Extraction system and method for coal seam gas through high-pressure air blasting and hot flue gas displacement

Abstract

The invention belongs to the technical field of coal bed gas exploitation, and particularly relates to an extraction system and method for high-pressure air blasting and hot flue gas displacement of coal bed gas. The system comprises a high-pressure air blasting unit, a hot flue gas injection unit, a gas extraction unit and a data monitoring unit, the high-pressure air blasting unit and the hot flue gas injection unit share the same blasting and gas injection well, an extraction well is arranged on the outer ring of the blasting and gas injection well, and the gas extraction unit extracts gas through the extraction well; the coal seam is subjected to fracturing and permeability increasing through high-pressure air blasting, the coal seam can be effectively fractured, and the permeability of the coal seam can be effectively improved; hot flue gas is injected after high-pressure air blasting permeability increasing is conducted on the coal seam, the hot flue gas can be smoothly injected into the coal seam, and the coal seam is further fractured; the temperature of the coal seam can be increased by injecting the hot flue gas, desorption and migration of CH4 are facilitated, meanwhile, CH4 in an adsorption state is replaced by CO2 by means of the adsorption characteristic of CO2, and CO2 is effectively sealed in the coal seam while the desorption amount of the coal seam gas is increased.

Description

Technical Field

[0001] The invention belongs to the technical field of coalbed methane extraction, and particularly relates to a coalbed methane extraction system and method for high-pressure air blasting and hot flue gas displacement of coalbed methane. Background Art

[0002] At present, global warming is becoming increasingly obvious, and CCUS (CO2 capture, utilization and storage) technology is an effective means to mitigate the greenhouse effect. The reserves of deep unminable coalbed natural gas in China are huge, with great resource utilization prospects. At the same time, due to the strong adsorption of coal to CO2, deep unminable coal seams become natural sites for CO2 geological storage. The technology of injecting hot flue gas into coal seams can improve the output of coalbed methane while effectively sequestering CO2 in hot flue gas. However, deep coal seams are characterized by high stress and low permeability. When directly injecting gas, gas resistance and gas blockage often occur, greatly increasing the difficulty of gas injection. Therefore, before gas injection, fracture stimulation measures need to be used to promote the development of the coal seam fracture network to ensure the effective progress of gas injection and methane extraction. Hydraulic fracturing is a relatively common coal seam fracture stimulation technology at present, but it has the disadvantages of single fracture propagation, large water consumption and groundwater pollution. At the same time, there are many problems in power plant flue gas CCUS (CO2 capture, utilization and storage), such as large capture difficulty, small sequestration volume and high operation cost, which cannot meet the huge demand for power plant carbon emission reduction. Summary of the Invention

[0003] Aiming at the above deficiencies of the prior art, the purpose of the present invention is to provide a coalbed methane extraction system and method for high-pressure air blasting and hot flue gas displacement of coalbed methane, which can effectively fracture the coal seam to improve the coal seam permeability and effectively sequester CO2 in hot flue gas while displacing coalbed methane.

[0004] The present invention provides the following technical solutions: A coalbed methane extraction system for high-pressure air blasting and hot flue gas displacement of coalbed methane includes a high-pressure air blasting unit, a hot flue gas injection unit, a methane extraction unit and a data monitoring unit; the high-pressure air blasting unit and the hot flue gas injection unit share the same blasting and gas injection well, and extraction wells are arranged outside the blasting and gas injection well, and the methane extraction unit extracts methane through the extraction wells; The high-pressure air blasting unit includes an air compression and transportation component and a high-pressure air release component. The high-pressure air release component is connected to the air compression and transportation component. Two gas injection plugging devices are arranged up and down within the coal seam range in the blasting and gas injection well, and the high-pressure air release component is placed in the closed space between the two gas injection plugging devices; The suction end of the hot flue gas injection unit is connected to the flue gas discharge device of the gas power plant, and the discharge end is led to the closed space between the two gas injection plugging devices; The data monitoring unit includes a barometric pressure sensor arranged in the blasting and gas injection well, an acoustic emission sensor and a resistivity sensor arranged in the coal seam around the blasting and gas injection well. The barometric pressure sensor is used to monitor the blasting pressure and air pressure in the enclosed space of the blasting and gas injection well; the acoustic emission sensor is used to monitor the intensity and frequency of acoustic emission events during the high-pressure air blasting process, and the resistivity sensor is used to monitor the change of the resistivity of the coal body at the monitoring point.

