A method for coalbed methane development and carbon emission reduction based on multi-stage CO2 utilization and storage

Abstract

This invention discloses a method for coalbed methane development and carbon emission reduction based on multi-stage CO2 utilization and storage. CO2 collected by a carbon capture device, after testing, is flowed through a storage well for geological storage due to high impurity carbon content. The intermediate circulating medium is gaseous CO2, which is processed into liquid CO2 and injected into shallow and medium-depth coal seams. After gasification, it continues to enter deep coal seams to form a supercritical state. The supercritical CO2 is extracted to a surface CO2 power plant for power generation and heat extraction, becoming a low-temperature working fluid. After further processing, it is converted back into liquid CO2 and injected underground. Using CO2 as the circulating working fluid, it absorbs heat in the reservoir to become a high-temperature working fluid for power generation. After completing its work, the CO2 is cooled and continues to absorb heat underground, thus completing the power generation task. On the other hand, it enters deep, unminable / difficult-to-mine coal seams through the supercritical CO2 injection well. In areas with high geothermal anomalies, the coal is gasified at high temperatures and extracted. The extracted mixed gas and the displaced gas are mixed and brought to the surface, realizing deep coal seam resource extraction and carbon storage.

Description

Technical Field

[0001] This invention relates to the fields of energy development and low-carbon technology, and in particular to a method for coalbed methane development and carbon emission reduction based on multi-stage CO2 utilization and storage. Background Technology

[0002] As is well known, CO2 is a greenhouse gas, and reducing its concentration in the atmosphere is an important research topic. Currently, CO2 is known to have the following characteristics underground:

[0003] In terms of displacement, CO2 is widely used in geological resource extraction and development due to its properties of dissolution, competitive adsorption, viscosity reduction, and conduction under formation conditions. The mechanisms by which CO2 injection into the formation improves gas recovery include: ① Reservoir pressure increases due to CO2 injection, leading to a larger reservoir pressure gradient and thus increasing gas flow velocity; ② The large density difference between CO2 and natural gas causes stratification due to gravity, with CO2 at the bottom of the reservoir, promoting the uplift of natural gas at the top; ③ The reservoir temperature and pressure are both high, and CO2 is often in a supercritical state under these conditions, while the viscosity of natural gas is much lower than that of supercritical CO2, resulting in a better displacement effect due to the resulting mobility ratio; ④ CO2 has a stronger adsorption capacity than CH4 in coal seams, and competitive adsorption can improve the development effect of coalbed methane.

[0004] In terms of heat extraction, CO2 is environmentally friendly, has high thermal efficiency, a large heat transfer coefficient, a large specific heat capacity, can be combined with various heat source systems, has low solubility in rocks and minerals, and low tendency to corrode and scale. Compared with water, it is a more ideal working fluid for power generation and heat transfer. It can be used as a working fluid for power generation or as a circulating working fluid to extract heat from coal and rock formations or store heat in sealed formations. Nowadays, coal mine construction and coal development are gradually moving towards deeper areas. There are more than 100 wells over 1,000 meters deep, some coal mines have a mining depth of over 1,500 meters, and some mine temperatures exceed 50°C. High-temperature mining areas and high-temperature mine water can be used for geothermal energy development and utilization.

[0005] In terms of storage, carbon sequestration refers to the process of transporting CO2 collected by carbon capture technology to a fixed location and using technical means to isolate it from the atmosphere for an extended period. Storage depths exceed 800 meters, and the geological temperature and pressure conditions can cause CO2 to reach a supercritical state. At ground level, the storage depth is approximately 1000 meters. 3 A volume of CO2 gas, after transforming into a supercritical state at a critical depth of 800 meters, compresses to a volume of 3.8 m³. 3 Furthermore, as the burial depth continues to increase, the volume further compresses, but the amount of compression decreases significantly, reaching approximately 3.2 m at 1 km. 3 At 1.5 km, it is approximately 2.8 m. 3 At 2 km, it is approximately 2.7 m 3The deep, special spaces in the coal mining sector, including closed / abandoned mine shafts, deep unminable coal seams and salt caverns, coal goaf areas, and carbonate rock caverns, are relatively ideal geological sites for CO2 sequestration.

