Coal bed gas exploitation and separation utilization method based on SCCO2 assistance

Abstract

The invention discloses a coal bed gas exploitation and separation utilization method based on SCCO2 assistance, and belongs to the technical field of coal bed gas development. Supercritical carbon dioxide is prepared through a high-pressure reaction kettle and stored in a supercritical carbon dioxide storage and collection tank, meanwhile, nitrogen mixed with graphene is introduced, and CO2 / CH4 adsorption selectivity is enhanced by means of the characteristic that the specific surface area of graphene is large. A variable-frequency sound wave diffuser is matched to excite coal seam micro cracks through low-frequency sound waves, and supercritical carbon dioxide and nitrogen mixed gas is injected into a coal seam injection well. In the injection process, the sound wave diffuser synchronously radiates high-frequency sound waves to improve the displacement efficiency, then the gas enters the gas separation tower integrated with the molecular sieve membrane, and the produced gas is divided into upper methane, middle carbon dioxide and other bottom miscellaneous gas. Methane is pressurized by an air compressor and then stored in a methane storage tank, carbon dioxide is purified and pressurized and then recycled for coalbed methane exploitation, and offensive gas is cooled and stored after generating power by a steam turbine. And efficient mining, separation and multi-path utilization of the coal bed gas are realized.

Description

Technical Field

[0001] This invention relates to a method for coalbed methane extraction and separation based on supercritical carbon dioxide, and more particularly to a method for efficient extraction and separation of coalbed methane based on supercritical carbon dioxide, belonging to the field of coalbed methane development technology. Background Technology

[0002] Coalbed methane (CBM), as a clean and efficient unconventional natural gas resource, occupies an increasingly important position in the global energy structure. my country possesses abundant coal reserves, along with a considerable amount of associated CBM resources. However, for a long time, the extraction and utilization rate of CBM has been relatively low, with large quantities remaining undeveloped within coal seams. This not only wastes energy but also poses safety hazards such as gas outbursts during coal mining. Furthermore, if CBM is released directly into the atmosphere without proper utilization, it will exacerbate environmental problems such as the greenhouse effect. Therefore, exploring efficient, safe, and environmentally friendly methods for CBM extraction and utilization is of paramount importance for optimizing my country's energy structure, ensuring safe coal production, and addressing climate change.

[0003] Traditional coalbed methane extraction technologies mainly include surface vertical well extraction and underground extraction. Surface vertical well extraction often faces problems of low gas production efficiency and low single-well output for coal seams with low permeability. This is because the low permeability of the coal seam makes it difficult for coalbed methane to desorb smoothly from the pores of the coal matrix and flow into the wellbore, resulting in long extraction cycles and poor economic benefits. While underground extraction can collect coalbed methane during the coal mining process to some extent, it is limited by the complex conditions of underground working space and ventilation, which restricts the extraction range and efficiency. Furthermore, it is difficult to achieve full recovery and utilization of coalbed methane, and there is also the possibility of interference with coal mining processes.

[0004] Supercritical carbon dioxide possesses unique physicochemical properties. Its density is close to that of a liquid, its viscosity is similar to that of a gas, and its diffusion coefficient lies between that of a gas and a liquid. This allows it to better penetrate the tiny pores of the coal seam after being injected into it. On the one hand, it can displace the coalbed methane adsorbed on the surface of the coal matrix, promoting the desorption of coalbed methane. On the other hand, supercritical carbon dioxide can also play a certain role in fracturing and permeability enhancement of coal seam fractures, improving the permeability of the coal seam and creating more favorable conditions for the subsequent flow of coalbed methane.

[0005] Based on the current status and challenges in the field of coalbed methane extraction, there is an urgent need for an innovative method that can fully leverage the synergistic effect of supercritical carbon dioxide and other auxiliary methods to achieve efficient extraction, precise separation, and recycling of coalbed methane, thereby improving the development and utilization level of coalbed methane resources and promoting the sustainable development of the coalbed methane industry. Summary of the Invention

[0006] Technical Problem: The purpose of this invention is to overcome the problems of insufficient gas production efficiency, limited gas separation accuracy, low carbon dioxide utilization rate, and uneven development of coal seam fractures caused by low permeability in traditional coalbed methane extraction. It provides a method for efficient extraction and separation of coalbed methane based on supercritical carbon dioxide assistance. By combining the synergistic effect of supercritical carbon dioxide and nano-nitrogen with acoustic diffusion technology, efficient extraction, precise separation, and recycling of coalbed methane can be achieved, thereby improving resource utilization and economic benefits.

[0007] Technical Solution: This invention provides a supercritical carbon dioxide (SCCO2) assisted coalbed methane extraction and separation system, comprising supercritical carbon dioxide (SCCO2) auxiliary equipment installed on the ground and connected to a coalbed injection well and a coalbed methane production well, respectively. The supercritical carbon dioxide auxiliary equipment includes a supercritical carbon dioxide storage tank. A high-pressure reactor is connected to one side of the supercritical carbon dioxide storage tank, and a temperature control system is connected to the other side via a back pressure valve. The outlet of the temperature control system is connected to a nitrogen cylinder outlet pipeline to form a mixing pipeline. A temperature and pressure indicator and a nitrogen cylinder switch are installed at the nitrogen cylinder outlet. The mixing pipeline is connected to the inlet of a gas injection pump via a mass flow meter and a static mixer. A multi-frequency motor is installed on one side of the gas injection pump, and the gas injection pump outlet is connected to the coalbed injection well pipeline via an injection well stop switch and an injection fluid temperature and pressure gauge. A distributed fiber optic sensor and a variable frequency acoustic diffuser are installed in the coalbed injection well. A distributed fiber optic sensor is installed in the coalbed methane production well, and a extraction pump is connected to the wellhead via a pipeline. The connected pipeline is equipped with… The well has an anomaly detection switch. The outlet of the extraction pump is connected to a solid-liquid sedimentation tank via a pipeline. Above the solid-liquid sedimentation tank is a solid particle separation tower connected to the bottom flow of the sedimentation tank. The gas flow at the top of the solid particle separation tower is connected via a pipeline to a gas capture tower integrating MEDA amine liquid and activated carbon. The gas capture tower integrating MEDA amine liquid and activated carbon is connected via a pipeline to a gas condensation and dehydration system. The gas condensation and dehydration system is connected via a pipeline to the lower part of a gas separation tower integrating a molecular sieve membrane. The gas from the integrated molecular sieve membrane... The lower part of the separation tower is connected via pipeline to a steam turbine with a battery pack and a miscellaneous gas settling tank. The upper part of the gas separation tower with integrated molecular sieve membrane is connected via pipeline to an air compressor connected to a methane storage tank. The middle part of the gas separation tower with integrated molecular sieve membrane is connected via pipeline to a carbon dioxide settling tank. The carbon dioxide settling tank is connected via pipeline to a spiral wound DD3R carbon dioxide molecular sieve membrane, a circulation circuit stop switch, and a centrifugal air compressor connected to the supercritical carbon dioxide storage tank and equipped with a temperature control device.

