Method and apparatus for concentrating bog tail gas

Abstract

The application discloses a BOG tail gas concentration method and device, relates to the technical field of compound processing, and comprises the following steps: transmitting BOG tail gas to a first reboiler to perform first heat exchange; transmitting the gas after the first heat exchange to a cold box to perform condensation; transmitting the first two-phase fluid to a first fractional distillation column, and performing first gas-liquid fractionation on the first two-phase fluid by using the heat of the first heat exchange; transmitting the gas-phase gas obtained after the first gas-liquid fractionation to a second reboiler to perform second heat exchange; transmitting the gas after the second heat exchange to a helium concentration heat exchanger to perform condensation; transmitting the second two-phase fluid to a second fractional distillation column, and performing second gas-liquid fractionation on the second two-phase fluid by using the heat of the second heat exchange; re-heating the gas-phase gas obtained after the second gas-liquid fractionation and collecting the gas-phase gas; throttling and cooling the liquid-phase liquid obtained after the second gas-liquid fractionation, and transmitting the liquid-phase liquid to the helium concentration heat exchanger as a cold source.

Description

Technical Field

[0001] This invention relates to the field of compound processing technology, and in particular to a method and apparatus for concentrating BOG tail gas. Background Technology

[0002] Helium plays an irreplaceable role in defense, industry, and science 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 strong chemical inertness, extremely low boiling point, and very low solubility in blood.

[0003] Helium exists throughout the universe, making up 23% of the total mass, second only to hydrogen. However, in nature, it is mainly found in natural gas or radioactive ores. The concentration of helium in Earth's atmosphere is extremely low, only 1 / 52,000. The helium contained in radioactive minerals on Earth is a product of alpha decay. Some natural gas contains economically extractable amounts of helium, up to 7%, but in my country's natural gas, helium accounts for approximately 0.04% to 0.2%, making extraction uneconomical. Therefore, my country has long relied on imports of helium. The high price of helium has significantly impacted sectors in my country that heavily utilize it, as well as related research and production units.

[0004] Existing technologies for helium recovery involve numerous complex processes, are cumbersome to operate, and have low recovery efficiency. Furthermore, the utilization rate of byproducts generated during the recovery process is low, leading to increased costs. Summary of the Invention

[0005] The main objective of this invention is to propose a method and apparatus for enriching BOG tail gas, aiming to solve the technical problems of numerous recovery processes, low recovery efficiency, and high recovery costs in the existing technology.

[0006] To achieve the above objectives, the present invention proposes a method for enriching BOG tail gas, the method comprising:

[0007] The BOG exhaust gas is transferred to the first reboiler for the first heat exchange.

[0008] The gas after the first heat exchange is transferred to a cold box for condensation, causing it to undergo a phase change to form the first two-phase fluid.

[0009] The first two-phase fluid is transferred to the first fractionation tower, and the heat from the first heat exchange is used to perform the first gas-liquid fractionation on the first two-phase fluid.

[0010] The gas phase obtained after the first gas-liquid fractionation is transferred to the second reboiler for a second heat exchange.

[0011] The gas after the second heat exchange is transferred to a helium enrichment heat exchanger for condensation, causing it to undergo a phase change to form a second two-phase fluid.

[0012] The second two-phase fluid is transferred to the second fractionation tower, and the heat from the second heat exchange is used to perform a second gas-liquid fractionation on the second two-phase fluid;

[0013] The gas phase obtained after the second gas-liquid fractionation is reheated and collected;

[0014] The liquid phase obtained after the second gas-liquid fractionation is throttled and cooled, and then used as a cold source to be transferred to the helium enrichment heat exchanger.

[0015] In one embodiment, after the step of transferring the first two-phase fluid to the first fractionation column and performing a first gas-liquid fractionation on the first two-phase fluid using the heat from the first heat exchange, the method further includes:

[0016] The liquid phase obtained after the first gas-liquid fractionation is transferred to the cold box for condensation.

