquefaction. In a preferred embodiment, the device is as follows: Figure 1 As shown, it includes a main heat exchanger 1, a heavy hydrocarbon separator, a denitrification tower 3, a denitrification tower condenser 4, a denitrification tower reflux tank 5, a helium distillation tower 6, a helium distillation tower condenser 7, a helium distillation tower reflux tank 8, a refrigerant cryogenic separator 9, an LNG storage tank 10, a BOG heater 11, a BOG compressor 12, a helium distillation tower reboiler 13, a mixed refrigerant compressor system 14, and a nitrogen compressor system 15.

[0026] In this embodiment, the main heat exchanger 1 is provided with a feed gas I channel A1, a feed gas II channel A2, a BOG reliquefaction channel A3, an LNG subcooling channel A4, a crude helium I channel A5, a nitrogen-rich I channel A6, a high-pressure nitrogen I channel A7, a low-pressure reflux nitrogen I channel A8, a low-pressure reflux refrigerant I channel A9, a high-pressure gas phase refrigerant channel IA10, a high-pressure gas phase refrigerant II channel A11, a high-pressure liquid phase refrigerant I channel A12, and a high-pressure liquid phase refrigerant II channel A13. The denitrification tower condenser 4 is provided with a nitrogen-rich II channel B1 and a low-pressure reflux refrigerant II channel B2. The helium distillation tower condenser 7 is provided with a low-pressure reflux nitrogen II channel C1, a crude helium II channel C2, a liquid nitrogen channel C3, a nitrogen-rich III channel C4, and a crude helium III channel C5. The inlet of raw gas channel A1 is connected to the purified raw gas from the outside. The outlet of raw gas channel A1 is connected to the feed inlet 2-A of heavy hydrocarbon separator 2. The bottom liquid phase outlet 2-B of heavy hydrocarbon separator 2 is connected to the external heavy hydrocarbon storage pipeline. The top gas phase outlet 2-C of heavy hydrocarbon separator 2 is divided into two parts: one part is connected to the inlet of raw gas channel A2, and the other part is connected to the feed inlet 3-F of denitrification tower 3.

[0027] In this embodiment, the outlet of feed gas channel II A2 is connected to the feed inlet 3-A of denitrification tower 3; the bottom liquid phase outlet 3-E of denitrification tower 3 is connected to the inlet of LNG subcooling channel A4; the outlet of LNG subcooling channel A4 is connected to the feed inlet 10-A of LNG storage tank 10; the top gas phase outlet 10-B of LNG storage tank 10 is connected to the inlet of BOG heater 11; the outlet of BOG heater 11 is connected to the inlet of BOG compressor 12; the outlet of BOG compressor 12 is connected to the inlet of BOG reliquefaction channel A3; and the outlet of BOG reliquefaction channel A3 is connected to the feed inlet 3-B of denitrification tower 3. The top gas phase outlet 3-C of the denitrification tower 3 is connected to the inlet of nitrogen-enriched gas II channel B1. The outlet of nitrogen-enriched gas II channel B1 is connected to the feed inlet 5-A of the denitrification tower reflux tank 5. The bottom liquid phase outlet 5-C of the denitrification tower reflux tank 5 is connected to the feed inlet 3-D of the denitrification tower 3. The top gas phase outlet 5-B of the denitrification tower reflux tank 5 is connected to the feed inlet 6-A of the helium distillation tower 6. The bottom liquid phase outlet 6-D of the helium distillation tower 6 is connected to the inlet of nitrogen-enriched gas III channel C4. The outlet of nitrogen-enriched gas III channel C4 is connected to the inlet of nitrogen-enriched gas I channel A6. The outlet of nitrogen-enriched gas I channel A6 is connected to the external nitrogen-enriched gas pipeline.

