System and method for extracting helium from BOG

Abstract

The invention discloses a system and a method for extracting helium from BOG (Boil Off Gas), and particularly relates to 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 in the crude helium, and a decarburization unit for removing carbon dioxide in the gas treated by the oxidation unit, the crude helium refining unit is used for carrying out helium extraction on the gas treated by the decarburization unit; and the circulating unit is used for recovering waste heat generated by the decarburization unit and realizing regeneration of a decarburization agent. The overall structure is clear in division of labor, BOG is treated firstly to obtain crude helium, the crude helium sequentially passes through the oxidation unit, the decarburization unit and the crude helium refining unit to remove impurities such as hydrogen, methane, carbon dioxide, water, nitrogen and oxygen, high-purity helium is finally obtained through refining, meanwhile, the circulation unit and the decarburization unit are added to be matched to achieve regeneration of a decarburization agent, and the production efficiency is improved. And the crude helium refining unit and the decarburization unit are matched to realize freezing removal of helium moisture, so that resource recycling is met.

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, i.e. BOG gas, is produced during the production and storage of liquefied natural gas. Since natural gas contains a certain amount of helium, helium will be enriched in BOG. ​​Helium is a scarce resource. Currently, helium extracted from natural gas, especially from BOG, is the only source of helium in industry. Currently, the methods for industrial helium extraction include cryogenic method, pressure swing adsorption method, low temperature adsorption method, membrane permeation separation method and their coupling processes.

[0003] Invention patent CN113154409B discloses a system and method for extracting helium from BOG gas and utilizing energy. Pure oxygen is used to burn and remove methane and hydrogen in BOG, and the gas after combustion is dehydrated, purified and liquefied to separate liquid nitrogen, liquid oxygen and liquid carbon dioxide. The mixed gas from which CO2, O2 and N2 are removed is purified at low temperature to obtain high-purity helium. The heat energy generated during the combustion process meets the production heat of the LNG plant and provides the energy consumption of this 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. by direct combustion is complicated 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, 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 in the crude helium, a decarbonization unit for removing carbon dioxide in 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 realizing regeneration of the decarbonizer.

[0006] Furthermore, the membrane separation unit includes a BOG compressor, a first-stage membrane separator and a second-stage membrane separator which are connected in sequence to form a loop, and the 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 which are 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 freezing and 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 which are connected in sequence 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 also includes a reboiler that forms 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 down the freeze dehydration module for freeze dehydration.

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

[0015] S1. BOG is connected to the BOG compressor, and after being pressurized by the BOG compressor, it enters the first-stage membrane separator, and the non-permeate gas enters the first-stage membrane separator to recover part of the helium. The permeate gas generated by the first-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 enters the oxidizer;

[0017] S3. The high-temperature gas after the oxidation reaction enters the steam generator, and then enters the decarbonization compressor to increase the pressure and send it to the carbon dioxide absorption tower after cooling and water separation in the cooling water separator;

[0018] S4. The crude helium gas after being absorbed by the carbon dioxide absorption tower is cooled by the tower top heat exchanger, separated by the gas-liquid separator and then enters the refrigeration dehydration equipment to remove the water in the crude helium gas, and 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. Part of the high-temperature steam generated by the steam generator is sent to the reboiler for regeneration of the decarbonizer, and the other part of the steam enters the waste heat refrigeration module for heat exchange and becomes condensed water, which is then merged with the condensed water generated by the reboiler and circulated. The waste heat refrigeration module absorbs heat to generate low-temperature chilled water, which is sent to the freeze-dehydration equipment to cool and freeze-dehydrate the water-containing helium;

[0020] S6. The carbon dioxide-rich liquid at the bottom of the carbon dioxide 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 clear division of labor and simple structure. BOG is first processed to obtain crude helium, and the crude helium is successively 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, and finally refined to obtain high-purity helium. At the same time, a circulation unit is added to cooperate with the decarbonization unit to realize the regeneration of the decarbonizer, and the crude helium refining unit cooperates with the decarbonization unit to realize the freezing and removal of helium water, thereby meeting the 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 attached 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. refrigeration and dehydration equipment; 4031. refrigeration and 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 technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than 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 in 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 in the crude helium, a decarbonization unit 3 for removing carbon dioxide in 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 first-stage second-stage membrane separator 103, which are connected in sequence and form a loop, and the first-stage second-stage membrane separator 103 is also connected to the oxidation unit 2. In this design, the first-stage membrane separation is set, which effectively reduces energy consumption compared with multi-stage membrane separation, and the helium is concentrated by a single-stage membrane separation process, which greatly reduces the processing gas flow after concentration, reduces the subsequent equipment load, and effectively reduces the energy consumption of helium extraction. It should also be noted that the first-stage second-stage membrane separator 103 also has a tail 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, and 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 gas is reacted in the oxidizer 202 to remove hydrogen and methane in the crude helium gas. It should be noted that oxygen is injected into the practical process of the oxidizer 202 in the present invention.