[0006] However, currently, each of the above-mentioned CO2 characteristics is implemented independently. How to combine these characteristics and ultimately seal CO2 underground after utilization can not only effectively improve the extraction efficiency of underground coalbed methane, but also effectively reduce carbon emissions through sealing. This is the direction that this invention needs to study. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a method for coalbed methane development and carbon emission reduction based on multi-stage CO2 utilization and storage, which can effectively solve the problems existing in the above-mentioned technologies.

[0008] To achieve the above objectives, the technical solution adopted by this invention is: a method for coalbed methane development and carbon emission reduction based on multi-stage CO2 utilization and storage, comprising the following steps:

[0009] Step 1, Phase Change Fracturing of Shallow Coal Seams: Construct the first injection well and inject low-temperature liquid CO2 into the shallow coal seams to conduct cold impact on the coal body. Utilize the thermal stress generated by temperature changes, the expansion pressure of CO2 gasification, and the expansion force of phase change of pore water in the coal to fracture the coal seam. Through cyclic injection, a freeze-thaw cycle effect is generated to continuously fracture and form a fracture network.

[0010] Step 2, Foam Fracturing of Shallow and Medium Coal Seams: After the shallow and medium coal seams have completed phase change fracturing, foaming liquid, proppant, and liquid CO2 are injected into the shallow and medium coal seams simultaneously in a set ratio. When the temperature of the shallow and medium coal seams exceeds 31.3℃, the liquid CO2 vaporizes and reacts with the foaming liquid to generate CO2 foam, which further fractures the shallow and medium coal seams and supports the previously fractured fracture network. After completion, the injection of liquid CO2 is stopped. After the proppant fills the fractures, it prevents them from closing again under ground pressure and other disturbance pressures, increases the fracture conductivity, and promotes efficient extraction of coalbed methane.

[0011] Step 3: Displacing Coalbed Methane in Deep Coal Seams: The CO2 produced in Step 2 continues to be transported to deep coal seams. As the depth increases, the formation temperature and pressure also increase. The deep coal seams heat the CO2 and convert it to a supercritical state. The supercritical CO2 fully exchanges heat with the deep coal seams, while simultaneously fracturing the deep coal seams and displacing the coalbed methane. Finally, the coalbed methane from the deep and shallow coal seams is extracted to the surface through gas extraction pipes for power generation.

[0012] Step 4, High-Temperature Supercritical CO2 Utilization: The high-temperature supercritical CO2 obtained in Step 3 is divided into two parts. One part is extracted into the shallow and medium-depth coal seam to heat the coal and rock mass, accelerating its heating process and providing melting heat for the freeze-thaw cycle in Step 1. After releasing the heat, it continues to be transported to the deep coal seam and Step 3 is repeated. The other part flows into the heating well and rises to the surface for power generation. Finally, the remaining part is injected into the high geothermal anomaly zone of the deep coal seam through the supercritical CO2 injection well, so that the coal body is gasified at high temperature, realizing the in-situ fluidized mining of deep coal seam resources.

[0013] Step 5: High-temperature supercritical CO2 power generation: The CO2 power plant uses the high temperature of supercritical CO2 to generate electricity, ultimately converting geothermal energy into electrical energy; the low-temperature CO2 emitted after power generation is tested, and the qualified gas is partially restored to normal and then enters the compressor to be integrated into the micro-circulation of the CO2 power plant, while the other part is prepared into liquid CO2.

[0014] Step Six: Recycling of Liquid CO2: The atmospheric pressure CO2 captured by the carbon capture device is cooled and compressed to form liquid CO2, which is then combined with the liquid CO2 prepared in Step Five and stored for reinjection into the ground after the fracturing begins in Step One, thus achieving recycling.

[0015] Step 7, Regular CO2 Recycling: The low-temperature CO2 from the CO2 power plant outlet in Step 5 and the low-temperature CO2 from the carbon capture device outlet in Step 6 are both subjected to quality testing. If the impurities are below the standard value, they are processed and re-entered into the micro-circulation of the CO2 power plant or the micro-circulation of liquid CO2 preparation. If the impurity content is too high and has no utilization value, it is transported to a high-impurity CO2 storage tank for storage and finally discharged to the underground target reservoir for carbon sequestration. After carbon sequestration, new CO2 is replenished through the carbon capture device.