[0017] The cooled liquid phase is recycled as the first product.

[0018] In one embodiment, the step of reheating and collecting the gaseous gas obtained after the second gas-liquid fractionation includes:

[0019] The gas phase obtained after the second gas-liquid fractionation is sequentially transferred to the helium enrichment heat exchanger and the cold box for reheating.

[0020] The reheated gas phase is recycled as a second product.

[0021] In one embodiment, after the step of throttling and cooling the liquid phase obtained after the second gas-liquid fractionation and then transferring it as a cold source to the helium enrichment heat exchanger, the method further includes:

[0022] The liquid phase, which serves as a cold source, is transferred to the cold box for reheating, causing it to change from a liquid phase to a gas phase.

[0023] The gaseous phase formed after reheating is recycled as a third product.

[0024] In one embodiment, the step of transferring the BOG exhaust gas to the first reboiler for the first heat exchange includes:

[0025] The BOG exhaust gas is compressed to bring the pressure of the compressed BOG exhaust gas to the preset pressure.

[0026] The BOG exhaust gas, compressed to the preset pressure, is transferred to the first reboiler for the first heat exchange.

[0027] Furthermore, to address the aforementioned problems, this invention also proposes a BOG tail gas enrichment device, which is applied to the BOG tail gas enrichment method described above. The BOG tail gas enrichment device comprises:

[0028] Cold box and helium enrichment heat exchanger;

[0029] A first reboiler and a first fractionating column disposed on the first reboiler;

[0030] The second reboiler and the second fractionation column disposed on the second reboiler;

[0031] A first pipeline, one end of which is connected to the first reboiler, and the other end of which passes through the cold box and is connected to the first fractionation tower;

[0032] The second pipeline has one end connected to the first fractionation tower and the other end connected to the second reboiler.

[0033] The third pipeline has one end connected to the second reboiler and the other end connected to the second fractionation tower through the helium enrichment heat exchanger.

[0034] The fourth pipeline has one end connected to the second reboiler and the other end passing through the helium enrichment heat exchanger.

[0035] In one embodiment, the BOG tail gas enrichment device further includes a first recovery pipe, the bottom of the first reboiler has a first recovery port, one end of the first recovery pipe is connected to the first recovery port, and the other end passes through the first cold box and is connected to an external recovery mechanism.

[0036] In one embodiment, the BOG tail gas enrichment device further includes a second recovery pipe, the second fractionation tower has a second recovery port, one end of the second recovery pipe is connected to the second recovery port, and the other end passes through the helium enrichment heat exchanger and the cold box in sequence and is connected to the external recovery mechanism.

[0037] In one embodiment, one end of the fourth pipeline is connected to the second reboiler, and the other end passes through the helium enrichment heat exchanger and the cold box in sequence, extends to a preset height, and is connected to an external recovery mechanism.

[0038] In one embodiment, the BOG tail gas enrichment device further includes a compressor, one end of which is connected to an external gas supply device and the other end of which is connected to the first reboiler.

[0039] The technical solution of this invention employs only two sets of reboilers and fractionation towers to enrich BOG tail gas. The BOG tail gas is used as a heat source in the first reboiler, and after heat exchange, it is fed into the first fractionation tower for enrichment. After the first enrichment, the remaining gas is again transferred to the second reboiler as a heat source, and after heat exchange, it is fed into the second fractionation tower for a second enrichment. This simplifies the process and improves enrichment and recovery efficiency. Simultaneously, the generated byproducts serve as a coolant, enabling effective energy recovery and utilization without the need for external cooling equipment, thus reducing the cost of the enrichment and recovery process. Attached Figure Description

[0040] 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.

[0041] Figure 1 This is a schematic flowchart of the first embodiment of the BOG tail gas enrichment method provided by the present invention.

[0042] Figure 2 This is a schematic flowchart of a second embodiment of the BOG tail gas enrichment method provided by the present invention.