[0028] In this embodiment, the top gas phase outlet of the helium distillation column 6 is connected to the inlet of crude helium III channel C5; the outlet of crude helium III channel C5 is connected to the feed inlet 8-A of the helium distillation column reflux tank 8; the bottom liquid phase outlet 8-C of the helium distillation column reflux tank 8 is connected to the feed inlet 6-C of the helium distillation column 6; the top gas phase outlet 8-B of the helium distillation column reflux tank 8 is connected to the inlet of crude helium II channel C2; the outlet of crude helium II channel C2 is connected to the inlet of crude helium I channel A5; the outlet of crude helium I channel A5 is connected to the external crude helium pipeline; the outlet of the nitrogen compressor system 15 is connected to the inlet of high-pressure nitrogen I channel A7; the outlet of high-pressure nitrogen I channel A7 is connected to the inlet of the helium distillation column reboiler 13; and the outlet of the helium distillation column reboiler 13 is connected to the liquid nitrogen channel. The C3 inlet is connected, the liquid nitrogen channel C3 outlet is connected to the low-pressure reflux nitrogen II channel C1 inlet, the low-pressure reflux nitrogen II channel C1 outlet is connected to the low-pressure reflux nitrogen I channel A8 inlet, the low-pressure reflux nitrogen I channel A8 outlet is connected to the nitrogen compressor system 15 inlet, the high-pressure mixed refrigerant liquid phase pipeline at the outlet of the mixed refrigerant compressor system 14 is connected to the high-pressure liquid phase refrigerant I channel A12 inlet, the high-pressure liquid phase refrigerant I channel A12 outlet is connected to the low-pressure reflux refrigerant I channel A9 inlet A9-A, the high-pressure mixed refrigerant gas phase at the outlet of the mixed refrigerant compressor system 14 is connected to the high-pressure gas phase refrigerant I channel A10 inlet, and the high-pressure gas phase refrigerant I channel A10 outlet is connected to the refrigerant cryogenic separator 9 inlet (9-A).

[0029] In this embodiment, the bottom liquid phase outlet 9-B of the refrigerant cryogenic separator 9 is connected to the inlet of the high-pressure liquid phase refrigerant II channel A13, the outlet of the high-pressure liquid phase refrigerant II channel A13 is connected to the inlet A9-B of the low-pressure reflux refrigerant I channel A9, the top gas phase outlet 9-C of the refrigerant cryogenic separator 9 is connected to the inlet of the high-pressure gas phase refrigerant II channel A11, the outlet of the high-pressure gas phase refrigerant II channel A11 is divided into two parts, one part is connected to the inlet A9-C of the low-pressure reflux refrigerant I channel A9, and the other part is connected to the inlet of the low-pressure reflux refrigerant II channel B2, the outlet of the low-pressure reflux refrigerant II channel B2 is connected to the inlet A9-C of the low-pressure reflux refrigerant I channel A9, and the outlet of the low-pressure reflux refrigerant I channel A9 is connected to the inlet of the mixed refrigerant compressor system 14.

[0030] In a preferred embodiment, a regulating valve a101 is installed on the pipeline between the top gas phase outlet 2-C of the heavy hydrocarbon separator 2 and the feed inlet 3-F of the denitrification tower 3 to regulate the bottom temperature of the denitrification tower 3; a regulating valve b102 is installed on the outlet pipeline of the raw material gas II channel A2; a regulating valve c103 is installed on the inlet pipeline of the low-pressure reflux refrigerant II channel B2; a regulating valve d104 is installed on the top gas phase outlet 5-B pipeline of the denitrification tower reflux tank 5 to regulate the top pressure of the denitrification tower 3; a regulating valve e105 is installed on the outlet pipeline of the LNG subcooling channel A4 to regulate the bottom liquid level of the denitrification tower 3; a regulating valve f106 is installed on the bottom liquid phase outlet 6-D pipeline of the helium distillation tower 6 to regulate the bottom liquid level of the helium distillation tower 6; a regulating valve g107 is installed on the top gas phase outlet 8-B pipeline of the helium distillation tower reflux tank 8 to regulate the top pressure of the helium distillation tower 6; and a regulating valve g107 is installed on the outlet of the liquid nitrogen channel C3 and the low-pressure reflux refrigerant II channel B2. A regulating valve h108 is installed between the inlet of nitrogen flow channel II (C1) and the outlet of crude helium channel III (C5); a regulating valve i109 is installed between the outlet of high-pressure gaseous refrigerant channel II (A11) and the inlet of low-pressure reflux refrigerant channel I (A9); a regulating valve j110 is installed between the outlet of high-pressure liquid refrigerant channel II (A13) and the inlet of low-pressure reflux refrigerant channel I (A9); a regulating valve k111 is installed between the outlet of high-pressure liquid refrigerant channel I (A12) and the inlet of low-pressure reflux refrigerant channel I (A9); a regulating valve l112 is installed at the outlet of BOG reliquefaction channel A3; a regulating valve m113 is installed at the top gaseous outlet 10-B of LNG storage tank 10 to control the top pressure of LNG storage tank 10; and a regulating valve n114 is installed between the inlet and outlet of helium distillation column reboiler 13 to control the bottom liquid temperature of helium distillation column 6.