[0016] The core principle of this invention is as follows: the CO2 source input end is flue gas collected by a carbon capture device from gas power plants and coal-fired power plants, and the digestion terminal is a high-impurity carbon stream that is not worth processing after being detected by a carbon quality detection and treatment center, and is geologically stored through a storage well. The intermediate circulating medium is gaseous CO2, which is processed into liquid CO2 by a surface cooler and compressor and injected into shallow and medium-depth coal seams. After gasification, it continues to enter the medium and deep coal seams to form a supercritical state. The supercritical CO2 is extracted to a surface CO2 power plant for power generation and heat extraction, and then becomes a low-temperature working fluid. It is then processed again by a cooler and compressor to become liquid CO2 and injected into the well. Using CO2 as the circulating working fluid, it absorbs heat in the reservoir to become a high-temperature working fluid, driving the CO2 power plant to generate electricity. After completing its work, the CO2 continues to go down into the well to absorb heat through a cooler and circulating pump, and then enters the turbine to expand and do work, thus completing the power generation task. On the other hand, the supercritical CO2 is injected into deep, unminable / difficult-to-mine coal seams. In areas with high geothermal anomalies, the coal is gasified at high temperature and extracted. The extracted mixed gas and the displaced gas are mixed and brought up to the well, realizing in-situ fluidized mining of deep coal seam resources.

[0017] Furthermore, in step two, the proppant is composed of one or a mixture of ceramic particles and quartz sand, and the foaming liquid is an anionic surfactant.

[0018] Furthermore, in step five, the heat from the waste heat flue gas (200℃~100℃) is used to heat supercritical CO2; in step six, liquid CO2 is produced using a low-temperature carbon capture process, and the waste heat from the generator set is used for cooling, so that the low-temperature flue gas (100℃~70℃) is cooled to 4℃ at room temperature by an absorption chiller; the high-grade heat energy in the flue gas is used to heat CO2, and the low-grade heat energy in the flue gas is used to cool CO2, and the CO2 comes from the flue gas; the power generation stage uses flue gas preheating to improve thermal efficiency, and the liquid CO2 production stage uses flue gas precooling to reduce the energy consumption of subsequent multi-stage compression and cooling.

[0019] Furthermore, in step seven, the high-impurity CO2 is transported to the underground storage target reservoir, including the goaf of shallow and medium-deep coal seams, closed / abandoned roadways, and special spaces such as deep unminable / difficult-to-mine coal seams, salt caverns, and saline water layers. The CO2 to be stored also contains surface industrial waste heat. The deep unminable / difficult-to-mine coal seams are used as heat storage devices to achieve a combination of carbon sequestration and heat storage. When the power and heat demand of surface equipment is high, the high-temperature and high-pressure CO2 stored in the deep reservoir is released into the CO2 gas turbine for power generation, improving energy utilization efficiency. Before implementing underground storage, some catalysts can be added in advance, or alkaline industrial solid waste can be pre-prepared into a slurry and mixed with CO2 on the surface to accelerate the chemical sequestration reaction rate.

[0020] Furthermore, the shallow coal seams are buried at a depth of less than 800m, the medium-deep coal seams are buried at a depth of 800-1500m, and the deep, difficult-to-mine coal seams are buried at a depth of more than 1500m.

[0021] The aforementioned system for coalbed methane development and carbon emission reduction based on CO2 multi-stage utilization and storage includes a surface power generation system, a surface carbon treatment subsystem, and a wellbore pipeline subsystem.

[0022] The ground-based power generation system includes a gas power plant, a coal-fired power plant, and a CO2 power plant. The gas power plant is used to generate electricity from extracted gas and produce hot flue gas; the coal-fired power plant is used to generate electricity from burning coal and produce hot flue gas; and the CO2 power plant is used to generate electricity from supercritical CO2 and produce low-temperature CO2.