[0043] Figure 3 This is a schematic flowchart of the third embodiment of the BOG tail gas enrichment method provided by the present invention.

[0044] Figure 4 This is a schematic flowchart of the fourth embodiment of the BOG tail gas enrichment method provided by the present invention.

[0045] Figure 5 This is a schematic flowchart of the fifth embodiment of the BOG tail gas enrichment method provided by the present invention.

[0046] Figure 6 This is a schematic diagram of the BOG tail gas enrichment device provided by the present invention.

[0047] Explanation of icon numbers:

[0048] 11. Cold box; 12. Helium enrichment heat exchanger; 20. First reboiler; 21. First recovery port; 30. First fractionation column; 40. Second reboiler; 50. Second fractionation column; 51. Second recovery port; 61. First pipeline; 62. Second pipeline; 63. Third pipeline; 64. Fourth pipeline; 65. First recovery pipe; 66. Second recovery pipe; 70. Compressor.

[0049] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0050] 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 a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0051] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0052] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0053] This invention proposes a method for enriching BOG exhaust gas.

[0054] Please see Figure 1 A schematic flowchart of the first embodiment of the BOG tail gas enrichment method of the present invention. In one embodiment of the present invention, the BOG tail gas enrichment method includes the following steps:

[0055] Step S10: Transfer the BOG exhaust gas to the first reboiler for the first heat exchange.

[0056] Step S20: The gas after the first heat exchange is transferred to a cold box for condensation, causing it to undergo a phase change to form the first two-phase fluid;

[0057] Step S30: The first two-phase fluid is transferred to the first fractionation tower, and the heat from the first heat exchange is used to perform the first gas-liquid fractionation on the first two-phase fluid.

[0058] Step S40: The gas phase obtained after the first gas-liquid fractionation is transferred to the second reboiler for a second heat exchange;

[0059] Step S50: The gas after the second heat exchange is transferred to a helium enrichment heat exchanger for condensation, causing it to undergo a phase change to form a second two-phase fluid;

[0060] Step S60: The second two-phase fluid is transferred to the second fractionation tower, and the heat from the second heat exchange is used to perform a second gas-liquid fractionation on the second two-phase fluid;

[0061] Step S70: Reheat and collect the gas phase obtained after the second gas-liquid fractionation;

[0062] Step S80: The liquid phase obtained after the second gas-liquid fractionation is throttled and cooled, and then transferred to the helium enrichment heat exchanger as a cold source.

[0063] The BOG tail gas enrichment method of this invention is applied to a BOG tail gas enrichment device. Please refer to [link / reference]. Figure 6 The BOG tail gas enrichment device includes a cold box 11, a helium enrichment heat exchanger 12, a first pipeline 61, a second pipeline 62, a third pipeline 63, a fourth pipeline 64, a first reboiler 20, a first fractionation column 30 disposed on the first reboiler 20, a second reboiler 40 disposed on the second reboiler 40, and a second fractionation column 50 disposed on the second reboiler 40.

[0064] One end of the first pipeline 61 is connected to the first reboiler 20, and the other end passes through the cold box 11 and is connected to the first fractionation column 30; one end of the second pipeline 62 is connected to the first fractionation column 30, and the other end is connected to the second reboiler 40; one end of the third pipeline 63 is connected to the second reboiler 40, and the other end passes through the helium enrichment heat exchanger 12 and is connected to the second fractionation column 50; one end of the fourth pipeline 64 is connected to the second reboiler 40, and the other end passes through the helium enrichment heat exchanger 12.

[0065] BOG tail gas contains helium, hydrogen, nitrogen, and methane. First, the BOG tail gas is piped to the first reboiler 20 for initial heat exchange. The first reboiler 20 is located at the bottom of the first fractionation column 30, using the heat from the BOG tail gas after the first heat exchange as a heat source for heating the first fractionation column 30.

