Liquid nitrogen freezing and carbon dioxide blasting combined anti-reflection device and anti-reflection method

Abstract

The invention discloses a liquid nitrogen freezing and carbon dioxide blasting combined anti-reflection device and method. The device comprises a freezing pipe and an anti-reflection assembly. The anti-reflection assembly is mounted on the inner side of the freezing pipe; the anti-reflection assembly comprises a flexible air bag, an excitation device and a sealing positioning ring; the sealing positioning ring sleeves the outer side of the flexible air bag, and the flexible air bag is provided with an extension section; an end socket is mounted outside the sealing positioning ring in a sleeving manner, and the sealing positioning ring fixes the extension section on the end socket; the exterior of the end head is fixedly connected with the freezing pipe; the excitation device is arranged in the flexible air bag; and a firing line is mounted on the excitation device. The mechanical property of the coal body is optimized and improved through liquid nitrogen freezing, so that the mechanical strength of the coal body is enhanced, the brittleness is greatly improved, and then CO2 phase change blasting is performed to crack the coal seam; for a low-permeability soft coal seam, hole collapse caused by soft coal in single blasting is avoided, more cracks can be generated in the coal seam after CO2 blasting, the fracturing and permeability increasing effects are greatly improved, and a good promoting effect is achieved on gas extraction.

Description

Technical Field

[0001] The invention relates to a coal seam permeability enhancement method, in particular to a liquid nitrogen freezing combined with carbon dioxide blasting permeability enhancement device and a permeability enhancement method, belonging to the technical field of gas mining. Background Art

[0002] Coal mines are the main source of energy in my country. During the coal mining process, gas extraction from coal seams is an important part of ensuring mine safety. However, for low-permeability and soft coal seams, due to their special physical properties, such as coal body fragmentation, low permeability, and high gas content, gas extraction efficiency is low, and may even cause safety hazards such as gas accumulation and gas explosion.

[0003] In order to overcome the difficulties of low-permeability and soft coal seams in gas extraction, researchers have been exploring new coal seam treatment methods. The coal seam permeability enhancement technologies currently used mainly include hydraulic fracturing, hydraulic slitting, pre-splitting blasting, loosening blasting, hydraulic punching, liquid nitrogen freeze-thaw fracturing, etc. The above methods can improve the permeability of coal seams to a certain extent and enhance gas extraction, but these methods themselves also have certain limitations.

[0004] Existing blasting technologies include pre-splitting blasting, loosening blasting, concentrated energy blasting and CO2 phase change blasting, all of which have the problem of poor fracturing effect due to the collapse of soft coal seams. Loosening blasting and pre-splitting blasting technologies produce greater pollution when increasing the permeability of coal bodies, and are prone to local excessive pressure or open flames, and gas explosion accidents when the gas in the tunnel exceeds the limit. Loosening blasting technology is mostly used for hard coal seams with weak protrusion strength.

[0005] In recent years, liquid nitrogen freezing technology has been gaining attention due to its technical advantages such as low consumption and no pollution. Compared with other unconventional oil and gas reservoirs, coal seams have strong heterogeneity and weak mechanical properties, which are more conducive to enhancing the damage effect of liquid nitrogen cryogenics. Therefore, applying liquid nitrogen to coal seam permeability enhancement will achieve better results. However, the existing liquid nitrogen fracturing technology mainly involves liquid nitrogen cycle freeze-thaw, which deteriorates the mechanical properties of coal, promotes the development of coal rock pores and cracks, increases permeability, and improves gas extraction rate. However, since liquid nitrogen cycle freeze-thaw technology requires dozens of cycles to achieve the permeability enhancement effect, it has the disadvantages of high cost, long time, and excessive nitrogen causing the oxygen concentration to drop. Summary of the invention

[0006] The purpose of the present invention is to provide a liquid nitrogen freezing combined with carbon dioxide blasting anti-reflection device and anti-reflection method, which can freeze liquid nitrogen and liquid CO 2 The two methods of gas phase explosion are combined into one, so that the liquid nitrogen can be quickly CO2-freezed in the same area after freezing. 2 Gas phase blasting simplifies the operation process of the two permeability enhancement methods and has a good promoting effect on gas extraction.