[0008] The aforementioned SCCO2-assisted coalbed methane extraction and separation method first prepares supercritical carbon dioxide in a high-pressure reactor and stores it in a supercritical carbon dioxide storage tank. Simultaneously, nitrogen mixed with graphene is introduced, leveraging the large specific surface area of ​​graphene to enhance CO2 / CH4 adsorption selectivity. This is combined with a variable-frequency acoustic diffuser installed in the coal seam injection well. Low-frequency acoustic waves excite micro-fractures in the coal seam, injecting the supercritical carbon dioxide and nitrogen mixture into the injection well. During injection, the variable-frequency acoustic diffuser simultaneously emits high-frequency acoustic waves to clean the coal reservoir's pore system. The gas is then pumped from the coalbed methane production well. A mixed gas of CH4, CO2, and N2 is fed into a gas separation tower with an integrated molecular sieve membrane. Inside the tower, the upper part of the mixed gas is methane, the middle part is carbon dioxide, and the bottom part is other gases. The upper methane is pressurized by a centrifugal air compressor and stored in a methane storage tank. The middle carbon dioxide is buffered and settled in a carbon dioxide settling tank, then purified by a spiral-wound DD3R carbon dioxide molecular sieve membrane, pressurized by a centrifugal air compressor, and heated and pressurized by a temperature control device. Controlled by a circuit breaker, it is then remixed with nitrogen and injected into the coal seam injection well. The other gases at the bottom are generated by a steam turbine and then cooled and stored in a settling tank. The specific steps are as follows: (a) Based on the coal seam geological structure map, coalbed methane reservoir distribution information and development plan, determine the spatial location and distance between the coal seam injection well and the coalbed methane production well on the surface. The surface drilling locations for the coal seam injection well and the coalbed methane production well should be selected in areas with a terrain slope of <15°, avoiding fault fracture zones and groundwater areas, and ensuring that the surface well site covers an area of ​​≥1500m². 2 To meet equipment layout requirements; (b) Supercritical carbon dioxide is prepared by a high-pressure reactor, with the reactor working pressure maintained at 7.38-30 MPa and the temperature controlled at 31.1-80℃. Temperature fluctuation is controlled at ±0.5℃ by a temperature control device. The prepared supercritical carbon dioxide is stored in a supercritical carbon dioxide storage tank with a design pressure ≥35 MPa and a volume of 180 m³. (c) Supercritical carbon dioxide gas flows out under the action of the pressure-resistant back pressure valve and temperature control system. The nitrogen cylinder switch is opened, and nitrogen gas with a mixed particle size of 5-10nm graphene flows out of the nitrogen cylinder and mixes with supercritical carbon dioxide gas. The nitrogen mixing ratio is controlled to be 3-5% by the temperature and pressure indicator and mass flow meter. The mixed gas flows through the static mixer to ensure that the uniformity of the two mixed gases, supercritical carbon dioxide gas and nitrogen gas, is ≥95%. (d) The two mixed gases are pressurized by a gas injection pump and then injected into the coal seam injection well by a pressure- and temperature-controlled injection fluid thermo-pressure gauge. The displacement of the gas injection pump is adjustable from 0.5 to 5 m³ / h, and a multi-frequency motor is configured to achieve stepless speed adjustment. The variable frequency acoustic diffuser in the coal seam injection well improves the development of coal seam fractures by using acoustic vibrations with a working frequency of 20-50 kHz and a power of 5-15 kW. The pressure monitored by the injection fluid thermo-pressure gauge is 10-25 MPa and the temperature is 40-60 ℃. (e) After the two mixed gases are injected into the coal seam injection well, the methane gas in the coal reservoir is desorbed and transformed into free gas. Under the action of the extraction pump, the mixed gas including methane, nitrogen, supercritical carbon dioxide after cooling and depressurization of the coal reservoir, and other free gases in the coal seam are transported to the coalbed methane production well and extracted. The extracted mixed gas is first transported into the solid-liquid sedimentation tank to remove solid particles with a particle size >10μm, and then undergoes deep purification through a solid particle separation tower with a filtration accuracy of 1μm. Subsequently, it enters the gas capture tower of integrated MDEA amine liquid and activated carbon, which is divided into layers by activated carbon as the middle baffle. The concentration of integrated MDEA amine liquid is 20-30%, and the liquid-to-gas ratio is controlled at 15-30L / m³ for desulfurization and impurity removal. (f) The gas produced from the production well after desulfurization and impurity removal enters the gas condensation and dehydration system. The condensation temperature is controlled at 2-5℃ for condensation and dehydration. The dried gas after condensation and dehydration is sent to the gas separation tower with integrated molecular sieve membrane. The methane and the cooled and depressurized supercritical carbon dioxide are separated and purified using spiral wound DD3R carbon dioxide molecular sieve membrane to obtain methane gas. The purification operation pressure is 2-4MPa and the temperature is 30-40℃. (g) Full-process monitoring is achieved through distributed fiber optic sensors installed in the coal seam injection well and distributed fiber optic sensors installed in the coalbed methane production well. The distributed fiber optic sensors in the injection well are installed in the surrounding coal seams of the coal seam injection well, mainly monitoring the temperature and pressure stability of the injected fluid and the response of coal seam fractures. At the same time, the distributed fiber optic sensors in the injection well indirectly verify the fracture improvement effect of the frequency converter acoustic diffuser, ensuring the integrity and safety of the entire system operation and monitoring. The distributed fiber optic sensors in the production well are installed in the coalbed methane production well and the production fluid transmission path, collecting the temperature and pressure of the produced gas and the composition ratio. The distributed fiber optic sensors in the production well are connected in series with the production well stop switch through the signal line to ensure the stop of the gas production process and ensure safety. (h) The methane gas separated and purified in the gas separation tower with integrated molecular sieve membrane is sent to an air compressor and pressurized to 1-5 MPa, and then transported and stored in a methane storage tank; the separated supercritical carbon dioxide, after being cooled and depressurized, enters a carbon dioxide settling tank for settling and buffering, is purified by a spiral wound DD3R carbon dioxide molecular sieve membrane, and is then pressurized to an injection pressure of 8 MPa by a centrifugal air compressor, and re-enters the supercritical carbon dioxide storage tank for recycling, and is then re-injected into the coal seam injection well; the impurities in the gas separation tower with integrated molecular sieve membrane are introduced from the bottom into a steam turbine for power generation. The steam turbine inlet steam pressure is 3-5 MPa, and the power generation efficiency is ≥30%. The exhaust gas generated by the combustion of the impurities is cooled to room temperature and then stored in the impurity gas settling tank.