[0066] After the first heat exchange, the BOG tail gas is cooled and led out from the first reboiler 20 through the first pipeline 61. The first pipeline 61 passes through the cold box 11, where the BOG tail gas is further cooled and condensed to produce a phase change and form a first two-phase fluid. The first two-phase fluid is introduced into the first fractionation tower 30 through the first pipeline 61. The heat from the first heat exchange in the first reboiler 20 is used to perform the first gas-liquid fractionation of the first two-phase fluid in the first fractionation tower 30.

[0067] After the first gas-liquid fractionation, most of the methane component in the first two-phase fluid is liquefied and falls as LNG (liquefied natural gas) to the bottom of the first fractionation tower 30, that is, to the bottom of the first reboiler 20, and is drawn out through the bottom of the first reboiler 20.

[0068] The remaining gaseous phase after the first gas-liquid fractionation is a helium-containing BOG gas, mainly composed of helium, hydrogen, nitrogen, and a small amount of methane. This gas is introduced from the first fractionation column 30 into the second reboiler 40 through the second pipeline 62. The gaseous phase undergoes a second heat exchange in the second reboiler 40.

[0069] The second reboiler 40 is located at the bottom of the second fractionation column 50, and uses the heat of the gas phase after the second heat exchange as the heat source for heating the second fractionation column 50.

[0070] After the second heat exchange, the gas phase is cooled and drawn out from the second reboiler 40 through the third pipe 63. The third pipe 63 passes through the helium enrichment heat exchanger 12, where the gas phase is further cooled and condensed to produce a phase change and form a second two-phase fluid. The second two-phase fluid is introduced into the second fractionation tower 50 through the third pipe 63. The heat from the second heat exchange in the second reboiler 40 is used to perform a second gas-liquid fractionation on the second two-phase fluid in the second fractionation tower 50.

[0071] After the second gas-liquid fractionation, most of the nitrogen component in the second two-phase fluid liquefies to form a liquid phase. This liquid phase falls to the bottom of the second fractionation column 50, which is also the bottom of the second reboiler 40. The liquid phase is then introduced into the helium enrichment heat exchanger 12 via the fourth pipe 64. A throttling device is installed on the fourth pipe 64 so that after throttling and cooling, the liquid phase is reused as a cold source for the helium enrichment heat exchanger 12.

[0072] After the second gas-liquid fractionation, the resulting gas phase contains more than 85% helium and hydrogen. This crude helium is drawn off from the top of the second fractionation tower 50 and collected, and then sent to the downstream helium purification unit for further processing.

[0073] The technical solution of this invention employs only two sets of reboilers and fractionation towers to enrich BOG tail gas. The BOG tail gas is fed into the first reboiler 20 as a heat source, and after heat exchange, it is fed into the first fractionation tower 30 for enrichment. After the first enrichment, the remaining gas is again transferred to the second reboiler 40 as a heat source, and after heat exchange, it is fed into the second fractionation tower 50 for a second enrichment. This simplifies the process and improves enrichment and recovery efficiency. Simultaneously, the generated byproducts serve as a coolant, enabling effective energy recovery and utilization without the need for external cooling equipment, thus reducing the cost of the enrichment and recovery process.

[0074] Further, please refer to Figure 2 , Figure 2 This is a schematic flowchart of the second embodiment of the BOG tail gas enrichment method of the present invention. After step S30, it further includes:

[0075] Step S31: The liquid phase obtained after the first gas-liquid fractionation is transferred to the cold box for condensation;

[0076] Step S32: The cooled liquid phase is recycled as the first product.

[0077] After the first gas-liquid fractionation, most of the methane component in the first two-phase fluid is liquefied and falls as the first product (LNG liquid, liquefied natural gas) to the bottom of the first fractionation tower 30, that is, to the bottom of the first reboiler 20. The bottom of the first reboiler 20 has a first recovery port 21, and one end of the first recovery pipe 65 is connected to the first recovery port 21. The first product is drawn out from the bottom of the first reboiler 20 through the first recovery pipe 65.