[0023] The ground-based carbon treatment subsystem includes a carbon trap, a carbon content detection and processing center, a condenser, a compressor, a liquid CO2 tanker, a high-impurity CO2 storage tank, a foaming liquid-based liquid tanker, and a foamer. The carbon trap is used to capture CO2 from hot flue gas as a CO2 source; the carbon content detection and processing center is used to monitor the impurity content in CO2 and perform diversion processing; the condenser is used to cool low-impurity CO2; the compressor is used to compress the cooled CO2 to form liquid CO2; the high-impurity CO2 storage tank is used to store high-impurity CO2; the liquid CO2 tanker is used to store liquid CO2; the foaming liquid-based liquid tanker is used to store foaming liquid; and the foamer is used to stir and foam the foaming liquid.

[0024] The wellbore piping subsystem includes a first injection well, a gas extraction well, a CO2 extraction well, a high-impurity CO2 storage well, a supercritical CO2 reflux well, and a supercritical CO2 injection well. The first injection well is used to inject liquid CO2 and CO2 foam into the shallow and medium-depth coal seams. The gas extraction well is used to extract gas. The CO2 extraction well is used to transport supercritical CO2 to the surface. The high-impurity CO2 storage well is used to transport high-impurity CO2 to underground storage. The supercritical CO2 reflux well is used to reflux supercritical CO2 formed in the deep and medium-depth coal seams to the shallow and medium-depth coal seams. The supercritical CO2 injection well is used to inject supercritical CO2 formed in the deep and medium-depth coal seams into the deep coal seams for supercritical CO2 fracturing.

[0025] Furthermore, the CO2 power plant includes a compressor, a heat exchanger, a CO2 gas turbine, a generator, a regenerator, and a cooler connected in sequence, and the CO2 power plant is connected to the CO2 extraction well.

[0026] Furthermore, the hot flue gas generated by gas power plants and coal-fired power plants is sent to the carbon detection and treatment center after CO2 is captured by the carbon capture device. The low-grade waste heat in the remaining flue gas is supplied to the condenser, and the high-grade waste heat is supplied to the regenerator.

[0027] Compared with existing technologies, this invention fully utilizes the supercritical characteristics of CO2, its competitive adsorption characteristics with methane gas, and its high heat transfer efficiency. Through multi-stage utilization and cyclic reinjection, it achieves an integrated engineering design for coal reservoir fracturing, coalbed methane displacement, power generation, heating, and carbon sequestration, while simultaneously realizing the effective utilization of energy resources at different burial depths. The main advantages are as follows:

[0028] 1) In this invention, the CO2 displacement process itself is a partial burial process. The integration of CO2 displacement and burial is an important method and green and low-carbon means to achieve a win-win situation of burial and utilization, emission reduction and efficiency improvement.

[0029] 2) When the associated gas volume in the mine is large and the CO2 content is high, the present invention utilizes a circulating injection system to achieve dynamic burial, and carbon burial can be carried out in an orderly manner in the later stage of gas driving, which can improve CO2 utilization and the added value of associated coalbed methane.

[0030] 3) This invention establishes an integrated geological-engineering development system for in-situ displacement extraction of coalbed methane, waste heat utilization, and CO2 geological storage; the CO2 in this system adopts a combination of "multi-phase utilization + geological storage", which is both economically effective and meets the requirements of low carbon.

[0031] 4) The CO2 used in this invention as a circulating working fluid has the advantages of good fluidity, high heat transfer efficiency, stable properties, low tendency to corrosion and scaling, large heat transfer coefficient and large specific heat capacity. It comprehensively utilizes the advantages of different phases of CO2 to implement different functions. At the same time, as the main target of carbon emission reduction, it can also be directly sealed in the circulating working fluid during the coalbed methane development process.

[0032] 5) This invention implements liquid cold shock fracturing or foam CO2 fracturing displacement in shallow and medium-depth reservoirs, reducing the difficulty of phase change control during long-distance transport; utilizing the formation temperature and pressure variation law, it implements supercritical CO2 fracturing displacement and heat extraction in medium and deep target layers, reducing the heating and pressurization process on the surface; for deep coal seams that are not easily minable, it conforms to the trend of fluidized bed mining, adopts CO2 displacement of gas and geological sealing method, which not only utilizes resources but also stores them in a low-carbon manner, and at the same time uses them as underground heat storage stations, transforming special spaces into underground heat storage and carbon sequestration spaces, which have great economic and ecological value. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the coalbed methane development and carbon sequestration method of the present invention.

