A method for preventing and treating gas and coal spontaneous combustion in full cycle in component layer mining of close distance coal seams

Abstract

This invention discloses a method for the coordinated prevention and control of gas and spontaneous combustion throughout the entire lifecycle of layered mining of extremely close-proximity coal seams. Before the upper layer is mined, high-negative-pressure extraction is implemented in both the upper and lower layers of the coal seam through cross-layer drilling to reduce the initial gas content. During the upper layer mining process, differentiated extraction and in-situ gas sampling and analysis are carried out in the cross-layer drilling and directional long boreholes in the fracture zone. When a risk of spontaneous combustion of coal is detected, low-temperature nitrogen and low-temperature carbon dioxide are simultaneously injected through boreholes at different spatial locations to cause the inert gas to converge towards the target area, achieving coordinated prevention and control of gas and spontaneous combustion. Before the lower layer is mined, low-negative-pressure extraction is used to eliminate residual gas accumulation. During the lower layer mining process, gas extraction or inerting treatment is implemented according to gas changes to eliminate the potential hazards of compound goaf areas. This invention solves the problems of the disconnect and delayed response of traditional gas control and spontaneous combustion prevention methods, and has significant engineering application value for ensuring the safe and efficient mining of extremely close-proximity coal seams.

Description

Technical Field

[0001] This invention belongs to the field of mine gas and coal spontaneous combustion prevention technology, specifically a method for the full-cycle synergistic prevention and control of gas and coal spontaneous combustion in extremely close-range coal seam layer mining. Background Technology

[0002] In recent years, shallow coal resources have been gradually depleted, and coal mining has continued to advance into deeper areas. This has led to increasing geothermal gradients and gas pressure, causing low-gas mines to gradually transform into high-gas or even outburst-prone mines. Coal seams that were originally not prone to spontaneous combustion are gradually evolving into seams with a higher tendency to spontaneously combust, significantly increasing the risk of combined gas and coal spontaneous combustion disasters. Spontaneous combustion of coal in goaf areas not only forces the working face to close, resulting in a significant waste of coal resources, but can also trigger gas explosions, causing serious casualties and economic losses.

[0003] Against the backdrop of continuous mining of deep coal resources, many mining areas are characterized by extremely close-proximity coal seam groups, with very small vertical spacing, typically 1-2 meters. These seams have high gas content and no protective layer is available. If a full-height mining method is used in a single pass, abnormal gas outbursts are highly likely, leading to gas exceedances and even explosions. Therefore, layered mining is commonly employed to reduce the risk of gas disasters. During the upper-layer mining process, the gas environment inside the goaf is complex, with multiple gas components coexisting and competing for adsorption and diffusion. Different gas ratios and oxygen concentrations significantly affect the oxidation heat release and gas production characteristics. Due to the thin interlayers, the lower coal seam experiences stress unloading and fracture penetration due to disturbance from the upper-layer mining, prompting significant gas desorption and upward migration. This migration pattern differs significantly from that of a single coal seam, leading to the formation of gas-rich zones within the goaf. Under the multi-field interaction of heat, flow, gasification and oxidation, the migration of coal seam gas and the coal oxidation process exhibit strong nonlinear coupling characteristics, which significantly increases the risk of combined disasters caused by gas and spontaneous combustion of coal in very close coal seam sub-mining.