[0031] The present invention also proposes a method for producing LNG co-production ammonia feedstock gas using liquid nitrogen washing and mixed refrigerant refrigeration, which includes the following steps: S1. Purified natural gas containing nitrogen and helium enters feed gas channel I A1. In feed gas channel I A1, it is cooled to -70~-60℃ by the backflow of cold stream. Some heavy components condense and enter the heavy hydrocarbon separator 2 for gas-liquid separation. The liquid at the bottom is sent outside as heavy hydrocarbon product. The gas phase at the top re-enters feed gas channel II A2 and is cooled to -145~-130℃ by the cold stream. It is then sent to the middle of the denitrification tower 3 for distillation separation. The temperature at the bottom of the denitrification tower 3 is regulated by taking a portion of the high-temperature natural gas from the top of the hydrocarbon separator 2 to ensure that the nitrogen content in the LNG at the bottom of the denitrification tower 3 is less than 1%. The LNG from the bottom of the denitrification tower 3 is sent to the LNG subcooling channel A4 of the main heat exchanger 1 for subcooling to -162℃, and then sent to the LNG storage tank 10 for storage through the regulating valve e105.

[0032] S2. The low-temperature nitrogen-rich gas (mainly nitrogen, helium and methane) at the top outlet 3-C of the denitrification tower 3 enters the nitrogen-rich gas II channel B1 and is cooled to -155~-163℃. The methane component is condensed again and then enters the denitrification tower reflux tank 5 for gas-liquid separation. The liquid at the bottom of the tank returns to the top feed port 3-D of the denitrification tower 3 for reflux. The nitrogen-rich gas at the top of the denitrification tower reflux tank 5 is depressurized by the regulating valve d104 and sent to the middle of the helium distillation tower 6 for distillation.

[0033] S3. Inside the helium distillation column 6, the rising helium gas and the downstream liquid (nitrogen-rich liquid) come into contact and transfer heat and mass on the surface of the structured packing. The nitrogen-rich liquid obtained at the bottom of the helium distillation column 6 is then depressurized by the regulating valve f106 and sent to the nitrogen-rich gas III channel C4 of the helium distillation column condenser 7 to provide cooling for the condensation reflux of the helium distillation column 6. After entering the nitrogen-rich gas I channel A6, it is reheated to room temperature by the hot flow and then sent out of the boundary as fuel gas.

[0034] S4. The helium-rich gas (containing nitrogen, helium and a small amount of methane) at the 3-C low temperature at the top outlet of the helium distillation column 6 is cooled to -182~-175℃ in the crude helium III channel C5 of the helium distillation column condenser 7. The methane component and part of the nitrogen component are condensed and enter the helium distillation column reflux tank 8 for gas-liquid separation. The liquid at the bottom of the tank returns to the top feed port 6-C of the helium distillation column 6 for reflux. The crude helium gas (helium component ≥60%mol) at the top of the helium distillation column reflux tank 8 enters the crude helium II channel C2 through the regulating valve g107 for cold recovery, and is then introduced into the crude helium I channel A5 to be reheated to room temperature and sent out of the boundary as crude helium product.

[0035] S5. In order to further recover methane and helium components, the BOG from LNG storage tank 10 is first heated to room temperature by BOG heater 11, then sent to BOG compressor 12 for pressurization to 0.6~1.0 MPa, and then introduced into BOG reliquefaction channel A3 to be cooled to -162~-155℃, and then enters the top feed port 3-B of denitrification tower 3 for distillation separation to recover methane and helium.

