A gas extraction device for soft coal seam and construction method

Abstract

This invention discloses a gas drainage device and construction method for soft coal seams, integrating the three major processes of borehole protection construction, leakage detection, and gas drainage into the field of gas drainage. It employs a first-section borehole protection pipe, multiple intermediate sections, and a final-section borehole protection pipe that can be assembled sequentially to support the borehole, while also providing the main support for the leakage monitoring mechanism, gas drainage pipeline, and grouting pipeline. It is also lightweight and energy-absorbing. A leakage monitoring device embedded in the first-section borehole protection pipe works in conjunction with an ultra-high-pressure bag for leakage detection, and the injection volume of non-condensable materials is controlled in a linked manner, thereby improving the quality of gas drainage concentration in a single borehole. This invention integrates leakage monitoring, energy-absorbing borehole protection, and gas drainage technologies into one unit, improving the efficiency of gas drainage in soft coal seams. Furthermore, the device is reusable and can overcome problems such as borehole collapse, borehole deformation, and leakage caused by inadequate sealing in the field of gas drainage.

Description

Technical Field

[0001] This invention relates to a gas extraction device and method, specifically to a gas extraction device and construction method for soft coal seams, belonging to the field of gas extraction. Background Technology

[0002] Gas drainage is not only the most effective means of preventing gas outburst disasters, but also the most basic technology for realizing gas utilization. However, the collapse of holes in soft coal seams, deformation of boreholes, and gas leakage caused by inadequate sealing have become technical barriers restricting the development of the gas drainage industry.

[0003] Currently, the main measure to prevent borehole collapse and deformation in soft coal seams is to insert protective pipes into pre-drilled boreholes for gas drainage. Traditional protective pipes are mainly made of iron or plastic. However, due to the extremely humid environment, high-stress complex environment, and confined working space in mines, iron is prone to corrosion, and plastic is prone to borehole deformation and collapse under high stress, seriously hindering the development of the gas drainage industry. Foamed concrete energy absorption technology is developing rapidly and has been applied in many industries, such as airport safety foamed concrete energy-absorbing panels, racetrack safety foamed concrete energy-absorbing panels and blocks, and safety foamed concrete energy-absorbing panels or blocks in accident-prone areas of highways. TPU granules are widely used in industrial manufacturing and are internationally recognized as one of the most environmentally friendly materials. A typical multi-block copolymer, its block structure of flexible and rigid segments determines its unique properties, exhibiting high strength and elasticity; excellent wear resistance, 2-10 times that of natural rubber; and superior performance compared to traditional plastic foams in terms of strength, elasticity, and wear resistance. The use of TPU granules in lightweight concrete production, and subsequently in coal mine borehole protection construction, has great development potential.

[0004] In the field of gas extraction from soft coal seams, borehole protection construction, leak detection, and gas extraction are three independent processes. On the one hand, it is impossible to use sealing materials to accurately seal the cracks around the borehole, resulting in a reduction in the service life of the borehole. On the other hand, the independent completion of the three processes results in a huge waste of manpower and material resources. Summary of the Invention

[0005] The purpose of this invention is to provide a gas extraction device and construction method for soft coal seams, which integrates the three major processes of borehole protection construction, gas leakage detection and gas extraction, and solves the problems of short effective extraction time, low extraction concentration and borehole collapse and deformation in the gas extraction process of soft coal seams.

[0006] To achieve the above objectives, the present invention provides a gas extraction device for soft coal seams, comprising:

[0007] The protective tube includes a first protective tube section, multiple intermediate protective tube sections, and a tail protective tube section, which can be assembled sequentially from front to back.

[0008] The first section of the protective pipe includes an inner pipe A and an outer pipe A. A conical mesh protective cover is installed at the front end of the first section of the protective pipe. A first ultra-high pressure bag and a leakage monitoring device are arranged sequentially near the conical mesh protective cover. The first ultra-high pressure bag is annularly fitted onto the outer wall of the inner pipe A and is connected to an external water pump through a water injection pipe installed inside the inner pipe A. An outer pipe A, coaxial with the inner pipe A, is installed in front of and behind the first ultra-high pressure bag in the axial direction. Lightweight buffer concrete is filled between the inner pipe A and the outer pipe A.