[0004] The risk levels of gas and spontaneous combustion in closely spaced coal seams vary significantly at different stages of layered mining. Before the upper layer is mined, the initial gas content of the coal seam is high, and the upper and lower layers are solid coal with a low risk of spontaneous combustion. Therefore, the focus of prevention and control at this stage is to reduce the gas content of the coal seam. During the upper layer mining process, as the working face advances dynamically, due to the thin interbedded rock, the depressurized gas from the lower layer migrates to the upper goaf, easily forming a gas-rich area. Furthermore, a drawback of fully mechanized longwall mining is the presence of a large amount of residual coal in the goaf. Under suitable air leakage and heat storage conditions within the goaf, this residual coal gradually heats up, potentially leading to spontaneous combustion or even inducing a gas explosion, causing serious consequences. Therefore, at this stage... The key prevention and control measures are the coordinated prevention and control of gas and spontaneous combustion of coal in the goaf. Before the lower layer is mined, the upper layer working face is closed, the goaf has less air leakage, and the risk of spontaneous combustion of coal is relatively small. However, the lower layer solid coal structure area may have incomplete pressure relief, and there is a risk of local gas accumulation. Therefore, the key prevention and control measures at this stage are to eliminate the local gas accumulation in the lower layer. During the lower layer mining process, the upper and lower goafs are connected to form a composite goaf. The air leakage channels are complex and difficult to measure. There is a risk of spontaneous combustion of coal in the double-layer residual coal in the goaf. Therefore, the key prevention and control measures at this stage are to eliminate the risk of spontaneous combustion of coal in the composite goaf.

[0005] Currently, scholars have conducted relatively mature studies on gas control and coal spontaneous combustion prevention in single coal seams or closely spaced coal seam groups. Gas control in the coal seam is achieved through pre-drainage boreholes along the seam or through-sea boreholes in adjacent roadways. Gas control in the goaf during mining is achieved through long directional boreholes in high-drainage roadways or fracture zones. Spontaneous combustion of residual coal in the goaf is monitored and prevented through pre-embedded bundled tube monitoring systems and nitrogen injection pipelines on the intake side. Significant field implementation results have been achieved.

[0006] However, due to the special working conditions of mining very close coal seams in layers, the difference from mining close coal seam groups is that close coal seam groups have thicker interbedded rock and lower intensity of decompression gas emission. Before mining the upper coal seam, it is basically not necessary to pre-drain the gas in the lower layer. On the contrary, the upper coal seam mining serves as a protective layer for the lower coal seam, and conventional goaf gas drainage can meet the needs. However, when mining the upper layer of a coal seam group, the intensity of decompression gas emission is greater, and it is necessary to control the gas in the coal seam group simultaneously before mining the upper layer. Meanwhile, under the condition of close-range coal seam mining, during the mining of the lower coal seam, due to the thick interbedded rock and the small connection between the fractures between the upper and lower goaf areas, field experience shows that under normal working face advancement conditions, it is generally not necessary to take separate coal spontaneous combustion prevention measures for the upper residual coal. However, during the mining of the lower layer of the coal seam group, the fractures between the two layers of residual coal are strongly connected, and even at the junction of the interbedded rock block fractures, the upper and lower layers of residual coal come into contact. The air leakage in the goaf has a more significant impact on the upper layer of residual coal, so it is necessary to simultaneously prevent and control the spontaneous combustion hazard of the two layers of residual coal. Currently, there are no mature prevention and control methods for this special working condition in publicly available research results. Therefore, it is necessary to overcome the existing technical deficiencies and propose a new method for the full-cycle coordinated prevention and control of gas and coal spontaneous combustion for the complex working condition of layered mining of extremely close-range coal seams. This method can provide targeted or coordinated prevention and control of gas and coal spontaneous combustion hazards at different mining stages, ensuring safe production throughout the entire cycle of layered mining of extremely close-range coal seams. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a method for the coordinated prevention and control of gas and spontaneous combustion of coal in the entire cycle of extremely close-range coal seam layered mining. Targeting the prevention and control priorities at different mining stages, it utilizes directional long boreholes in fracture zones and U-shaped floor roadway cross-layer boreholes, combined with three-way switching valves and in-situ gas detection devices, to achieve intelligent switching between gas extraction and inert injection to prevent spontaneous combustion of coal, greatly ensuring safe production throughout the entire cycle of extremely close-range coal seam layered mining.

[0008] According to the present invention, a method for the coordinated prevention and control of gas and spontaneous combustion of coal in the entire life cycle of coal seam layer mining at extremely close proximity is proposed, characterized by comprising the following steps:

[0009] S1: Delineate the upper and lower working faces of the coal seam group. Construct a U-shaped bottom roadway in the lower part of the coal seam group, and construct cross-layer boreholes along the top of the bottom roadway to the upper coal seam group. The initial and final borehole positions of the cross-layer boreholes are located at the top of the upper layer of the coal seam group. Construct directional long boreholes to the upper part of the coal seam group. The number of boreholes is determined based on the predicted gas emission intensity and the gas extraction concentration of a single borehole during the mining period.