[0036] S6. The natural gas denitrification and liquefaction process is cooled by a mixed refrigerant refrigeration cycle. First, the high-pressure liquid refrigerant from the mixed refrigerant compressor system 14 is subcooled to -30~-70℃ in the high-pressure liquid refrigerant I channel A12 of the main heat exchanger 1. After being throttled and depressurized by regulating valve k111, it enters the low-pressure return refrigerant I channel A9 inlet A9-A. The high-pressure gaseous refrigerant from the mixed refrigerant compressor system 14 is cooled to -30~-70℃ in the high-pressure gaseous refrigerant I channel A10 of the main heat exchanger 1, and then enters the refrigerant cryogenic separator 9 for gas-liquid separation. The liquid separated at the bottom enters the high-pressure liquid refrigerant II channel A13 and is subcooled to -130~-80℃. After being throttled and depressurized by regulating valve j110, it enters the low-pressure return refrigerant I channel A9 inlet A9-B. The liquid from the top of the refrigerant cryogenic separator 9... The high-pressure gaseous refrigerant enters the high-pressure gaseous refrigerant II channel A11 and is cooled and condensed to -165~-160℃. It is divided into two parts. Most of it is throttled and depressurized by regulating valve i109 and enters the low-pressure reflux refrigerant I channel A9 inlet A9-C. A small part is throttled and depressurized by regulating valve c103 and enters the low-pressure reflux refrigerant II channel B2, which provides a cold source for the separation of methane at the top of the denitrification tower 3. It exits the low-pressure reflux refrigerant II channel B2 and returns to the low-pressure reflux refrigerant I channel A9 inlet A9-C. The mixed refrigerant entering the low-pressure reflux refrigerant I channel A9 absorbs heat and evaporates. After evaporating into gas and being reheated to room temperature, it exits the main heat exchanger 1 and then returns to the mixed refrigerant compressor system 14 to complete the mixed refrigerant refrigeration cycle.

[0037] S7. Helium separation is achieved by providing cooling energy through a nitrogen cycle. First, high-pressure nitrogen from the nitrogen compression system 15 is cooled to approximately -155~-145℃ in the high-pressure nitrogen I channel A7, and then enters the reboiler 13 of the helium distillation column as a heat source for the helium distillation column 6. The helium content in the nitrogen-rich liquid is controlled to be ≤50ppm. After being cooled by the liquid in the bottom of the helium distillation column 6, it is reintroduced into the liquid nitrogen channel C3 for subcooling to -180℃. After being throttled and depressurized by the regulating valve h (108), it enters the low-pressure reflux nitrogen II channel C1 to provide cooling energy for the distillation of helium in the helium distillation column 6. Then, it returns to the low-pressure reflux nitrogen I channel A8 to be reheated to room temperature and exits the main heat exchanger 1. Finally, it returns to the inlet of the nitrogen compression system 15 to complete the nitrogen refrigeration cycle.

[0038] This invention proposes an LNG unit and method integrating natural gas helium extraction, denitrification, and BOG reliquefaction. It innovatively integrates a mixed refrigerant refrigeration cycle and a nitrogen refrigeration cycle: the mixed refrigerant refrigeration cycle primarily provides the cooling capacity required for methane and nitrogen liquefaction, while the nitrogen refrigeration cycle supplies cooling capacity for the cryogenic separation process of helium purification. Simultaneously, it discloses a process for co-producing LNG from natural gas denitrification and BOG reliquefaction. While achieving efficient LNG production, it also re-distills and purifies the helium in the nitrogen-rich tail gas, simultaneously producing crude helium. The beneficial effects are: through the co-production mode of LNG and crude helium, it significantly reduces the plant's overall energy consumption and improves economic efficiency; moreover, the unit has outstanding advantages such as strong raw material adaptability, safe and reliable operation, and wide application scenarios, realizing the diversified and efficient utilization of natural gas resources.

[0039] For the foregoing embodiments, in order to simplify the description, they are all described as a series of actions. However, those skilled in the art should understand that this application is not limited to the described order of actions, because according to this application, some steps can be performed in other orders or simultaneously. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions involved are not necessarily essential to this application.