[0007] In order to achieve the above-mentioned purpose, the present invention provides a liquid nitrogen freezing combined with carbon dioxide blasting anti-reflection device, comprising a freezing tube and at least one anti-reflection component; the cross-sectional shape of the freezing tube is U-shaped; the anti-reflection component is installed on the inner side of the freezing tube; the anti-reflection component comprises a flexible airbag, an excitation device and two sealing positioning rings; the two sealing positioning rings are respectively sleeved on the outer sides of the two ends of the flexible airbag, and the ends of the flexible airbag extend to the outer sides of the sealing positioning rings, which are extended sections; the outer sleeve of the sealing positioning ring is sleeved with an end head, the inner side surface of the end head and the outer side surface of the sealing positioning ring are threadedly connected and fixed, and the sealing positioning ring squeezes and fixes the extended section of the flexible airbag on the end head; the outer side of the end head is fixedly connected to the freezing tube; the excitation device is arranged inside the flexible airbag; a fuse is installed on the excitation device, and the fuse runs through the end head.

[0008] The invention provides a liquid inlet at one end of the freezing pipe and a liquid outlet at the other end; a liquid outlet control valve is installed at the liquid outlet.

[0009] The anti-reflection components of the present invention are configured in plurality; the plurality of anti-reflection components are arranged in series inside the freezing tube; and the ignition wires of two adjacent excitation devices are connected.

[0010] The cross-sectional shape of the end head of the present invention is H-shaped; a circular partition is arranged in the middle of the end head, and the outer side surface of the circular partition is fixedly connected to the inner side surface of the end head; the two sealing positioning rings close to each other in two adjacent anti-reflection components are installed on both sides of the circular partition of the same end head.

[0011] The circular partition of the present invention is provided with a liquid filling tube, which penetrates through the circular partition.

[0012] A liquid supply unit is connected to the liquid inlet of the freezing tube; the liquid supply unit includes a liquid nitrogen tank, a liquid nitrogen valve, a flow monitor, a pressure detector, an insulated stainless steel hose and a liquid nitrogen distributor; the liquid nitrogen distributor is connected to the liquid inlet; both ends of the insulated stainless steel hose are connected to the liquid nitrogen distributor and the liquid nitrogen tank; the liquid nitrogen valve, the flow monitor and the pressure detector are installed on the liquid nitrogen tank.

[0013] A liquid nitrogen freezing combined with carbon dioxide blasting permeability enhancement method comprises the following steps: S1. Drilling: construct freezing blasting holes, extraction holes, and temperature measurement holes in coal seams; S2, water injection: inject water into the freezing blasting hole to moisten the coal body; S3. Establish an integrated freezing and blasting system: place the connected liquid nitrogen freezing combined with carbon dioxide blasting permeability enhancement device into the freezing and blasting hole, place the extraction pipe into the extraction hole, and place the temperature sensor into the temperature measuring hole; connect the freezing pipe to the liquid nitrogen distributor and connect it to the liquid nitrogen tank through an insulated stainless steel hose; S4, hole sealing: grouting and sealing the freezing blasting hole and the outer section of the extraction hole to form a grouting and hole sealing section; S5. Freezing: Open the liquid nitrogen valve to allow the liquid nitrogen in the liquid nitrogen tank to enter the liquid nitrogen distributor through the heat-insulating stainless steel hose and enter the freezing pipe from the liquid inlet. The liquid nitrogen gradually gasifies into nitrogen in the freezing pipe, absorbs the heat of the coal seam, and freezes and embrittles the coal seam. When the pressure monitor detects that the liquid nitrogen pressure rises to a predetermined value, the liquid outlet control valve of the freezing pipe opens, and the nitrogen is discharged from the liquid outlet through the freezing pipe. During the liquid injection process, the amount of liquid nitrogen is adjusted by the flow monitor. S6, filling: After a certain period of freezing, the temperature of the temperature sensor of the temperature measuring hole reaches below 5°C, and after being below 5°C for 1 hour, close the liquid nitrogen valve and stop injecting liquid nitrogen; fill liquid CO2 through the filling pipe, and CO2 enters the flexible airbag; S7. Blasting: The blasting is carried out by detonating the excitation device through the fuse, and the liquid CO2 rapidly expands and transforms into gas. The formed high-pressure gas directly acts on the frozen hole wall, and the rock mass cracks, thus achieving rock mass fracturing; S8. Extraction: Within 48 hours after the blasting, the high-pressure CO2 gas in the frozen blasting hole is allowed to fully replace and displace the CH4 in the coal to achieve the purpose of enhanced gas extraction; at the same time, the frozen coal body is fully thawed and restored to normal temperature to achieve the effect of freeze-thaw cracking of the coal body; after 48 hours, gas extraction is carried out through the extraction pipe.