[0009] The air leakage monitoring device is installed in the lightweight buffer concrete behind the first ultra-high pressure bag. It includes an air outlet at the front, penetrating the wall of the first section of the protective tube; an air inlet at the rear, also penetrating the wall of the first section of the protective tube; and a connecting hole inside the lightweight buffer concrete connecting the air outlet and the air inlet. The air inlet and outlet are each provided with a lightweight, self-opening cover at one end near the inner wall of the first section of the protective tube, and a coal dust screen at the other end near the outer wall of the first section of the protective tube. The first section of the protective tube contains high-pressure water nozzles corresponding to the air inlet and outlet, controlled by a high-pressure water solenoid valve. The high-pressure water solenoid valve is electrically connected to a terminal controller and to the water injection pipe. An airflow sensor is installed inside the connecting hole.

[0010] The tail section protective tube includes an inner tube B and a second ultra-high pressure bag. The second ultra-high pressure bag is annularly fitted onto the tail end of the outer wall of the inner tube B and is connected to the water injection pump through the water injection pipe. An outer tube B, coaxial with the inner tube B, is installed in front of the second ultra-high pressure bag in the axial direction. Lightweight buffer concrete is filled between the inner tube B and the outer tube B. Both the first ultra-high pressure bag and the second ultra-high pressure bag are controlled by switch A.

[0011] The intermediate protective pipe includes an inner pipe C, an outer pipe C coaxially fitted outside the inner pipe, and lightweight buffer concrete filling the space between the inner pipe C and the outer pipe C; stress patches are attached to the outer wall of the intermediate protective pipe; a grouting port penetrating the wall of the intermediate protective pipe is provided on the intermediate protective pipe, and the grouting port is connected to an external grouting pump through a grouting pipe; a solenoid valve is installed at the grouting port, and a switch C is installed on the grouting pipe; the grouting material is a non-curing grout with a viscosity of 6000-8000 Pa·S.

[0012] The extraction pipe is located inside the first section of the protective pipe, the middle section of the protective pipe, and the last section of the protective pipe, and the inner diameter of the extraction pipe is smaller than the inner diameter of the first section of the protective pipe, the middle section of the protective pipe, and the last section of the protective pipe; a gas concentration sensor is installed inside the extraction pipe; an internal pipeline space is formed between the extraction pipe and the first section of the protective pipe, the middle section of the protective pipe, and the last section of the protective pipe for accommodating the water injection pipe and the grouting pipe. A high-pressure gas pipe is also installed in this internal pipeline space. The first end of the high-pressure gas pipe extends into the conical mesh protective cover in front of the first section of the protective pipe and is equipped with a high-pressure gas nozzle. The last end is connected to an external air compressor and controlled by switch B; a tray for sealing the last end of the last section of the protective pipe and the internal pipeline space is fitted on the extraction pipe.

[0013] Switches A, B, and C, the gas concentration sensor, and the stress patch are all electrically connected to the terminal controller, and an alarm is also provided that is electrically connected to the terminal controller.

[0014] Preferably, the built-in pipe space is also equipped with a sewage drainage trough for draining the water sprayed from the high-pressure water nozzle.

[0015] Preferably, the lightweight buffer concrete comprises cement, sand, fiber, ceramsite, TPU particles, and bentonite in a weight ratio of 3:5-7:0.05:0.5:2:0.2-0.5 and a water-cement ratio of 0.7-0.8.

[0016] Preferably, the inner tube is a thin-walled iron pipe, and the outer tube is a thin-walled PVC pipe.

[0017] A method for gas extraction in soft coal seams, using the aforementioned gas extraction device for soft coal seams, includes the following steps:

[0018] S1: Install the first section of the protective tube, multiple intermediate sections of the protective tube, and the tail section of the protective tube.

[0019] The first section of the protective pipe is slowly inserted into the preset gas extraction hole, and switch B is turned on. High-pressure air is sprayed out from the high-pressure gas nozzle, which carries the coal debris in the hole into the first section of the protective pipe and sends it out of the hole.

[0020] After the first section of the protective casing is fully inserted into the pre-set gas drainage hole and is 50mm from the hole opening, close switch B. Connect the first intermediate section of the protective casing to the first section of the protective casing, then open switch B and slowly push the first section of the protective casing into the pre-set gas drainage hole. After the first intermediate section of the protective casing is inserted into the pre-set gas drainage hole, close switch B. Connect the second intermediate section of the protective casing to the first intermediate section of the protective casing, open switch B, and insert the second section of the protective casing into the pre-set gas drainage hole. Repeat this process until all intermediate protective casings are inserted into the pre-set gas drainage holes.

