Device and method for stereoscopically and intelligently monitoring, preventing and treating spontaneous ignition in composite goaf during short-distance coal seam group mining

Abstract

The invention discloses a device and a method for three-dimensional intelligent monitoring and prevention of spontaneous ignition in a composite goaf during short-distance coal seam group mining, and the method comprises the following steps: firstly, determining the overall layout and construction of a directional drilling hole in a high-position fissure zone, and then sequentially installing a three-loop switching device, an expansion bag plug and an intelligent analysis control box; during normal gas extraction, different drilling gas is extracted to detect and analyze the concentration change of the index gas, the position and depth of the position are determined when a natural ignition hidden danger occurs, a closed nitrogen injection space is constructed, nitrogen is accurately injected, after coal in the area is fully inerted and cooled, gas extraction is recovered, and the index gas detection is enhanced; the upper natural fire risk of the composite goaf is eliminated. According to the method, through the mode that one hole is used for multiple purposes by replacing a roadway with a hole, the natural ignition hidden danger of the upper portion of the composite goaf can be intelligently monitored while gas of an adjacent layer and the goaf is treated, the specific position of a hidden danger area is determined in a short time, nitrogen is accurately injected, and natural ignition three-dimensional intelligent monitoring and prevention are truly achieved; a powerful support is provided for solving the problem that the upper natural ignition hidden danger cannot be monitored and prevented due to the complex internal environment of the composite goaf at present, and safe production of the mining working face of the close-range coal seam group is guaranteed.

Description

Technical Field

[0001] The present invention belongs to the technical field of prevention and control of spontaneous combustion of coal residue in goaf of mines, and specifically relates to a device and method for three-dimensional intelligent monitoring and prevention of spontaneous combustion in composite goaf of close-range coal seam group mining. Background Art

[0002] The top coal recovery rate of comprehensive top coal caving mining is only about 86%, resulting in a large amount of residual coal accumulation on the floor of the goaf. Under the action of air leakage, the residual coal is oxidized at low temperature with oxygen. Under suitable heat storage conditions, the heat of the residual coal accumulates, eventually leading to spontaneous combustion of the coal. In addition, the distance between adjacent coal seams in many mining areas is very close, and the upper adjacent layer is located in the caving zone of the goaf of the mined coal seam and does not meet the mining conditions. The spontaneous combustion tendency belongs to the easy spontaneous combustion or spontaneous combustion coal seam. After mining, it collapses into the goaf. Under the action of air leakage, there is a double risk of spontaneous combustion of residual coal in the goaf, which greatly increases the risk of spontaneous combustion of coal in the composite goaf, seriously restricting the safe production of mines.

[0003] The technology for monitoring and preventing spontaneous combustion in goafs has been continuously developing. At present, the main means of monitoring spontaneous combustion in mines is the bundle tube monitoring system, which analyzes the composition and concentration changes of the index gas to infer and judge the degree of spontaneous combustion. However, due to the particularity of the layout of the bundle tube monitoring system, it is impossible to monitor the potential spontaneous combustion hazards in the upper part of the composite goaf. Currently, the most widely used goaf fire prevention and extinguishing technology is nitrogen injection technology. Most coal mines have installed underground mobile nitrogen production equipment or ground high-power nitrogen production equipment, and nitrogen is injected into the goaf through the nitrogen injection pipeline laid in advance in the air intake tunnel. However, due to the complex internal environment of the composite goaf, the risk of spontaneous combustion of the remaining coal in the upper part of the goaf is often ignored. When there is a risk of spontaneous combustion in the upper part of the goaf, accurate nitrogen injection cannot be achieved.