[0005] Further, the bottom hole of the blasting and gas injection well is located below the coal seam floor; the bottom hole of the gas extraction well is located in the coal seam.

[0006] Further, the air compression and transportation assembly includes an air compressor, a high-pressure air storage tank, a first one-way solenoid valve, a high-pressure air booster pump, a second one-way solenoid valve and a three-way device connected in sequence through a high-pressure air transportation pipeline. The upper pipe orifice of the three-way device is connected to a pressure relief solenoid valve and a pressure relief port in sequence through a high-pressure air transportation pipeline. The lower pipe orifice of the three-way device is connected to an electromagnetic blasting valve and a high-pressure air release assembly in sequence through a high-pressure air transportation pipeline. The high-pressure air release assembly is a blasting cylinder.

[0007] Further, the hot flue gas injection unit includes a hot flue gas transportation pipeline. The suction direction of the hot flue gas transportation pipeline is connected to the flue gas discharge device of the gas power plant, and the discharge direction is connected to a hot flue gas storage tank, a fourth one-way solenoid valve, an injection controller, a hot flue gas booster pump and a third one-way solenoid valve in sequence and then descends into the blasting and gas injection well.

[0008] Further, the gas drainage unit includes a gas filtering device, a gas drainage pump and a gas separation device connected in sequence through a gas drainage pipeline. The outlet pipeline of the gas separation device is divided into a gas pipeline and a carbon dioxide pipeline. The gas pipeline is connected to the gas power generation device of the gas power plant, and the carbon dioxide pipeline is connected to the hot flue gas storage tank.

[0009] Further, a second pressure gauge and a flow meter are connected between the hot flue gas booster pump and the third one-way solenoid valve; a first pressure gauge is connected between the high-pressure air booster pump and the second one-way solenoid valve.

[0010] Further, the acoustic emission sensor and the resistivity sensor are arranged between the gas extraction well and the blasting and gas injection well.

[0011] Further, the gas injection plug in the blasting and gas injection well is located at the junction of the coal seam and the rock stratum.

[0012] Further, the distance between the blasting and gas injection well and the gas extraction well is 200 - 400m.

[0013] A method for extracting coal seam gas by high-pressure air blasting and hot flue gas displacement uses the aforementioned extraction system for high-pressure air blasting and hot flue gas displacement of coal seam gas to complete the following steps: S1: Conduct high-pressure air blasting and fracturing on the coal seam. The high-pressure air blasting unit pressurizes the air to 80 Mpa, opens the electromagnetic blasting valve, and the high-pressure air rapidly and violently expands and is pressed into the blasting cylinder to break the bursting disc, so that the high-pressure air is instantaneously released in the closed space of the blasting and gas injection well, and the blasting pressure is 70 - 75 MPa; S2: After the blasting is completed and the air pressure in the blasting and gas injection well is stable, relieve the air pressure in the blasting and gas injection well; S3: Repeat steps S1 and S2. During this period, judge the development degree of the coal seam fissures by monitoring the signals of the resistivity sensor and the acoustic emission sensor; when the resistivity at the monitoring point deviates from the resistivity of the coal seam before high-pressure air blasting by 3 - 5 times, and the acoustic emission sensor monitors more low-frequency acoustic emission signals than high-frequency acoustic emission signals, it indicates that the development degree of the coal seam fissures is relatively high at this time, and thus the high-pressure air blasting operation is completed; S4: Inject hot flue gas for storage and displace CH4 desorption. The hot flue gas injection unit pressurizes the hot flue gas to 10 MPa and then injects it into the closed space of the blasting and gas injection well; S5: Extract CH4 gas. The gas extraction unit starts to extract while injecting hot flue gas; S6: The hot flue gas injection unit continuously injects hot flue gas, and the gas extraction unit continuously extracts CH4 gas until the CO2 gas concentration in the extracted mixed gas reaches more than 7%, and the flue gas storage volume of this coal seam reaches saturation, and thus the hot flue gas storage and CH4 extraction operation is completed.