[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, and 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 realizes the elimination of carbon dioxide in 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 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 the outlet. In this design, the refrigeration dehydration device 403 is used to further remove the moisture in the crude helium to meet the impurity moisture requirements of the product helium. At the same time, the pressure swing adsorption module 404 effectively removes a small amount of impurities such as nitrogen and oxygen in the crude helium to obtain a high-purity helium product. It should be noted that the pressure swing adsorption module 404 can be directly purchased in the prior art, and no further details are given 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 to circulate and extract 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 and form a loop, and the lean-rich liquid exchanger 501 is connected to the carbon dioxide absorption tower 304 to form a loop. In this design, the carbon dioxide-rich liquid at the bottom of the carbon dioxide absorption tower 304 enters the regeneration tower 502 for regeneration after heat exchange through the lean-rich liquid exchanger 501, and the regenerated lean liquid is pressurized by the solution pump 503 and heat exchanged by 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. In this design, by making full use of part of the steam generated by the steam generator 301, it is used for regeneration of the decarbonization process, and a carbon dioxide product can be obtained at the same time.

[0036] In one embodiment, the freezing and dehydration equipment 403 includes a freezing and 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 and freeze dehydrate the freezing and dehydration module 4031. This design further makes full use of the other part of the steam generated by the steam generator 301, and the condensed water generated by the steam after heat exchange with the refrigerant of the waste heat refrigeration module 4032 merges with the condensed water generated by the reboiler 504 and re-enters the loop, and the waste heat refrigeration module 4032 absorbs heat to generate low-temperature refrigerated water, which is sent to the freezing and dehydration module 4031 to cool down 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, and after being pressurized by the BOG compressor 101, it enters the first-stage membrane separator 102, and 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. The high-temperature gas after the reaction in the oxidizer 202 enters the steam generator 301, and then enters the decarbonization compressor 303 to increase the pressure, and is sent to the carbon dioxide absorption tower 304;

[0041] 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 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;

[0042] S5. Part of the high-temperature steam generated by the steam generator 301 is sent to the reboiler 504 for regeneration of the decarbonizing agent, and the other part of the steam enters the waste heat refrigeration module 4032 for heat exchange and becomes condensed water, which is then merged 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 and freeze-dehydrate the water-containing helium;

[0043] S6. Absorbing carbon dioxide. The carbon dioxide-rich liquid at the bottom of the absorption tower 304 enters the regeneration tower 502 for regeneration after heat exchange in the lean-rich liquid exchanger 501. 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.

[0044] S7. The desorbed gas generated by the pressure swing adsorption module 404 is returned to the mixed gas compressor 201 for recycling and extracting helium. In summary, the present invention is divided into multiple units, and the overall structure has clear division of labor and simple structure. BOG is first processed to obtain crude helium, and the crude helium is successively 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, oxygen, etc., and finally refined to obtain high-purity helium. At the same time, the circulation unit 5 is added to cooperate with the decarbonization unit 3 to realize the regeneration of the decarbonizer, and the crude helium refining unit 4 cooperates with the decarbonization unit 3 to realize the freezing and removal of helium water, which meets the resource recycling. It should also be noted that the decarbonizer is a carbon dioxide-rich absorbent.

[0045] It should be understood that the examples and implementation modes 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 the examples and implementation modes. 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 components in 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 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 defined as "first" and "second" may explicitly or implicitly include at least one of the 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 that A and B meet 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 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.

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, and 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 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, and 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).

5. The system for extracting helium from BOG according to any one of claims 1 to 4, characterized in that: 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.

6. The system for extracting helium from BOG according to claim 5, characterized in that: The outlet of the pressure swing adsorption module (404) is also connected to the inlet of the oxidation unit (2).

7. The system for extracting helium from BOG according to claim 5, characterized in that: The circulation unit (5) comprises a lean-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-rich liquid exchanger (501) is connected to the carbon dioxide absorption tower (304) to form a loop.

8. The system for extracting helium from BOG according to claim 7, characterized in that: The circulation unit (5) further comprises 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).

9. The system for extracting helium from BOG according to claim 7, characterized in that: The freeze-dehydration equipment (403) comprises 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 and freeze-dehydrate the freeze-dehydration module (4031).

10. 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), and 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 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), and then enters the decarbonization compressor (303) to increase the pressure, and is sent to the carbon dioxide absorption tower (304); S4. The crude helium gas after being absorbed by the carbon dioxide absorption tower (304) is cooled by the tower 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 purify the crude helium gas to obtain a 99.999% high-purity helium product; S5. A portion of the high-temperature steam generated by the steam generator (301) is sent to the reboiler (504) for regeneration of the decarbonizing agent, and another portion 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 freezing and dehydration equipment (403) to cool and freeze-dehydrate the water-containing helium; S6. The carbon dioxide-rich liquid at the bottom of the carbon dioxide absorption tower (304) enters the regeneration tower (502) for regeneration after heat exchange in the lean-rich liquid exchanger (501). 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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