[0078] The first recovery pipe 65 passes through the cold box 11, where the first product is further cooled and liquefied. The other end of the first recovery pipe 65 is used to connect with an external recovery mechanism to achieve effective recovery of the methane component.

[0079] Further, please refer to Figure 3 , Figure 3 This is a schematic flowchart of the third embodiment of the BOG tail gas enrichment method of the present invention. Step S70 includes:

[0080] Step S71: The gas phase obtained after the second gas-liquid fractionation is sequentially transferred to the helium enrichment heat exchanger and the cold box for reheating;

[0081] Step S72: The reheated gas phase is recycled as a second product.

[0082] After the second gas-liquid fractionation, most of the nitrogen in the second two-phase fluid has liquefied, leaving a residual helium and hydrogen content of over 85%, which is used as the second product (crude helium). A second recovery port 51 is located at the top of the second fractionation tower 50, and one end of a second recovery pipe 66 is connected to the second recovery port 51. The gaseous phase of the second two-phase fluid, as crude helium, is drawn out from the second recovery port 51 through the second recovery pipe 66.

[0083] The second recovery pipe 66 passes sequentially through the helium enrichment heat exchanger 12 and the cold box 11. Since the temperature of the gas phase after the second gas-liquid fractionation is low, the gas phase is reheated after passing through the helium enrichment heat exchanger 12 and the cold box 11. The other end of the second recovery pipe 66 is used to connect to an external recovery mechanism, such as a downstream helium purification unit, so that the second product can be further processed in the helium purification unit.

[0084] Further, please refer to Figure 4 , Figure 4 This is a schematic flowchart of the fourth embodiment of the BOG tail gas enrichment method of the present invention. After step S80, it further includes:

[0085] Step S81: The liquid phase, which serves as a cold source, is transferred to the cold box for reheating, so that it changes from a liquid phase to a gas phase.

[0086] Step S82: The gas phase formed after reheating is recycled as a third product.

[0087] After the second gas-liquid fractionation, most of the nitrogen component in the second two-phase fluid liquefies to form liquid nitrogen, one end of the fourth pipe 64 is connected to the second reboiler 40. To further improve utilization, the liquid nitrogen is introduced into the helium enrichment heat exchanger 12 through the fourth pipe 64. A throttle is installed on the fourth pipe 64 so that after throttling and cooling, it can be reused as a cold source for the helium enrichment heat exchanger 12.

[0088] After being heated in the helium enrichment heat exchanger 12, the liquid nitrogen is reheated into a gaseous phase and then passes through the cold box 11 via the fourth pipeline. Due to its low temperature, it is further reheated under the action of the cold box 11, thus forming the third product (nitrogen-enriched gas).

[0089] In this embodiment, the third product is a by-product, so the other end of the fourth pipeline 64 extends to a preset height to release the third product at a high point.

[0090] Further, please refer to Figure 5 , Figure 5 This is a schematic flowchart of the fifth embodiment of the BOG tail gas enrichment method of the present invention. Step S10 includes:

[0091] Step S11: Compress the BOG exhaust gas to bring the pressure of the compressed BOG exhaust gas to the preset pressure.

[0092] Step S12: The BOG exhaust gas compressed to the preset pressure is transferred to the first reboiler for the first heat exchange.

[0093] BOG tail gas at normal temperature and pressure is first transported to compressor 70 through pipeline. Compressor 70 pressurizes the BOG tail gas to above 2MPa, and then sends it to the first reboiler 20 for heat exchange, serving as the heat source for the first fractionation tower 30. By pressurizing the BOG tail gas, its concentration is increased, ensuring the efficiency of BOG tail gas enrichment.

