BOG tail gas concentration method and device

Abstract

The invention discloses a BOG tail gas concentration method and device, and relates to the technical field of compound treatment. BOG tail gas is conveyed into a first reboiler for first heat exchange; transmitting the gas subjected to the first heat exchange into a cold box for condensation; transferring the first two-phase fluid into a first fractionating tower, and performing first gas-liquid fractionation on the first two-phase fluid by utilizing heat of the first heat exchange; gas-phase gas obtained after the first-time gas-liquid fractionation is conveyed into a second reboiler for second-time heat exchange; transmitting the gas subjected to the second heat exchange to a helium concentration heat exchanger for condensation; transferring the second two-phase fluid into a second fractionating tower, and performing second gas-liquid fractionation on the second two-phase fluid by utilizing the heat of the second heat exchange; reheating and collecting the gas-phase gas obtained after the secondary gas-liquid fractionation; and throttling and cooling the liquid-phase liquid obtained after the second gas-liquid fractionation, and transmitting the liquid-phase liquid as a cold source to a helium concentration heat exchanger.

Description

Technical Field

[0001] The present invention relates to the technical field of compound processing, and in particular to a BOG tail gas concentration method and device. Background Art

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

[0003] Helium exists in the entire universe, accounting for 23% by mass, second only to hydrogen. But in nature, it mainly exists in natural gases or radioactive ores. In the earth's atmosphere, the concentration of helium is very low, only one in 52,000. The helium contained in radioactive minerals on the earth is a product of alpha decay. Helium contains an amount that is economically worth extracting in some natural gases, up to 7%. In my country's natural gas, helium contains about 0.04% to 0.2%, which is not worth economically extracting. Therefore, my country has always relied on importing the required helium from abroad. Due to the high price of helium, it has a significant impact on the fields in my country that use a large amount of helium and related scientific research and production units.

[0004] In the prior art, the recovery process of helium involves many processes, the operation is complicated, and the recovery efficiency is low. In addition, the utilization rate of by-products generated during the recovery process is low, which increases the cost of the recovery process. Summary of the invention

[0005] The main purpose of the present invention is to provide a BOG tail gas concentration method and device, aiming to solve the technical problems of more recovery process flows, lower recovery efficiency and high cost of the recovery process in the prior art.

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

[0007] The BOG tail 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, so that the gas undergoes a phase change to form a first two-phase fluid;

[0009] The first two-phase fluid is transferred to a first fractionation tower, and the first two-phase fluid is subjected to a first gas-liquid fractionation using the heat from the first heat exchange;

[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 transmitted to the helium concentration heat exchanger for condensation, so that the gas undergoes a phase change to form a second two-phase fluid;

[0012] The second two phase fluids are transferred to a second fractionation tower, and the second two phase fluids are subjected to a second gas-liquid fractionation using the heat from the second heat exchange;

[0013] Reheating and collecting the gas phase obtained after the second gas-liquid fractionation;

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

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

[0016] transferring the liquid phase obtained after the first gas-liquid fractionation to the cold box for condensation;

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

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

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

[0020] The reheated gas phase is recovered as the 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 transmitting it to the helium concentration heat exchanger as a cold source, the method further includes:

[0022] The liquid phase liquid as a cold source is transferred to the cold box for reheating, so that the liquid phase liquid is changed into the gas phase gas;

[0023] The gas phase formed by phase change after reheating is recovered as the third product.

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

[0025] Compress the BOG tail gas to make the pressure of the compressed BOG tail gas reach the preset pressure;

[0026] The BOG tail gas compressed to the preset gas pressure is transmitted to the first reboiler for the first heat exchange.

[0027] In addition, in order to solve the above problems, the present invention also proposes a BOG tail gas concentration device, which is applied to the above-mentioned BOG tail gas concentration method, and the BOG tail gas concentration device comprises:

[0028] Cold box and helium enrichment heat exchanger;

[0029] a first reboiler and a first fractionation tower disposed on the first reboiler;

[0030] a second reboiler and a second fractionation tower 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] a second pipeline, one end of which is connected to the first fractionation tower, and the other end of which is connected to the second reboiler;

[0033] A third pipeline, one end of which is connected to the second reboiler, and the other end of which passes through the helium concentration heat exchanger and is connected to the second fractionation tower;

[0034] A fourth pipeline, one end of which is connected to the second reboiler, and the other end of which is passed through the helium concentration heat exchanger.