[0010] S2: Before the upper layer is mined, the bottom roadway is not closed. The cross-layer borehole is connected to the extraction pipe for negative pressure extraction. At the same time, the gas in the upper and lower layers of the coal seam is extracted until the gas concentration in the upper layer drops to the set threshold.

[0011] S3: In the upper layer mining, one of the fifteen groups of cross-layer boreholes in the adjacent positions of the bottom roadway is connected to the intelligent three-way switching valve. The interface is connected to the low temperature nitrogen box and the extraction pipe respectively. The remaining boreholes are removed from the extraction pipe and the bottom extraction roadway is closed. Negative pressure extraction is carried out at the roadway entrance. Each directional long borehole is connected to the intelligent three-way switching valve. The interface is connected to the low temperature carbon dioxide box and the extraction pipe respectively.

[0012] S4: Before the lower layer mining, the negative pressure of the bottom roadway is reduced to the set value, and the residual gas in the lower layer of the coal seam is extracted to eliminate the potential risk of gas accumulation.

[0013] S5: During the lower-level mining, stop negative pressure extraction, conduct normal drilling and gas extraction, and coordinate with ventilation to control residual gas and prevent local gas accumulation.

[0014] Furthermore, in step S1, during the upper-layer mining, the final borehole of the cross-layer borehole that did not enter the upper-layer goaf is located on the roof of the upper-layer coal seam, and the final borehole of the cross-layer borehole that entered the upper-layer goaf is located on the floor of the upper-layer coal seam. During the lower-layer mining, the final borehole of the cross-layer borehole that did not enter the lower-layer goaf is located on the floor of the upper-layer coal seam, and the final borehole of the cross-layer borehole that entered the lower-layer goaf is located on the floor of the lower-layer coal seam.

[0015] Furthermore, in step S1, the vertical distance between the U-shaped bottom roadway and the lower layer bottom plate of the coal seam group is 10-15m, the final position of the directional long borehole is located in the fracture zone of the goaf, the height of the fracture zone is determined according to the actual field measurement, and the vertical or horizontal distance between the final positions of adjacent boreholes is 5m.

[0016] Furthermore, in step S2, before the upper layer is mined, the negative pressure of the cross-layer drilling extraction is set to 15-20 kPa, and a high negative pressure extraction system is used to quickly reduce the gas content of the coal seam group.

[0017] Furthermore, in step S3, the intelligent three-way switching valve of the cross-layer drilling and the directional long drilling is routinely connected to the extraction pipe for gas extraction. Each extraction pipe leads out a gas extraction branch pipe and is connected to an automatic chromatographic analysis box. An intelligent valve is installed at the branch pipe opening. The valve automatically opens every day to sample and analyze the components of spontaneous combustion index gas, gas, oxygen, etc. in the extracted gas. After the sampling is completed, the valve automatically closes.

[0018] Furthermore, in step S3, during the upper layer mining, the negative pressure of the bottom drainage roadway and the directional long borehole is 5-8 kPa. A low negative pressure extraction system is selected to reduce air leakage in the goaf. The negative pressure of the cross-layer borehole is maintained at 15-20 kPa to enhance the gas extraction detection range in the area near the end of the cross-layer borehole.

[0019] Furthermore, in step S3, the indicator gases are specifically CO, C2H2, and C2H4, and the threshold is set to a CO concentration greater than 10 ppm or the presence of C2H2 and C2H4 in the test.

