A biomethanation system and method for CO2 sequestration in a salt cavern gas storage facility

Abstract

The application discloses a biological methanation system and method for sealing CO2 in a salt cave gas storage, and the methanation system comprises a salt cave cavity arranged underground, a first channel conveying device provided with a first channel which is arranged to extend from the ground to the salt cave cavity and is configured to input a biomass waste suspension into the salt cave cavity or output biomass reaction residues, and a second channel conveying device provided with a second channel which is connected with the salt cave cavity and is configured to input supercritical CO2 into the salt cave cavity or discharge methane from the salt cave cavity. The application can meet the requirement of sealing supercritical CO2 in the underground salt cave, and can realize energy and resource utilization of the sealed supercritical CO2, and the final product is high-quality biological methane gas which can be used as household and industrial fuel gas after simple treatment.

Description

Technical Field

[0001] This invention relates to the field of CO2 geological storage and utilization technology, and in particular to a biomethanation system and method for CO2 storage in a salt cavern gas storage facility. Background Technology

[0002] Excessive emissions of greenhouse gases such as CO2 have led to global warming, posing a serious challenge to humankind today. To address climate change, countries worldwide have implemented a series of effective carbon reduction measures, among which CO2 geological sequestration and utilization is considered the most economical and effective carbon reduction solution. Research has confirmed that underground salt rock has extremely low permeability, good creep behavior, and strong self-healing capabilities, making artificially constructed salt cavern spaces (i.e., salt cavern gas storage facilities) excellent geological formations for CO2 sequestration. Currently, underground salt caverns are widely used as ideal sites for storing oil, natural gas, and high-level radioactive waste, offering numerous advantages such as huge storage capacity, reliable safety, durability, and low operating costs.

[0003] Studies have confirmed that various microorganisms thrive in underground salt caverns, including bacteria from the phyla Archaea, Firmicutes, Proteobacteria, and Thermosporidis, with Archaea being the most abundant, accounting for approximately 62%–74%. Archaea are commonly referred to as methanogens and can be divided into six orders: Methanobacteria, Methanococci, Methanosarcina, Methanogenics, Methanopyrobacteria, and Methanosporales. Methanogens are strictly anaerobic and can be further divided into hydrogen-eating methanogens and acetic acid-eating methanogens. Hydrogen-eating methanogens can use hydrogen to reduce carbon dioxide to produce methane and water (CO2 + 4H2 → CH4 + 2H2O); while acetic acid-eating methanogens can directly decompose acetic acid to produce methane and carbon dioxide (CH3COOH → CH4 + CO2).

[0004] Currently, biomethanation methods for geological CO2 sequestration have been reported in coalbed methane and oil reservoirs. Chinese patent application number 202111171518.8 discloses a "carbon emission reduction method based on coalbed methane bioengineering," which uses acetic acid and hydrogen produced during microbial coal melting as substrates, converting CO2 into methane under the action of methanogenic bacteria. Chinese patent application number 201310479743.7 discloses a "method for activating methanogenic bacteria in oil reservoirs to convert carbon dioxide into methane," which involves injecting acetic acid or acetate into the reservoir, where acetic acid oxidizing bacteria oxidize to produce hydrogen, and then methanogenic bacteria utilize the hydrogen and CO2 to generate methane. To date, biomethanation methods for CO2 sequestration in salt cavern gas storage facilities are rarely reported. Existing geological CO2 sequestration methanation technologies are not suitable for salt cavern gas storage facilities for the following reasons:

[0005] (1) Unlike the macromolecular organic matter in coal and rock, salt rock is an inorganic rock that cannot induce microbial fermentation to produce hydrogen. That is, it lacks the hydrogen source conditions required for CO2 methanation. Without supplementing organic matter, it is difficult to achieve CO2 bio-methanation.

[0006] (2) Since the amount of CO2 stored in the salt cavern gas storage is huge, the amount of nutrients required for CO2 methanation is also very large. If organic acids or organic acid salts are injected into the gas storage to achieve CO2 bio-methanation, the economic cost will be high. Summary of the Invention

[0007] This solution addresses the problems and needs raised above by proposing a bio-methanation system and method for CO2 sequestration within a salt cavern gas storage facility. The above-mentioned technical objectives are achieved through the adoption of the following technical features, which also bring about several other technical benefits.