[0004] In order to ensure the normal production of the mining face, it is necessary to extract gas from the adjacent layers and goafs above the mining face. With the improvement of high-power directional drilling equipment and drilling construction technology at home and abroad, the "hole-in-place-lane" technology of directional drilling in high-position fracture zones has gradually matured. More and more mine working faces have replaced high-position high-extraction lanes with "holes-in-place-lanes", and the gas control effect of the adjacent layers and goafs is outstanding. According to the differences in the occurrence characteristics of coal seams in different mines, the number and arrangement of "hole-in-place-lane" drilling holes are determined by predicting the gas outburst volume of the mining face. At present, scholars' research on the application effect of "hole-in-place-lane" is mainly concentrated in the field of mine gas extraction, and there is a lack of research on the multi-purpose use of "hole-in-place-lane", especially in the field of mine fire prevention and extinguishing. The different final holes of "hole-in-place-lane" control different layers, which provides the possibility of realizing three-dimensional intelligent monitoring and prevention of spontaneous combustion in the upper part of the composite goaf.

[0005] At present, scholars have made relatively mature research on the monitoring and prevention technology of spontaneous combustion in goafs. Through the bundle pipe monitoring system and the method of laying pipelines to inject nitrogen into the goaf, the risk of spontaneous combustion of coal left in the goaf mining coal seam has been greatly reduced, but the risk of spontaneous combustion of coal left in the upper part of the composite goaf is often ignored. Due to the influence of mining disturbance, the goaf has serious air leakage. The upper part of the composite goaf is oxidized at low temperature under the conditions of suitable oxygen concentration and heat storage, which has great hidden dangers of coal spontaneous combustion. If the prevention and control measures are not appropriate, serious consequences may occur. Therefore, it is necessary to overcome the existing technical defects and propose a new device and method, which can intelligently monitor the hidden dangers of spontaneous combustion in the upper part of the composite goaf while controlling the gas in the adjacent layers and goaf during normal mining, determine the specific location of the hidden danger area in a short time and accurately inject nitrogen, and truly realize the three-dimensional intelligent monitoring and prevention of spontaneous combustion, taking into account the prevention and control of gas and coal spontaneous combustion disasters in the coal mining working face, and ensuring the safe production of the mining working face of the close-range coal seam group. Summary of the invention

[0006] In view of the problems existing in the above-mentioned prior art, the present invention provides a device and method for three-dimensional intelligent monitoring and prevention of spontaneous combustion in composite goafs of close-range coal seam group mining. By adopting the method of "using holes instead of tunnels" to drill multiple holes, it is possible to intelligently monitor the hidden dangers of spontaneous combustion in the upper part of the composite goaf while controlling the gas in the adjacent layers and goafs. The specific location of the hidden danger area can be determined in a short period of time and nitrogen can be accurately injected to eliminate the hidden dangers of spontaneous combustion and ensure the safe production of the close-range coal seam group mining working face.

[0007] According to the purpose of the present invention, a method for three-dimensional intelligent monitoring and prevention of spontaneous combustion in a composite goaf area of ​​a close-range coal seam group mining is proposed. A device for three-dimensional intelligent monitoring and prevention of spontaneous combustion in a composite goaf area of ​​a close-range coal seam group mining is used. The device comprises a three-circuit switching device (3), an extraction pipe (4), an exhaust pipe (5), a nitrogen injection pipe (6), a nitrogen injection pipe check valve (7), an exhaust pipe check valve (8), an extraction pipe check valve (9), an expansion bag (10), a pressure valve (11) and an intelligent analysis control box (12);

[0008] The three-circuit switching device (3) is arranged at the opening of each borehole, and is respectively connected to the extraction pipe (4), the air extraction pipe (5) and the nitrogen injection pipe (6); the air extraction pipe (5) and the nitrogen injection pipe (6) are telescopic soft sleeves, which can synchronously enter the deep part of the borehole along the inner wall of the borehole, and the three pipelines are respectively provided with an extraction pipe check valve (9), an air extraction pipe check valve (8) and a nitrogen injection pipe check valve (7);

[0009] The expansion bag (10) is respectively arranged at the front end and the outer wall of the nitrogen injection pipe (6). During normal extraction, the expansion bag (10) is in an uninflated state, and its volume can be ignored. It can enter the deep part of the borehole along with the air extraction pipe (5) and the nitrogen injection pipe (6). A pressure valve (11) is arranged in the middle of the nitrogen injection pipe (6). When a certain pressure is reached, the pressure valve (11) opens.