[0094] This invention also proposes a BOG tail gas enrichment device, please refer to... Figure 6 The BOG tail gas enrichment device includes a cold box 11, a helium enrichment heat exchanger 12, a first pipeline 61, a second pipeline 62, a third pipeline 63, a fourth pipeline 64, a first reboiler 20, a first fractionation column 30 installed on the first reboiler 20, a second reboiler 40 installed on the second reboiler 40, and a second fractionation column 50 installed on the second reboiler 40.

[0095] One end of the first pipeline 61 is connected to the first reboiler 20, and the other end passes through the cold box 11 and is connected to the first fractionation column 30; one end of the second pipeline 62 is connected to the first fractionation column 30, and the other end is connected to the second reboiler 40; one end of the third pipeline 63 is connected to the second reboiler 40, and the other end passes through the helium enrichment heat exchanger 12 and is connected to the second fractionation column 50; one end of the fourth pipeline 64 is connected to the second reboiler 40, and the other end passes through the helium enrichment heat exchanger 12.

[0096] BOG tail gas contains helium, hydrogen, nitrogen, and methane. First, the BOG tail gas is piped to the first reboiler 20 for initial heat exchange. The first reboiler 20 is located at the bottom of the first fractionation column 30, using the heat from the BOG tail gas after the first heat exchange as a heat source for heating the first fractionation column 30.

[0097] After the first heat exchange, the BOG tail gas is cooled and led out from the first reboiler 20 through the first pipeline 61. The first pipeline 61 passes through the cold box 11, where the BOG tail gas is further cooled and condensed to produce a phase change and form a first two-phase fluid. The first two-phase fluid is introduced into the first fractionation tower 30 through the first pipeline 61. The heat from the first heat exchange in the first reboiler 20 is used to perform the first gas-liquid fractionation of the first two-phase fluid in the first fractionation tower 30.

[0098] After the first gas-liquid fractionation, most of the methane component in the first two-phase fluid is liquefied and falls as LNG (liquefied natural gas) to the bottom of the first fractionation tower 30, that is, to the bottom of the first reboiler 20, and is drawn out through the bottom of the first reboiler 20.

[0099] The remaining gaseous phase after the first gas-liquid fractionation is a helium-containing BOG gas, mainly composed of helium, hydrogen, nitrogen, and a small amount of methane. This gas is introduced from the first fractionation column 30 into the second reboiler 40 through the second pipeline 62. The gaseous phase undergoes a second heat exchange in the second reboiler 40.

[0100] The second reboiler 40 is located at the bottom of the second fractionation column 50, and uses the heat of the gas phase after the second heat exchange as the heat source for heating the second fractionation column 50.

[0101] After the second heat exchange, the gas phase is cooled and drawn out from the second reboiler 40 through the third pipe 63. The third pipe 63 passes through the helium enrichment heat exchanger 12, where the gas phase is further cooled and condensed to produce a phase change and form a second two-phase fluid. The second two-phase fluid is introduced into the second fractionation tower 50 through the third pipe 63. The heat from the second heat exchange in the second reboiler 40 is used to perform a second gas-liquid fractionation on the second two-phase fluid in the second fractionation tower 50.

[0102] After the second gas-liquid fractionation, most of the nitrogen component in the second two-phase fluid liquefies to form a liquid phase. This liquid phase falls to the bottom of the second fractionation column 50, which is also the bottom of the second reboiler 40. The liquid phase is then introduced into the helium enrichment heat exchanger 12 via the fourth pipe 64. A throttling device is installed on the fourth pipe 64 so that after throttling and cooling, the liquid phase is reused as a cold source for the helium enrichment heat exchanger 12.

[0103] After the second gas-liquid fractionation, the resulting gas phase contains more than 85% helium and hydrogen. This crude helium is drawn off from the top of the second fractionation tower 50 and collected, and then sent to the downstream helium purification unit for further processing.