[0035] In one embodiment, the BOG tail gas concentration 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 cooling box and is connected to an external recovery mechanism.

[0036] In one embodiment, the BOG tail gas concentration device also includes a second recovery pipe, the second distillation 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 concentration heat exchanger and the cold box in sequence and is connected to an 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 concentration 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 concentration device further comprises a compressor, one end of the compressor is connected to an external gas supply device, and the other end of the compressor is connected to the first reboiler.

[0039] The technical solution of the present invention adopts only two groups of reboilers and fractionation towers to carry out the BOG tail gas concentration process, and uses the BOG tail gas to be charged into the first reboiler as a heat source, and then passes into the first fractionation tower for concentration after heat exchange. After the first concentration, the remaining gas is transferred to the second reboiler as a heat source again, and then passes into the second fractionation tower for the second supply after heat exchange, which simplifies the process flow and improves the concentration recovery efficiency. At the same time, the generated by-product is used as a coolant, and the energy is effectively recycled, and no external cooling equipment is required, which reduces the cost of the concentration recovery process. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0041] Figure 1 A schematic flow chart of a first embodiment of a BOG tail gas enrichment method provided by the present invention;

[0042] Figure 2 A schematic flow chart of a second embodiment of the BOG tail gas enrichment method provided by the present invention;

[0043] Figure 3 A schematic flow chart of a third embodiment of the BOG tail gas enrichment method provided by the present invention;

[0044] Figure 4 A schematic flow chart of a fourth embodiment of the BOG tail gas enrichment method provided by the present invention;

[0045] Figure 5 A schematic flow chart of a fifth embodiment of the BOG tail gas enrichment method provided by the present invention;

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

[0047] Description of Figure Numbers:

[0048] 11. Cold box; 12. Helium concentration heat exchanger; 20. First reboiler; 21. First recovery port; 30. First distillation tower; 40. Second reboiler; 50. Second distillation tower; 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 purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0050] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

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

[0052] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features limited to "first" and "second" may explicitly or implicitly include at least one of the features. In addition, if "and / or" or "and / or" appears in the full text, its meaning includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, solution B, or solutions that satisfy both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0053] The present invention provides a method for concentrating BOG tail gas.

[0054] See also Figure 1 , a flow chart of a first embodiment of a method for enriching BOG tail gas according to the present invention, in one embodiment of the present invention, the method for enriching BOG tail gas comprises the following steps:

[0055] Step S10: transmitting the BOG tail gas to the first reboiler for the first heat exchange;

[0056] Step S20: transmitting the gas after the first heat exchange to a cold box for condensation, so that the gas undergoes a phase change to form a first two-phase fluid;

[0057] Step S30: transferring the first two-phase fluid to a first fractionation tower, and performing a first gas-liquid fractionation on the first two-phase fluid using the heat from the first heat exchange;

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

[0059] Step S50: transmitting the gas after the second heat exchange to the helium concentration heat exchanger for condensation, so that the gas undergoes a phase change to form a second two-phase fluid;

[0060] Step S60: transferring the second two phase fluids to a second fractionation tower, and performing a second gas-liquid fractionation on the second two phase fluid using the heat from the second heat exchange;

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

[0062] Step S80: throttling and cooling the liquid phase obtained after the second gas-liquid fractionation and then transmitting it to the helium concentration heat exchanger as a cold source.

[0063] The BOG tail gas concentration method of the present invention is applied to the BOG tail gas concentration device, please refer to Figure 6 The BOG tail gas concentration device includes a cold box 11, a helium concentration heat exchanger 12, a first pipeline 61, a second pipeline 62, a third pipeline 63, a fourth pipeline 64, a first reboiler 20 and a first distillation tower 30 arranged on the first reboiler 20, a second reboiler 40 and a second distillation tower 50 arranged 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 distillation tower 30; one end of the second pipeline 62 is connected to the first distillation tower 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 concentration heat exchanger 12 and is connected to the second distillation tower 50; one end of the fourth pipeline 64 is connected to the second reboiler 40, and the other end is penetrated into the helium concentration heat exchanger 12.