[0010] The intelligent analysis control box (12) is arranged inside the drilling site to control the opening and closing of the extraction pipe check valve (9), the air extraction pipe check valve (8) and the nitrogen injection pipe check valve (7), the opening and closing of the pressure valve (11), the expansion and contraction state of the air extraction pipe (5) and the nitrogen injection pipe (6), and the expansion and decompression of the expansion bag (10);

[0011] The method includes the following four steps:

[0012] S1: Determine the overall layout of directional drilling in high-position fracture zones and carry out construction:

[0013] Determine the control layer position of different drilling end holes and the distance of the inner staggered return air tunnel, set up a drilling site on the side wall of the return air tunnel, construct according to the overall layout of the predetermined drilling holes, and install a three-dimensional intelligent monitoring and prevention device for spontaneous combustion in the composite goaf area of ​​close-range coal seam group mining;

[0014] S2: Regularly pump out gas for testing, determine the layer where the potential fire hazard occurs, and realize three-dimensional intelligent monitoring of spontaneous combustion:

[0015] Set the concentration threshold of the spontaneous combustion index gas in the intelligent analysis control box, open and close the one-way valve of each borehole exhaust pipe in turn at a fixed time every day, extract different borehole gases for inspection and analyze the changes in index gas concentration, and realize three-dimensional intelligent monitoring of spontaneous combustion. When the index gas concentration reaches or exceeds the threshold, it indicates that there is a risk of spontaneous combustion in the layer where the end hole of the borehole is located;

[0016] S3: Determine the depth of the spontaneous combustion hazard area, build a closed nitrogen injection space and accurately inject nitrogen to achieve three-dimensional intelligent prevention and control of spontaneous combustion:

[0017] The one-way valve of the extraction pipe is closed, and negative pressure extraction is stopped for 1 hour. The extraction pipe and nitrogen injection pipe are extended to the deep part of the borehole in coordination with the expansion bag. When the end hole is reached, the one-way valve of the extraction pipe is opened every 10m to check the index gas concentration until the index gas concentration exceeds the threshold for the first time, so as to determine the depth of the spontaneous combustion hazard area. At this time, the one-way valve of the nitrogen injection pipe is opened, and the expansion bags at both ends are expanded to completely fit the inner wall of the borehole to construct a closed nitrogen injection space. At the same time, the pressure valve in the middle of the nitrogen injection pipe is opened, and low-temperature nitrogen is injected for a period of time to fully inert and cool the coal body in this area.

[0018] S4: Resume gas extraction and strengthen indicator gas detection:

[0019] After the nitrogen injection is completed, the bag is gradually depressurized to complete, and as the exhaust pipe and nitrogen injection pipe shrink and withdraw to the borehole mouth, the one-way valve of the nitrogen injection pipe is closed, and the one-way valve of the extraction pipe is opened. Gas extraction is resumed and the index gas detection of the borehole is strengthened to eliminate the risk of spontaneous combustion in the upper part of the composite goaf.

[0020] Furthermore, in the step S1, the overall layout of the drilling holes gives priority to arranging directional drilling holes in the high-position fracture zone according to the predicted law of the gas outburst volume of the adjacent layer on the working face to meet the gas control requirements, and then reasonably additional drilling holes are added according to the arrangement of the drilling hole layers and the position of the upper adjacent layer to control the different layers above the composite goaf and eliminate the blank zone for spontaneous combustion monitoring. The inner diameter Φ of the extraction pipe is 200 mm, the inner diameter Φ of the exhaust pipe is 20 mm, and the inner diameter Φ of the nitrogen injection pipe is 30 mm.

[0021] Furthermore, in step S2, the intelligent analysis control box checks the gas threshold alarm, the indicator gases are specifically CO, C2H2 and C2H4, and the alarm threshold is that the CO concentration is greater than 5ppm or C2H2 and C2H4 appear in the test.

[0022] Furthermore, in step S3, the distance between the two bags is 20m, and the nitrogen injection flow rate of a single hole is 90m 3 / h, and the nitrogen injection duration is 3 days.