[0021] After all intermediate protective pipes have entered the preset gas drainage hole, connect the tail section protective pipe and send the tail section protective pipe into the preset gas drainage hole. Close switch B, put the drainage pipe into the first section protective pipe, multiple intermediate protective pipes, and tail section protective pipe, install the tray, seal the opening of the preset gas drainage hole, and then connect the drainage pipe into the underground drainage network.

[0022] S2: Check if the preset gas extraction hole is leaking.

[0023] Start the water injection pump and open switch A. High-pressure water enters the first and second ultra-high-pressure bags, causing them to expand and adhere tightly to the borehole wall of the preset gas extraction hole, maintaining a certain pressure. Start the grouting pump and open switch C and the solenoid valve, allowing non-coagulating grout to be injected through the grouting port into the gap between the protective pipe and the preset gas extraction hole, as well as into the cracks on the borehole wall. After grouting, the solenoid valve automatically closes.

[0024] The air volume is recorded by the air volume sensor on the air leakage monitoring device to determine whether the preset gas extraction hole is leaking. If there is a leak, grouting continues until there is no leak.

[0025] S3: Negative pressure high-efficiency gas extraction:

[0026] The gas extraction network is activated, and gas is extracted through the extraction pipe. At the same time, the air volume sensor records the gas leakage in real time. When the stress data monitored by the stress patch is greater than the preset value, a signal is sent to the grouting solenoid valve to start working. After grouting continues for a certain period of time, the solenoid valve is automatically closed.

[0027] S4: When the gas sensor detects that the gas content is lower than the preset value, the alarm will sound. After 10-20 minutes of waiting for the alarm to sound, the extraction will be stopped, the excess slurry used for sealing will be discharged, the bag will change from an inflated state to its original state, the excess water will be discharged into the roadway, the equipment will be slowly removed for reuse, and the borehole opening will be sealed with cement mortar.

[0028] Furthermore, in step S2, if the air volume sensor data is 0, it means that the preset borehole sealing quality is good. The terminal controller will open the high-pressure nozzle after 20 minutes of timing, and the working time is 2 minutes to flush the coal dust screen of the air outlet and air inlet.

[0029] The borehole casing used in this invention has good compressive strength and elasticity, which can greatly reduce the occurrence of borehole collapse and drilling deformation, and improve the service life of gas drainage boreholes; it also has a lower density than iron borehole casing, which can reduce the complexity of the borehole casing construction process to a certain extent.

[0030] This invention features automatic gas leakage monitoring and grouting interlock control, as well as ultra-high pressure bag plugging function. It can form a well-sealed space between the extraction device and the preset gas extraction hole, preventing the formation of gas leakage channels. By setting up a gas leakage monitoring device in the sealed space formed by two ultra-high pressure bags on the protective pipe, the gas leakage detection is carried out, and the injection amount of non-condensable material is controlled in a linked manner. This can improve the concentration and quality of gas extraction in a single hole and reduce the cost of gas extraction.

[0031] Advantages: This invention integrates gas leakage monitoring, high-pressure sealing, and energy-absorbing borehole protection technologies, combining these technologies to improve the extraction effect of soft coal seams. At the same time, the device is reusable and can overcome gas leakage problems caused by borehole collapse, borehole deformation, and inadequate sealing. It has strong innovation and practical applicability, and can effectively promote the development of the gas extraction industry. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the axial side structure of the first section of the protective tube in this invention;

[0033] Figure 2 This is a schematic diagram of the axial side structure of the intermediate protective tube in this invention;

[0034] Figure 3 This is a schematic diagram of the axial side structure of the tail section protective tube in this invention;

[0035] Figure 4 This is a schematic diagram of the structure of a gas extraction device for soft coal seams according to the present invention;

[0036] Figure 5 This is a schematic diagram of the installation and construction of the first section of the protective pipe in this invention;

[0037] Figure 6 This is a schematic diagram of the installation and construction of the intermediate protective hole pipe in this invention;

[0038] Figure 7 This is a schematic diagram illustrating the construction principle of gas extraction in soft coal seams according to the present invention.