[0008] One object of the present invention is to provide a biomethanation system for CO2 sequestration in a salt cavern gas storage facility, comprising:

[0009] Salt caverns located underground;

[0010] The first channel conveying device has a first channel extending from the ground to the salt cavern, and is configured to input biomass waste suspension into the salt cavern or output biomass reaction residue.

[0011] The second channel conveying device has a second channel that is connected to the salt cavern cavity and is configured to input supercritical CO2 into the salt cavern cavity or discharge methane from the salt cavern cavity.

[0012] In this technical solution, firstly, supercritical CO2 is injected into the salt cavern through the second channel, while brine is discharged through the first channel to seal the supercritical CO2 in the salt cavern. Microbiological analysis of the discharged brine confirms the presence of both hydrogen-producing bacteria and hydrogen-consuming methanogens within the salt cavern. Secondly, the collected biomass waste is air-dried and pulverized, and a biomass waste suspension is prepared using water as a background solution. This suspension is pretreated for a specified time in a vacuum mixing chamber. The biomass waste suspension is then injected into the salt cavern through the first channel for biomass fermentation and supercritical CO2 methanation. The methane produced in the salt cavern is collected through the second channel. These steps are repeated multiple times until the supercritical CO2 sealed in the salt cavern is completely consumed. Finally, the methane in the salt cavern is drained, and supercritical CO2 is injected into the salt cavern through the second channel to seal the supercritical CO2 within the salt cavern. The biomass reaction residue and waste liquid are discharged from the salt cavern through the first channel. This invention enables the storage of supercritical CO2 in underground salt caverns, while also achieving the energy and resource utilization of this stored supercritical CO2. The final product is high-quality biomethane gas, which, after simple treatment, can be used as fuel for household and industrial applications. This invention utilizes biomass waste such as straw, kitchen waste, and feces to provide a hydrogen source for the methanation of CO2. Biomass waste is readily available, easy to process, and inexpensive, effectively addressing the environmental pollution problems caused by biomass waste. Furthermore, the fermentation residue from the biomass waste in this invention can be used as feed and fertilizer, generating additional economic value.

[0013] In addition, the biomethanation system for CO2 storage in a salt cavern gas storage facility according to the present invention may also have the following technical features:

[0014] In one example of the present invention, the first channel conveying device includes:

[0015] The pump body is connected to the first channel and configured to apply driving force to the first channel to input biomass waste suspension or output biomass reaction residue.

[0016] In one example of the present invention, the first channel conveying device further includes:

[0017] A vacuum mixing tank, connected to the pump body, is configured to prepare biomass waste suspension under vacuum conditions.

[0018] In one example of the present invention, the first channel conveying device further includes:

[0019] A first valve is installed on the first channel and configured to open or close the first channel;

[0020] The first pressure gauge is installed on the first channel and configured to monitor the pressure information in the first channel in real time.

[0021] In one example of the present invention, the second channel conveying device includes:

[0022] A second valve is installed on the second channel and configured to open or close the second channel;

[0023] A second pressure gauge is installed on the second channel and configured to monitor the pressure information in the second channel in real time.

[0024] In one example of the invention, the first channel extends to the bottom of the salt cavern and is located inside the second channel; wherein the first channel and the second channel are not interconnected.

[0025] Another objective of this invention is to provide a biomethanation method for CO2 sequestration within a salt cavern gas storage facility, comprising the following steps:

[0026] S10: Supercritical CO2 is injected into the salt cavern cavity through the second channel, while brine is discharged through the first channel to seal the supercritical CO2 in the salt cavern cavity. Microbial analysis of the discharged brine is performed to determine that hydrogen-producing bacteria and hydrogen-consuming methanogens coexist in the salt cavern cavity.

[0027] S20: The collected biomass waste is air-dried and crushed, and then a biomass waste suspension is prepared with water as the background solution. The suspension is pretreated in a vacuum mixing chamber for a specified time. The biomass waste suspension is then injected into the salt cavern through the first channel for biomass fermentation and supercritical CO2 methanation. The methane produced in the salt cavern is collected through the second channel.

[0028] S30: Repeat step S20 multiple times until the supercritical CO2 sealed in the salt cavern is completely consumed.

[0029] S40: Drain the methane from the salt cavern cavity, inject supercritical CO2 into the salt cavern cavity through the second channel to seal the supercritical CO2 in the salt cavern cavity, and discharge the biomass reaction residue from the salt cavern cavity through the first channel.