[0023] Furthermore, when gas extraction is restored in step S4, the one-way valve of the gas extraction pipe is opened, and the concentration of the spontaneous combustion index gas in the stratum where the borehole is located is detected at all times. If the index gas concentration does not exceed the threshold within a week, the one-way valve of the gas extraction pipe is closed and restored to normal state.

[0024] Compared with the prior art, the device and method for three-dimensional intelligent monitoring and prevention of spontaneous combustion in composite goaf areas of close-range coal seam group mining disclosed in the present invention have the following advantages:

[0025] (1) During normal gas extraction, the present invention extracts gas from different boreholes for inspection and analyzes changes in index gas concentration by sequentially opening and closing the one-way valves of the gas extraction pipes of each borehole to sample and realize three-dimensional intelligent monitoring of spontaneous combustion.

[0026] (2) During the period when there is a risk of spontaneous combustion, the present invention determines the depth of the spontaneous combustion risk area by extending the exhaust pipe and the nitrogen injection pipe to the deep part of the borehole and conducting exhaust detection. By expanding the bag to construct a closed nitrogen injection space and accurately injecting nitrogen, three-dimensional intelligent prevention and control of spontaneous combustion is achieved, which greatly ensures the safe production of the close-range coal seam group mining working face. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to make the purpose, method and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with the accompanying drawings. Obviously, the accompanying drawings in the following description are only some practical examples of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the accompanying drawings without creative work, among which:

[0028] Figure 1 The present invention discloses a flow chart of a device and method for three-dimensional intelligent monitoring and prevention of spontaneous combustion in composite goaf areas of close-range coal seam group mining.

[0029] Figure 2 It is a three-dimensional and cross-sectional schematic diagram of the overall layout of a device and method for three-dimensional intelligent monitoring and prevention of spontaneous combustion in composite goaf areas of close-range coal seam group mining disclosed in an embodiment of the present invention.

[0030] Figure 3 A schematic diagram of the interior of a borehole under normal extraction conditions is provided for a device and method for three-dimensional intelligent monitoring and prevention of spontaneous combustion in composite goafs of close-range coal seam group mining disclosed in an embodiment of the present invention.

[0031] Figure 4 A schematic diagram of daily sampling monitoring of drilling holes under normal extraction conditions is provided for a device and method for three-dimensional intelligent monitoring and prevention of spontaneous combustion in composite goaf areas of close-range coal seam group mining disclosed in an embodiment of the present invention.

[0032] Figure 5 A schematic diagram of the interior of a borehole when a potential spontaneous combustion hazard occurs is provided for a device and method for three-dimensional intelligent monitoring and prevention of spontaneous combustion in a composite goaf of a close-range coal seam group mining disclosed in an embodiment of the present invention.

[0033] Figures 2 to 5 The numbers in the figure represent the names of the parts:

[0034] 1-mined coal seam; 2-upper adjacent layer; 3-three-circuit switching device; 4-extraction pipe; 5-extraction pipe; 6-nitrogen injection pipe; 7-nitrogen injection pipe one-way valve; 8-extraction pipe one-way valve; 9-extraction pipe one-way valve; 10-expansion bag; 11-pressure valve; 12-intelligent analysis control box. DETAILED DESCRIPTION

[0035] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings; the preferred embodiments are only for illustrating the present invention, not for limiting the scope of protection of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] Figure 1 A flowchart provided for an embodiment of the present invention; Figure 2 A three-dimensional and cross-sectional schematic diagram of the overall arrangement of drilling holes provided in an embodiment of the present invention; Figure 3 A schematic diagram of the interior of a borehole under normal extraction conditions provided by an embodiment of the present invention; Figure 4 A schematic diagram of daily sampling monitoring of boreholes under normal extraction conditions is provided for a device and method for three-dimensional intelligent monitoring and prevention of spontaneous combustion in composite goaf areas of close-range coal seam group mining disclosed in an embodiment of the present invention; Figure 5 The present invention discloses a device and method for three-dimensional intelligent monitoring and prevention of spontaneous combustion in composite goafs of close-range coal seam group mining, which specifically includes the following four steps.