[0034] Figure 2 This is a structural diagram of the CO2 power plant of the present invention. Detailed Implementation

[0035] The present invention will be further described below.

[0036] like Figure 1 As shown, a method for coalbed methane development and carbon emission reduction based on multi-stage CO2 utilization and storage includes the following steps:

[0037] Step 1, Phase Change Fracturing of Shallow Coal Seams: Construct the first injection well and inject low-temperature liquid CO2 into the shallow coal seams to conduct cold impact on the coal body. Utilize the thermal stress generated by temperature changes, the expansion pressure of CO2 gasification, and the expansion force of phase change of pore water in the coal to fracture the coal seam. Through cyclic injection, a freeze-thaw cycle effect is generated to continuously fracture and form a fracture network.

[0038] Step 2, Foam Fracturing of Shallow and Medium Coal Seams: After the shallow and medium coal seams have completed phase change fracturing, foaming liquid, proppant, and liquid CO2 are injected into the shallow and medium coal seams simultaneously in a set ratio. The proppant is composed of one or a mixture of ceramic particles and quartz sand, and the foaming liquid is an anionic surfactant. When the temperature of the shallow and medium coal seams exceeds 31.3℃, the liquid CO2 vaporizes and reacts with the foaming liquid to generate CO2 foam, which further fractures the shallow and medium coal seams and supports the previously fractured fracture network. After completion, the injection of liquid CO2 is stopped. After the proppant fills the fractures, it prevents them from closing again under ground pressure and other disturbance pressures, increases the fracture conductivity, and promotes efficient extraction of coalbed methane.

[0039] Step 3: Displacing Coalbed Methane in Deep Coal Seams: The CO2 produced in Step 2 continues to be transported to deep coal seams. As the depth increases, the formation temperature and pressure also increase. The deep coal seams heat the CO2 and convert it to a supercritical state. The supercritical CO2 fully exchanges heat with the deep coal seams, while simultaneously fracturing the deep coal seams and displacing the coalbed methane. Finally, the coalbed methane from the deep and shallow coal seams is extracted to the surface through gas extraction pipes for power generation.

[0040] Step 4, High-Temperature Supercritical CO2 Utilization: The high-temperature supercritical CO2 obtained in Step 3 is divided into two parts. One part is extracted into the shallow and medium-depth coal seam to heat the coal and rock mass, accelerating its heating process and providing melting heat for the freeze-thaw cycle in Step 1. After releasing the heat, it continues to be transported to the deep coal seam and Step 3 is repeated. The other part flows into the heating well and rises to the surface for power generation. Finally, the remaining part is injected into the high geothermal anomaly zone of the deep coal seam through the supercritical CO2 injection well, so that the coal body is gasified at high temperature, realizing the in-situ fluidized mining of deep coal seam resources.

[0041] Step 5, High-Temperature Supercritical CO2 Power Generation: The heat from the waste flue gas (200℃~100℃) is used to heat supercritical CO2. The CO2 power plant uses the high temperature of supercritical CO2 to generate electricity, ultimately converting geothermal energy into electrical energy. The low-temperature CO2 emitted after power generation is tested. A portion of the qualified gas is restored to its normal state and then enters the compressor to be integrated into the micro-circulation of the CO2 power plant. The other portion is prepared into liquid CO2.

[0042] Step Six: Recycling of Liquid CO2: The atmospheric CO2 captured by the carbon capture device is cooled and compressed to form liquid CO2, which is then combined with the liquid CO2 prepared in Step Five and stored for reinjection into the ground after the fracturing begins in Step One, thus achieving recycling. The liquid CO2 is produced using a low-temperature carbon capture process, and the waste heat from the generator set is used for cooling. The low-temperature flue gas (100℃~70℃) is cooled to 4℃ by an absorption chiller.