[0009] In step (a), the spatial arrangement of coal seam injection wells and coalbed methane production wells is related to the permeability distribution of the coal seam. For areas with permeability below 0.1 mD, the distance between two wells is 40-60 m. For areas with permeability above 0.1 mD, the distance between two wells is 60-80 m, so as to ensure that supercritical carbon dioxide can effectively displace coalbed methane. When constructing the well site, a dedicated fire lane with a width of not less than 4 m must be set up, and there must be no flammable or explosive materials stored within 50 m of the well site.

[0010] In step (b), the high-pressure reactor is made of 316L stainless steel, with the inner wall polished and equipped with a double safety interlock device. When the pressure exceeds 10% or the temperature exceeds 5°C, it will automatically depressurize and shut down.

[0011] In step (c), the pressure reducing and stabilizing valve at the outlet of the nitrogen cylinder is set to maintain a stable output pressure of 0.5-1MPa. The graphene particles are pretreated by ultrasonic dispersion, and the dispersion concentration is controlled at 0.01-0.05g / L to ensure that the suspension stability in nitrogen is ≥72h. The measurement accuracy of the mass flow meter (13) is ±0.5% to ensure accurate control of the nitrogen mixing ratio.

[0012] In step (d), the injection fluid temperature and pressure gauge is an intelligent instrument with data storage and wireless transmission functions, which can transmit the monitored pressure and temperature data to the central control system in real time; the gas injection pump body adopts a double cylinder structure to achieve continuous and stable injection and reduce flow fluctuations; the casing of the coal seam injection well (18) is made of N80 steel grade with a wall thickness ≥12.7mm, the cementing return height is 50m below the surface, the cement slurry density is controlled at 1.85-1.95g / cm³, and the setting time is ≥48h.

[0013] In step (e), the effective volume of the solid-liquid sedimentation tank is determined based on the daily gas volume, and is 1.5-2 times the volume corresponding to the gas volume. A sedimentation hopper with an inclination angle of 15°-20° is set at the bottom of the tank to facilitate the collection and cleaning of solid particles. The regeneration temperature of MDEA amine liquid is controlled at 110-120℃, the regeneration steam consumption is ≤0.3t / t amine liquid, the activated carbon is replaced every 3 months, and saturated activated carbon needs to be rendered harmless.

[0014] In step (f), the gas capture tower integrating MDEA amine liquid and activated carbon adopts a countercurrent contact method. The amine liquid is sprayed down from the top of the tower, and the gas enters from the bottom of the tower. The gas-liquid contact time is ≥3s. The refrigeration unit of the gas condensation and dehydration system adopts a screw compressor with a cooling capacity of 50-100kW, which can quickly reduce the gas temperature to the required condensation temperature to ensure the dehydration effect. The spiral wound DD3R carbon dioxide molecular sieve membrane has a single membrane area of ​​≥50m² and a service life of ≥3 years. During operation, it needs to be backwashed regularly once a month. The backwashing medium is dry nitrogen gas with a pressure of 0.5-0.8MPa.

[0015] In step (g), the spacing between the distributed fiber optic sensors in the injection well and the distributed fiber optic sensors in the production well is ≤5m, they are fixed by spiral winding along the well wall, the bending radius of the fiber is ≥30mm, and the attenuation rate is ≤0.2dB / km when the signal transmission distance is ≤10km.

[0016] In step (h), the spiral wound DD3R carbon dioxide molecular sieve membrane in the gas separation tower with integrated molecular sieve membrane has a double-layer structure, with a flow guide net between each layer of membrane to improve the gas permeation rate; the centrifugal air compressor adopts three-stage compression, with an exhaust temperature ≤100℃, a lubricating oil flash point ≥200℃, and the filter element needs to be replaced every 1000 hours of operation to ensure that the oil content of the compressed gas is ≤5ppm.

[0017] Beneficial Effects: By adopting the above technical solution, this invention overcomes the problems of low permeability, insufficient separation efficiency, low carbon dioxide utilization, and uneven fracture development in traditional coalbed methane extraction. Through the synergistic effect of supercritical carbon dioxide and nano-nitrogen combined with acoustic diffusion technology, it achieves efficient extraction and recycling of coalbed methane. First, by utilizing the high permeability of supercritical carbon dioxide and the synergistic displacement effect of nitrogen, combined with acoustic vibration to improve coal seam fracture development, it significantly enhances coalbed methane desorption efficiency. Second, through multi-stage purification and high-precision membrane separation technology, it achieves efficient separation of methane and carbon dioxide and carbon dioxide recycling, reducing carbon emissions while improving resource utilization. It enables efficient extraction, separation, and multi-pathway utilization of coalbed methane, significantly improving coalbed methane resource utilization and overall economic benefits. The method is simple, easy to operate, and has good results. Its main advantages compared to existing technologies are: ① The synergistic effect of supercritical carbon dioxide and nano nitrogen combined with acoustic diffusion technology can increase coal seam permeability by more than 30%, significantly improving coalbed methane extraction efficiency. ② The separation system with integrated molecular sieve membranes achieves methane purity ≥98% and carbon dioxide recovery rate ≥90%, significantly improving resource utilization; ③ The carbon dioxide recycling injection model reduces greenhouse gas emissions by more than 80%, which is in line with the concept of low-carbon development; ④ The full-process intelligent monitoring and automatic control system ensures the safety of system operation, extends the service cycle of a single well by 2-3 years, and increases the cumulative gas production efficiency by more than 40%. Attached Figure Description

[0018] Figure 1 This is a layout diagram of the supercritical carbon dioxide displacement gas extraction device of the present invention.

[0019] Figure 2 This is a schematic flowchart of the supercritical carbon dioxide displacement gas recovery method of the present invention.