[0014] Preferably, the extraction hole is more than 5m away from the freezing blasting hole; and the temperature measuring hole is 2m away from the freezing blasting hole.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1) Easy operation: Compared with other combined permeability enhancement methods, it avoids the complicated process caused by the use of multiple permeability enhancement methods together, and freezing and blasting can be implemented in the same borehole. The entire operation process includes steps such as freezing, blasting and extraction. The steps are clear and the operation is simple. The operating parameters can be flexibly adjusted according to the actual situation to adapt to the mining conditions of different coal seams.

[0016] 2) High economic benefits: Compared with liquid nitrogen freezing and liquid CO 2 The two permeability enhancement measures of blasting are carried out in different boreholes. The integrated permeability enhancement device and method greatly improve the liquid nitrogen and liquid CO 2 It can improve the utilization rate and avoid freezing and poor blasting effect caused by distance problems between different drill holes; and the flexible airbag has low production cost, is easy to bend and fold, and is convenient to transport.

[0017] 3) Coal body structure reinforcement: Through the low-temperature freezing process, the water inside the coal body freezes and expands in volume, which effectively reinforces the coal body structure and enhances its mechanical strength, making the coal body more stable in subsequent operations.

[0018] 4) Improve the brittleness of coal: The low temperature effect of liquid nitrogen changes the internal microstructure of the coal, and the brittleness of the coal is increased. 2 During phase change blasting, more cracks can be produced in the coal seam, thereby improving the efficiency of gas extraction.

[0019] 5) Avoiding hole collapse: The mechanical strength of the coal mass is enhanced to 2 During the phase change blasting process, the hole collapse phenomenon caused by the soft coal quality was effectively avoided, ensuring the safety and efficiency of the blasting operation.

[0020] 6) Improve the fracturing and permeability-enhancing effect: The significant increase in coal brittleness makes CO 2 After blasting, more cracks can be generated in the coal seam. These cracks provide more circulation channels for gas, greatly improving the fracturing and permeability-enhancing effect of the coal seam. The flexible pipe body can be cut according to the designed length, and has good applicability to the drilling length. At the same time, the flexible pipe body fits tightly with the drill hole after expansion, reducing the gap between the traditional rigid fracturing pipe and the blast hole, and the fracturing effect is good.

[0021] 7) Enhanced gas extraction: After the blasting is completed, the blasting pipe valve is tightly closed for 48 hours to allow the high-pressure CO in the blasting hole to 2 The gas fully replaces and displaces CH in the coal 4 , which effectively strengthens the gas extraction process and improves the gas recovery rate.

[0022] 8) Secondary fracturing effect: The freeze-thaw deterioration of the coal seam after freezing will cause the mechanical properties of the coal seam to decrease when the coal seam returns to normal temperature, thereby causing the coal body to fracture again, achieving secondary fracturing and further improving the efficiency and effectiveness of gas extraction.

[0023] 9) Strong practicality: The flexible airbag cooperates with the sealing positioning ring to facilitate the assembly of the flexible airbag. Multiple flexible airbags can be connected in series to adapt to different drilling lengths. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the structure of the present invention; Figure 2 It is a cross-sectional structural diagram of the present invention; Figure 3 It is a schematic diagram of the specific use of the present invention.

[0025] 1. Freezing pipe, 2. Liquid inlet, 3. Liquid outlet, 4. Liquid outlet control valve, 5. End, 6. Sealing positioning ring, 7. Flexible airbag, 8. Excitation device, 9. Ignition wire, 10. Liquid filling pipe, 11. Pipe clamp, 12. Coal seam, 13. Grouting sealing section, 14. Freezing blasting hole, 15. Extraction hole, 16. Extraction pipe, 17. Temperature measuring hole, 18. Temperature sensor, 19. Liquid nitrogen tank, 20. Liquid nitrogen valve, 21. Flow monitor, 22. Pressure detector, 23. Insulated stainless steel hose, 24. Liquid nitrogen dispenser. DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with the accompanying drawings. Example