[0043] Step 7, Regular CO2 Recycling: The low-temperature CO2 from the CO2 power plant outlet in Step 5 and the low-temperature CO2 from the carbon capture device outlet in Step 6 are both subjected to quality testing. If the impurities are lower than the standard values ​​(the impurities and standard values ​​monitored for CO2 are as follows: carbon dioxide purity ≥99%, oil content ≤5mg / kg, total sulfur ≤1ppm, total hydrocarbons ≤50ppm), then after treatment, it is reintroduced into the microcirculation of the CO2 power plant or the microcirculation of liquid CO2 preparation. If the impurity content is too high and has no utilization value, it is transported to a high-impurity CO2 storage tank for storage, and finally discharged to the underground target reservoir for carbon sequestration. After carbon sequestration, new CO2 is replenished through the carbon capture device. The high-impurity CO2 transported to underground storage target reservoirs includes goaf areas, closed / abandoned roadways, and special spaces such as deep, unminable / difficult-to-mine coal seams, salt caverns, and saline water layers in shallow and medium-deep coal seams. The CO2 to be stored also contains surface industrial waste heat. The deep unminable / difficult-to-mine coal seams are used as heat storage devices to achieve a combination of carbon sequestration and heat storage. When the power and heat demand of surface equipment is high, the high-temperature and high-pressure CO2 stored in the deep reservoirs is released into CO2 gas turbines to generate electricity, improving energy utilization efficiency. Before implementing underground storage, some catalysts can be added in advance, or alkaline industrial solid waste can be pre-prepared into a slurry and mixed with CO2 on the surface to accelerate the chemical sequestration reaction rate.

[0044] The shallow coal seams mentioned above are buried at a depth of less than 800m, the medium-deep coal seams are buried at a depth of 800~1500m, and the deep, difficult-to-mine coal seams are buried at a depth of more than 1500m.

[0045] The aforementioned system for coalbed methane development and carbon emission reduction based on CO2 multi-stage utilization and storage includes a surface power generation system, a surface carbon treatment subsystem, and a wellbore pipeline subsystem.

[0046] The ground-based power generation system includes a gas power plant, a coal-fired power plant, and a CO2 power plant. The gas power plant is used to generate electricity from extracted gas and produce hot flue gas; the coal-fired power plant is used to burn coal to generate electricity and produce hot flue gas; the CO2 power plant is used to generate electricity from supercritical CO2 and produces low-temperature CO2; such as Figure 2As shown, the CO2 power plant includes a compressor, a heat exchanger, a CO2 gas turbine, a generator, a regenerator, and a cooler connected in sequence. The CO2 power plant is connected to the CO2 extraction well.

[0047] The ground-based carbon treatment subsystem includes a carbon trap, a carbon content detection and processing center, a condenser, a compressor, a liquid CO2 tanker, a high-impurity CO2 storage tank, a foaming liquid-based liquid tanker, and a foamer. The carbon trap is used to capture CO2 from hot flue gas as a CO2 source; the carbon content detection and processing center is used to monitor the impurity content in CO2 and perform diversion processing; the condenser is used to cool low-impurity CO2; the compressor is used to compress the cooled CO2 to form liquid CO2; the high-impurity CO2 storage tank is used to store high-impurity CO2; the liquid CO2 tanker is used to store liquid CO2; the foaming liquid-based liquid tanker is used to store foaming liquid; and the foamer is used to stir and foam the foaming liquid. Hot flue gas generated by gas power plants and coal-fired power plants is sent to the carbon content detection and processing center after CO2 is captured by the carbon trap, and the low-grade waste heat in the remaining flue gas is supplied to the condenser, and the high-grade waste heat is supplied to the regenerator.

[0048] The wellbore piping subsystem includes a first injection well, a gas extraction well, a CO2 extraction well, a high-impurity CO2 storage well, a supercritical CO2 reflux well, and a supercritical CO2 injection well. The first injection well is used to inject liquid CO2 and CO2 foam into the shallow and medium-depth coal seams. The gas extraction well is used to extract gas. The CO2 extraction well is used to transport supercritical CO2 to the surface. The high-impurity CO2 storage well is used to transport high-impurity CO2 to underground storage. The supercritical CO2 reflux well is used to reflux supercritical CO2 formed in the deep and medium-depth coal seams to the shallow and medium-depth coal seams. The supercritical CO2 injection well is used to inject supercritical CO2 formed in the deep and medium-depth coal seams into the deep coal seams for supercritical CO2 fracturing.