[0039] Figure 8 yes Figure 7 A magnified view of region Z in the middle;

[0040] In the picture:

[0041] 1. First section of protective pipe; 11. Inner pipe A; 12. Outer pipe A; 13. First ultra-high pressure bag; 131. Water injection pipe; 132. Water injection pump; 14. Leakage monitoring device; 141. Air inlet; 142. Coal dust screen; 143. Connection hole; 144. Air volume sensor; 145. Lightweight cover plate; 146. Air outlet; 15. High-pressure water nozzle; 151. Sewage drainage trough; 16. High-pressure gas nozzle; 161. High-pressure gas pipe; 162. Air compressor; 17. Conical mesh protective cover;

[0042] 2. Intermediate protective pipe; 21. Inner pipe C; 23. Outer pipe C; 24. Grouting port; 241. Grouting solenoid valve; 242. Grouting pipe; 243. Grouting pump;

[0043] 3. Tail section protective tube; 31. Inner tube B; 33. Outer tube B; 34. Second ultra-high pressure bladder; 35. Tray;

[0044] 4. Lightweight buffer concrete;

[0045] 5. Terminal controller; 51. Alarm;

[0046] 6. Rock mass;

[0047] 7. Pre-set gas extraction holes;

[0048] 8. Cracks;

[0049] 9. Extraction tube. Detailed Implementation

[0050] The present invention will now be described in further detail with reference to the accompanying drawings.

[0051] like Figures 1 to 4 As shown, a gas extraction device for soft coal seams includes:

[0052] The borehole protection casing, used to protect and support the borehole, includes a first section of borehole protection casing 1, multiple intermediate sections of borehole protection casing 2, and a last section of borehole protection casing 3, which can be assembled sequentially. The borehole protection casing is the main component of the extraction device. The number of intermediate sections of borehole protection casing 2 can be selected according to the borehole depth, thereby adjusting the length of the borehole protection casing so that the first section of borehole protection casing 1 can reach the deepest point of the borehole, improving extraction efficiency. The first section of borehole protection casing 1, intermediate sections of borehole protection casing 2, and last section of borehole protection casing 3 can be assembled using a first-to-last threaded connection. The extraction pipe 9 is placed inside the borehole protection casing.

[0053] like Figure 1The first section of the borehole protection pipe 1 includes an inner pipe A11 and an outer pipe A12. A conical mesh protective cover 17 is installed at the front end of the first section of the borehole protection pipe 1. The conical mesh protective cover 17 can prevent coal dust from collapsing deep in the borehole from blocking the extraction pipe 9. A first ultra-high pressure bag 13 and a leakage monitoring device 14 are arranged in sequence near the conical mesh protective cover 17. The first ultra-high pressure bag 13 is ring-shaped and fitted on the outer wall of the inner pipe A11. It is connected to the external water injection pump 132 through a water injection pipe 131 set in the inner pipe A11. After the first ultra-high pressure bag 13 is filled with high-pressure water, it can expand and stick tightly to the inner wall of the borehole. The outer pipe A12, which is coaxial with the inner pipe A11, is installed in front of and behind the first ultra-high pressure bag 13 in the axial direction. Lightweight buffer concrete 4 is filled between the inner pipe A11 and the outer pipe A12.

[0054] like Figure 3 The tail section protective tube 3 includes an inner tube B31 and a second ultra-high pressure bag 34. The second ultra-high pressure bag 34 is annularly fitted onto the tail end of the outer wall of the inner tube B31 and is connected to the water injection pump 132 through a water injection pipe 131. An outer tube B33, coaxial with the inner tube B31, is installed in front of the second ultra-high pressure bag 34 in the axial direction. Lightweight buffer concrete 4 is filled between the inner tube B31 and the outer tube B33. The first ultra-high pressure bag 13 and the second ultra-high pressure bag 34 are both controlled by switch A. The working principle of the second ultra-high pressure bag 34 is the same as that of the first ultra-high pressure bag 13.

[0055] like Figure 2 The intermediate protective pipe 2 includes an inner pipe C21, an outer pipe C23 coaxially fitted outside the inner pipe, and lightweight buffer concrete 4 filling the space between the inner pipe C21 and the outer pipe C23; stress patches are attached to the outer wall of the intermediate protective pipe 2; a grouting port 24 penetrating the hole wall of the intermediate protective pipe 2 is provided on the intermediate protective pipe 2, and the grouting port 24 is connected to the external grouting pump 243 through the grouting pipe 242; a high-pressure water solenoid valve is provided at the grouting port 24, and a switch C is provided on the grouting pipe 242; the grouting material is a non-coagulating grout with a viscosity of 6000-8000 Pa·S.

[0056] When the second ultra-high pressure bag 34 and the first ultra-high pressure bag 13 are filled with high-pressure water, a sealed space is formed in the annular gap between the protective tube and the borehole between the second ultra-high pressure bag 34 and the first ultra-high pressure bag 13. This sealed space is filled with grouting material using the intermediate protective tube 2, thereby forming a seal on the borehole.