[0014] Compared with the prior art, the advantages of the present invention are as follows: The present invention uses high-pressure air blasting to fracture and enhance the permeability of the coal seam, which can effectively fracture the coal seam, improve the coal seam permeability, improve the gas injectability and the gas extraction efficiency. Compared with the traditional hydraulic fracturing, the formed fracture network is complex, and the waste of water resources and the pollution of underground water resources are greatly reduced; due to the general characteristics of deep coal seams with low permeability and high stress, the coal body fissures are easily compressed by stress. After blasting, the high-pressure air is pressed into the coal seam to support the coal seam fissures, maintain the gas migration channel, and at the same time reduce the partial pressure of CH4 in the pores, so that CH4 is desorbed; the high-pressure air blasting can control the blasting pressure and range according to the actual coal seam stress and coal seam thickness, and the process is simple, which helps to speed up the project progress.

[0015] After the coal seam is enhanced in permeability by high-pressure air blasting, hot flue gas is injected. The hot flue gas can be smoothly injected into the coal seam and further fracture the coal seam; the CO2 in the hot flue gas contacts the moisture in the coal seam to produce a chemical acidification effect to modify the coal body, causing the minerals in the coal body to dissolve or change, promoting the formation of new pores and fractures in the coal body, and further improving the permeability of the coal body; the injection of hot flue gas can increase the temperature of the coal seam, which is beneficial to the desorption and migration of CH4. At the same time, due to the adsorption characteristics of CO2 itself, the adsorbed CH4 is displaced, increasing the desorption amount of coalbed methane while effectively sealing CO2 in the coal seam, which helps to achieve the goal of green and environmental protection energy development. Description of the Drawings

[0016] Figure 1 It is a schematic structural diagram of a coalbed methane extraction system for high-pressure air blasting and hot flue gas displacement of coalbed methane.

[0017] In the figure: 1 - coal seam; 2 - rock stratum; 3 - gas extraction pump; 4 - gas separation device; 5 - high-pressure air storage tank; 6 - air compressor; 7 - first one-way solenoid valve; 8 - high-pressure air booster pump; 9 - first pressure gauge; 10 - second one-way solenoid valve; 11 - tee device; 12 - pressure relief port; 13 - pressure relief solenoid valve; 14 - third one-way solenoid valve; 15 - second pressure gauge; 16 - flow meter; 17 - hot flue gas booster pump; 18 - gas injection controller; 19 - fourth one-way solenoid valve; 20 - hot flue gas storage tank; 21 - flue gas emission device of a gas power plant; 22 - extraction plugging device; 23 - gas filtration device; 24 - acoustic emission sensor; 25 - resistivity sensor; 26 - air pressure sensor; 27 - gas injection plugging device; 28 - electromagnetic blasting valve; 29 - blasting cylinder; 30 - high-pressure air delivery pipeline; 31 - hot flue gas delivery pipeline; 32 - gas extraction pipeline. Detailed Embodiments

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0019] In view of the problems that directly injecting hot flue gas into deep coal seams results in poor gas injection effect, small displacement range, low gas drainage efficiency, and the conventional permeability enhancement technologies (such as hydraulic fracturing) have problems such as single fracture propagation and environmental pollution. The gas source required for conventional gas injection displacement requires certain economic costs during gas production or gas distribution, while the hot flue gas discharged from a gas power plant can just be used as the displacement gas source. Therefore, directly using the hot flue gas discharged from a gas power plant to displace gas is expected to achieve the dual goals of carbon emission reduction and improved gas recovery rate. Therefore, a gas drainage system and method for high-pressure air blasting and hot flue gas displacement of coal seam gas are proposed.