[0030] In one example of the present invention, the biomass waste is at least one of crop straw, human and animal manure, weeds, food processing waste, wood processing waste, and sewage sludge.

[0031] In one example of the present invention, the biomass mass fraction in the biomass waste suspension is 10% to 20%, the vacuum stirring pretreatment time of the biomass waste suspension is not less than 12 hours, and the stirring speed is 30 to 100 r / min.

[0032] In one example of the present invention, the particle size of the pulverized biomass waste is less than 0.83 mm.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] 1) This invention can not only meet the requirements of CO2 sequestration in underground salt caverns, but also realize the energy and resource utilization of sequestered CO2. Its final product is high-quality biomethane gas, which can be used as fuel for domestic and industrial use after simple treatment.

[0035] 2) This invention uses biomass waste such as straw, kitchen waste, and feces to provide a hydrogen source for the methanation of CO2. Biomass waste is easy to obtain, simple to process, and low in cost, which can solve the environmental pollution problem caused by biomass waste.

[0036] 3) The biomass waste injected into the underground salt cavern in this invention has a particle size of less than 0.83mm. The residue after fermentation is easily washed out of the salt cavern and will not cause pipe blockage, thus ensuring the reuse of the underground salt cavern space.

[0037] 4) The biomass waste fermentation residue in this invention can be used as feed, fertilizer, etc., generating additional economic value.

[0038] The preferred embodiments of the invention will be described in more detail below with reference to the accompanying drawings, so as to facilitate an understanding of the features and advantages of the invention. Attached Figure Description

[0039] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments of the present invention will be briefly described below. The drawings are merely illustrative of some embodiments of the present invention and are not intended to limit the scope of the present invention to all embodiments.

[0040] Figure 1 This is a schematic diagram of the structure of a biomethanation system for CO2 storage in a salt cavern gas storage facility according to an embodiment of the present invention;

[0041] Figure 2 This is a flowchart of a biomethanation method for CO2 sequestration in a salt cavern gas storage facility according to an embodiment of the present invention.

[0042] List of reference numerals in the attached diagram:

[0043] Methanation system 100;

[0044] Salt cavern 110;

[0045] Biomass waste suspension 111;

[0046] Supercritical CO2 112;

[0047] Methane 113;

[0048] First channel conveyor device 120;

[0049] First Channel 121;

[0050] Pump body 122;

[0051] Vacuum mixing box 123;

[0052] First valve 124;

[0053] First pressure gauge: 125;

[0054] Second channel conveyor device 130;

[0055] Second Channel 131;

[0056] Second valve 132;

[0057] Second pressure gauge 133;

[0058] Stratum 140;

[0059] Surface sleeve 150;

[0060] Technical sleeve 160;

[0061] Production sleeve 170. Detailed Implementation

[0062] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The same reference numerals in the drawings represent the same components. It should be noted that the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0063] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms “first,” “second,” and similar terms used in this patent application specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, “an” or “a” and similar terms do not necessarily indicate a quantity limitation. Terms such as “comprising” or “including” mean that the element or object preceding the word encompasses the element or object listed following the word and its equivalents, without excluding other elements or objects. Terms such as “connected” or “linked” are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as “upper,” “lower,” “left,” and “right” are used only to indicate relative positional relationships; these relative positional relationships may change accordingly when the absolute position of the described object changes.

[0064] According to a first aspect of the present invention, a biomethanation system 100 for CO2 sequestration within a salt cavern gas storage facility, such as... Figure 1 As shown, it includes:

[0065] Salt cavern 110 located underground;

[0066] The first channel conveying device 120 has a first channel 121, which extends from the ground to the salt cavern 110 and is configured to input biomass waste suspension 111 into the salt cavern 110 or output biomass reaction residue.

[0067] The second channel conveying device 130 has a second channel 131, which is connected to the salt cavern 110 and is configured to input supercritical CO2 112 into the salt cavern 110 or discharge methane 113 from the salt cavern 110.