[0057] The structures of the first protective pipe 1, the middle protective pipe 2, and the tail protective pipe 3 are similar, all employing a structure where lightweight concrete is filled between the inner and outer pipes. All inner pipes, including inner pipe A11, inner pipe B31, and inner pipe C21, maintain the same material, thickness, and inner and outer diameters; all outer pipes, including outer pipe A12, outer pipe B33, and outer pipe C23, maintain the same material, thickness, and inner and outer diameters.

[0058] As a preferred embodiment, the lightweight buffer concrete 4 comprises cement, sand, fiber, ceramsite, TPU granules, and bentonite, with a weight ratio of 3:5-7:0.05:0.5:2:0.2-0.5 and a water-cement ratio of 0.7-0.8. The inner pipe can be made of thin-walled iron, and the outer pipe can be made of thin-walled PVC. This structure has excellent energy absorption properties, effectively coping with borehole deformation and thus protecting the extraction pipe 9 and other internal equipment.

[0059] like Figure 1 and Figure 8 As shown, the air leakage monitoring device 14 is installed in the lightweight buffer concrete 4 behind the first ultra-high pressure bag 13. It includes an air outlet 146 located at the front and penetrating the wall of the first section of the protective tube 1, an air inlet 141 located at the rear and penetrating the wall of the first section of the protective tube 1, and a connecting hole 143 located inside the lightweight buffer concrete 4 connecting the air outlet 146 and the air inlet 141. The air inlet 141 and the air outlet 146 are provided with a lightweight cover plate 145 that can be opened outward at one end near the inner wall of the first section of the protective tube 1, and a coal dust screen 142 is provided at one end near the outer wall of the first section of the protective tube 1. The first section of the protective tube 1 is provided with high-pressure water nozzles 15 corresponding to the air inlet 141 and the air outlet 146 respectively. The high-pressure water nozzles 15 are controlled by a high-pressure water solenoid valve, which is electrically connected to the terminal controller 5 and connected to the water injection pipe 131. An air volume sensor 144 is provided in the connecting hole 143.

[0060] The lightweight cover plate 145 can be kept closed by spring tension without any external force. The coal dust screen 142 mainly prevents larger particles on the borehole wall from clogging the air inlet 141 and air outlet 146. If coal dust or particles clog the air inlet 141 and air outlet 146, the high-pressure water nozzle 15 is activated, and the high-pressure water sprays out to open the lightweight cover plate 145, thus achieving the purpose of self-opening. The high-pressure water directly washes the coal dust screen 142, and the wastewater flows out through the air inlet and air outlet. After washing is completed and the high-pressure water stops, the lightweight cover plate 145 closes under the action of the spring.

[0061] The built-in pipe space is also equipped with a sewage drain trough 151 for draining water sprayed from the high-pressure water nozzle 15; sewage is discharged out of the borehole through the sewage drain trough 151.

[0062] The principle of the leak detection device 14 is as follows: Figure 8As shown, the lightweight cover plate 145 is normally closed, sealing the air inlet 141 and the end of the air outlet 146 near the inner wall of the first section of the borehole casing 1. If a crack 8 appears in the inner wall of the borehole, extending to the outside, the borehole is leaking. Due to the negative pressure of the extraction pipe 9, air will enter the air inlet 141 through the crack 8, and then re-enter the crack 8 through the outlet 146 via the connecting hole 143, eventually reaching the depth of the borehole. The presence of airflow monitored by the highly sensitive airflow sensor 144 indicates a leak in the borehole. Conversely, a lack of airflow indicates good sealing of the borehole. The sealing performance of the borehole directly affects the extraction efficiency.

[0063] The extraction pipe 9 is located inside the first section of the protective pipe 1, the intermediate protective pipe 2, and the last section of the protective pipe 3, and the inner diameter of the extraction pipe 9 is smaller than the inner diameter of the first section of the protective pipe 1, the intermediate protective pipe 2, and the last section of the protective pipe 3; a gas concentration sensor is installed inside the extraction pipe 9; an internal pipeline space is formed between the extraction pipe 9 and the first section of the protective pipe 1, the intermediate protective pipe 2, and the last section of the protective pipe 3 for accommodating the water injection pipe 131 and the grouting pipe 242. A high-pressure air pipe 161 is also installed in this internal pipeline space. The first end of the high-pressure air pipe 161 extends into the conical mesh protective cover 17 in front of the first section of the protective pipe 1 and is equipped with a high-pressure gas nozzle 16. The last end is connected to an external air compressor 162 and controlled by switch B; a tray 35 is fitted on the extraction pipe 9 to seal the last end of the last section of the protective pipe 3 and the internal pipeline space; the tray 35 has sealing performance.