[0065] The BOG tail gas contains helium, hydrogen, nitrogen, methane, etc. First, the BOG tail gas is transported to the first reboiler 20 through a pipeline for the first heat exchange. The first reboiler 20 is arranged at the bottom of the first distillation tower 30, and the heat of the BOG tail gas after the first heat exchange is used as a heat source for heating the first distillation tower 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. Under the action of the cold box 11, the BOG tail gas is further cooled and condensed to produce a phase change to form a first two-phase fluid. The first two-phase fluid is introduced into the first distillation tower 30 through the first pipeline 61. The heat of the first heat exchange in the first reboiler 20 is used to perform the first gas-liquid fractionation on the first two-phase fluid in the first distillation tower 30.

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

[0068] The remaining gas phase gas after the first gas-liquid fractionation is gas phase helium-containing BOG, whose main components include helium, hydrogen, nitrogen and a small amount of methane, etc., which is introduced from the first fractionation tower 30 to the second reboiler 40 through the second pipeline 62. The gas phase gas undergoes a second heat exchange in the second reboiler 40.

[0069] The second reboiler 40 is disposed at the bottom of the second distillation tower 50 , and uses the heat of the gas phase gas after the second heat exchange as a heat source for supplying heat to the second distillation tower 50 .

[0070] After the second heat exchange, the gas phase is cooled and led out from the second reboiler 40 through the third pipeline 63. The third pipeline 63 passes through the helium concentration heat exchanger 12. Under the action of the helium concentration heat exchanger 12, the gas phase is further cooled and condensed to produce a phase change to form a second two-phase fluid. The second two-phase fluid is introduced into the second distillation tower 50 through the third pipeline 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 distillation tower 50.

[0071] After the second gas-liquid fractionation, most of the nitrogen components in the second two-phase fluid are liquefied to form liquid phase liquid, and the liquid phase liquid falls to the bottom of the second fractionation tower 50, that is, falls to the bottom of the second reboiler 40, and is introduced into the helium concentration heat exchanger 12 through the fourth pipeline 64. A throttle is provided on the fourth pipeline 64, so that it can be reused as a cold source of the helium concentration heat exchanger 12 after throttling and cooling.

[0072] After the second gas-liquid fractionation, the gas phase has a helium and hydrogen content of more than 85%, which is drawn out from the top of the second fractionation tower 50 as crude helium and collected, and further sent to the downstream helium purification device for treatment.

[0073] The technical solution of the present invention adopts only two sets of reboilers and fractionation towers to carry out the BOG tail gas concentration process, and uses the BOG tail gas to be charged into the first reboiler 20 as a heat source, and is passed into the first fractionation tower 30 for concentration after heat exchange. After the first concentration, the remaining gas is again transferred to the second reboiler 40 as a heat source, and is passed into the second fractionation tower 50 for the second supply after heat exchange, which simplifies the process flow and improves the concentration recovery efficiency. At the same time, the generated by-product is used as a coolant, and the energy is effectively recycled, and no external cooling equipment is required, which reduces the cost of the concentration recovery process.

[0074] For further information, please refer to Figure 2 , Figure 2 This is a flow chart of a second embodiment of the BOG tail gas enrichment method of the present invention. After step S30, the method further includes:

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

[0076] Step S32: recovering the cooled liquid phase 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 to the bottom of the first distillation tower 30 as the first product (LNG liquid, liquefied natural gas), that is, falls 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, and the first product is led 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, and the first product is further cooled and liquefied under the action of the cold box 11. The other end of the first recovery pipe 65 is used to communicate with an external recovery mechanism to achieve effective recovery of the methane component.

[0079] For further information, please refer to Figure 3 , Figure 3 This is a flow chart of a 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 concentration heat exchanger and the cold box for reheating;

[0081] Step S72: recovering the reheated gas phase as the second product.

[0082] After the second gas-liquid fractionation, the second two fluids have a residual helium and hydrogen content greater than 85% due to the liquefaction of most of the nitrogen, and are used as the second product (crude helium). The top of the second fractionating tower 50 is provided with a second recovery port 51, and one end of a second recovery pipe 66 is connected to the second recovery port 51, and the gaseous phase gas in the second two fluids is drawn out from the second recovery port 51 through the second recovery pipe 66 as crude helium.