[0027] like Figure 1 , Figure 2 As shown, a liquid nitrogen freezing combined with carbon dioxide blasting anti-reflection device comprises a freezing tube 1 and at least one anti-reflection component; the cross-sectional shape of the freezing tube 1 is U-shaped; the anti-reflection component is installed on the inner side of the freezing tube 1; the anti-reflection component comprises a flexible airbag 7, an excitation device 8 and two sealing positioning rings 6; the two sealing positioning rings 6 are respectively sleeved on the outer sides of the two ends of the flexible airbag 7, and the ends of the flexible airbag 7 extend to the outer sides of the sealing positioning rings 6, which are extended sections; the outer sleeve of the sealing positioning ring 6 is sleeved with an end cap 5, and the inner side surface of the end cap 5 and the outer side surface of the sealing positioning ring 6 are threadedly connected and fixed, and the sealing positioning ring 6 squeezes and fixes the extended section of the flexible airbag 7 on the end cap 5, and seals and fixes the flexible airbag 7; the outer side of the end cap 5 is fixedly connected to the freezing tube 1; the excitation device 8 is arranged inside the flexible airbag 7; a ignition wire 9 is installed on the excitation device 8, and the ignition wire 9 runs through the end cap 5.

[0028] The flexible airbag 7 is made of rubber or plastic material and has a certain deformation capability.

[0029] In this embodiment, a liquid inlet 2 is provided at one end of the freezing tube 1, and a liquid outlet 3 is provided at the other end. Liquid nitrogen is injected from the liquid inlet 2 and flows out from the liquid outlet 3. A liquid outlet control valve 4 is installed at the liquid outlet 3 to control the flow rate of the liquid nitrogen so that it can be fully vaporized and cooled inside the coal body.

[0030] In this embodiment, multiple anti-reflection assemblies are configured; multiple anti-reflection assemblies are arranged in series inside the freezing tube 1; the ignition wires 9 of two adjacent excitation devices 8 are connected. In this example, two groups are connected in series, and the number of series groups can be increased or decreased according to the drilling situation to adapt to the mine conditions.

[0031] In this embodiment, the cross-sectional shape of the end cap 5 is H-shaped; a circular partition is provided in the middle of the end cap 5, and the outer side surface of the circular partition is fixedly connected to the inner side surface of the end cap 5; two sealing positioning rings 6 close to each other in two adjacent anti-reflection components are installed on both sides of the circular partition of the same end cap 5.

[0032] In this embodiment, a liquid filling pipe 10 is installed on the circular partition. The liquid filling pipe 10 is a one-way valve. 2 It can only flow in but not out, preventing air leakage during inflation; the filling pipe 10 is set through the circular partition; the length of the filling pipe 10 can be extended according to the sealing needs, so that liquid CO can be injected after the hole is sealed. 2 .

[0033] In this embodiment, the liquid inlet 2 of the freezing tube 1 is connected to a liquid supply unit; the liquid supply unit includes a liquid nitrogen tank 19, a liquid nitrogen valve 20, a flow monitor 21, a pressure detector 22, an insulated stainless steel hose 23 and a liquid nitrogen distributor 24; the liquid nitrogen distributor 24 is connected to the liquid inlet 2; both ends of the insulated stainless steel hose 23 are connected to the liquid nitrogen distributor 24 and the liquid nitrogen tank 19; the liquid nitrogen valve 20, the flow monitor 21, and the pressure detector 22 are installed on the liquid nitrogen tank 19. Example

[0034] like Figure 3 As shown, a liquid nitrogen freezing combined with carbon dioxide blasting permeability enhancement method comprises the following steps: S1. Drilling: Construct freezing blasting holes 14, extraction holes 15 and temperature measuring holes 17 in the coal seam 12. In this embodiment, the extraction hole 15 is more than 5 m away from the freezing blasting hole 1 to prevent the collapse caused by the blasting from affecting the extraction pipe 16; the temperature measuring hole 17 is 2 m away from the freezing blasting hole 1.

