A system and method for extracting helium from BOG

Abstract

The present invention discloses a system and method for extracting helium from BOG. ​​The system comprises a membrane separation unit for separating BOG to obtain crude helium, an oxidation unit for removing hydrogen and methane from the crude helium, a decarbonization unit for removing carbon dioxide from the gas treated by the oxidation unit, a crude helium refining unit for extracting helium from the gas treated by the decarbonization unit, and a circulation unit for recovering waste heat generated by the decarbonization unit and regenerating a decarbonizer. The overall structure of the present invention has a clear division of labor. BOG is first processed to obtain crude helium. The crude helium then passes through the oxidation unit, the decarbonization unit, and the crude helium refining unit in sequence to remove impurities such as hydrogen, methane, carbon dioxide, water, nitrogen, and oxygen. Finally, high-purity helium is refined. A circulation unit is added to cooperate with the decarbonization unit to regenerate the decarbonizer. Furthermore, the crude helium refining unit and the decarbonization unit cooperate to freeze and remove moisture from the helium, thereby achieving resource recycling.

Description

Technical Field

[0001] The present invention relates to the technical field of helium extraction, and in particular to a system and method for extracting helium from BOG. Background Art

[0002] As we all know, flash gas, or BOG, is generated during the production and storage of liquefied natural gas (LNG). Because natural gas contains a certain amount of helium, helium tends to accumulate in BOG. ​​Helium is a scarce resource, and currently, extracting helium from natural gas, particularly BOG, is the only source of helium for industrial production. Current methods for industrial helium extraction include cryogenics, pressure swing adsorption, cryogenic adsorption, membrane permeation separation, and their coupled processes.

[0003] Invention patent CN113154409B discloses a system and method for extracting helium from BOG gas and utilizing its energy. Pure oxygen is used to combust and remove methane and hydrogen from BOG. ​​The combusted gas is then dehydrated, purified, and liquefied to separate liquid nitrogen, liquid oxygen, and liquid carbon dioxide. The mixed gas from which CO2, O2, and N2 have been removed is then cryogenically purified to obtain high-purity helium. The heat energy generated during the combustion process meets the production heat needs of the LNG plant and provides the energy consumption of the system and the electricity consumption of the LNG plant. BOG is usually generated during storage and transportation, and the gas volume fluctuates greatly and is unstable. Therefore, the process of removing CH4, H2, CO2, O2, N2, etc. through direct combustion is complex and difficult to maintain, and needs further improvement. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a system and method for extracting helium from BOG with energy recycling and utilization, low energy consumption and simple process.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solution: a system for extracting helium from BOG, comprising a membrane separation unit for separating BOG to obtain crude helium, an oxidation unit for removing hydrogen and methane from the crude helium, a decarbonization unit for removing carbon dioxide from the gas treated by the oxidation unit, a crude helium refining unit for extracting helium from the gas treated by the decarbonization unit, and a circulation unit for recovering waste heat generated by the decarbonization unit and regenerating a decarbonizer.

[0006] Furthermore, the membrane separation unit includes a BOG compressor, a first-stage membrane separator and a first-stage second-stage membrane separator which are connected in sequence to form a loop, and the first-stage second-stage membrane separator is also connected to the oxidation unit.

[0007] Furthermore, the oxidation unit includes a mixed gas compressor and an oxidizer which are connected in sequence, and the mixed gas compressor is connected to the membrane separation unit, and the oxidizer is connected to the decarbonization unit.

[0008] Furthermore, the decarbonization unit includes a steam generator, a cooling water splitter, a decarbonization compressor and a carbon dioxide absorption tower connected in sequence, and the steam generator is connected to the oxidation unit, and the carbon dioxide absorption tower is connected to the crude helium refining unit.

[0009] Furthermore, the crude helium refining unit includes a tower top heat exchanger, a gas-liquid separator, a freeze-dehydration device and a pressure swing adsorption module which are connected in sequence, and the tower top heat exchanger is connected to the decarbonization unit, and the pressure swing adsorption module outputs helium at its outlet.

[0010] Furthermore, the outlet of the pressure swing adsorption module is also connected to the inlet of the oxidation unit.

[0011] Furthermore, the circulation unit includes a lean-rich liquid exchanger, a regeneration tower, and a solution pump that are sequentially connected to form a loop, and the lean-rich liquid exchanger is connected to the carbon dioxide absorption tower to form a loop.