[0083] The second recovery pipe 66 passes through the helium concentration heat exchanger 12 and the cold box 11 in sequence. Since the temperature of the gas phase after the second gas-liquid fractionation is relatively low, the gas phase gas is reheated after passing through the helium concentration heat exchanger 12 and the cold box 11. The other end of the second recovery pipe 66 is used to communicate with an external recovery mechanism, such as a downstream helium purification device, so as to further send the second product to the helium purification device for processing.

[0084] For further information, please refer to Figure 4 , Figure 4 This is a flow chart of a fourth embodiment of the BOG tail gas enrichment method of the present invention. After step S80, the method further includes:

[0085] Step S81: transferring the liquid phase liquid as a cold source to the cold box for reheating, so that the liquid phase liquid is changed into the gas phase gas;

[0086] Step S82: recovering the gas phase formed by phase change after reheating as the third product.

[0087] After the second gas-liquid fractionation, most of the nitrogen components in the second two fluids are liquefied to form liquid nitrogen, and one end of the fourth pipeline 64 is connected to the second reboiler 40. In order to further improve the utilization rate, the liquid nitrogen is introduced into the helium concentration heat exchanger 12 through the fourth pipeline 64. A throttle is set on the fourth pipeline 64, so that it can be reused as a cold source of the helium concentration heat exchanger 12 after throttling and cooling.

[0088] After the liquid nitrogen is heated in the helium enrichment heat exchanger 12, it is reheated into gas phase, and the fourth pipeline further passes through the cold box 11. Due to its low temperature, it is further reheated under the action of the cold box 11 to form the third product (nitrogen-rich 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 discharge the third product at a high point.

[0090] For further information, please refer to Figure 5 , Figure 5 This is a flow chart of a fifth embodiment of the BOG tail gas enrichment method of the present invention, step S10 comprises:

[0091] Step S11: compressing the BOG tail gas to make the pressure of the compressed BOG tail gas reach a preset pressure;

[0092] Step S12: transmitting the BOG tail gas compressed to the preset gas pressure to the first reboiler for a first heat exchange.

[0093] The BOG tail gas at normal temperature and pressure is first transported to the compressor 70 through a pipeline, the BOG tail gas is pressurized to above 2 MPa by the compressor 70, and then sent to the first reboiler 20 for heat exchange to serve as a heat source for the first fractionation tower 30. By pressurizing the BOG tail gas, the concentration of the BOG tail gas is increased to ensure the efficiency of the concentration of the BOG tail gas.

[0094] The present 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, and a first distillation tower 30 arranged on the first reboiler 20, a second reboiler 40, and a second distillation tower 50 arranged 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 distillation tower 30; one end of the second pipeline 62 is connected to the first distillation tower 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 concentration heat exchanger 12 and is connected to the second distillation tower 50; one end of the fourth pipeline 64 is connected to the second reboiler 40, and the other end is penetrated into the helium concentration heat exchanger 12.

[0096] The BOG tail gas contains helium, hydrogen, nitrogen, methane, etc. First, the BOG tail gas is transported to the first reboiler 20 through a pipeline for the first heat exchange. The first reboiler 20 is arranged at the bottom of the first distillation tower 30, and the heat of the BOG tail gas after the first heat exchange is used as a heat source for heating the first distillation tower 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. Under the action of the cold box 11, the BOG tail gas is further cooled and condensed to produce a phase change to form a first two-phase fluid. The first two-phase fluid is introduced into the first distillation tower 30 through the first pipeline 61. The heat of the first heat exchange in the first reboiler 20 is used to perform the first gas-liquid fractionation on the first two-phase fluid in the first distillation tower 30.

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

[0099] The remaining gas phase gas after the first gas-liquid fractionation is gas phase helium-containing BOG, whose main components include helium, hydrogen, nitrogen and a small amount of methane, etc., which is introduced from the first fractionation tower 30 to the second reboiler 40 through the second pipeline 62. The gas phase gas undergoes a second heat exchange in the second reboiler 40.

[0100] The second reboiler 40 is disposed at the bottom of the second distillation tower 50 , and uses the heat of the gas phase gas after the second heat exchange as a heat source for supplying heat to the second distillation tower 50 .