[0064] When in use, the borehole protector is slowly inserted into the borehole, and the high-pressure gas nozzle 16 can spray high-pressure gas to remove coal dust and particles from the borehole. The airflow can carry the coal dust and particles out of the borehole from the borehole protector.

[0065] Switches A, B, and C, the gas concentration sensor, and the stress patch are all electrically connected to the terminal controller 5, and an alarm 51 electrically connected to the terminal controller 5 is also provided.

[0066] This invention also proposes a method for gas extraction in soft coal seams, such as... Figures 5 to 7 The above-mentioned gas extraction device for soft coal seams includes the following steps:

[0067] S1: Install the first section of the protective tube 1, multiple intermediate sections of the protective tube 2, and the last section of the protective tube 3.

[0068] like Figure 5 The first section of the protective pipe 1 is slowly sent into the preset gas extraction hole 7, and the switch B is turned on. High-pressure air is sprayed out from the high-pressure gas nozzle 16, which carries the coal debris in the hole into the first section of the protective pipe 1 and sends it out of the hole.

[0069] like Figure 6After the first section of the protective tube 1 is fully inserted into the preset gas extraction hole 7 and is 50mm away from the hole opening, close switch B, connect the first intermediate protective tube 2 to the first protective tube 1, open switch B, and slowly push the first protective tube 1 into the preset gas extraction hole 7; after the first intermediate protective tube 2 is inserted into the preset gas extraction hole 7, close switch B, connect the second intermediate protective tube 2 to the first intermediate protective tube 2, open switch B, and insert the second protective tube into the preset gas extraction hole 7; repeat this method until all intermediate protective tubes 2 are inserted into the preset gas extraction hole 7;

[0070] like Figure 7 After all the intermediate protective pipes 2 have entered the preset gas extraction hole 7, connect the tail section protective pipe 3 and send the tail section protective pipe 3 into the preset gas extraction hole 7. Close the switch B and put the extraction pipe 9 into the first section protective pipe 1, multiple intermediate protective pipes 2, and tail section protective pipe 3. Install the tray 35 to seal the opening of the preset gas extraction hole 7, and then connect the extraction pipe 9 into the underground extraction network.

[0071] S2: Check if the preset gas extraction hole 7 is leaking.

[0072] Start the water injection pump 132 and open switch A. High-pressure water enters the first ultra-high pressure bag 13 and the second ultra-high pressure bag 34, causing the first ultra-high pressure bag 13 and the second ultra-high pressure bag 34 to expand and adhere tightly to the borehole wall of the preset gas extraction hole 7, maintaining a certain pressure. Start the grouting pump 243 and open switch C and grouting solenoid valve 241, allowing non-coagulating grout to be injected through grouting port 24 into the gap 8 between the protective pipe and the preset gas extraction hole 7, as well as on the borehole wall of the preset gas extraction hole 7. After grouting, grouting solenoid valve 241 automatically closes.

[0073] The air volume is recorded by the air volume sensor 144 on the air leakage monitoring device 14 to determine whether the preset gas extraction hole 7 is leaking. If air volume is detected, it means that the preset gas extraction hole 7 is leaking. If there is a leak, grouting continues until there is no leak.

[0074] If the data of the air volume sensor 144 is 0, that is, no air volume is detected, it means that the preset borehole sealing quality is good. The terminal controller 5 will open the high-pressure nozzle after 20 minutes of timing, and the working time is 2 minutes to flush the coal dust screen 142 of the air outlet 146 and the air inlet 141.

[0075] S3: Negative pressure high-efficiency gas extraction:

[0076] The gas extraction network is activated, and gas is extracted through the extraction pipe 9. At the same time, the air volume sensor 144 records the gas leakage in real time. When the stress data monitored by the stress patch is greater than the preset value, a signal is sent to the grouting solenoid valve 241 to start working. After grouting continues for a certain period of time, the grouting solenoid valve 241 is automatically closed.

[0077] S4: When the gas sensor detects that the gas content is lower than the preset value, alarm 51 will sound. After 10-20 minutes of waiting for the alarm, the extraction will be stopped, the excess slurry used for sealing will be discharged, the bag will change from an expanded state to its original state, the excess water will be discharged into the roadway, the equipment will be slowly removed for reuse, and the borehole opening will be sealed with cement mortar.