[0068] First, supercritical CO2 112 is injected into the salt cavern 110 through the second channel 131, while brine is discharged through the first channel 121 to seal the supercritical CO2 112 in the salt cavern 110. Microbiological analysis of the discharged brine confirms the presence of both hydrogen-producing bacteria and hydrogen-consuming methanogens within the salt cavern 110. Second, the collected biomass waste is air-dried and pulverized, and a biomass waste suspension 111 is prepared using water as a background solution. This suspension is pretreated for a specified time in a vacuum mixing chamber 123, and then the biomass waste suspension 111 is injected through the first channel 121. Biomass fermentation and supercritical CO2 112 methanation are carried out in the salt cavern 110, and the methane 113 produced in the salt cavern 110 is collected by the second channel 131. Then, the above steps are repeated multiple times until the supercritical CO2 112 sealed in the salt cavern 110 is completely consumed. Finally, the methane 113 in the salt cavern 110 is drained, and supercritical CO2 112 is injected into the salt cavern 110 through the second channel 131 to seal the supercritical CO2 112 in the salt cavern 110. The biomass reaction residue after the reaction is discharged from the salt cavern 110 through the first channel 121. This invention enables the storage of supercritical CO2 in underground salt caverns, while also achieving the energy and resource utilization of the stored supercritical CO2. The final product is high-quality biomethane gas, which, after simple treatment, can be used as fuel for domestic and industrial applications. This invention utilizes biomass waste such as straw, kitchen waste, and manure to provide a hydrogen source for the methanation of supercritical CO2. Biomass waste is readily available, easy to process, and inexpensive, effectively addressing the environmental pollution problems caused by biomass waste. Furthermore, the fermentation residue from the biomass waste in this invention can be used as feed and fertilizer, generating additional economic value.

[0069] In one example of the invention, the system further includes a surface casing 150, a technical casing 160, and a production casing 170, wherein the technical casing 160 is located within the surface casing 150, and the production casing 170 is located within the technical casing 160. The production casing 170 extends to a depth close to the salt cavern 110, and the depth of the surface casing 150 is less than the depth of the technical casing 160, which is less than the depth of the production casing 170. Specifically, during drilling, the first section is drilled, the surface casing 150 is run in, and cemented; then the second section is drilled, the technical casing 160 is run in, and cemented; finally, the third section is drilled, the production casing 170 is run in, and cemented. The production casing 170 also serves as a channel for injecting and producing fluids into the gas storage tank. Cement is injected between the surface casing 150 and the formation 140, between the surface casing 150 and the technical casing 160, between the technical casing 160 and the production casing 170, and between the production casing 170 and the formation 140 to reinforce and seal the area.

[0070] For example, the production sleeve 170, technical sleeve 160, and surface sleeve 150, as well as the first channel 121 and the second channel 131, are all steel pipes.

[0071] It is understandable that the second channel 131 can be an independent pipe or a channel formed by the production sleeve 160 and the first channel 121.

[0072] In one example of the present invention, the first channel conveying device 120 includes:

[0073] Pump body 122 is connected to the first channel 121 and is configured to apply driving force to the first channel 121 to input biomass waste suspension or output biomass reaction residue;

[0074] In other words, the forward and reverse rotation of the pump body 122 can apply a driving force to the biomass waste suspension located in the vacuum mixing tank described below and input it into the salt cavern 110, or after the reaction is completed, apply a driving force to the biomass reaction residue located in the salt cavern and extract it out of the salt cavern 110.

[0075] By setting up the pump body 122, pressure can be delivered into the first channel 121 to facilitate the transport of biomass waste into the salt cavern, and at the same time, it is also convenient to extract biomass waste residue and waste liquid from the first channel 121 out of the salt cavern cavity 110.

[0076] In one example of the present invention, the first channel conveying device 120 further includes:

[0077] The vacuum mixing chamber 123 is connected to the pump body 122 and is configured to prepare biomass waste suspension 111 under vacuum conditions. For example, the vacuum mixing pretreatment time of the biomass waste suspension 111 is not less than 12 hours and the mixing speed is 30 to 100 r / min. By setting the vacuum mixing chamber 123, biomass waste suspension 111 can be easily formed.

[0078] Since the salt cavern 110 contains anaerobic organisms, the biomass waste suspension 111 needs to be input under vacuum conditions. The vacuum mixing box 123 has two main functions: first, to create a vacuum in the biomass waste suspension; and second, to stir the biomass waste suspension 111 to avoid clogging the first channel 121.

[0079] In one example of the present invention, the first channel conveying device 120 further includes:

[0080] A first valve 124 is installed on the first channel 121 and configured to open or close the first channel 121.

[0081] Opening the first valve 124 allows biomass waste suspension to be introduced into the salt cavern 110 or biomass reaction residue to be discharged, while closing the first valve 124 blocks the first channel 121. For example, when injecting supercritical CO2 into the salt cavern 110, the second valve 132 needs to be opened, and the first valve 124 needs to be opened simultaneously.