[0037] S1: Determine the overall layout of directional drilling in high-position fracture zones and carry out construction:

[0038] The number of boreholes to be arranged is determined based on the prediction of gas outburst volume of the specific mine working face and the single-hole extraction volume, and the height of the caving zone in the composite goaf is investigated to determine the control layer of different borehole terminal holes and the distance to the inner return air tunnel. The overall layout of the boreholes gives priority to arranging directional drilling holes in the high-position fracture zone according to the prediction law of the gas outburst volume of the adjacent layer on the working face to meet the requirements of gas control. Then, according to the arrangement of the borehole layers, reasonable additional boreholes are added to control the different layers above the composite goaf and eliminate the blank zone for spontaneous combustion monitoring. A drilling site is set up on the inner side wall of the return air tunnel. According to the overall layout of the predetermined boreholes, construction is completed to complete the processes of hole opening expansion, hole sealing, hole opening, directional drilling, expansion, and screen pipe lowering.

[0039] Each borehole in the drilling site is connected to an extraction pipe (4), an air extraction pipe (5) and a nitrogen injection pipe (6) through a three-circuit switching device (3). The inner diameter of the extraction pipe (4) is 200 mm, the inner diameter of the air extraction pipe (5) is 20 mm, and the inner diameter of the nitrogen injection pipe (6) is 30 mm. The air extraction pipe (5) and the nitrogen injection pipe (6) are telescopic soft sleeves. When a spontaneous combustion hazard occurs, they can simultaneously enter the deep part of the borehole along the inner wall of the borehole. The three pipelines are all provided with a one-way valve. Under normal conditions, the one-way valve (9) of the extraction pipe is open, and the one-way valve (8) of the air extraction pipe is closed. The two cannot be opened at the same time.

[0040] An expansion bag (10) is laid at the front end and the outer wall of the nitrogen injection pipe (6). During normal extraction, the expansion bag (10) is in an uninflated state, and its volume can be ignored. The intelligent analysis control box (12) is arranged inside the drilling site to control the opening and closing of the extraction pipe check valve (9), the air extraction pipe check valve (8) and the nitrogen injection pipe check valve (7), the opening and closing of the pressure valve (11), the expansion and contraction state of the air extraction pipe (5) and the nitrogen injection pipe (6), and the expansion and decompression of the expansion bag (10). The intelligent analysis control box (12) is directly connected to the ground control room to transmit and display the test concentration and change of each gas in the borehole in real time.

[0041] S2: Regularly pump out gas for testing, determine the layer where the potential fire hazard occurs, and realize three-dimensional intelligent monitoring of spontaneous combustion:

[0042] A concentration threshold of a spontaneous combustion index gas is set in the intelligent analysis control box (12), where the index gas is specifically CO, C2H2 and C2H4, and the alarm threshold is when the CO concentration is greater than 5 ppm or when C2H2 and C2H4 are detected. During normal extraction, the one-way valves (8) of the gas extraction pipes of each borehole are opened and closed in sequence at a fixed time period every day, and gases from different boreholes are extracted for inspection and analysis of changes in the concentration of the index gas, thereby realizing three-dimensional intelligent monitoring of spontaneous combustion. When the concentration of the index gas reaches or exceeds the threshold, it indicates that a spontaneous combustion hazard exists in the stratum where the end hole of the borehole is located.