[0020] Embodiment 1 As Figure 1 shown: A gas drainage system for high-pressure air blasting and hot flue gas displacement of coal seam gas includes a high-pressure air blasting unit, a hot flue gas injection unit, a gas drainage unit, and a data monitoring unit; the high-pressure air blasting unit and the hot flue gas injection unit share the same blasting and gas injection well, and drainage wells are arranged outside the outer circle of the blasting and gas injection well, and the gas drainage unit drains gas through the drainage wells; The high-pressure air blasting unit includes an air compression and transportation component and a high-pressure air release component. The high-pressure air release component is connected to the air compression and transportation component. Two gas injection plugging devices 27 are arranged vertically within the coal seam range in the blasting and gas injection well, and the high-pressure air release component is placed in the closed space between the two gas injection plugging devices 27; The suction end of the hot flue gas injection unit is connected to the flue gas discharge device 21 of the gas power plant, and the discharge end is led to the closed space between the two gas injection plugging devices 27; The data monitoring unit includes a pressure sensor 26 arranged in the blasting and gas injection well, an acoustic emission sensor 24 and a resistivity sensor 25 arranged in the coal seam around the blasting and gas injection well. The pressure sensor 26 is used to monitor the blasting pressure and air pressure in the closed space of the blasting and gas injection well; the acoustic emission sensor 24 is used to monitor the intensity and frequency of acoustic emission events during the high-pressure air blasting process, and the resistivity sensor 25 is used to monitor the change in the resistivity of the coal body at the monitoring point to judge the degree of crack development of the coal body.

[0021] The high-pressure air blasting unit, hot flue gas injection unit, gas drainage unit, and data monitoring unit work together to extract gas and improve gas recovery rate. First, the coal seam is fractured by high-pressure air blasting, which can effectively fracture the coal seam, improve gas injectability, and gas drainage efficiency. After the coal seam is fractured by high-pressure air blasting, hot flue gas is injected. The hot flue gas can be smoothly injected into the coal seam. The CO2 in the hot flue gas contacts the moisture in the coal seam to produce a chemical acidification effect, modifying the coal body, causing the minerals in the coal body to dissolve or change, promoting the formation of new pore fractures in the coal body, and further improving the permeability of the coal body. At the same time, the injection of hot flue gas can increase the temperature of the coal seam, which is beneficial to the desorption and migration of CH4. The CO2 in the hot flue gas, relying on its own adsorption characteristics, displaces the adsorbed CH4, increasing the gas desorption volume while effectively sealing the CO2 in the coal seam.

[0022] The end hole of the blasting and gas injection well is located below the coal seam floor; the end hole of the drainage well is located in the coal seam.

[0023] The air compression and transportation assembly includes an air compressor 6, a high-pressure air storage tank 5, a first one-way solenoid valve 7, a high-pressure air booster pump 8, a second one-way solenoid valve 10, and a tee device 11 connected in sequence through a high-pressure air transportation pipeline 30. The upper pipe orifice of the tee device 11 is connected to a pressure relief solenoid valve 13 and a pressure relief port 12 in sequence through the high-pressure air transportation pipeline 30. The lower pipe orifice of the tee device 11 is connected to an electromagnetic blasting valve 28 and a high-pressure air release assembly in sequence through the high-pressure air transportation pipeline 30. The high-pressure air release assembly is a blasting cylinder 29. A first pressure gauge 9 is connected between the high-pressure air booster pump 8 and the second one-way solenoid valve 10.

[0024] The air inlet of the air compressor 6 is connected to the atmosphere. The air compressor 6 compresses the air to 35 MPa and stores it in the high-pressure air storage tank 5 for subsequent engineering use. The high-pressure air storage tank 5 stores a large amount of high-pressure gas for high-pressure air blasting projects, which can avoid the situation of insufficient gas supply during construction and the need for long-term pressurization, and helps to achieve continuous and efficient high-pressure air blasting operations. The high-pressure air in the high-pressure air storage tank 5 enters the subsequent high-pressure air transportation pipeline 30 after being pressurized twice by the high-pressure air booster pump 8. The blasting cylinder 29 can instantaneously and directionally release the high-pressure air into the coal seam to be transformed, fracturing the coal body and forming a complex fracture network in the coal seam, effectively increasing the gas permeability of the coal seam.

[0025] The hot flue gas injection unit includes a hot flue gas transportation pipeline 31. The suction direction of the hot flue gas transportation pipeline 31 is connected to the flue gas emission device 21 of the gas power plant, and the discharge direction is connected to a hot flue gas storage tank 20, a fourth one-way solenoid valve 19, an injection controller 18, a hot flue gas booster pump 17, and a third one-way solenoid valve 14 in sequence and then descends into the blasting and gas injection well. A second pressure gauge 15 and a flow meter 16 are connected between the hot flue gas booster pump 17 and the third one-way solenoid valve 14.