[0104] The technical solution of this invention employs only two sets of reboilers and fractionation towers to enrich BOG tail gas. The BOG tail gas is fed into the first reboiler 20 as a heat source, and after heat exchange, it is fed into the first fractionation tower 30 for enrichment. After the first enrichment, the remaining gas is again transferred to the second reboiler 40 as a heat source, and after heat exchange, it is fed into the second fractionation tower 50 for a second enrichment. This simplifies the process and improves enrichment and recovery efficiency. Simultaneously, the generated byproducts serve as a coolant, enabling effective energy recovery and utilization without the need for external cooling equipment, thus reducing the cost of the enrichment and recovery process.

[0105] Furthermore, after the first gas-liquid fractionation, most of the methane component in the first two-phase fluid is liquefied and falls as the first product (LNG liquid, liquefied natural gas) to the bottom of the first fractionation tower 30, that is, to the bottom of the first reboiler 20. The bottom of the first reboiler 20 has a first recovery port 21, and one end of the first recovery pipe 65 is connected to the first recovery port 21. The first product is drawn out from the bottom of the first reboiler 20 through the first recovery pipe 65.

[0106] The first recovery pipe 65 passes through the cold box 11, where the first product is further cooled and liquefied. The other end of the first recovery pipe 65 is used to connect with an external recovery mechanism to achieve effective recovery of the methane component.

[0107] Furthermore, after the second gas-liquid fractionation, since most of the nitrogen in the second two-phase fluid has liquefied, the remaining helium and hydrogen content is greater than 85%, which is used as the second product (crude helium). A second recovery port 51 is located at the top of the second fractionation tower 50, and one end of a second recovery pipe 66 is connected to the second recovery port 51. The gaseous phase gas in the second two-phase fluid, as crude helium, is drawn out from the second recovery port 51 through the second recovery pipe 66.

[0108] The second recovery pipe 66 passes sequentially through the helium enrichment heat exchanger 12 and the cold box 11. Since the temperature of the gas phase after the second gas-liquid fractionation is low, the gas phase is reheated after passing through the helium enrichment heat exchanger 12 and the cold box 11. The other end of the second recovery pipe 66 is used to connect to an external recovery mechanism, such as a downstream helium purification unit, so that the second product can be further processed in the helium purification unit.

[0109] Furthermore, after the second gas-liquid fractionation, most of the nitrogen component in the second two-phase fluid liquefies to form liquid nitrogen, one end of the fourth pipe 64 is connected to the second reboiler 40. To further improve utilization, the liquid nitrogen is introduced into the helium enrichment heat exchanger 12 through the fourth pipe 64. A throttling device is installed on the fourth pipe 64 so that after throttling and cooling, it can be reused as a cold source for the helium enrichment heat exchanger 12.

[0110] After being heated in the helium enrichment heat exchanger 12, the liquid nitrogen is reheated into a gaseous phase and then passes through the cold box 11 via the fourth pipeline. Due to its low temperature, it is further reheated under the action of the cold box 11, thus forming the third product (nitrogen-enriched gas).

[0111] In this embodiment, the third product is a by-product, so the other end of the fourth pipeline 64 extends to a preset height to release the third product at a high point.

[0112] Furthermore, the BOG tail gas enrichment device also includes a compressor 70, one end of which is connected to an external gas supply device, and the other end is connected to the first reboiler 20.

[0113] BOG tail gas at normal temperature and pressure is first transported to compressor 70 through pipeline. Compressor 70 pressurizes the BOG tail gas to above 2MPa, and then sends it to the first reboiler 20 as a heat source for the first fractionation column 30. By pressurizing the BOG tail gas, the concentration of the BOG tail gas is increased, ensuring the efficiency of BOG tail gas enrichment.