[0040] The above embodiments describe the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Modifications and variations made by those skilled in the art without departing from the spirit and scope of the invention should be within the protection scope of the appended claims.

Claims

1. An LNG unit integrating natural gas helium extraction, denitrification, and BOG reliquefaction, characterized in that, The unit includes a main heat exchanger (1), a heavy hydrocarbon separator (2), a denitrification tower (3), a denitrification tower condenser (4), a denitrification tower reflux tank (5), a helium distillation tower (6), a helium distillation tower condenser (7), a helium distillation tower reflux tank (8), a refrigerant cryogenic separator (9), an LNG storage tank (10), a BOG heater (11), a BOG compressor (12), a helium distillation tower reboiler (13), a mixed refrigerant compressor system (14), and a nitrogen compressor system (15). The main heat exchanger (1) is provided with the following channels: raw gas I channel (A1), raw gas II channel (A2), BOG reliquefaction channel (A3), LNG subcooling channel (A4), crude helium I channel (A5), nitrogen-rich I channel (A6), high-pressure nitrogen I channel (A7), low-pressure reflux nitrogen I channel (A8), low-pressure reflux refrigerant I channel (A9), high-pressure gas phase refrigerant I channel (A10), high-pressure gas phase refrigerant II channel (A11), high-pressure liquid phase refrigerant I channel (A12) and high-pressure liquid phase refrigerant II channel (A13). The denitrification tower condenser (4) is equipped with a nitrogen-rich gas II channel (B1) and a low-pressure reflux refrigerant II channel (B2). The helium distillation column condenser (7) is equipped with a low-pressure reflux nitrogen II channel (C1), a crude helium II channel (C2), a liquid nitrogen channel (C3), a nitrogen-rich III channel (C4), and a crude helium III channel (C5).

2. The LNG unit integrating natural gas helium extraction, denitrification, and BOG reliquefaction as described in claim 1, characterized in that, The inlet of the raw gas I channel (A1) is connected to the purified raw gas from the outside, and the outlet is connected to the feed inlet (2-A) of the heavy hydrocarbon separator (2). The bottom liquid phase outlet (2-B) of the heavy hydrocarbon separator (2) is connected to the external heavy hydrocarbon storage pipeline. The top gas phase outlet (2-C) of the heavy hydrocarbon separator (2) is divided into two parts: one part is connected to the inlet of the raw gas II channel (A2), and the other part is connected to the feed inlet (3-F) of the denitrification tower (3). The outlet of the raw gas II channel (A2) is connected to the feed inlet (3-A) of the denitrification tower (3).

3. An LNG unit integrating natural gas helium extraction, denitrification, and BOG reliquefaction as described in claim 2, characterized in that, The bottom liquid phase outlet (3-E) of the denitrification tower (3) is connected to the inlet of the LNG subcooling channel (A4), and the outlet of the LNG subcooling channel (A4) is connected to the feed inlet (10-A) of the LNG storage tank (10); the top gas phase outlet (10-B) of the LNG storage tank (10) is connected to the inlet of the BOG heater (11), the outlet of the BOG heater (11) is connected to the inlet of the BOG compressor (12), the outlet of the BOG compressor (12) is connected to the inlet of the BOG reliquefaction channel (A3), and the outlet of the BOG reliquefaction channel (A3) is connected to the feed inlet (3-B) of the denitrification tower (3).

4. An LNG unit integrating natural gas helium extraction, denitrification, and BOG reliquefaction as described in claim 3, characterized in that, The top gas phase outlet (3-C) of the denitrification tower (3) is connected to the inlet of the nitrogen-rich II channel (B1), and the outlet of the nitrogen-rich II channel (B1) is connected to the feed inlet (5-A) of the denitrification tower reflux tank (5); the bottom liquid phase outlet (5-C) of the denitrification tower reflux tank (5) is connected to the feed inlet (3-D) of the denitrification tower (3), and the top gas phase outlet (5-B) is connected to the feed inlet (6-A) of the helium distillation tower (6); the bottom liquid phase outlet (6-D) of the helium distillation tower (6) is connected to the inlet of the nitrogen-rich III channel (C4), the outlet of the nitrogen-rich III channel (C4) is connected to the inlet of the nitrogen-rich I channel (A6), and the outlet of the nitrogen-rich I channel (A6) is connected to the external nitrogen-rich pipeline; The top gas phase outlet of the helium distillation column (6) is connected to the inlet of the crude helium III channel (C5), and the outlet of the crude helium III channel (C5) is connected to the feed inlet (8-A) of the helium distillation column reflux tank (8); the bottom liquid phase outlet (8-C) of the helium distillation column reflux tank (8) is connected to the feed inlet (6-C) of the helium distillation column (6), and the top gas phase outlet (8-B) is connected to the inlet of the crude helium II channel (C2); the outlet of the crude helium II channel (C2) is connected to the inlet of the crude helium I channel (A5), and the outlet of the crude helium I channel (A5) is connected to the external crude helium pipeline.