[0026] The hot flue gas discharged by the flue gas emission device 21 of the gas power plant is stored in the hot flue gas storage tank 20 through the hot flue gas transmission pipeline 31. After being pressurized by the hot flue gas transmission pipeline 21 and the hot flue gas booster pump 17, the hot flue gas is injected into the coal seam, displacing the coal seam gas while effectively sealing CO2 in the hot flue gas.

[0027] A drainage plug 22 is provided at the wellhead of the drainage well. The gas drainage unit includes a gas filtration device 23, a gas drainage pump 3, and a gas separation device 4 connected in sequence through a gas drainage pipeline 32. The gas separation device 4 separates CO2 and CH4. The outlet pipeline of the gas separation device 4 is divided into a gas pipeline and a carbon dioxide pipeline. The gas pipeline is connected to the power generation device of the gas power plant, and the carbon dioxide pipeline is connected to the hot flue gas storage tank 20. The gas filtration device 23 is used to filter solid impurities such as coal cinder in the mixed gas to ensure the stable operation of the drainage system.

[0028] The blasting and gas injection well and the drainage well are vertically drilled, and the distance from the blasting and gas injection well to the drainage well is 200 - 400m. The acoustic emission sensor 24 and the resistivity sensor 25 are arranged between the drainage well and the blasting and gas injection well, and the acoustic emission sensor 24 and the resistivity sensor 25 are arranged in a wellbore about 20m away from the blasting and gas injection well.

[0029] The gas injection plug 27 in the blasting and gas injection well is located at the junction of the coal seam and the rock stratum.

[0030] Embodiment 2 A method for draining coal seam gas by high-pressure air blasting and hot flue gas displacement uses the high-pressure air blasting and hot flue gas displacement coal seam gas drainage system of Embodiment 1 to complete the following steps: S1: Perform high-pressure air blasting and fracturing on the coal seam. Before injecting high-pressure air, it is necessary to ensure the integrity of the wellbore and each device and the tightness of the gas injection system; start the air compressor 6, compress the outside air to 35MPa and store it in the high-pressure air storage tank 5; open the first one-way solenoid valve 7 and the second one-way solenoid valve 10, start the high-pressure air booster pump 8, pressurize the compressed air in the high-pressure air storage tank 5 to about 80MPa through the high-pressure air booster pump 8. During the pressurization period, monitor the air pressure in the high-pressure air transmission pipeline 30 through the first pressure gauge 9. When the air pressure stabilizes at about 80MPa, close the first one-way solenoid valve 7, stop the high-pressure air booster pump 8, open the electromagnetic blasting valve 28, and the high-pressure air rapidly expands violently and is pressed into the blasting cylinder 29 to break the bursting disc, so that the high-pressure air is instantly released in the closed space of the blasting and gas injection well. The blasting pressure is 70 - 75MPa. The blasting shock wave formed by the instant release of the high-pressure air exerts a strong destructive effect on the coal body around the blasting and gas injection well, breaking the coal body and generating new cracks, and at the same time extending the original cracks to form a complex crack network, effectively increasing the coal seam permeability; S2: After the blasting is completed, close the second one-way solenoid valve 10, measure the air pressure inside the blasting and gas injection well through the air pressure sensor 26. After the air pressure in the blasting and gas injection well stabilizes, open the pressure relief solenoid valve 13 to relieve the air pressure in the blasting and gas injection well; S3: Repeat steps S1 and S2. During this period, judge the development degree of coal seam fissures by monitoring the signals of the resistivity sensor 25 and the acoustic emission sensor 24; when the resistivity at the monitoring point deviates from the coal seam resistivity before high-pressure air blasting by 3 to 5 times, and the acoustic emission sensor 24 monitors more low-frequency acoustic emission signals (10 - 50 kHz) than high-frequency acoustic emission signals, it indicates that the development degree of coal seam fissures is relatively high at this time, and thus the high-pressure air blasting operation is completed; S4: Thermal flue gas injection for storage and displacement of CH4 desorption. Transport the thermal flue gas discharged from the gas-fired power plant flue gas emission device 21 to the thermal flue gas storage tank 20 for storage through the thermal flue gas pipeline 31; set the initial pressure of thermal flue gas injection through the injection controller 18; open the third one-way solenoid valve 14 and the fourth one-way solenoid valve 19, start the thermal flue gas booster pump 17, and inject the thermal flue gas into the closed space of the blasting and gas injection well after pressurizing it to 10 MPa; the high temperature effect of the thermal flue gas can further promote the development of pores and fissures in the coal body, improve the migration channel of coalbed methane, and promote the desorption and flow of coalbed methane; the CO2 in the thermal flue gas contacts with the moisture in the coal seam to produce a chemical acidification effect to modify the coal body, making the minerals in the coal body dissolve or change, promoting the formation of new pores and fissures in the coal body, and further improving the permeability of the coal body; the CO2 in the thermal flue gas can displace CH4 in the coal seam due to its competitive adsorption advantage, so as to realize the storage of CO2 in the thermal flue gas while increasing the output of CH4; during the injection of the thermal flue gas, adjust the injection pressure accordingly by observing the flow rate change of the flow meter 16 to ensure the best thermal flue gas storage effect and CH4 displacement effect; S5: CH4 gas extraction. Start the gas extraction pump 3 while injecting the thermal flue gas. Under the action of the extraction negative pressure and the injection drive, the CH4 gas desorbed by the blasting effect, the CH4 gas displaced by the thermal flue gas, and the remaining thermal flue gas migrate to the extraction well together; the extracted mixed gas first passes through the gas filtration device 23 to remove solid impurities in the mixed gas, and then enters the gas separation device 4. The gas separation device 4 separates the mixed gas into CO2 gas and CH4 gas; the separated CH4 gas is transported through the pipeline to the power generation device of the gas-fired power plant to be mixed with the gas extracted from the coalbed methane extraction pump station in the mine area for power generation to improve the power generation efficiency; the separated CO2 gas is transported through the pipeline to the thermal flue gas storage tank 20 for mixing and then injected into the coal seam continuously; S6: The hot flue gas injection unit continuously injects hot flue gas, and the gas drainage unit continuously drains CH4 gas until the CO2 gas concentration in the drained mixed gas reaches more than 7%, and the flue gas storage volume of this coal seam reaches saturation. Thus, the hot flue gas storage and CH4 drainage operations are completed.