[0049] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A coal bed methane development and carbon emission reduction method based on CO2 multi-stage utilization and sequestration, characterized in that, The method comprises the following steps: Step one, phase change and fracturing of the middle and shallow coal seam: a first injection well is constructed, and low-temperature liquid CO2 is injected into the middle and shallow coal seam to cold-impact the coal body, and the coal seam is fractured by thermal stress generated by temperature change, CO2 gasification expansion pressure, and expansion force of coal pore water phase change, and a freeze-thaw cycle effect is generated by cyclic injection to continuously fracture and form a fracture network; Step two, foam fracturing of the middle and shallow coal seam: after the phase change and fracturing of the middle and shallow coal seam is completed, a foaming liquid, a proppant, and liquid CO2 are synchronously injected into the middle and shallow coal seam at a set ratio, when the temperature of the middle and shallow coal seam exceeds 31.3 DEG C, the liquid CO2 is gasified and reacts with the foaming liquid to generate CO2 foam, the middle and shallow coal seam is further fractured and the previously cracked fracture network is supported, and after the completion, the injection of liquid CO2 is stopped, the proppant is filled into the fracture to prevent the fracture from being re-closed under the ground pressure and other disturbance pressures, the conductivity of the fracture is increased, and the efficient extraction of coal seam gas is promoted; Step three, displacement of coal seam gas in the middle and deep coal seam: the CO2 gasified in step two is continuously transported to the middle and deep coal seam, as the depth increases, the temperature and pressure of the stratum are increased, the middle and deep coal seam heats and converts the CO2 into a supercritical state; the supercritical CO2 fully exchanges heat with the middle and deep coal seam, fractures the middle and deep coal seam, and displaces coal seam gas, and finally the coal seam gas in the middle and deep and shallow coal seams is extracted to the ground through a gas extraction pipe to generate electricity; Step four, utilization of high-temperature supercritical CO2: the high-temperature supercritical CO2 obtained in step three is divided into two parts, one part is extracted to the middle and shallow coal seam to provide melting heat for the freeze-thaw cycle in step one, and after the heat is released, the high-temperature supercritical CO2 is continuously transported to the middle and deep coal seam, and step three is repeated; the other part flows into a heat extraction well and is lifted to the ground to generate electricity; finally, the remaining part is injected into a high-geothermal anomaly area of the deep coal seam through a supercritical CO2 injection well, so that the coal body is high-temperature gasified, and the in-situ fluidized mining of the deep coal seam resources is realized; Step five, high-temperature supercritical CO2 power generation: a CO2 power station generates electricity by using the high temperature of the supercritical CO2; the low-temperature CO2 discharged after power generation is detected, part of the qualified gas is restored to a normal state and enters a CO2 power station microcycle, and the other part is prepared into liquid CO2; Step six, cyclic utilization of liquid CO2: atmospheric CO2 captured by a carbon capture device is cooled and compressed to form liquid CO2, and is stored together with the liquid CO2 prepared in step five, and is re-injected into the ground after the fracturing in step one to realize cyclic utilization; Step seven, cyclic utilization of normal CO2: the low-temperature CO2 at the outlet of the CO2 power station in step five and the low-temperature CO2 at the outlet of the carbon capture device in step six are both detected in quality, if the impurities are lower than the standard value, the low-temperature CO2 is treated and re-enters the CO2 power station microcycle or the liquid CO2 preparation microcycle, if the impurity content is relatively high and has no utilization value, the low-temperature CO2 is transported to a high-impurity CO2 storage tank for storage, and finally is discharged to a target stratum for carbon sequestration; after the carbon sequestration, new CO2 is supplemented through the carbon capture device.

2. The coal bed gas development and carbon emission reduction method based on multi-stage utilization and storage of CO2 according to claim 1, characterized in that, In step two, the proppant is one of ceramic particles and quartz sand or a mixture of both, and the foaming liquid is an anionic surfactant.