[0012] Furthermore, the circulation unit further includes a reboiler forming a circulation loop with the steam generator, and the reboiler is also connected to the solution pump and the regeneration tower.

[0013] Furthermore, the freeze dehydration equipment includes a freeze dehydration module connected between the pressure swing adsorption module and the gas-liquid separator and a waste heat refrigeration module connected between the reboiler and the steam generator, and the waste heat refrigeration module is used to cool the freeze dehydration module for freeze dehydration.

[0014] A method for extracting helium from BOG comprises the following steps:

[0015] S1. BOG is fed into the BOG compressor. After being pressurized by the BOG compressor, it enters the first-stage membrane separator. Non-permeate gas enters the second-stage membrane separator to recover some helium. The permeate gas produced by the second-stage membrane separator returns to the inlet of the BOG compressor.

[0016] S2. The permeate gas from the first stage membrane separator is pressurized by the mixed gas compressor, mixed with pure oxygen, and then enters the oxidizer;

[0017] S3. The high-temperature gas after the oxidizer reaction enters the steam generator, then passes through the cooling water separator to cool and separate the water, enters the decarbonization compressor to increase the pressure, and is sent to the carbon dioxide absorption tower;

[0018] S4. The crude helium gas after absorption by the carbon dioxide absorption tower is cooled by the top heat exchanger, separated by the gas-liquid separator, and then enters the refrigeration dehydration equipment to remove water from the crude helium gas. It then enters the pressure swing adsorption module to further refine the crude helium gas to obtain a 99.999% high-purity helium product;

[0019] S5. A portion of the high-temperature steam generated by the steam generator is sent to the reboiler for decarbonization agent regeneration. The remaining portion of the steam enters the waste heat refrigeration module for heat exchange, converting it into condensed water. This condensed water is then combined with the condensed water generated by the reboiler and circulated. The waste heat refrigeration module absorbs heat to produce low-temperature chilled water, which is sent to the freeze-dehydration equipment to cool and freeze-dehydrate the water-containing helium.

[0020] S6. Absorbing carbon dioxide. The carbon dioxide-rich liquid at the bottom of the absorption tower enters the regeneration tower for regeneration after heat exchange in the lean-rich liquid exchanger. The regenerated lean liquid is pressurized by the solution pump and heat exchanged in the lean-rich liquid exchanger before returning to the absorption tower to absorb carbon dioxide.

[0021] S. The desorbed gas produced by the pressure swing adsorption module returns to the mixed gas compressor to circulate and extract helium.

[0022] The beneficial effects of the present invention are embodied in:

[0023] The system for extracting helium from BOG of the present invention is divided into multiple units, and the overall structure has a clear division of labor and a simple structure. The BOG is first processed to obtain crude helium, and the crude helium is sequentially passed through an oxidation unit, a decarbonization unit, and a crude helium refining unit to remove impurities such as hydrogen, methane, carbon dioxide, water, nitrogen, and oxygen. Finally, high-purity helium is refined. At the same time, a circulation unit is added to cooperate with the decarbonization unit to achieve decarbonizer regeneration, and the crude helium refining unit cooperates with the decarbonization unit to achieve frozen removal of helium water, thereby meeting resource recycling requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a system flow chart of extracting helium from BOG according to the present invention.

[0025] The components in the accompanying drawings are marked as follows: 1. Membrane separation unit; 101. BOG compressor; 102. First-stage membrane separator; 103. First-stage membrane separator; 2. Oxidation unit; 201. Mixed gas compressor; 202. Oxidizer; 3. Decarbonization unit; 301. Steam generator; 302. Cooling water splitter; 303. Decarbonization compressor; 304. Carbon dioxide absorption tower; 4. Crude helium refining unit; 401. Top heat exchanger; 402. Gas-liquid separator; 403. Freeze-dehydration equipment; 4031. Freeze-dehydration module; 4032. Waste heat refrigeration module; 404. Pressure swing adsorption module; 5. Circulation unit; 501. Lean-rich liquid exchanger; 502. Regeneration tower; 503. Solution pump; 504. Reboiler. DETAILED DESCRIPTION

[0026] 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 embodiments described are only part of the embodiments of the present invention, not all of the embodiments. In the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0027] See also Figure 1 .