[0020] In the diagram: 1-Ground; 2-High-pressure reactor; 3-Temperature control device; 4-Centrifugal air compressor; 5-Circulation circuit stop switch; 6-Roll-up DD3R carbon dioxide molecular sieve membrane; 7-Nitrogen cylinder switch; 8-Nitrogen cylinder; 9-Temperature and pressure gauge; 10-Supercritical carbon dioxide storage tank; 11-Pressure-resistant back pressure valve; 12-Temperature control equipment; 13-Mass flow meter; 14-Gas injection pump; 15-Injection well stop switch; 16-Injection fluid temperature and pressure gauge; 17-Injection well distributed fiber optic sensor; 18-Coal seam injection well; 19-Variable frequency acoustic diffuser; 2 0-Extraction pump; 21-Coalbed methane production well; 22-Solid-liquid sedimentation tank; 23-Solid particle separation tower; 24-Check valve; 25-Integrated MEDA amine liquid and activated carbon gas capture tower; 26-Gas condensation and dehydration system; 27-Methane storage tank; 28-Air compressor; 29-Integrated molecular sieve membrane gas separation tower; 30-Carbon dioxide settling tank; 31-Distributed fiber optic sensor for production well; 32-Production well anti-interference switch; 33-Miscellaneous gas settling tank; 34-Steam turbine; 35-Battery pack; 36-Static mixer; 37-Multi-frequency motor. Detailed Implementation

[0021] The present invention will be further described below with reference to the embodiments shown in the accompanying drawings: This invention discloses a coalbed methane extraction and separation system based on SCCO2 assistance, mainly composed of supercritical carbon dioxide auxiliary equipment located on the ground 1 and connected to a coalbed injection well 18 and a coalbed methane production well 21 respectively. The supercritical carbon dioxide auxiliary equipment includes a reaction vessel 2 located on the ground 1, a temperature control device 3, a centrifugal air compressor 4, a high-pressure switch 5, a spiral wound DD3R carbon dioxide molecular sieve membrane 6, a nitrogen cylinder 8, a temperature and pressure gauge 9, a supercritical carbon dioxide storage tank 10, a pressure-resistant back pressure valve 11, a temperature control device 12, a mass flow meter 13, a gas injection pump 14, an injection well anti-slip switch 15, an injection fluid temperature and pressure gauge 16, an injection well distributed fiber optic sensor 17, and a frequency conversion acoustic diffuser 19. The system includes a pumping pump 20, a solid-liquid sedimentation tank 22, a solid particle separation tower 23, a gas capture tower 25, a gas condensation and dehydration system 26, a methane storage tank 27, an air compressor 28, a gas separation tower with integrated molecular sieve membrane 29, a carbon dioxide settling tank 30, a distributed fiber optic sensor for the production well 31, an anti-abnormal switch for the production well 32, a mixed gas settling tank 33, a steam turbine 34, a battery pack 35, a static mixer 36, and a multi-frequency motor 37. One side of the supercritical carbon dioxide storage tank 10 is connected to a high-pressure reactor 2, and the other side is connected to a temperature control device 12 via a back pressure valve 11. The outlet of the temperature control device 12 is connected to the outlet pipeline of a nitrogen cylinder 8 via a pipeline to form a mixing pipeline. A temperature and pressure indicator is installed at the outlet of the nitrogen cylinder 8. 9 and nitrogen cylinder switch 7, the mixing pipeline is connected to the inlet of gas injection pump 14 via mass flow meter 13 and static mixer 36. A multi-frequency motor 37 is provided on one side of gas injection pump 14. The outlet of gas injection pump 14 is connected to coal seam injection well 18 via injection well stop switch 15 and injection fluid temperature and pressure gauge 16. The coal seam injection well 18 is equipped with injection well distributed fiber optic sensor 17 and variable frequency acoustic wave diffuser 19. The coalbed methane production well 21 is equipped with production well distributed fiber optic sensor 31. A pumping pump 20 is connected to the wellhead via a pipeline. A production well stop switch 32 is provided on the connected pipeline. The outlet of pumping pump 20 is connected to solid-liquid sedimentation tank 22 via a pipeline. Above, a solid particle separation tower 23 is connected to the bottom flow of a solid-liquid sedimentation tank. The upper part of the solid particle separation tower 23 is connected via pipeline to a gas capture tower 25 integrating MEDA amine liquid and activated carbon. The gas capture tower 25 integrating MEDA amine liquid and activated carbon is connected via pipeline to a gas condensation and dehydration system 26. The gas condensation and dehydration system 26 is connected via pipeline to the lower part of a gas separation tower 29 integrating a molecular sieve membrane. The bottom of the gas separation tower 29 integrating a molecular sieve membrane is connected via pipeline to a steam turbine 34 connected to a battery pack 35 and a miscellaneous gas settling tank 33. The upper part of the gas separation tower 29 integrating a molecular sieve membrane is connected via pipeline to an air compressor 28 connected to a methane storage tank 27.A carbon dioxide settling tank 30 is connected to the middle of the gas separation tower 29 with an integrated molecular sieve membrane. The carbon dioxide settling tank 30 is sequentially connected via pipelines to a spiral wound DD3R carbon dioxide molecular sieve membrane 6, a circulation circuit stop switch 5, and a centrifugal air compressor 4 connected to a supercritical carbon dioxide storage tank 10 and equipped with a temperature control device 3.

[0022] This invention relates to a method for coalbed methane extraction and separation based on SCCO2-assisted gas extraction: A complete gas injection, extraction, and utilization process is constructed through a synergistic design involving multi-stage precise temperature control, fluid-acoustic field coupling, fluid separation, and closed-loop recycling. First, supercritical carbon dioxide is prepared in a high-pressure reactor 2 and stored in a supercritical carbon dioxide storage tank 10. Simultaneously, nitrogen mixed with graphene is introduced. The mixed graphene has a particle size of 5-10 nm and a diffusion concentration of 0.1-0.3 wt%. Utilizing the large specific surface area of ​​graphene, the CO2 / CH4 adsorption selectivity is enhanced. In conjunction with a variable-frequency acoustic diffuser 19 installed in the coal seam injection well 18, low-frequency acoustic waves excite micro-fractures in the coal seam, injecting the supercritical carbon dioxide and nitrogen mixture into the coal seam injection well 18. During the injection process, the variable-frequency acoustic diffuser 19 simultaneously radiates high-frequency acoustic waves to clean the coal reservoir pore system. The mixture of CH4, CO2, and N2 is then extracted from the coalbed methane production well 21 via a pumping pump 20. The gas is fed into the gas separation tower 29, which integrates a molecular sieve membrane. The mixed gas in the gas separation tower 29 consists of methane at the top, supercritical carbon dioxide after cooling and depressurization in the middle, and impurities at the bottom, namely N2 and other gases displaced from the coal seam. The upper methane is pressurized by a centrifugal air compressor 28 and stored in a methane storage tank 27. The middle carbon dioxide is buffered and settled in a carbon dioxide settling tank 30, then purified by a spiral-wound DD3R carbon dioxide molecular sieve membrane 6, pressurized by a centrifugal air compressor 4, and heated and pressurized by a temperature control device 3. Controlled by a circulation circuit stop switch 5, it is remixed with nitrogen and injected into the coal seam injection well. The other impurities at the bottom are generated by a steam turbine 34 and then cooled and stored in an impurity gas settling tank 33. The specific steps are as follows: (a) Based on the coal seam geological structure map, coalbed methane reservoir distribution information and development plan, determine the spatial location and distance between the coal seam injection well 18 and the coalbed methane production well 21 on surface 1; the drilling locations of the coal seam injection well 18 and the coalbed methane production well 21 on surface 1 should be selected in areas with a terrain slope of <15°, taking care to avoid fault fracture zones and groundwater areas, and ensuring that the surface well site covers an area of ​​≥1500m². 2To meet equipment layout requirements, the foundation bearing capacity must be ≥250kPa. The spatial arrangement of the coal seam injection well 18 and the coalbed methane production well 21 is related to the permeability distribution of the coal seam. For areas with permeability below 0.1mD, the distance between the two wells is 40-60m, and for areas with permeability above 0.1mD, the distance between the two wells is 60-80m, to ensure that supercritical carbon dioxide can effectively displace coalbed methane. When constructing the well site, a dedicated fire lane with a width of not less than 4m must be set up, and no flammable or explosive materials shall be stored within 50m of the well site.