[0082] The first pressure gauge 125 is installed on the first channel 121 and is configured to monitor the pressure information in the first channel 121 in real time. Generally, the working pressure in the salt cavern 110 needs to be lower than its upper limit pressure for safe operation. The first pressure gauge 125 can obtain the working pressure status of the system in real time, which is convenient for its safe operation.

[0083] In one example of the present invention, the second channel conveying device 130 includes:

[0084] The second valve 132 is installed on the second channel 131 and is configured to open or close the second channel 131.

[0085] By opening the second valve 132, supercritical CO2 can be introduced into the salt cavern 110 or methane gas can be output, while closing the second valve 132 can block the second channel 131. For example, when injecting biomass waste suspension 111 into the salt cavern 110, the first valve 124 needs to be opened and the second valve 132 closed. Furthermore, the second valve 132 should be opened in a timely manner according to the pressure of the methane gas generated in the salt cavern 110, and the first valve 124 should be closed.

[0086] The second pressure gauge 133 is installed on the second channel 131 and is configured to monitor the pressure information in the second channel 131 in real time. Generally, the working pressure in the salt cavern 110 needs to be lower than its upper limit pressure for safe operation. The second pressure gauge 133 can obtain the working pressure status of the system in real time, which is convenient for its safe operation.

[0087] In one example of the invention, the first channel 121 extends to the bottom of the salt cavern 110, and the first channel 121 is located inside the second channel 131; wherein the first channel 121 and the second channel 131 are not interconnected. Extending the first channel 121 to the bottom of the salt cavern 110 allows for sufficient reaction of the biomass waste suspension 111, and the methane gas generated in the salt cavern 110 is transported to the ground along the second channel 131.

[0088] According to a second aspect of the present invention, a method for biomethanation of CO2 encapsulated in a salt cavern gas storage facility, such as... Figure 2 As shown, it includes the following steps:

[0089] S10: Supercritical CO2 112 is injected into the salt cavern 110 through the second channel 131, while brine is discharged through the first channel 121. The supercritical CO2 112 in the salt cavern 110 is sealed, and the discharged brine is subjected to microbial analysis to determine that hydrogen-producing bacteria and hydrogen-consuming methanogens coexist in the salt cavern 110. It should be noted that the brine can be increased by introducing supercritical CO2 112 into the salt cavern 110, thereby increasing the pressure in the salt cavern 110 and discharging the brine along the first channel 121. Alternatively, it can be extracted by the pump body 122.

[0090] S20: The collected biomass waste is air-dried and crushed, and then a biomass waste suspension 111 is prepared with water as a background solution. The suspension is pretreated in a vacuum mixing chamber 123 for a specified time. Then, the biomass waste suspension 111 is injected into the salt cavern 110 through the first channel 121 for biomass fermentation and supercritical CO2 methanation. The methane 113 produced in the salt cavern 110 is collected through the second channel 131.

[0091] S30: Repeat step S20 multiple times until the supercritical CO2112 sealed in the salt cavern 110 is completely consumed.

[0092] S40: Drain the methane 113 from the salt cavern 110, inject supercritical CO2 112 into the salt cavern 110 through the second channel 131, seal the supercritical CO2 112 in the salt cavern 110, and discharge the biomass reaction residue from the salt cavern 110 through the first channel 121.

[0093] This method can simultaneously achieve the energy and resource utilization of supercritical CO2 in underground salt caverns, while also fulfilling the requirement of supercritical CO2 sequestration. The final product is high-quality biomethane gas, which can be used as fuel for domestic and industrial applications after simple treatment. This method uses biomass waste such as straw, kitchen waste, and manure to provide a hydrogen source for the methanation of supercritical CO2. Biomass waste is readily available, simple to process, and inexpensive, effectively addressing the environmental pollution problems caused by biomass waste. The fermentation residue from the biomass waste in this method can be used as feed and fertilizer, generating additional economic value.

[0094] In one example of the present invention, the biomass waste is at least one of crop straw, human and animal manure, weeds, food processing waste, wood processing waste, and sewage sludge.

[0095] In one example of the present invention, the biomass mass fraction in the biomass waste suspension 111 is 10% to 20%, the vacuum stirring pretreatment time of the biomass waste suspension 111 is not less than 12 hours, and the stirring speed is 30 to 100 r / min.