[0043] S3: Determine the depth of the spontaneous combustion hazard area, build a closed nitrogen injection space and accurately inject nitrogen to achieve three-dimensional intelligent prevention and control of spontaneous combustion:

[0044] The one-way valve (9) of the extraction pipe is closed, and negative pressure extraction is stopped for 1 hour. Then, the extraction pipe (5) and the nitrogen injection pipe (6) cooperate with the expansion bag (10) to extend deep into the borehole. When the end hole is reached, the one-way valve (8) of the extraction pipe is opened every 10m to check the index gas concentration. This is repeated until the index gas concentration exceeds the threshold for the first time, so as to determine the depth of the spontaneous combustion hazard area. At this time, the one-way valve (7) of the nitrogen injection pipe is opened, and the expansion bags (10) at both ends are expanded to completely fit the inner wall of the borehole to construct a closed nitrogen injection space. At the same time, the pressure valve (11) in the middle of the nitrogen injection pipe is opened to inject low-temperature nitrogen for a period of time to fully inert and cool the coal body in this area. The distance between the two bags is 20m, and the nitrogen injection flow rate of a single hole is 90m 3 / h, and the nitrogen injection duration is 3 days.

[0045] S4: Resume gas extraction and strengthen indicator gas detection:

[0046] After the nitrogen injection is completed, the expansion bag (10) gradually releases pressure until it is completely exhausted, and as the gas extraction pipe (5) and the nitrogen injection pipe (6) shrink and withdraw to the borehole mouth, the one-way valve (7) of the nitrogen injection pipe is closed, and the one-way valve (9) of the extraction pipe is opened. When gas extraction is resumed, the one-way valve (8) of the gas extraction pipe is opened, and the concentration of the index gas of spontaneous combustion in the stratum where the borehole is located is detected at all times. If the index gas concentration does not exceed the threshold value within one week, the one-way valve (8) of the gas extraction pipe is closed, and the normal state is restored, thereby eliminating the risk of spontaneous combustion in the upper part of the composite goaf.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the method of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that the method described in the aforementioned embodiments can still be modified, or part or all of the technical features thereof can be replaced by equivalents. However, these modifications or replacements do not cause the essence of the corresponding method to deviate from the scope defined by the claims of the present invention.

Claims

1. A method for three-dimensional intelligent monitoring and prevention of spontaneous combustion in composite goaf areas of close-range coal seam group mining, using a device for three-dimensional intelligent monitoring and prevention of spontaneous combustion in composite goaf areas of close-range coal seam group mining, the device comprising a three-circuit switching device (3), an extraction pipe (4), an exhaust pipe (5), a nitrogen injection pipe (6), a nitrogen injection pipe check valve (7), an exhaust pipe check valve (8), an extraction pipe check valve (9), an expansion bag (10), a pressure valve (11) and an intelligent analysis control box (12); The three-circuit switching device (3) is arranged at the opening of each borehole, and is respectively connected to the extraction pipe (4), the air extraction pipe (5) and the nitrogen injection pipe (6); the air extraction pipe (5) and the nitrogen injection pipe (6) are telescopic soft sleeves, which can synchronously enter the deep part of the borehole along the inner wall of the borehole, and the three pipelines are respectively provided with an extraction pipe check valve (9), an air extraction pipe check valve (8) and a nitrogen injection pipe check valve (7); The expansion bag (10) is respectively arranged at the front end and the outer wall of the nitrogen injection pipe (6). During normal extraction, the expansion bag (10) is in an uninflated state, and its volume can be ignored. It can enter the deep part of the borehole along with the air extraction pipe (5) and the nitrogen injection pipe (6). A pressure valve (11) is arranged in the middle of the nitrogen injection pipe (6). When a certain pressure is reached, the pressure valve (11) opens. The intelligent analysis control box (12) is arranged inside the drilling site to control the opening and closing of the extraction pipe check valve (9), the air extraction pipe check valve (8) and the nitrogen injection pipe check valve (7), the opening and closing of the pressure valve (11), the expansion and contraction state of the air extraction pipe (5) and the nitrogen injection pipe (6), and the expansion and decompression of the expansion bag (10); The method includes the following four steps: S1: Determine the overall layout of directional drilling in high-position fracture zones and carry out construction: Determine the control layer position of different drilling end holes and the distance of the inner staggered return air tunnel, set up a drilling site on the side wall of the return air tunnel, construct according to the overall layout of the predetermined drilling holes, and install a three-dimensional intelligent monitoring and prevention device for spontaneous combustion in the composite goaf area of ​​close-range coal seam group mining; S2: Regularly pump out gas for testing, determine the layer where the potential fire hazard occurs, and realize three-dimensional intelligent monitoring of spontaneous combustion: Set the concentration threshold of the spontaneous combustion index gas in the intelligent analysis control box, open and close the one-way valve of each borehole exhaust pipe in turn at a fixed time every day, extract different borehole gases for inspection and analyze the changes in index gas concentration, and realize three-dimensional intelligent monitoring of spontaneous combustion. When the index gas concentration reaches or exceeds the threshold, it indicates that there is a risk of spontaneous combustion in the layer where the end hole of the borehole is located; S3: Determine the depth of the spontaneous combustion hazard area, build a closed nitrogen injection space and accurately inject nitrogen to achieve three-dimensional intelligent prevention and control of spontaneous combustion: The one-way valve of the extraction pipe is closed, and negative pressure extraction is stopped for 1 hour. The extraction pipe and nitrogen injection pipe are extended to the deep part of the borehole in coordination with the expansion bag. When the end hole is reached, the one-way valve of the extraction pipe is opened every 10m to check the index gas concentration until the index gas concentration exceeds the threshold for the first time, so as to determine the depth of the spontaneous combustion hazard area. At this time, the one-way valve of the nitrogen injection pipe is opened, and the expansion bags at both ends are expanded to completely fit the inner wall of the borehole to construct a closed nitrogen injection space. At the same time, the pressure valve in the middle of the nitrogen injection pipe is opened, and low-temperature nitrogen is injected for a period of time to fully inert and cool the coal body in this area. S4: Resume gas extraction and strengthen indicator gas detection: After the nitrogen injection is completed, the bag is gradually depressurized to complete, and as the exhaust pipe and nitrogen injection pipe shrink and withdraw to the borehole mouth, the one-way valve of the nitrogen injection pipe is closed, and the one-way valve of the extraction pipe is opened. Gas extraction is resumed and the index gas detection of the borehole is strengthened to eliminate the risk of spontaneous combustion in the upper part of the composite goaf.