[0023] (b) Supercritical carbon dioxide is prepared by high-pressure reactor 2. The working pressure of the reactor is maintained at 7.38-30 MPa and the temperature is controlled at 31.1-80℃. Temperature fluctuation is controlled at ±0.5℃ by temperature control device 3. The prepared supercritical carbon dioxide is stored in supercritical carbon dioxide storage tank 10. The design pressure of supercritical carbon dioxide storage tank 10 is ≥35 MPa and the volume is 180 m³. The high-pressure reactor 2 is made of 316L stainless steel and the inner wall is polished. It is equipped with a double safety interlock device. When the pressure exceeds 10% or the temperature exceeds 5℃, the pressure is automatically released and the machine is stopped.

[0024] (c) Supercritical carbon dioxide gas flows out under the action of pressure-resistant back pressure valve 11 and temperature control system 12. Nitrogen cylinder switch 7 is turned on, and nitrogen gas mixed with graphene with a particle size of 5-10nm flows out from nitrogen cylinder 8 and mixes with supercritical carbon dioxide gas. The nitrogen mixing ratio is controlled to be 3-5% by temperature and pressure indicator 9 and mass flow meter 13. The mixed gas flows through static mixer 36 to ensure that the uniformity of the two mixed gases, supercritical carbon dioxide gas and nitrogen gas, is ≥95%. The pressure reducing and stabilizing valve set at the outlet of nitrogen cylinder 8 outputs a stable pressure of 0.5-1MPa. The graphene particles are pretreated by ultrasonic dispersion, and the dispersion concentration is controlled at 0.01-0.05g / L to ensure suspension stability in nitrogen gas ≥72h. The measurement accuracy of mass flow meter 13 is ±0.5% to ensure accurate control of nitrogen mixing ratio.

[0025] (d) Two mixed gases (CH4 and N2) are pressurized by the gas injection pump 14 and injected into the coal seam injection well 18 after being monitored by the injection well stop switch 15 and the injection fluid temperature and pressure gauge 16. The discharge range of the gas injection pump 14 is 0.5-5 m³ / h. A multi-frequency motor 37 is configured on one side of the gas injection pump 14 to achieve stepless speed adjustment. The variable frequency acoustic diffuser 19 in the coal seam injection well 18 improves the degree of coal seam fracture development with acoustic vibration with a working frequency of 20-50 kHz and a power of 5-15 kW. The injection fluid temperature and pressure gauge 16 monitors... The pressure is 10-25 MPa and the temperature is 40-60℃; the injection fluid temperature and pressure gauge 16 is an intelligent instrument with data storage and wireless transmission functions, which can transmit the monitored pressure and temperature data to the central control system in real time; the gas injection pump 14 adopts a double-cylinder structure to achieve continuous and stable injection and reduce flow fluctuations; the casing of the coal seam injection well 18 is made of N80 steel grade with a wall thickness ≥12.7mm, the cementing return height is 50m below the surface, the cement slurry density is controlled at 1.85-1.95g / cm³, and the setting time is ≥48h.

[0026] (e) After the two mixed gases (CH4 and N2) are injected into the coal seam injection well 18, due to the different adsorption properties of the coal reservoir for different gases, the purpose of carbon dioxide gas displacing coalbed methane is achieved. The methane gas in the coal reservoir is desorbed and converted into free gas, which is then displaced into the coalbed methane production well 21 by the pumping pump 20. The mixed gas in the coal reservoir, including methane, nitrogen, supercritical carbon dioxide after cooling and depressurization of the coal reservoir, and other free gases in the coal seam, is transported to the coalbed methane production well 21 and extracted. The extracted mixed gas is first transported into the solid-liquid sedimentation tank 22 to remove solid particles with a particle size >10μm. The inclination angle of the sedimentation hopper at the bottom of the tank is 15°-20°. Then, it is passed through the solid particle separation tower 2 with a filtration accuracy of 1μm. 3. After deep purification, the gas enters the integrated MEDA amine liquid and activated carbon gas collection tower 25, which uses activated carbon as a central partition to separate the internal space, through check valve 24. The concentration of the integrated MDEA amine liquid is 20-30%, and the liquid-to-gas ratio is controlled at 15-30 L / m³ for desulfurization and impurity removal. The effective volume of the solid-liquid sedimentation tank 22 is determined according to the daily gas volume and is 1.5-2 times the volume corresponding to the gas volume. The bottom of the tank is equipped with a sludge hopper with an inclination angle of 15°-20° to facilitate the collection and cleaning of solid particles. The regeneration temperature of the MDEA amine liquid is controlled at 110-120℃, the regeneration steam consumption is ≤0.3t / t amine liquid, the activated carbon is replaced every 3 months, and saturated activated carbon needs to be rendered harmless.

[0027] (f) The gas produced from the desulfurized and impurity-removed production well enters the gas condensation and dehydration system 26. The condensation temperature is controlled at 2-5℃ for condensation and dehydration. The dried gas after condensation and dehydration is sent to the gas separation tower 29 with integrated molecular sieve membrane. The methane and the cooled and depressurized supercritical carbon dioxide are separated and purified using the spiral wound DD3R carbon dioxide molecular sieve membrane 6 to obtain methane gas. The purification operation pressure is 2-4MPa and the temperature is 30-40℃. The gas capture tower 25 with integrated MDEA amine liquid and activated carbon adopts countercurrent flow. The contact method involves spraying amine solution from the top of the tower and introducing gas from the bottom, with a gas-liquid contact time of ≥3 seconds. The refrigeration unit of the gas condensation and dehydration system 26 uses a screw compressor with a cooling capacity of 50-100kW, which can quickly reduce the gas temperature to the required condensation temperature to ensure the dehydration effect. The spiral wound DD3R carbon dioxide molecular sieve membrane 6 has a single membrane area of ​​≥50m² and a service life of ≥3 years. During operation, it needs to be backwashed regularly, once a month, with dry nitrogen as the backwashing medium and a pressure of 0.5-0.8MPa.