5. An LNG unit integrating natural gas helium extraction, denitrification, and BOG reliquefaction as described in claim 4, characterized in that, The outlet of the nitrogen compressor system (15) is connected to the inlet of the high-pressure nitrogen I channel (A7), and the outlet of the high-pressure nitrogen I channel (A7) is connected to the inlet of the helium distillation column reboiler (13). The outlet of the helium distillation column reboiler (13) is connected to the inlet of the liquid nitrogen channel (C3), and the outlet of the liquid nitrogen channel (C3) is connected to the inlet of the low-pressure reflux nitrogen II channel (C1). The outlet of the low-pressure reflux nitrogen II channel (C1) is connected to the inlet of the low-pressure reflux nitrogen I channel (A8). The outlet of the low-pressure reflux nitrogen I channel (A8) is connected to the inlet of the nitrogen compressor system (15), and the high-pressure mixed refrigerant liquid phase pipeline at the outlet of the mixed refrigerant compressor system (14) is connected to the inlet of the high-pressure liquid phase refrigerant I channel (A12).

6. An LNG unit integrating natural gas helium extraction, denitrification, and BOG reliquefaction as described in claim 5, characterized in that, The outlet of the high-pressure liquid refrigerant I channel (A12) is connected to the inlet (A9-A) of the low-pressure reflux refrigerant I channel (A9); the outlet of the mixed refrigerant compressor system (14) is connected to the inlet of the high-pressure gaseous refrigerant I channel (A10), and the outlet of the high-pressure gaseous refrigerant I channel (A10) is connected to the inlet (9-A) of the refrigerant cryogenic separator (9); the bottom liquid phase outlet (9-B) of the refrigerant cryogenic separator (9) is connected to the inlet of the high-pressure liquid refrigerant II channel (A13), and the outlet of the high-pressure liquid refrigerant II channel (A13) is connected to the inlet (A9-A) of the low-pressure reflux refrigerant I channel (A9-A). B) Connection; The top gas phase outlet (9-C) of the refrigerant cryogenic separator (9) is connected to the inlet of the high-pressure gas phase refrigerant II channel (A11). The outlet of the high-pressure gas phase refrigerant II channel (A11) is divided into two parts. One part is connected to the inlet (A9-C) of the low-pressure reflux refrigerant I channel (A9), and the other part is connected to the inlet of the low-pressure reflux refrigerant II channel (B2). The outlet of the low-pressure reflux refrigerant II channel (B2) is connected to the inlet (A9-C) of the low-pressure reflux refrigerant I channel (A9), and the outlet of the low-pressure reflux refrigerant I channel (A9) is connected to the inlet of the mixed refrigerant compressor system (14).

7. An LNG unit integrating natural gas helium extraction, denitrification, and BOG reliquefaction as described in claim 1, characterized in that, The denitrification tower (3) and the helium distillation tower (6) are packed towers or plate towers; the reboiler (13) of the helium distillation tower can be built-in or external.