[0114] The above description is merely an exemplary embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for enriching BOG exhaust gas, characterized in that, The BOG exhaust gas enrichment method includes: The BOG exhaust gas is transferred to the first reboiler (20) for the first heat exchange; The gas after the first heat exchange is transferred to the cold box (11) for condensation, so that it undergoes a phase change to form the first two-phase fluid; The first two-phase fluid is transferred to the first fractionation tower (30), and the heat from the first heat exchange is used to perform the first gas-liquid fractionation on the first two-phase fluid. The liquid phase obtained after the first gas-liquid fractionation is transferred to the cold box (11) for condensation; The cooled liquid phase is recycled as the first product; The gas phase obtained after the first gas-liquid fractionation is transferred to the second reboiler (40) for a second heat exchange; The gas after the second heat exchange is transferred to a helium enrichment heat exchanger for condensation, causing it to undergo a phase change to form a second two-phase fluid. The second two-phase fluid is transferred to the second fractionation tower (50) and the heat from the second heat exchange is used to perform a second gas-liquid fractionation on the second two-phase fluid; The gas phase obtained after the second gas-liquid fractionation is sequentially transferred to the helium enrichment heat exchanger and the cold box (11) for reheating; The reheated gas phase is recycled as a second product; The liquid phase obtained after the second gas-liquid fractionation is throttled and cooled, and then used as a cold source to be transferred to the helium enrichment heat exchanger (12). The liquid phase, which serves as a cold source, is transferred to the cold box (11) for reheating, so that it changes from a liquid phase to a gas phase. The gaseous phase formed after reheating is recycled as a third product.

2. The BOG tail gas enrichment method as described in claim 1, characterized in that, The steps for transferring the BOG exhaust gas to the first reboiler (20) for the first heat exchange include: The BOG exhaust gas is compressed to bring the pressure of the compressed BOG exhaust gas to the preset pressure. The BOG exhaust gas compressed to the preset pressure is transmitted to the first reboiler (20) for the first heat exchange.

3. A BOG tail gas enrichment device, characterized in that, The BOG tail gas enrichment device is used in the BOG tail gas enrichment method as described in any one of claims 1 to 2, and the BOG tail gas enrichment device comprises: Cold box (11) and helium enrichment heat exchanger (12); The first reboiler (20) and the first fractionation column (30) disposed on the first reboiler (20); The second reboiler (40) and the second fractionation column (50) disposed on the second reboiler (40); The first pipeline (61) has one end connected to the first reboiler (20) and the other end passing through the cold box (11) and connected to the first distillation column (30); The second pipeline (62) has one end connected to the first fractionation tower (30) and the other end connected to the second reboiler (40); The third pipeline (63) has one end connected to the second reboiler (40) and the other end connected to the second fractionation tower (50) through the helium enrichment heat exchanger (12). The fourth pipeline (64) is connected at one end to the second reboiler (40) and at the other end to the helium enrichment heat exchanger (12).

4. The BOG tail gas enrichment device as described in claim 3, characterized in that, The BOG tail gas enrichment device also includes a first recovery pipe (65), the bottom of the first reboiler (20) has a first recovery port (21), one end of the first recovery pipe (65) is connected to the first recovery port (21), and the other end passes through the cold box (11) and is connected to the external recovery mechanism.

5. The BOG tail gas enrichment device as described in claim 3, characterized in that, The BOG tail gas enrichment device also includes a second recovery pipe (66), and the second fractionation tower (50) has a second recovery port (51). One end of the second recovery pipe (66) is connected to the second recovery port (51), and the other end passes through the helium enrichment heat exchanger (12) and the cold box (11) in sequence and is connected to the external recovery mechanism.

6. The BOG tail gas enrichment device as described in claim 3, characterized in that, One end of the fourth pipeline (64) is connected to the second reboiler (40), and the other end passes through the helium enrichment heat exchanger (12) and the cold box (11) in sequence, and extends to a preset height and connects with the external recovery mechanism.

7. The BOG tail gas enrichment device as described in claim 3, characterized in that, The BOG tail gas enrichment device also includes a compressor (70), one end of which is connected to an external gas supply device and the other end is connected to the first reboiler (20).

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