[0101] After the second heat exchange, the gas phase is cooled and led out from the second reboiler 40 through the third pipeline 63. The third pipeline 63 passes through the helium concentration heat exchanger 12. Under the action of the helium concentration heat exchanger 12, the gas phase is further cooled and condensed to produce a phase change to form a second two-phase fluid. The second two-phase fluid is introduced into the second distillation tower 50 through the third pipeline 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 distillation tower 50.

[0102] After the second gas-liquid fractionation, most of the nitrogen components in the second two-phase fluid are liquefied to form liquid phase liquid, and the liquid phase liquid falls to the bottom of the second fractionation tower 50, that is, falls to the bottom of the second reboiler 40, and is introduced into the helium concentration heat exchanger 12 through the fourth pipeline 64. A throttle is provided on the fourth pipeline 64, so that it can be reused as a cold source of the helium concentration heat exchanger 12 after throttling and cooling.

[0103] After the second gas-liquid fractionation, the gas phase has a helium and hydrogen content of more than 85%, which is drawn out from the top of the second fractionation tower 50 as crude helium and collected, and further sent to the downstream helium purification device for treatment.

[0104] The technical solution of the present invention adopts only two sets of reboilers and fractionation towers to carry out the BOG tail gas concentration process, and uses the BOG tail gas to be charged into the first reboiler 20 as a heat source, and is passed into the first fractionation tower 30 for concentration after heat exchange. After the first concentration, the remaining gas is again transferred to the second reboiler 40 as a heat source, and is passed into the second fractionation tower 50 for the second supply after heat exchange, which simplifies the process flow and improves the concentration recovery efficiency. At the same time, the generated by-product is used as a coolant, and the energy is effectively recycled, and no external cooling equipment is required, which reduces the cost of the concentration 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 into the bottom of the first distillation tower 30 as the first product (LNG liquid, liquefied natural gas), that is, into 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, and 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, and the first product is further cooled and liquefied under the action of the cold box 11. The other end of the first recovery pipe 65 is used to communicate with an external recovery mechanism to achieve effective recovery of the methane component.

[0107] Further, after the second gas-liquid fractionation, the second two fluids have a residual helium and hydrogen content greater than 85% due to the liquefaction of most of the nitrogen, and are used as the second product (crude helium). The top of the second fractionating tower 50 has a second recovery port 51, and one end of a second recovery pipe 66 is connected to the second recovery port 51, and the gaseous phase gas in the second two fluids is drawn from the second recovery port 51 through the second recovery pipe 66 as crude helium.

[0108] The second recovery pipe 66 passes through the helium concentration heat exchanger 12 and the cold box 11 in sequence. Since the temperature of the gas phase after the second gas-liquid fractionation is relatively low, the gas phase gas is reheated after passing through the helium concentration heat exchanger 12 and the cold box 11. The other end of the second recovery pipe 66 is used to communicate with an external recovery mechanism, such as a downstream helium purification device, so as to further send the second product to the helium purification device for processing.

[0109] Further, after the second gas-liquid fractionation, most of the nitrogen components in the second two fluids are liquefied to form liquid nitrogen, and one end of the fourth pipeline 64 is connected to the second reboiler 40. In order to further improve the utilization rate, the liquid nitrogen is introduced into the helium concentration heat exchanger 12 through the fourth pipeline 64. A throttle is provided on the fourth pipeline 64, so that it can be reused as a cold source of the helium concentration heat exchanger 12 after throttling and cooling.

[0110] After the liquid nitrogen is heated in the helium enrichment heat exchanger 12, it is reheated into gas phase, and the fourth pipeline further passes through the cold box 11. Due to its low temperature, it is further reheated under the action of the cold box 11 to form the third product (nitrogen-rich 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 discharge the third product at a high point.

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

[0113] The BOG tail gas at normal temperature and pressure is first transported to the compressor 70 through a pipeline, and the BOG tail gas is pressurized to above 2 MPa by the compressor 70, and then sent to the first reboiler 20 as a heat source for the first fractionation tower 30. By pressurizing the BOG tail gas, the concentration of the BOG tail gas is increased, and the efficiency of the concentration of the BOG tail gas is ensured.