8. An LNG unit integrating natural gas helium extraction, denitrification, and BOG reliquefaction as described in claim 1, characterized in that, A regulating valve a (101) is installed on the pipeline between the top gas phase outlet (2-C) of the heavy hydrocarbon separator (2) and the feed inlet (3-F) of the denitrification tower (3) to regulate the bottom temperature of the denitrification tower (3); a regulating valve b (102) is installed on the pipeline at the outlet of the raw gas II channel (A2); a regulating valve c (103) is installed on the inlet pipeline of the low-pressure reflux refrigerant II channel (B2); a regulating valve d (104) is installed on the pipeline at the top gas phase outlet (5-B) of the denitrification tower reflux tank (5) to regulate the top pressure of the denitrification tower (3); and a regulating valve e (105) is installed on the pipeline at the outlet of the LNG subcooling channel (A4) to regulate the bottom liquid level of the denitrification tower (3). The bottom liquid outlet (6-D) pipeline of the helium distillation column (6) is equipped with a regulating valve f (106) for adjusting the bottom liquid level of the helium distillation column (6); the top gas outlet (8-B) pipeline of the helium distillation column reflux tank (8) is equipped with a regulating valve g (107) for adjusting the top pressure of the helium distillation column (6); a regulating valve h (108) is provided between the outlet of the liquid nitrogen channel (C3) and the inlet of the low-pressure reflux nitrogen channel II (C1) for controlling the outlet temperature of the crude helium channel III (C5); A regulating valve i (109) is installed on the pipeline between the outlet of the high-pressure gas phase refrigerant II channel (A11) and the inlet of the low-pressure reflux refrigerant I channel (A9); a regulating valve j (110) is installed on the pipeline between the outlet of the high-pressure liquid phase refrigerant II channel (A13) and the inlet of the low-pressure reflux refrigerant I channel (A9); a regulating valve k (111) is installed on the pipeline between the outlet of the high-pressure liquid phase refrigerant I channel (A12) and the inlet of the low-pressure reflux refrigerant I channel (A9); a regulating valve l (112) is installed on the outlet pipeline of the BOG reliquefaction channel (A3); a regulating valve m (113) is installed on the top gas phase outlet (10-B) pipeline of the LNG storage tank (10) to control the top pressure of the LNG storage tank (10); a regulating valve n (114) is installed on the pipeline between the inlet and outlet of the helium distillation column reboiler (13) to control the bottom liquid temperature of the helium distillation column (6).

9. A method for LNG integrating helium extraction, denitrification, and BOG reliquefaction from natural gas, implemented based on an LNG device integrating helium extraction, denitrification, and BOG reliquefaction from natural gas as described in any one of claims 1 to 8, characterized in that, This includes pretreatment and further helium extraction, denitrification, and BOG reliquefaction. The pretreatment specifically includes the following steps: Step S1: Purified natural gas containing nitrogen and helium enters the feed gas I channel (A1). In the feed gas I channel (A1), it is cooled to -70~-60℃ by the backflow of cold stream. Some of the heavy components are condensed and enter the heavy hydrocarbon separator (2) for gas-liquid separation. The liquid at the bottom is sent out as heavy hydrocarbon product. The gas phase at the top enters the feed gas II channel (A2) again and is cooled to -145~-130℃ by the cold stream. It is then sent to the middle of the denitrification tower (3) for distillation separation. The LNG from the bottom of the denitrification tower (3) is sent to the LNG subcooling channel (A4) of the main heat exchanger (1) for subcooling to -162℃. Then, it is sent to the LNG storage tank (10) for storage through the regulating valve e (105). Step S2: The low-temperature nitrogen-rich gas at the top outlet (3-C) of the denitrification tower (3) enters the nitrogen-rich gas II channel (B1) and is cooled to -155~-163℃. The methane component is condensed again and then enters the denitrification tower reflux tank (5) for gas-liquid separation. The liquid at the bottom of the tank returns to the top feed port (3-D) of the denitrification tower (3) for reflux. The nitrogen-rich gas at the top of the denitrification tower reflux tank (5) is depressurized by the regulating valve d (104) and then sent to the middle of the helium distillation tower (6) for distillation. Step S3: Inside the helium distillation column (6), the rising helium gas and the downstream nitrogen-rich liquid come into contact on the surface of the structured packing for heat and mass transfer. The nitrogen-rich liquid obtained at the bottom of the helium distillation column (6) is depressurized by the regulating valve f (106) and sent to the nitrogen-rich III channel (C4) of the helium distillation column condenser (7) to provide cooling for the condensation reflux of the helium distillation column (6). After entering the nitrogen-rich I channel (A6), it is reheated to room temperature by the hot flow and then sent out of the boundary as fuel gas. Step S4: The low-temperature helium-rich gas at the top outlet (3-C) of the helium distillation column (6) is cooled to -182~-175℃ in the crude helium III channel (C5) of the helium distillation column condenser (7). The methane component and part of the nitrogen component are condensed and enter the helium distillation column reflux tank (8) for gas-liquid separation. The liquid at the bottom of the tank is returned to the top feed port (6-C) of the helium distillation column (6) for reflux. The crude helium gas at the top of the helium distillation column reflux tank (8) is introduced into the crude helium II channel (C2) through the regulating valve g (107) for cold recovery. Then it is introduced into the crude helium I channel (A5) to be reheated to room temperature and sent out of the boundary as crude helium product.