[0028] The system for extracting helium from BOG of the present invention comprises a membrane separation unit 1 for separating BOG to obtain crude helium, an oxidation unit 2 for removing hydrogen and methane from the crude helium, a decarbonization unit 3 for removing carbon dioxide from the gas treated by the oxidation unit 2, a crude helium refining unit 4 for extracting helium from the gas treated by the decarbonization unit 3, and a circulation unit 5 for recovering waste heat generated by the decarbonization unit 3 and regenerating a decarbonizing agent.

[0029] In one embodiment, the membrane separation unit 1 includes a BOG compressor 101, a first-stage membrane separator 102, and a second-stage membrane separator 103, which are connected in sequence to form a loop. The second-stage membrane separator 103 is also connected to the oxidation unit 2. This design, with a single-stage membrane separation, effectively reduces energy consumption compared to multi-stage membrane separation. The single-stage membrane separation process is used to concentrate helium, significantly reducing the processed gas flow rate after concentration, reducing the load on subsequent equipment, and effectively reducing the energy consumption of helium extraction. It should also be noted that the second-stage membrane separator 103 also has an exhaust gas outlet.

[0030] In one embodiment, the oxidation unit 2 includes a mixed gas compressor 201 and an oxidizer 202, which are connected in sequence. The mixed gas compressor 201 is connected to the membrane separation unit 1, and the oxidizer 202 is connected to the decarbonization unit 3. In this design, the crude helium is reacted in the oxidizer 202 to remove hydrogen and methane from the crude helium. It should be noted that oxygen is injected into the oxidizer 202 during operation.

[0031] In one embodiment, the decarbonization unit 3 includes a steam generator 301, a cooling water splitter 302, a decarbonization compressor 303, and a carbon dioxide absorption tower 304, which are connected in sequence. The steam generator 301 is connected to the oxidation unit 2, and the carbon dioxide absorption tower 304 is connected to the crude helium refining unit 4. This design eliminates carbon dioxide from the crude helium.

[0032] In one embodiment, the crude helium refining unit 4 includes a tower top heat exchanger 401, a gas-liquid separator 402, a refrigerated dehydration device 403, and a pressure swing adsorption module 404, which are sequentially connected. The tower top heat exchanger 401 is connected to the decarbonization unit 3, and the pressure swing adsorption module 404 outputs helium. This design utilizes the refrigerated dehydration device 403 to further remove moisture from the crude helium, meeting the impurity moisture requirements of the helium product. Simultaneously, the pressure swing adsorption module 404 effectively removes small amounts of impurities such as nitrogen and oxygen from the crude helium, resulting in a high-purity helium product. It should be noted that the pressure swing adsorption module 404 is readily available commercially and will not be further described here.

[0033] In one embodiment, the outlet of the pressure swing adsorption module 404 is also connected to the inlet of the oxidation unit 2. This design allows the desorbed gas generated by the pressure swing adsorption module 404 to return to the mixed gas compressor 201 for recycling and extracting helium, thereby improving the recovery rate of helium.

[0034] In one embodiment, the circulation unit 5 includes a lean-rich liquid exchanger 501, a regeneration tower 502, and a solution pump 503, which are connected in sequence to form a loop. The lean-rich liquid exchanger 501 is connected to the carbon dioxide absorption tower 304 to form a loop. With this design, the carbon dioxide-rich liquid at the bottom of the carbon dioxide absorption tower 304 undergoes heat exchange in the lean-rich liquid exchanger 501 and then enters the regeneration tower 502 for regeneration. The regenerated lean liquid is then pressurized by the solution pump 503 and heat exchanged in the lean-rich liquid exchanger 501 before returning to the carbon dioxide absorption tower 304 to absorb carbon dioxide. It should also be noted that the regeneration tower 502 also has a carbon dioxide outlet.

[0035] In one embodiment, the circulation unit 5 further includes a reboiler 504 forming a circulation loop with the steam generator 301, and the reboiler 504 is also connected to the solution pump 503 and the regeneration tower 502. This design fully utilizes part of the steam generated by the steam generator 301 for regeneration in the decarbonization process, and simultaneously obtains carbon dioxide product.

[0036] In one embodiment, the freeze-dehydration equipment 403 includes a freeze-dehydration module 4031 connected between the pressure swing adsorption module 404 and the gas-liquid separator 402, and a waste heat refrigeration module 4032 connected between the reboiler 504 and the steam generator 301. The waste heat refrigeration module 4032 is used to cool and freeze-dehydrate the freeze-dehydration module 4031. This design further fully utilizes the steam generated by the steam generator 301. The condensed water generated by this steam after heat exchange with the refrigerant in the waste heat refrigeration module 4032 is combined with the condensed water generated by the reboiler 504 and then re-enters the circuit. The waste heat refrigeration module 4032 absorbs heat to produce low-temperature chilled water, which is then delivered to the freeze-dehydration module 4031 to cool and freeze-dehydrate the water-containing helium.