[0078] The borehole casing used in this invention has good compressive strength and elasticity, which can greatly reduce the occurrence of borehole collapse and drilling deformation, and improve the service life of gas drainage boreholes; it also has a lower density than iron borehole casing, which can reduce the complexity of the borehole casing construction process to a certain extent.

[0079] This invention features automatic gas leakage monitoring and grouting interlock control functions, as well as ultra-high pressure bag plugging function. It can form a well-sealed space between the extraction device and the preset gas extraction hole 7, preventing the formation of gas leakage channels. By setting up a gas leakage monitoring device 14 in the sealed space formed by two ultra-high pressure bags on the protective pipe, gas leakage detection is performed, and the injection amount of non-condensable material is controlled in a linked manner. This can improve the quality of gas extraction concentration in a single hole and reduce gas extraction costs.

[0080] Advantages: This invention integrates gas leakage monitoring, high-pressure sealing, and energy-absorbing borehole protection technologies, combining these technologies to improve the extraction effect of soft coal seams. At the same time, the device is reusable and can overcome gas leakage problems caused by borehole collapse, borehole deformation, and inadequate sealing. It has strong innovation and practical applicability, and can effectively promote the development of the gas extraction industry.

Claims

1. A gas extraction device for soft coal seams, characterized in that, include: The protective tube includes a first protective tube section, multiple intermediate protective tube sections, and a tail protective tube section, which can be assembled sequentially from front to back. The first section of the protective pipe includes an inner pipe A and an outer pipe A. A conical mesh protective cover is installed at the front end of the first section of the protective pipe. A first ultra-high pressure bag and a leakage monitoring device are arranged sequentially near the conical mesh protective cover. The first ultra-high pressure bag is annularly fitted onto the outer wall of the inner pipe A and is connected to an external water pump through a water injection pipe installed inside the inner pipe A. An outer pipe A, coaxial with the inner pipe A, is installed in front of and behind the first ultra-high pressure bag in the axial direction. Lightweight buffer concrete is filled between the inner pipe A and the outer pipe A. The air leakage monitoring device is installed in the lightweight buffer concrete behind the first ultra-high pressure bag. It includes an air outlet at the front, penetrating the wall of the first section of the protective tube; an air inlet at the rear, also penetrating the wall of the first section of the protective tube; and a connecting hole inside the lightweight buffer concrete connecting the air outlet and the air inlet. The air inlet and outlet are each provided with a lightweight, self-opening cover at one end near the inner wall of the first section of the protective tube, and a coal dust screen at the other end near the outer wall of the first section of the protective tube. The first section of the protective tube contains high-pressure water nozzles corresponding to the air inlet and outlet, controlled by a high-pressure water solenoid valve. The high-pressure water solenoid valve is electrically connected to a terminal controller and to the water injection pipe. An airflow sensor is installed inside the connecting hole. The tail section protective tube includes an inner tube B and a second ultra-high pressure bag. The second ultra-high pressure bag is annularly fitted onto the tail end of the outer wall of the inner tube B and connected to the water injection pump through the water injection pipe. An outer tube B, coaxial with the inner tube B, is installed in front of the second ultra-high pressure bag in the axial direction. Lightweight buffer concrete is filled between the inner tube B and the outer tube B. Both the first ultra-high pressure bag and the second ultra-high pressure bag are controlled by switch A. The intermediate protective pipe includes an inner pipe C, an outer pipe C coaxially fitted outside the inner pipe C, and lightweight buffer concrete filling the space between the inner pipe C and the outer pipe C; stress patches are attached to the outer wall of the intermediate protective pipe; a grouting port penetrating the bore wall of the intermediate protective pipe is provided on the intermediate protective pipe, and the grouting port is connected to an external grouting pump through a grouting pipe; a grouting solenoid valve is provided at the grouting port, and a switch C is provided on the grouting pipe; the grouting material is a non-curing grout with a viscosity of 6000-8000 Pa·S. The extraction pipe is located inside the first section of the protective pipe, the intermediate section of the protective pipe, and the last section of the protective pipe, and the inner diameter of the extraction pipe is smaller than the inner diameter of the first section of the protective pipe, the intermediate section of the protective pipe, and the last section of the protective pipe; a gas concentration sensor is installed inside the extraction pipe; an internal pipeline space is formed between the extraction pipe and the first section of the protective pipe, the intermediate section of the protective pipe, and the last section of the protective pipe for accommodating the water injection pipe and the grouting pipe. A high-pressure gas pipe is also installed in this internal pipeline space. The first end of the high-pressure gas pipe extends into the conical mesh protective cover in front of the first section of the protective pipe and is equipped with a high-pressure gas nozzle. The last end is connected to an external air compressor and controlled by switch B; a tray is fitted on the extraction pipe to seal the last end of the last section of the protective pipe and the internal pipeline space. Switches A, B, and C, the gas concentration sensor, and the stress patch are all electrically connected to the terminal controller, and an alarm is also provided that is electrically connected to the terminal controller.