[0028] (g) Full-process monitoring is achieved through the distributed fiber optic sensor 17 installed in the coal seam injection well 18 and the distributed fiber optic sensor 31 installed in the coalbed methane production well 21. The distributed fiber optic sensor 17 is installed in the surrounding coal seam within the coal seam injection well 18, mainly monitoring the temperature and pressure stability of the injected fluid and the response of coal seam fractures. At the same time, the distributed fiber optic sensor 17 indirectly verifies the fracture improvement effect of the frequency converter acoustic diffuser 19, ensuring the integrity and safety of the entire system operation and monitoring. The distributed fiber optic sensor 31 is installed in the coalbed methane production well 21 and the production fluid transmission path, collecting the temperature and pressure of the produced gas and the composition ratio. The distributed fiber optic sensor 31 is connected to the production well stop switch 32 via a signal line to ensure the cessation of the gas extraction process and ensure safety. The laying distance between the distributed fiber optic sensor 17 and the distributed fiber optic sensor 31 is ≤5m, and they are fixed by spiral winding along the well wall. The bending radius of the optical fiber is ≥30mm, and the attenuation rate is ≤0.2dB / km when the signal transmission distance is ≤10km.

[0029] (h) The methane gas separated and purified in the gas separation tower 29 with integrated molecular sieve membrane is sent to the air compressor 28 and pressurized to 1-5 MPa. The pressure is adjusted according to the storage requirements and then transported and stored in the methane storage tank 27. The design pressure is 6 MPa and the air tightness level meets the first-class standard of GB50341. The separated supercritical carbon dioxide, after being cooled and depressurized, enters the carbon dioxide settling tank 30 for settling and buffering. It is then purified by the spiral wound DD3R carbon dioxide molecular sieve membrane 6, and then pressurized to the injection pressure of 8 MPa by the centrifugal air compressor 4. It is then reintroduced into the supercritical carbon dioxide storage tank 10 for recycling and then reinjected into the coal seam injection well 18. The impurities in the gas separation tower 29 with integrated molecular sieve membrane are introduced into the steam turbine 34 from the bottom to generate electricity. The steam turbine inlet steam pressure is 3-5 MPa and the power generation efficiency is ≥30%. The exhaust gas generated by the combustion of the impurities is cooled to room temperature and then stored in the impurities settling tank 33. The spiral wound DD3R carbon dioxide molecular sieve membrane 6 inside the gas separation tower 29 with integrated molecular sieve membrane has a double-layer structure, with a guide net between each layer of membrane to improve the gas permeation rate; the centrifugal air compressor (4) adopts three-stage compression, with an exhaust temperature ≤100℃, a lubricating oil flash point ≥200℃, and the filter element needs to be replaced every 1000 hours of operation to ensure that the oil content of the compressed gas is ≤5ppm.

[0030] A supercritical carbon dioxide and nitrogen mixed gas injection system, consisting of a nitrogen cylinder (7), a supercritical carbon dioxide storage tank (10), a pressure-resistant back pressure valve (11), a temperature control device (12), a mass flow meter (13), a static mixer (36), and a gas injection pump (14), is used in conjunction with a variable frequency acoustic diffuser to excite micro-fractures in the coal seam using low-frequency acoustic waves of 20-50Hz with an amplitude of 2MPa. The supercritical carbon dioxide and nitrogen mixed gas is injected into the coal seam injection well (18). During the injection process, the acoustic diffuser simultaneously emits high-frequency acoustic waves of 120-180Hz to improve the displacement efficiency with an amplitude of 0.5MPa. The gas in the injection well shaft and the coal reservoir is transported towards the production well by the extraction pump (20). A gas purification and separation device, namely a solid particle separation tower (23), is set at the gas extraction end of the coalbed methane production well (21). The system integrates MEDA amine liquid and activated carbon. The gas capture tower (25), gas condensation and dehydration system (26), and gas separation tower (29) with integrated molecular sieve membrane will separate the mixed gas in the gas separation tower (29) through the bottom MEDA amine liquid and activated carbon partition to form a pattern in which the upper part is methane, the middle part is supercritical carbon dioxide with cooling and depressurization, and the bottom part is miscellaneous gas. The upper methane is pressurized by centrifugal air compressor (28) and stored in methane storage tank (27). The supercritical carbon dioxide in the middle is cooled and depressurized and then placed in carbon dioxide settling tank (30) for settling and buffering. If necessary, it can be purified by spiral DD3R carbon dioxide molecular sieve membrane (6), pressurized by centrifugal air compressor (4), and heated and purified by temperature control device (3) and then mixed with nitrogen and injected into the well group to improve the utilization rate. The other miscellaneous gas at the bottom is generated by steam turbine (34) and then cooled and stored in miscellaneous gas settling tank (33).

Claims

1. A system for SCCO2 assisted coal bed methane extraction and separation based utilization, comprising a supercritical carbon dioxide assisted equipment arranged on the ground and connected to a coal bed injection well (18) and a coal bed methane production well (21) respectively, characterized in that: The supercritical carbon dioxide auxiliary equipment comprises a supercritical carbon dioxide storage tank (10), one side of the supercritical carbon dioxide storage tank (10) is connected with a high-pressure reaction kettle (2), the other side is connected with a temperature control device (12) through a pressure-resistant back pressure valve (11), the outlet of the temperature control device (12) is communicated with the outlet pipeline of a nitrogen cylinder (8) to form a mixing pipeline, a temperature and pressure indicating table (9) and a nitrogen cylinder switch (7) are arranged at the outlet of the nitrogen cylinder (8); the mixing pipeline is connected with the inlet of a gas injection pump (14) through a mass flow meter (13) and a static mixer (36), one side of the gas injection pump (14) is provided with a multi-frequency motor (37), the outlet of the gas injection pump (14) is communicated with the pipeline of a coal seam injection well (18) through an injection well abnormal stop switch (15) and an injection fluid temperature and pressure table (16); the coal seam injection well (18) is provided with an injection well distributed optical fiber sensor (17) and a variable frequency sound wave diffuser (19); the coal seam gas production well (21) is provided with a production well distributed optical fiber sensor (31), the well mouth is provided with a pumping pump (20) communicated through a pipeline, and the pumping pump (20) is provided with a production well abnormal stop switch (32) on the communicated pipeline, the outlet end of the pumping pump (20) is communicated with a solid-liquid precipitation tank (22) through a pipeline, the solid-liquid precipitation tank (22) is provided with a solid particle separation tower (23) connected with the bottom flow of the solid-liquid precipitation tank, the upper air flow of the solid particle separation tower (23) is connected with a gas capture tower (25) integrated with MEDA amine liquid and activated carbon through a pipeline, the gas capture tower (25) integrated with MEDA amine liquid and activated carbon is connected with a gas condensation and dehydration system (26) through a pipeline, the gas condensation and dehydration system (26) is connected with a gas separation tower (29) integrated with a molecular sieve membrane at the lower part through a pipeline, the bottom of the gas separation tower (29) is connected with a steam turbine (34) and a mixed gas static storage tank (33) in sequence through a pipeline, the lower part of the steam turbine (34) is connected with a battery pack (35), an air compressor (28) connected with a methane storage tank (27) is connected with the upper part of the gas separation tower (29) through a pipeline, and the middle part of the gas separation tower (29) is connected with a carbon dioxide static tank (30) through a pipeline; the carbon dioxide static tank (30) is connected with a roll type DD3R carbon dioxide molecular sieve membrane (6), a circulating line abnormal stop switch (5), a centrifugal air compressor (4) connected with the supercritical carbon dioxide storage tank (10) and provided with a temperature control device (3) in sequence through a pipeline.