10. The method for LNG integrating helium extraction, nitrogen removal, and BOG reliquefaction as described in claim 9, characterized in that, The further helium extraction, denitrification, and BOG reliquefaction specifically include: Step S5: The BOG from the LNG storage tank (10) is first heated to room temperature by the BOG heater (11), then sent to the BOG compressor (12) for pressurization to 0.6~1.0 MPa, and then introduced into the BOG reliquefaction channel (A3) to be cooled to -162~-155℃, and then enters the top feed port (3-B) of the denitrification tower (3) for distillation separation to recover methane and helium; Step S6: The high-pressure liquid refrigerant from the mixed refrigerant compressor system (14) is subcooled to -30~-70℃ in the high-pressure liquid refrigerant I channel (A12) of the main heat exchanger (1), and after being throttled and depressurized by regulating valve k (111), it enters the inlet (A9-A) of the low-pressure return refrigerant I channel (A9). The high-pressure gaseous refrigerant from the mixed refrigerant compressor system (14) is cooled to -30~-70℃ in the high-pressure gaseous refrigerant I channel (A10) of the main heat exchanger (1), and then enters the refrigerant cryogenic separator (9) for gas-liquid separation. The liquid separated at the bottom enters the high-pressure liquid refrigerant II channel (A13) and is subcooled to -130~-80℃. After being throttled and depressurized by regulating valve j (110), it enters the inlet (A9-B) of the low-pressure return refrigerant I channel (A9). The high-pressure gaseous refrigerant at the top enters the high-pressure gaseous refrigerant II channel (A11) and is cooled and condensed to -165~-160℃. It is divided into two parts. Most of it enters the inlet (A9-C) of the low-pressure reflux refrigerant I channel (A9) after being throttled and depressurized by regulating valve i (109). A small part enters the low-pressure reflux refrigerant II channel (B2) after being throttled and depressurized by regulating valve c (103). It provides a cold source for the separation of methane at the top of the denitrification tower (3). It exits the low-pressure reflux refrigerant II channel (B2) and returns to the inlet (A9-C) of the low-pressure reflux refrigerant I channel (A9). The mixed refrigerant entering the low-pressure reflux refrigerant I channel (A9) absorbs heat and evaporates. After evaporating into gas and reheating to room temperature, it exits the main heat exchanger (1) and then returns to the mixed refrigerant compressor system (14) to complete the mixed refrigerant refrigeration cycle. Step S7: High-pressure nitrogen from the nitrogen compression system (15) is cooled to approximately -155~-145°C in the high-pressure nitrogen I channel (A7), and then enters the reboiler (13) of the helium distillation column as a heat source for the helium distillation column (6). The helium component in the nitrogen-rich liquid is controlled to be ≤50ppm. After being cooled by the liquid in the bottom of the helium distillation column (6), it is introduced again into the liquid nitrogen channel (C3) for subcooling to -180°C. After being throttled and depressurized by the regulating valve h (108), it enters the low-pressure reflux nitrogen II channel (C1) to provide cooling for the helium distillation of the helium in the helium distillation column (6). Then it returns to the low-pressure reflux nitrogen I channel (A8) to be reheated to room temperature and exits the main heat exchanger (1). Finally, it returns to the inlet of the nitrogen compression system (15) to complete the nitrogen refrigeration cycle.

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