[0035] S2, water injection: injecting water into the freezing blasting hole 14 to moisten the coal body; S3, establish a freezing and blasting integrated system: put the connected liquid nitrogen freezing combined with carbon dioxide blasting and permeability enhancement device into the freezing and blasting hole 14, put the extraction pipe 16 into the extraction hole 15, and put the temperature sensor into the temperature measuring hole 17; the freezing pipe 1 is connected to the liquid nitrogen distributor 24 and connected to the liquid nitrogen tank 19 through the heat-insulating stainless steel hose 23; S4, hole sealing: grouting and sealing the outer sections of the freezing blasting hole 14 and the extraction hole 15 to form a grouting and hole sealing section 13; S5, freezing: open the liquid nitrogen valve 20, so that the liquid nitrogen in the liquid nitrogen tank 19 enters the liquid nitrogen distributor 24 through the heat-insulating stainless steel hose 23, and enters the freezing pipe 1 from the liquid inlet 2. The liquid nitrogen gradually gasifies into nitrogen in the freezing pipe 1, absorbs the heat of the coal seam 12, and freezes and embrittles the coal seam 12; when the pressure monitor 22 on the liquid nitrogen tank 19 detects that the liquid nitrogen pressure rises to a predetermined value, the liquid outlet control valve 4 of the return air part of the freezing pipe 1 is opened, and the nitrogen is discharged from the liquid outlet 3 through the freezing pipe 1; during the liquid injection process, the amount of liquid nitrogen is adjusted by the flow monitor 21 on the liquid nitrogen tank 19; S6, filling: After a certain period of freezing, the temperature of the temperature sensor of the temperature measuring hole 17 reaches below 5°C, and after being below 5°C for 1 hour, close the liquid nitrogen valve 20 and stop injecting liquid nitrogen; fill the liquid CO through the filling pipe 10. 2 , liquid CO 2 When multiple anti-reflection components are installed in series, the bottom liquid filling tube 10 is installed in a one-way air intake mode from outside to inside, and carbon dioxide enters other flexible air bags 7 through the middle liquid filling tube 10 without leakage, and finally the flexible air bags 7 of the entire liquid nitrogen freezing combined with carbon dioxide blasting anti-reflection device are all filled with isobaric liquid CO 2 ; S7, blasting: blasting by detonating the excitation device 8 through the ignition wire 9, liquid CO 2 Rapid expansion and conversion into gaseous state, the high-pressure gas formed directly acts on the frozen hole wall, causing the rock mass to crack, thus achieving rock mass fracturing; S8, extraction: within 48 hours after the blasting, freeze the high-pressure CO in the blasting hole 14. 2 The gas fully replaces and displaces CH in the coal body. 4 , to achieve the purpose of strengthening gas extraction; at the same time, the frozen coal body is fully thawed and restored to normal temperature, achieving the effect of freeze-thaw cracking of the coal body; after 48 hours, gas extraction is carried out through the extraction pipe 16.

[0036] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A liquid nitrogen freezing combined with carbon dioxide blasting and permeability enhancement device, characterized in that: The invention comprises a freezing tube (1) and at least one anti-reflection component; the freezing tube (1) has a U-shaped cross-section; the anti-reflection component is installed on the inner side of the freezing tube (1); the anti-reflection component comprises a flexible airbag (7), an excitation device (8) and two sealing positioning rings (6); the two sealing positioning rings (6) are respectively sleeved on the outer sides of both ends of the flexible airbag (7), and the ends of the flexible airbag (7) extend to the outer sides of the sealing positioning rings (6) to form an extension section; an end head (5) is sleeved and installed on the outer side of the sealing positioning ring (6), the inner side surface of the end head (5) and the outer side surface of the sealing positioning ring (6) are threadedly connected and fixed, and the sealing positioning ring (6) squeezes and fixes the extension section of the flexible airbag (7) on the end head (5); the outer side of the end head (5) is fixedly connected to the freezing tube (1); the excitation device (8) is arranged inside the flexible airbag (7); an ignition wire (9) is installed on the ignition device (8), and the ignition wire (9) passes through the end head (5).

2. A liquid nitrogen freezing combined with carbon dioxide blasting anti-reflection device according to claim 1, characterized in that: One end of the freezing pipe (1) is provided with a liquid inlet (2), and the other end is provided with a liquid outlet (3); a liquid outlet control valve (4) is installed at the liquid outlet (3).

3. The liquid nitrogen freezing combined with carbon dioxide blasting anti-reflection device according to claim 1, characterized in that: The anti-reflection components are configured in plurality; the plurality of anti-reflection components are arranged in series on the inner side of the freezing tube (1); and the ignition wires (9) of two adjacent excitation devices (8) are connected.