2. The method for SCCO2 assisted coalbed methane extraction and separation and utilization according to claim 1, characterized in that: The supercritical carbon dioxide is prepared through the high-pressure reaction kettle (2) and stored in the supercritical carbon dioxide storage tank (10), and nitrogen mixed with graphene is introduced, the specific surface area of the graphene is large, and the CO2 / CH4 adsorption selectivity is enhanced. And cooperate with the frequency conversion sound wave diffuser (19) set in the coal seam injection well (18), through the low frequency sound wave to stimulate coal seam micro crack, the supercritical carbon dioxide and nitrogen mixed gas injection into the coal seam injection well (18); In the process of gas injection, using the variable frequency sound wave diffuser (19) to radiate high frequency sound wave to clean the coal reservoir pore system, through the extraction pump (20) from the coalbed methane production well (21) to extract CH4, CO2 and N2 mixed gas into the integrated molecular sieve membrane gas separation tower (29), the mixed gas in the upper part of the gas separation tower (29) is methane, the middle part is supercritical carbon dioxide, the bottom is miscellaneous gas; The upper part of the methane is stored in the methane storage tank (27) after being pressurized by the centrifugal air compressor (28), the middle part of the carbon dioxide is buffered by the carbon dioxide standing tank (30), and then purified by the DD3R carbon dioxide molecular sieve membrane (6), pressurized by the centrifugal air compressor (4), and heated by the temperature control device (3). After being pressurized, purified and heated, it is controlled by the circulating line stop switch (5), and is mixed with nitrogen and injected into the coal seam injection well. The bottom other miscellaneous gas is cooled and stored in the miscellaneous gas standing storage tank (33) after generating electricity by the steam turbine (34); The specific steps are as follows: (a) According to the coal seam geological structure map, coalbed methane reservoir distribution information characteristics and development planning, the spatial position of the coal seam injection well (18) and the coalbed methane production well (21) and the distance between the two wells are determined on the ground (1), the ground (1) drilling position selection area of the coal seam injection well (18) and the coalbed methane production well (21) is selected in the area with a terrain slope <15°, avoiding fault fracture zones and underground water bodies, ensuring that the ground well site occupies an area ≥1500m 2 To meet the equipment layout requirements; (b) supercritical carbon dioxide is prepared by a high-pressure reaction kettle (2), the working pressure of the reaction kettle is maintained at 7.38-30 MPa, and the temperature is controlled at 31.1-80℃, and the temperature fluctuation control of ±0.5℃ is realized by a temperature control device (3), the prepared supercritical carbon dioxide is stored in a supercritical carbon dioxide storage tank (10), the design pressure of the supercritical carbon dioxide storage tank (10) is ≥35 MPa, and the volume is 180 m³; (c) the supercritical carbon dioxide gas flows out under the action of the pressure-resistant back pressure valve (11) and the temperature control device (12), the nitrogen bottle switch (7) is opened, the nitrogen mixed with the graphene with a particle size of 5-10 nm flows out of the nitrogen bottle (8) and mixes with the supercritical carbon dioxide gas, the nitrogen mixing ratio is controlled to be 3-5% through the temperature and pressure indication table (9) and the mass flow meter (13), and the mixed gas flows through the static mixer (36), so that the uniformity of the supercritical carbon dioxide gas and the nitrogen is ≥95%; (d) the two kinds of mixed gas are pressurized by the gas injection pump (14), monitored by the injection fluid temperature and pressure gauge (16) with pressure and temperature control, and injected into the coal seam injection well (18), the displacement adjustment range of the gas injection pump (14) is 0.5-5 m³ / h, and the multi-frequency motor (37) is configured to realize stepless speed regulation; The frequency conversion sound wave diffuser (19) in the coal seam injection well (18) vibrates at a working frequency of 20-50 kHz and a power of 5-15 kW to improve the coal seam crack development degree; The pressure monitored by the injection fluid temperature and pressure gauge (16) is 10-25 MPa, and the temperature is 40-60℃. (e) After the two mixed gases are injected into the coal seam injection well (18), the methane gas in the coal reservoir is desorbed and converted into free gas. Under the action of the extraction pump (20), the mixed gas including methane, nitrogen, supercritical carbon dioxide after the coal reservoir is cooled and depressurized, and other free gas in the coal seam is transported to the coalbed methane production well (21) and is extracted; the extracted mixed gas is first transported into the solid-liquid precipitation tank (22) to remove solid particles with a particle size greater than 10 μm, and then is subjected to deep purification through the solid particle separation tower (23) with a filtration precision of 1 μm. Subsequently, the mixed gas enters the gas capture tower (25) integrated with MDEA amine liquid and activated carbon, in which the internal space is layered by activated carbon as a middle partition. The concentration of the integrated MDEA amine liquid is 20-30%, and the liquid-gas ratio is controlled at 15-30 L / m³ for desulfurization and impurity removal; (f) The production well gas after desulfurization and impurity removal enters the gas condensation and dehydration system (26), and the condensation temperature is controlled at 2-5℃ for condensation and dehydration. The dry gas after condensation and dehydration is sent to the gas separation tower (29) integrated with molecular sieve membranes, and the roll-type DD3R carbon dioxide molecular sieve membrane (6) is used to separate and purify the methane and the supercritical carbon dioxide after being cooled and depressurized to obtain methane gas. The operation pressure for purification is 2-4 MPa, and the temperature is 30-40℃; (g) The whole process is monitored by the injection well distributed optical fiber sensor (17) arranged in the coal seam injection well (18) and the production well distributed optical fiber sensor (31) arranged in the coalbed methane production well (21). The injection well distributed optical fiber sensor (17) is installed in the surrounding coal seam of the coal seam injection well (18) and mainly monitors the stability of the injection fluid temperature and pressure and the response of the coal seam fracture. At the same time, the injection well distributed optical fiber sensor (17) indirectly verifies the fracture improvement effect of the variable frequency acoustic wave diffuser (19), ensuring the integrity and safety of the whole system operation and monitoring. The production well distributed optical fiber sensor (31) is installed in the coalbed methane production well (21) and the output fluid transmission path, and collects the temperature and pressure of the output gas and the component ratio. The production well distributed optical fiber sensor (31) is connected in series with the production well anti-reverse switch (32) through a signal line to ensure the interruption of the gas extraction process and ensure safety. (h) The methane gas separated and purified in the integrated molecular sieve membrane gas separation tower (29) is sent to the air compressor (28) to pressurize to 1-5 MPa, and then transported and stored in the methane storage tank (27); the separated and cooled and depressurized supercritical carbon dioxide enters the carbon dioxide standing tank (30) for standing and buffering, then purified by the DD3R carbon dioxide molecular sieve membrane (6), and then pressurized to the injection pressure of 8 MPa by the centrifugal air compressor (4) to re-enter the supercritical carbon dioxide storage tank (10) for recycling, and then re-injected into the coal seam injection well (18); the mixed gas in the integrated molecular sieve membrane gas separation tower (29) is introduced into the steam turbine (34) from the bottom to generate electricity, the steam turbine inlet steam pressure is 3-5 MPa, the power generation efficiency is ≥30%, and the tail gas generated by burning the mixed gas is cooled to room temperature and stored in the mixed gas standing storage tank (33).