3. The coal bed gas development and carbon emission reduction method based on multi-stage utilization and storage of CO2 according to claim 1, characterized in that, In the step five, the heat of the waste heat flue gas is used for heating the supercritical CO2; in the step six, the low-temperature carbon capture process is used to prepare liquid CO2, and the waste heat of the generator set is used for refrigeration, and the low-temperature flue gas is used to reduce the temperature of the CO2 at normal temperature to 4℃ by the absorption refrigeration unit.

4. The coal bed gas development and carbon emission reduction method based on multi-stage utilization and storage of CO2 according to claim 1, characterized in that, In the step seven, the high-impurity-content CO2 is transported to the target storage layer in the underground, including the goaf of the middle-shallow coal seam, the closed / abandoned roadway and the deep non / minable coal seam, the salt cave and the saline aquifer; the CO2 to be stored also contains the industrial waste heat on the ground, the deep non / minable coal seam is used as a heat accumulator to store heat, the carbon storage and heat storage are combined, when the demand for power and heat of the ground equipment is large, the high-temperature and high-pressure CO2 stored in the deep is released to the CO2 gas turbine to generate power, and the energy utilization rate is improved.

5. The coal bed gas development and carbon emission reduction method based on multi-stage utilization and storage of CO2 according to claim 1, characterized in that, The buried depth of the middle-shallow coal seam is 800m or less, the buried depth of the middle-deep coal seam is 800-1500m, and the buried depth of the deep non-minable coal seam is 1500m or more.

6. A system for coal bed methane development and carbon emission reduction based on multi-stage utilization and storage of CO2 according to any one of claims 1 to 5, characterized in that, The system comprises a ground power generation system, a ground carbon treatment subsystem and a wellbore pipeline subsystem. The ground power generation system comprises a gas power plant, a coal-fired power plant and a CO2 power station; the gas power plant is used for generating power by using the extracted gas and generating hot flue gas; the coal-fired power plant is used for generating power by burning coal and generating hot flue gas; and the CO2 power station is used for generating power by using supercritical CO2 and generating low-temperature CO2. The ground carbon treatment subsystem comprises a carbon collector, a carbon quality detection and treatment center, a condenser, a compressor, a liquid CO2 tank truck, a high-impurity-content CO2 storage tank, a foaming liquid base liquid tank truck and a foaming device; the carbon collector is used for collecting CO2 in the hot flue gas as a CO2 source; the carbon quality detection and treatment center is used for monitoring the impurity content in the CO2 for shunt treatment; the condenser is used for reducing the temperature of the low-impurity-content CO2; the compressor is used for compressing the cooled CO2 to form liquid CO2; the high-impurity-content CO2 storage tank is used for storing high-impurity-content CO2; the liquid CO2 tank truck is used for storing liquid CO2; the foaming liquid base liquid tank truck is used for storing foaming liquid; and the foaming device is used for stirring and foaming the foaming liquid. The wellbore pipeline subsystem comprises a first injection well, a gas extraction well, a CO2 extraction well, a high-impurity-content CO2 storage well, a supercritical CO2 backflow well and a supercritical CO2 injection well; the first injection well is used for injecting liquid CO2 and CO2 foam into the middle-shallow part; the gas extraction well is used for extracting gas; the CO2 extraction well is used for transporting supercritical CO2 to the ground; the high-impurity-content CO2 storage well is used for transporting high-impurity-content CO2 to the underground storage; the supercritical CO2 backflow well is used for making the supercritical CO2 formed in the middle-deep coal seam backflow to the middle-shallow coal seam; and the supercritical CO2 injection well is used for making the supercritical CO2 formed in the middle-deep coal seam inject into the deep coal seam to perform supercritical CO2 fracturing.

7. The system of claim 6, wherein, The CO2 power station comprises a compressor, a heat exchanger, a CO2 gas turbine, a generator, a regenerator and a cooler connected in sequence, and is connected with the CO2 extraction well.

8. The system of claim 7, wherein, The hot flue gas generated by the gas power plant and the coal power plant is sent to the carbon detection processing center after CO2 is captured by the carbon capturer, and the low-grade waste heat in the remaining flue gas is supplied to the condenser and the high-grade waste heat is supplied to the regenerator.

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