[0031] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A coal seam gas extraction system using high-pressure air blasting and hot flue gas displacement, characterized in that: It includes a high-pressure air blasting unit, a hot flue gas injection unit, a gas drainage unit, and a data monitoring unit; the high-pressure air blasting unit and the hot flue gas injection unit share the same blasting and gas injection well, and drainage wells are arranged on the outer circle of the blasting and gas injection well, and the gas drainage unit drains gas through the drainage wells; The high-pressure air blasting unit includes an air compression and transportation component and a high-pressure air release component. The high-pressure air release component is connected to the air compression and transportation component. Two gas injection plugging devices (27) are arranged up and down within the coal seam range in the blasting and gas injection well, and the high-pressure air release component is placed in the sealed space between the two gas injection plugging devices (27); The suction end of the hot flue gas injection unit is connected to the flue gas discharge device (21) of the gas power plant, and the discharge end is led to the sealed space between the two gas injection plugging devices (27); The data monitoring unit includes a pressure sensor (26) arranged in the blasting and gas injection well, an acoustic emission sensor (24) and a resistivity sensor (25) arranged in the coal seam around the blasting and gas injection well. The pressure sensor (26) is used to monitor the blasting pressure and air pressure in the sealed space of the blasting and gas injection well; the acoustic emission sensor (24) is used to monitor the intensity and frequency of acoustic emission events during the high-pressure air blasting process, and the resistivity sensor (25) is used to monitor the change of the coal body resistivity at the monitoring point.

2. The coal seam gas drainage system for high-pressure air blasting and hot flue gas displacement according to claim 1, characterized in that: The end hole of the blasting and gas injection well is located below the coal seam floor; the end hole of the drainage well is located in the coal seam.

3. The gas drainage system for high-pressure air blasting and hot flue gas displacement of coal seam gas according to claim 1, characterized in that: The air compression and transportation component includes an air compressor (6), a high-pressure air storage tank (5), a first one-way solenoid valve (7), a high-pressure air booster pump (8), a second one-way solenoid valve (10), and a three-way device (11) connected in sequence through a high-pressure air transportation pipeline (30). The upper pipe orifice of the three-way device (11) is connected to a pressure relief solenoid valve (13) and a pressure relief port (12) in sequence through a high-pressure air transportation pipeline (30). The lower pipe orifice of the three-way device (11) is connected to an electromagnetic blasting valve (28) and a high-pressure air release component in sequence through a high-pressure air transportation pipeline (30), and the high-pressure air release component is a blasting cylinder (29).