4. A liquid nitrogen freezing combined with carbon dioxide blasting anti-reflection device according to claim 3, characterized in that: The cross-sectional shape of the end head (5) is H-shaped; a circular partition is provided in the middle of the end head (5), and the outer side surface of the circular partition is fixedly connected to the inner side surface of the end head (5); and two sealing positioning rings (6) close to each other in two adjacent anti-reflection assemblies are installed on both sides of the circular partition of the same end head (5).

5. A liquid nitrogen freezing combined with carbon dioxide blasting anti-reflection device according to claim 4, characterized in that: A liquid filling tube (10) is installed on the circular partition; the liquid filling tube (10) is arranged to penetrate the circular partition.

6. The liquid nitrogen freezing combined with carbon dioxide blasting anti-reflection device according to claim 2, characterized in that: The liquid inlet (2) of the freezing tube (1) is connected to a liquid supply unit; the liquid supply unit comprises a liquid nitrogen tank (19), a liquid nitrogen valve (20), a flow monitor (21), a pressure detector (22), a heat-insulating stainless steel hose (23) and a liquid nitrogen distributor (24); the liquid nitrogen distributor (24) is connected to the liquid inlet (2); both ends of the heat-insulating stainless steel hose (23) are connected to the liquid nitrogen distributor (24) and the liquid nitrogen tank (19); the liquid nitrogen valve (20), the flow monitor (21) and the pressure detector (22) are installed on the liquid nitrogen tank (19).

7. A liquid nitrogen freezing combined with carbon dioxide blasting permeability enhancement method, characterized in that: The following steps are involved: S1. Drilling: constructing freezing blasting holes (14), extraction holes (15), and temperature measurement holes (17) in the coal seam (12); S2, water injection: injecting water into the freezing blasting hole (14) to moisten the coal body; S3. Establishing a freezing and blasting integrated system: placing the connected liquid nitrogen freezing combined with carbon dioxide blasting and permeability enhancement device into the freezing and blasting hole (14), placing the extraction pipe (16) into the extraction hole (15), and placing the temperature sensor into the temperature measuring hole (17); connecting the freezing pipe (1) to the liquid nitrogen distributor (24) and connecting to the liquid nitrogen tank (19) through the heat-insulating stainless steel hose (23); S4, hole sealing: grouting and sealing the outer sections of the freezing blasting hole (14) and the extraction hole (15) to form a grouting and hole sealing section (13); S5, freezing: opening the liquid nitrogen valve (20), allowing the liquid nitrogen in the liquid nitrogen tank (19) to enter the liquid nitrogen distributor (24) through the heat-insulating stainless steel hose (23), and enter the freezing pipe (1) from the liquid inlet (2), and the liquid nitrogen gradually gasifies into nitrogen in the freezing pipe (1), absorbs the heat of the coal seam (12), and freezes and embrittles the coal seam (12); when the pressure monitor detects that the liquid nitrogen pressure rises to a predetermined value, the liquid outlet control valve (4) of the freezing pipe (1) is opened, and the nitrogen is discharged from the liquid outlet (3) through the freezing pipe (1); during the liquid injection process, the amount of liquid nitrogen is adjusted by the flow monitor (21); S6, filling: after a certain period of freezing, the temperature of the temperature sensor of the temperature measuring hole (17) reaches below 5°C, and after being below 5°C for 1 hour, the liquid nitrogen valve (20) is closed and the injection of liquid nitrogen is stopped; liquid CO2 is filled through the filling pipe (10), and the CO2 enters the flexible airbag (7); S7, blasting: the ignition wire (9) detonates the excitation device (8) to blast, and the liquid CO2 rapidly expands and transforms into gaseous state, and the formed high-pressure gas directly acts on the frozen hole wall, causing the rock mass to crack, thereby achieving rock mass fracturing; S8. Extraction: Within 48 hours after the blasting is completed, the high-pressure CO2 gas in the frozen blasting hole (14) is allowed to fully replace and displace the CH4 in the coal, and at the same time, the frozen coal body is fully thawed and restored to normal temperature. After 48 hours, gas extraction is carried out through the extraction pipe (16).

8. A liquid nitrogen freezing combined with carbon dioxide blasting permeability enhancement method according to claim 7, characterized in that: The extraction hole (15) is at least 5 m away from the freezing blasting hole (14); and the temperature measuring hole (17) is 2 m away from the freezing blasting hole (14).

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