[0114] The above description is only an exemplary embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for enriching BOG tail gas, characterized in that: The BOG tail gas concentration method comprises: The BOG tail gas is transferred to the first reboiler (20) for a first heat exchange; The gas after the first heat exchange is transferred to a cold box (11) for condensation, so that the gas undergoes a phase change to form a first two-phase fluid; The first two-phase fluid is transferred to a first fractionation tower (30), and the first two-phase fluid is subjected to a first gas-liquid fractionation using the heat from the first heat exchange; 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 transmitted to the helium concentration heat exchanger for condensation, so that the gas undergoes a phase change to form a second two-phase fluid; The second two phase fluids are transferred to a 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; Reheating and collecting the gas phase obtained after the second gas-liquid fractionation; The liquid phase obtained after the second gas-liquid fractionation is throttled and cooled, and then transmitted to the helium concentration heat exchanger (12) as a cold source.

2. The BOG tail gas concentration method according to claim 1, characterized in that: After the step of transferring the first two-phase fluid to a first fractionation tower (30), and performing a first gas-liquid fractionation on the first two-phase fluid using the heat from the first heat exchange, the method further comprises: transferring the liquid phase obtained after the first gas-liquid fractionation to the cold box for condensation; The cooled liquid phase is recovered as the first product.

3. The BOG tail gas enrichment method according to claim 1, characterized in that: The steps of reheating and collecting the gas phase gas obtained after the second gas-liquid fractionation include: The gas phase obtained after the second gas-liquid fractionation is sequentially transmitted to the helium concentration heat exchanger and the cold box for reheating; The reheated gas phase is recovered as the second product.

4. The BOG tail gas enrichment method according to claim 1, characterized in that: After the step of throttling and cooling the liquid phase liquid obtained after the second gas-liquid fractionation and transmitting it to the helium concentration heat exchanger as a cold source, the method further includes: The liquid phase liquid as a cold source is transferred to the cold box for reheating, so that the liquid phase liquid is changed into the gas phase gas; The gas phase formed by phase change after reheating is recovered as the third product.

5. The BOG tail gas enrichment method according to claim 1, characterized in that: The step of transferring the BOG tail gas to the first reboiler (20) for the first heat exchange comprises: Compress the BOG tail gas to make the pressure of the compressed BOG tail gas reach the preset pressure; The BOG tail gas compressed to the preset gas pressure is transmitted to the first reboiler (20) for the first heat exchange.

6. A BOG tail gas enrichment device, characterized in that: The BOG tail gas concentration device is applied to the BOG tail gas concentration method according to any one of claims 1 to 5, and the BOG tail gas concentration device comprises: A cold box (11) and a helium concentration heat exchanger (12); A first reboiler (20) and a first fractionation tower (30) disposed on the first reboiler (20); A second reboiler (40) and a second fractionation tower (50) disposed on the second reboiler (40); a first pipeline (61), one end of which is connected to the first reboiler (20), and the other end of which passes through the cold box (11) and is connected to the first fractionation tower (30); a second pipeline (62), one end of the second pipeline (62) being connected to the first fractionation tower (30), and the other end of the second pipeline (62) being connected to the second reboiler (40); a third pipeline (63), one end of the third pipeline (63) being connected to the second reboiler (40), and the other end of the third pipeline (63) passing through the helium concentration heat exchanger (12) and connected to the second fractionation tower (50); A fourth pipeline (64), one end of which is connected to the second reboiler (40), and the other end of which is passed through the helium concentration heat exchanger (12).

7. The BOG tail gas enrichment device according to claim 6, characterized in that: The BOG tail gas enrichment device further comprises a first recovery pipe (65), the bottom of the first reboiler (20) is provided with 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 first cooling box (11) and is connected to an external recovery mechanism.

8. The BOG tail gas enrichment device according to claim 6, characterized in that: The BOG tail gas concentration device further comprises a second recovery pipe (66), the second fractionation tower (50) is provided with 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 of the second recovery pipe (66) passes through the helium concentration heat exchanger (12) and the cold box (11) in sequence and is connected to an external recovery mechanism.

9. The BOG tail gas enrichment device according to claim 6, 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 concentration heat exchanger (12) and the cold box (11) in sequence, and then extends to a preset height and is connected to an external recovery mechanism.

10. The BOG tail gas enrichment device according to claim 6, characterized in that: The BOG tail gas enrichment device further comprises a compressor (70), one end of the compressor (70) is connected to an external gas supply device, and the other end of the compressor (70) is connected to the first reboiler (20).

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