[0037] A method for extracting helium from BOG comprises the following steps:

[0038] S1. BOG is connected to the BOG compressor 101. After the BOG compressor 101 increases the pressure, it enters the first-stage membrane separator 102. The non-permeate gas enters the first-stage membrane separator 103 to recover part of the helium. The permeate gas generated by the first-stage membrane separator 103 returns to the inlet of the 1-BOG compressor 101.

[0039] S2. The permeate gas from the first stage membrane separator 102 is pressurized by the mixed gas compressor 201 and mixed with pure oxygen and enters the oxidizer 202;

[0040] S3 oxidizer 202 after the reaction of the high-temperature gas into the steam generator 301, and then after cooling the water separator cooling water, into the decarbonization compressor 303 boost, sent to the carbon dioxide absorption tower 304;

[0041] S4. The crude helium gas after absorption by the carbon dioxide absorption tower 304 passes through the overhead heat exchanger 401 for cooling, and then enters the refrigeration dehydration equipment 403 after separation by the gas-liquid separator 402. After the water in the crude helium gas is removed, it enters the pressure swing adsorption module 404 to further refine the crude helium gas to obtain a 99.999% high-purity helium product;

[0042] S5. Part of the high-temperature steam generated by the steam generator 301 is sent to the reboiler 504 for decarbonization agent regeneration. The other part of the steam enters the waste heat refrigeration module 4032 for heat exchange and becomes condensed water. It is then combined with the condensed water generated by the reboiler 504 and circulated. The waste heat refrigeration module 4032 absorbs heat to produce low-temperature chilled water, which is sent to the freeze-dehydration equipment 403 to cool and freeze-dehydrate the water-containing helium.

[0043] S6 absorbs carbon dioxide at the bottom of the absorption tower 304 rich carbon dioxide liquid, after the lean and rich liquid exchanger 501 heat exchanger enters the regeneration tower 502 for regeneration, the regenerated lean liquid is pressurized by the solution pump 503, the lean and rich liquid exchanger 501 heat exchanger returns to the absorption tower to absorb carbon dioxide;

[0044] S7. The desorbed gas generated by the pressure swing adsorption module 404 is returned to the mixed gas compressor 201 for recycling and extraction of helium. In summary, the present invention utilizes multiple units, resulting in a clear division of labor and a simple overall structure. BOG is first processed to obtain crude helium, which is then sequentially passed through the oxidation unit 2, the decarbonization unit 3, and the crude helium refining unit 4 to remove impurities such as hydrogen, methane, carbon dioxide, water, nitrogen, and oxygen. Finally, high-purity helium is refined. Simultaneously, a circulation unit 5 is added to cooperate with the decarbonization unit 3 to regenerate the decarbonizer, and the crude helium refining unit 4 cooperates with the decarbonization unit 3 to freeze and remove moisture from the helium, thereby satisfying resource recycling requirements. Furthermore, it should be noted that the decarbonizer is a carbon dioxide-rich absorbent.

[0045] It should be understood that the examples and implementation methods described herein are for illustrative purposes only and are not intended to limit the present invention. Those skilled in the art may make various modifications or changes based on them. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0046] It should be noted that if the embodiments of the present invention involve directional indications such as up, down, left, right, front, back, etc., then the directional indications are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture as shown in the accompanying drawings. If the specific posture changes, the directional indication will also change accordingly.

[0047] 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 for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features limited to "first" and "second" may explicitly or implicitly include at least one of such features. In addition, the meaning of "and / or" appearing in the full text includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or schemes in which A and B are satisfied at the same time. In addition, "multiple" refers to more than two. 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 mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