[0096] In one example of the present invention, the particle size of the biomass waste after crushing is less than 0.83 mm (20 mesh). By injecting biomass waste with a particle size of less than 0.83 mm into the underground salt cavern, the residue after fermentation reaction is easily washed out of the salt cavern and will not cause pipe blockage, thereby ensuring the reuse of the underground salt cavern space.

[0097] The foregoing description, with reference to preferred embodiments, details an exemplary implementation of the biomethanation system 100 and method for CO2 sequestration in a salt cavern gas storage facility proposed in this invention. However, those skilled in the art will understand that various modifications and alterations can be made to the above specific embodiments without departing from the concept of this invention, and various combinations can be made to the various technical features and structures proposed in this invention without exceeding the protection scope of this invention, which is determined by the appended claims.

Claims

1. A biomethanation system for CO2 sequestration within a salt cavern gas storage facility, characterized in that, include: Salt caverns located underground (110); The first channel conveying device (120) has a first channel (121) extending from the ground to a salt cavern (110), configured to input biomass waste suspension (111) into the salt cavern (110) or output biomass reaction residue; The first channel conveying device (120) includes: a pump body (122) connected to the first channel (121), configured to apply driving force to the first channel (121) to input biomass waste suspension or output biomass reaction residue; a vacuum stirring tank (123) connected to the pump body (122), configured to prepare biomass waste suspension (111) under vacuum conditions; a first valve (124) installed on the first channel (121), configured to open or close the first channel (121); and a first pressure gauge (125) installed on the first channel (121), configured to monitor the pressure information in the first channel (121) in real time; The second channel conveying device (130) has a second channel (131) connected to the salt cavern (110) and configured to input supercritical CO2 (112) into the salt cavern (110) or discharge methane (113) from the salt cavern (110); the second channel conveying device (130) includes: a second valve (132) installed on the second channel (131) and configured to open or close the second channel (131); and a second pressure gauge (133) installed on the second channel (131) and configured to monitor the pressure information in the second channel (131) in real time.

2. The biomethanation system for CO2 sequestration within a salt cavern gas storage facility according to claim 1, characterized in that, The first channel (121) extends to the bottom of the salt cavern (110), and the first channel (121) is located inside the second channel (131); wherein the first channel (121) and the second channel (131) are not interconnected.

3. A methanation method for a biomethanation system for CO2 sequestration within a salt cavern gas storage facility as described in claim 1 or claim 2, characterized in that, Includes the following steps: S10: Supercritical CO2 (112) is injected into the salt cavern (110) through the second channel (131), while brine is discharged through the first channel (121) to seal the supercritical CO2 (112) in the salt cavern (110) and to perform microbial analysis on the discharged brine to determine that hydrogen-producing bacteria and hydrogen-consuming methanogens coexist in the salt cavern (110). S20: The collected biomass waste is air-dried and crushed, and then a biomass waste suspension (111) is prepared with water as the background solution. The suspension is pretreated in a vacuum mixing tank (123) for a specified time. Then the biomass waste suspension (111) is injected into the salt cavern (110) through the first channel (121) for biomass fermentation and supercritical CO2 (112) methanation. The methane (113) produced in the salt cavern (110) is collected through the second channel (131). S30: Repeat step S20 multiple times until the supercritical CO2 (112) sealed in the salt cavern (110) is completely consumed; S40: Drain the methane (113) in the salt cavern (110), inject supercritical CO2 (112) into the salt cavern (110) through the second channel (131), seal the supercritical CO2 (112) in the salt cavern (110), and discharge the biomass reaction residue after the reaction from the salt cavern (110) through the first channel (121).

4. The methanation method of the biomethanation system for CO2 sequestration in a salt cavern gas storage facility according to claim 3, characterized in that, The biomass waste includes at least one of the following: crop straw, human and animal manure, weeds, food processing waste, wood processing waste, and sewage sludge.

5. The methanation method of the biomethanation system for CO2 sequestration in a salt cavern gas storage facility according to claim 3, characterized in that, The biomass mass fraction in the biomass waste suspension (111) is 10%~20%, and the vacuum stirring pretreatment time of the biomass waste suspension (111) is not less than 12 h, and the stirring speed is 30~100 r / min.

6. The methanation method of the biomethanation system for CO2 sequestration in a salt cavern gas storage facility according to claim 3, characterized in that, The particle size of the crushed biomass waste is less than 0.83 mm.

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