3. The method for SCCO2 assisted coalbed methane extraction and separation utilization according to claim 2, characterized in that: In step (a), the spatial arrangement of the coal seam injection well (18) and the coal seam gas production well (21) is related to the permeability distribution of the coal seam. For the area with a permeability lower than 0.1 mD, the distance between the two wells is 40-60 m, and for the area with a permeability higher than 0.1 mD, the distance between the two wells is 60-80 m, to ensure that the supercritical carbon dioxide can effectively displace the coal seam gas; when the well site is constructed, a dedicated fire fighting passage with a width not less than 4 m should be provided, and there should be no flammable and explosive materials within 50 m of the well site.

4. The method for SCCO2 assisted coalbed methane extraction and separation utilization according to claim 2, characterized in that: In step (b), the high-pressure reaction kettle (2) is made of 316L stainless steel and the inner wall is polished, and is equipped with double safety interlocking devices which automatically depressurize and shut down when the overpressure is 10% or the overtemperature is 5°C.

5. The method for SCCO2 assisted coalbed methane extraction and separation utilization according to claim 2, characterized in that: In step (c), the pressure stabilizing valve at the outlet of the nitrogen gas cylinder (8) outputs a stable pressure of 0.5-1 MPa, the graphene particles are pretreated by ultrasonic dispersion, the dispersion concentration is controlled at 0.01-0.05 g / L, the suspension stability in nitrogen is ≥72 h, and the measurement accuracy of the mass flow meter (13) is ±0.5%, to ensure accurate control of the nitrogen mixing ratio.

6. The method for SCCO2 assisted coalbed gas exploitation and separation utilization according to claim 2, characterized in that: In step (d), the injection fluid temperature and pressure meter (16) is an intelligent instrument with data storage and wireless transmission functions, which can transmit the monitored pressure and temperature data to the central control system in real time; the pump body of the gas injection pump (14) adopts a double-cylinder structure to realize continuous and stable injection and reduce flow fluctuations; the casing of the coal seam injection well (18) is made of N80 steel with a wall thickness of ≥12.7 mm, the cementing cement returns to 50 m below the ground surface, the cement slurry density is controlled at 1.85-1.95 g / cm³, and the waiting time is ≥48 h.

7. The method for SCCO2 assisted coalbed gas exploitation and separation utilization according to claim 2, characterized in that: In step (e), the effective volume of the solid-liquid sedimentation tank (22) is determined according to the daily gas treatment capacity, which is 1.5-2 times the corresponding volume, and the tank bottom is provided with a sedimentation hopper with an inclination angle of 15°-20° for easy collection and cleaning of solid particles; the MDEA amine liquid regeneration temperature is controlled at 110-120°C, the regeneration steam consumption is ≤0.3 t / t of amine liquid, the activated carbon is replaced every 3 months, and the saturated activated carbon needs harmless treatment.

8. The method for SCCO2 assisted coalbed gas exploitation and separation utilization according to claim 2, characterized in that: In step (f), the gas capture tower (25) integrated with MDEA amine solution and activated carbon uses countercurrent contact mode, the amine solution is sprayed from the top of the tower, and the gas enters from the bottom, the gas-liquid contact time is ≥3s; The refrigeration unit of the gas condensation and dehydration system (26) uses a screw compressor, the refrigeration capacity is 50-100kW, which can quickly reduce the gas temperature to the required condensation temperature, ensuring the dehydration effect; The single membrane area of the DD3R carbon dioxide molecular sieve membrane (6) is ≥50m², the service life is ≥3 years, and backwashing is required during operation, once a month, the flushing medium is dry nitrogen, and the pressure is 0.5-0.8MPa.

9. The method for SCCO2 assisted coalbed gas exploitation and separation utilization according to claim 2, characterized in that: In step (g), the laying interval of the injection well distributed optical fiber sensor (17) and the production well distributed optical fiber sensor (31) is ≤5m, which is fixed by spiral winding along the well wall, the fiber bending radius is ≥30mm, and the attenuation rate is ≤0.2dB / km when the signal transmission distance is ≤10km.

10. The method for SCCO2 assisted coalbed gas extraction and separation utilization according to claim 2, characterized in that: In step (h), the DD3R carbon dioxide molecular sieve membrane (6) in the gas separation tower (29) integrated with molecular sieve membrane is a double-layer structure, and a flow guide net is arranged between each layer of membrane to improve the gas transmission rate; The centrifugal air compressor (4) uses three-stage compression, the exhaust temperature is ≤100℃, the lubricating oil flash point is ≥200℃, the filter element needs to be replaced every 1000h of operation, and the oil content in the compressed gas is ≤5ppm.

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