Claims

1. A system for extracting helium from BOG, characterized in that: The invention comprises a membrane separation unit (1) for separating BOG to obtain crude helium, an oxidation unit (2) for removing hydrogen and methane from the crude helium, a decarbonization unit (3) for removing carbon dioxide from the gas treated by the oxidation unit (2), a crude helium refining unit (4) for extracting helium from the gas treated by the decarbonization unit (3), and a circulation unit (5) for recovering waste heat generated by the decarbonization unit (3) and regenerating a decarbonizing agent. The decarbonization unit (3) comprises a steam generator (301), a cooling water splitter (302), a decarbonization compressor (303), and a carbon dioxide absorption tower (304) which are connected in sequence, wherein the steam generator (301) is connected to the oxidation unit (2), and the carbon dioxide absorption tower (304) is connected to the crude helium refining unit (4); The crude helium refining unit (4) comprises a tower top heat exchanger (401), a gas-liquid separator (402), a refrigeration dehydration device (403), and a pressure swing adsorption module (404) which are connected in sequence, and the tower top heat exchanger (401) is connected to the decarbonization unit (3), and the pressure swing adsorption module (404) outputs helium at an outlet; The circulation unit (5) comprises a lean and rich liquid exchanger (501), a regeneration tower (502), and a solution pump (503) which are connected in sequence to form a loop, and the lean and rich liquid exchanger (501) is connected to the carbon dioxide absorption tower (304) to form a loop; The circulation unit (5) further includes a reboiler (504) forming a circulation loop with the steam generator (301), and the reboiler (504) is also connected to the solution pump (503) and the regeneration tower (502); The freeze dehydration equipment (403) includes a freeze dehydration module (4031) connected between the pressure swing adsorption module (404) and the gas-liquid separator (402), and a waste heat refrigeration module (4032) connected between the reboiler (504) and the steam generator (301), and the waste heat refrigeration module (4032) is used to cool down the freeze dehydration module (4031) for freeze dehydration.

2. The system for extracting helium from BOG according to claim 1, characterized in that: The membrane separation unit (1) comprises a BOG compressor (101), a first-stage membrane separator (102), and a first-stage second-stage membrane separator (103) which are connected in sequence to form a loop, and the first-stage second-stage membrane separator (103) is also connected to the oxidation unit (2).

3. The system for extracting helium from BOG according to claim 1, characterized in that: The oxidation unit (2) comprises a mixed gas compressor (201) and an oxidizer (202) which are connected in sequence, wherein the mixed gas compressor (201) is connected to the membrane separation unit (1), and the oxidizer (202) is connected to the decarbonization unit (3).

4. The system for extracting helium from BOG according to claim 1, characterized in that: The outlet of the pressure swing adsorption module (404) is also connected to the inlet of the oxidation unit (2).

5. A method for extracting helium from BOG, characterized in that: The following steps are involved: S1. BOG is introduced into the BOG compressor (101), and after being pressurized by the BOG compressor (101), it enters the first-stage membrane separator (102). The non-permeate gas enters the first-stage membrane separator (103) to recover part of the helium. The permeate gas generated by the first-stage membrane separator (103) returns to the inlet of the 1-BOG compressor (101); S2. The permeate gas from the first stage membrane separator (102) is pressurized by the mixed gas compressor (201) and then mixed with pure oxygen and enters the oxidizer (202); S3. The high-temperature gas after the reaction in the oxidizer (202) enters the steam generator (301), is cooled and separated by the cooling water separator, enters the decarbonization compressor (303) for pressure increase, and is sent to the carbon dioxide absorption tower (304); S4. The crude helium gas absorbed by the carbon dioxide absorption tower (304) is cooled by the top heat exchanger (401), separated by the gas-liquid separator (402), and then enters the refrigeration dehydration equipment (403). After the water in the crude helium gas is removed, it enters the pressure swing adsorption module (404) to further refine the crude helium gas to obtain a 99.999% high-purity helium product; S5. Part of the high-temperature steam generated by the steam generator (301) is sent to the reboiler (504) for regeneration of the decarbonizer, and the other part of the steam enters the waste heat refrigeration module (4032) for heat exchange and is converted into condensed water, which is then combined with the condensed water generated by the reboiler (504) and circulated. The waste heat refrigeration module (4032) absorbs heat to generate low-temperature chilled water, which is sent to the freeze-dehydration equipment (403) to cool the water-containing helium and freeze-dehydrate it; S6. The carbon dioxide-rich liquid at the bottom of the carbon dioxide absorption tower (304) is subjected to heat exchange in the lean-rich liquid exchanger (501) and then enters the regeneration tower (502) for regeneration. The regenerated lean liquid is pressurized by the solution pump (503) and heat exchanged in the lean-rich liquid exchanger (501) before returning to the absorption tower to absorb carbon dioxide. S7. The desorbed gas generated by the pressure swing adsorption module (404) returns to the mixed gas compressor (201) to circulate and extract helium.

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