2. A three-dimensional intelligent monitoring and prevention method for spontaneous combustion in composite goaf areas of close-range coal seam group mining as claimed in claim 1, characterized in that: In the step S1, the overall layout of the drilling holes is preferentially arranged according to the predicted law of the gas outburst volume of the adjacent layers on the working face, directional drilling of high-position fracture zones is arranged to meet the gas control requirements, and then additional drilling holes are reasonably added according to the arrangement of the drilling holes and the position of the upper adjacent layers to control the different layers above the composite goaf and eliminate the blank zone for spontaneous combustion monitoring. The inner diameter Φ of the extraction pipe is 200 mm, the inner diameter Φ of the exhaust pipe is 20 mm, and the inner diameter Φ of the nitrogen injection pipe is 30 mm.

3. The method for three-dimensional intelligent monitoring and prevention of spontaneous combustion in composite goaf areas of close-range coal seam group mining as claimed in claim 1 is characterized in that: In step S2, the intelligent analysis control box checks the gas threshold alarm, the indicator gases are specifically CO, C2H2 and C2H4, and the alarm threshold is that the CO concentration is greater than 5ppm or C2H2 and C2H4 appear in the test.

4. The method for three-dimensional intelligent monitoring and prevention of spontaneous combustion in composite goaf areas of close-range coal seam group mining as claimed in claim 1 is characterized in that: In step S3, the distance between the two bags is 20m, and the nitrogen injection flow rate of a single hole is 90m 3 / h, and the nitrogen injection duration is 3 days.

5. The method for three-dimensional intelligent monitoring and prevention of spontaneous combustion in composite goaf areas of close-range coal seam group mining as claimed in claim 1, characterized in that: When gas extraction is restored in step S4, the one-way valve of the gas extraction pipe is opened, and the concentration of the spontaneous combustion index gas in the stratum where the borehole is located is detected at all times. If the index gas concentration does not exceed the threshold within one week, the one-way valve of the gas extraction pipe is closed and restored to normal state.

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