2. A gas extraction device for soft coal seams according to claim 1, characterized in that, The built-in pipe space is also equipped with a sewage drainage trough for draining water sprayed from the high-pressure water nozzle.

3. A gas extraction device for soft coal seams according to claim 1, characterized in that, The lightweight buffer concrete comprises cement, sand, fiber, ceramsite, TPU particles, and bentonite, with a weight ratio of 3:5-7:0.05:0.5:2:0.2-0.5 and a water-cement ratio of 0.7-0.

8.

4. A gas extraction device for soft coal seams according to any one of claims 1 to 3, characterized in that, The inner pipe A, the inner pipe B, and the inner pipe C are thin-walled iron pipes, while the outer pipe A, the outer pipe B, and the outer pipe C are thin-walled PVC pipes.

5. A method for gas extraction from soft coal seams, characterized in that, The gas extraction device for soft coal seams as described in any one of claims 1 to 3 comprises the following steps: S1: Install the first section of the protective tube, multiple intermediate sections of the protective tube, and the tail section of the protective tube. The first section of the protective pipe is slowly inserted into the preset gas extraction hole, and switch B is turned on. High-pressure air is ejected from the high-pressure gas nozzle, which carries the coal debris in the hole into the first section of the protective pipe and sends it out of the hole. After the first section of the protective casing is fully inserted into the pre-set gas drainage hole and is 50mm from the hole opening, close switch B. Connect the first intermediate section of the protective casing to the first section of the protective casing, then open switch B and slowly push the first section of the protective casing into the pre-set gas drainage hole. After the first intermediate section of the protective casing is inserted into the pre-set gas drainage hole, close switch B. Connect the second intermediate section of the protective casing to the first intermediate section of the protective casing, open switch B, and insert the second section of the protective casing into the pre-set gas drainage hole. Repeat this process until all intermediate protective casings are inserted into the pre-set gas drainage holes. After all intermediate protective pipes have entered the preset gas drainage hole, connect the tail section protective pipe and send the tail section protective pipe into the preset gas drainage hole. Close switch B, put the drainage pipe into the first section protective pipe, multiple intermediate protective pipes, and tail section protective pipe, install the tray, seal the opening of the preset gas drainage hole, and then connect the drainage pipe into the underground drainage network. S2: Check if the preset gas extraction hole is leaking. Start the water injection pump and open switch A. High-pressure water enters the first and second ultra-high-pressure bags, causing them to expand and adhere tightly to the borehole wall of the preset gas extraction hole, maintaining a certain pressure. Start the grouting pump and open switch C and the grouting solenoid valve, allowing non-coagulating grout to be injected through the grouting port into the gap between the protective pipe and the preset gas extraction hole, as well as into the cracks on the borehole wall. After grouting, the grouting solenoid valve automatically closes. The air volume is recorded by the air volume sensor on the air leakage monitoring device to determine whether the preset gas extraction hole is leaking. If there is a leak, grouting continues until there is no leak. S3: Negative pressure high-efficiency gas extraction: The gas extraction network is activated, and gas is extracted through the extraction pipe. At the same time, the air volume sensor records the gas leakage in real time. When the stress data monitored by the stress patch is greater than the preset value, a signal is sent to the grouting solenoid valve to start working. After grouting continues for a certain period of time, the grouting solenoid valve is automatically closed. S4: When the gas sensor detects that the gas content is lower than the preset value, the alarm will sound. After 10-20 minutes of waiting for the alarm to sound, the extraction will be stopped, the excess slurry used for sealing will be discharged, the bag will change from an inflated state to its original state, the excess water will be discharged into the roadway, the equipment will be slowly removed for reuse, and the borehole opening will be sealed with cement mortar.

6. A method for gas extraction from soft coal seams according to claim 5, characterized in that, In step S2, if the air volume sensor data is 0, it means that the preset borehole sealing quality is good. The terminal controller will open the high-pressure nozzle after 20 minutes of timing, and the working time is 2 minutes to flush the coal dust screen of the air outlet and air inlet.

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