4. The gas drainage system for high-pressure air blasting and hot flue gas displacement of coal seam gas according to claim 3, wherein: The hot flue gas injection unit includes a hot flue gas transportation pipeline (31). The suction direction of the hot flue gas transportation pipeline (31) is connected to the flue gas discharge device (21) of the gas power plant, and the discharge direction is connected to a hot flue gas storage tank (20), a fourth one-way solenoid valve (19), an injection controller (18), a hot flue gas booster pump (17), and a third one-way solenoid valve (14) in sequence and then lowered into the blasting and gas injection well.

5. The gas drainage system for high-pressure air blasting and hot flue gas displacement of coal seam gas according to claim 4, characterized in that: The gas drainage unit includes a gas filtration device (23), a gas drainage pump (3), and a gas separation device (4) connected in sequence through a gas drainage pipeline (32). The outlet pipeline of the gas separation device (4) is divided into a gas pipeline and a carbon dioxide pipeline. The gas pipeline is connected to the gas power generation device of the gas power plant, and the carbon dioxide pipeline is connected to the hot flue gas storage tank (20).

6. The gas drainage system for high-pressure air blasting and hot flue gas displacement of coal seam gas according to claim 5, characterized in that: A second pressure gauge (15) and a flow meter (16) are connected between the hot flue gas booster pump (17) and the third one-way solenoid valve (14); a first pressure gauge (9) is connected between the high-pressure air booster pump (8) and the second one-way solenoid valve (10).

7. The coal seam gas extraction system for high-pressure air blasting and hot flue gas displacement according to claim 1, characterized in that: The described acoustic emission sensor (24) and resistivity sensor (25) are arranged between the gas drainage well and the blasting and gas injection well.

8. The coal seam gas extraction system for high-pressure air blasting and hot flue gas displacement according to claim 1, characterized in that: The gas injection plugging device (27) in the blasting and gas injection well is located at the junction of the coal seam and the rock stratum.

9. The gas drainage system for high-pressure air blasting and hot flue gas displacement of coal seam gas according to claim 1, characterized in that: The distance from the blasting and gas injection well to the gas drainage well is 200 - 400 m.

10. A method for extracting coal seam gas by high-pressure air blasting and hot flue gas displacement, characterized in that, The following steps are completed using the gas drainage system for high-pressure air blasting and hot flue gas displacement of coal seam gas described in claim 6: S1: Conduct high-pressure air blasting fracturing on the coal seam. The high-pressure air blasting unit pressurizes the air to 80 Mpa, opens the electromagnetic blasting valve (28), and the high-pressure air rapidly and violently expands and is pressed into the blasting cylinder (29) to break the bursting disc, so that the high-pressure air is instantaneously released in the closed space of the blasting and gas injection well, and the blasting pressure is 70 - 75 MPa. S2: After the blasting is completed and the air pressure in the blasting and gas injection well is stable, relieve the air pressure in the blasting and gas injection well. S3: Repeat steps S1 and S2. During this period, judge the degree of coal seam fracture development by monitoring the signals of the resistivity sensor (25) and the acoustic emission sensor (24); when the resistivity at the monitoring point deviates from the coal seam resistivity before high-pressure air blasting by 3 - 5 times, and the acoustic emission sensor (24) monitors more low-frequency acoustic emission signals than high-frequency acoustic emission signals, it indicates that the degree of coal seam fracture development is relatively high at this time, and the high-pressure air blasting operation is completed. S4: Inject and seal hot flue gas and displace CH4 desorption. The hot flue gas injection unit pressurizes the hot flue gas to 10 MPa and then injects it into the closed space of the blasting and gas injection well. S5: Conduct CH4 gas drainage. The gas drainage unit starts to drain gas while injecting hot flue gas. S6: The hot flue gas injection unit continuously injects hot flue gas, and the gas drainage unit continuously drains CH4 gas until the CO2 gas concentration in the drained mixed gas reaches more than 7%, and the flue gas seal storage volume of this coal seam reaches saturation, and the hot flue gas sealing and CH4 drainage operations are completed.

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