[0020] Furthermore, in step S3, if the spontaneous combustion index gas in a certain area of ​​the goaf is detected to exceed the threshold, the intelligent three-way switching valve of the cross-layer borehole in that area is automatically connected to the low-temperature carbon dioxide tank, and the intelligent three-way switching valve of the directional long borehole in that area is automatically connected to the low-temperature nitrogen tank. Through the cooling and buoyancy effect of low-temperature nitrogen and the cooling and settling effect of low-temperature carbon dioxide, the inert gas eventually converges in the residual coal area, reducing the oxygen concentration in the target area to the asphyxiation zone. At the same time, the extraction negative pressure of the adjacent borehole is reduced to 6-10 kPa, and the number of daily sampling and analysis is increased to 3 times. When the oxygen and index gas concentrations in the target area are simultaneously restored to the safe range for 8 hours, the intelligent three-way switching valve is automatically connected to the extraction pipe, and the extraction negative pressure of the adjacent borehole is restored to the initial value.

[0021] Furthermore, in step S4, before the lower layer mining, the negative pressure setting for the bottom roadway sealing extraction is 3-5 kPa. Based on the low negative pressure extraction, the extraction negative pressure is further reduced to reduce air leakage in the upper layer goaf.

[0022] Furthermore, in step S5, during the lower-level mining process, if the gas concentration in a certain area exceeds 10%, the intelligent three-way switching valve of the target area through-layer drilling is connected to the extraction pipe for gas extraction until the gas concentration in the extraction pipe is lower than 3%.

[0023] Furthermore, in step S5, during the lower-level mining, if the concentration of spontaneous combustion indicator gas in a certain area of ​​the cross-layer borehole or directional long borehole exceeds the threshold, it indicates that there is a risk of spontaneous combustion of coal in the coal seam group's composite goaf. By injecting low-temperature nitrogen into the cross-layer borehole in the target area and low-temperature carbon dioxide into the directional long borehole, precise inerting is achieved, and the risk of spontaneous combustion of coal in the composite goaf is eliminated.

[0024] Furthermore, if the gas concentration and the concentration of the spontaneous combustion indicator gas both exceed the threshold in the same borehole sampling results, the intelligent three-way switching valve of the borehole in the target area will still be connected to the low-temperature nitrogen box or the low-temperature carbon dioxide box to prioritize the elimination of coal spontaneous combustion hazards. Attached Figure Description

[0025] To make the objectives, methods, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the drawings described below are merely some practical examples of this invention. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort. In particular:

[0026] Figure 1This is a schematic diagram of a method for the coordinated prevention and control of gas and spontaneous combustion of coal in the whole cycle of layered mining of coal seams at extremely close distances, as disclosed in an embodiment of the present invention.

[0027] Figure 2 This is a schematic diagram of the layout before upper-layer mining in a method for the coordinated prevention and control of gas and spontaneous combustion of coal in the whole cycle of extremely close-range coal seam layered mining, as disclosed in an embodiment of the present invention.

[0028] Figure 3 This is a schematic diagram of the upper-layer mining layout in a method for the coordinated prevention and control of gas and spontaneous combustion of coal in the whole cycle of extremely close-range coal seam layered mining, as disclosed in an embodiment of the present invention.

[0029] Figure 4 This is a schematic diagram of the pre-mining layout of a method for the coordinated prevention and control of gas and spontaneous combustion of coal in the whole cycle of extremely close-range coal seam layer mining, as disclosed in an embodiment of the present invention.

[0030] Figure 5 This is a schematic diagram of the layout during the lower-level mining stage of a method for the coordinated prevention and control of gas and spontaneous combustion of coal in the whole cycle of extremely close-range coal seam layered mining, as disclosed in an embodiment of the present invention.

[0031] Figure 6 This is a schematic diagram of the cross-layer borehole layout for a method for the coordinated prevention and control of gas and spontaneous combustion of coal in the whole cycle of extremely close-range coal seam layered mining, as disclosed in an embodiment of the present invention.

[0032] Figure 7 This is a schematic diagram of the directional long borehole layout for a method of coordinated prevention and control of gas and spontaneous combustion of coal in the whole cycle of extremely close-range coal seam layered mining, as disclosed in an embodiment of the present invention.

[0033] In the diagram: 1-Upper layer of coal seam group; 2-Lower layer of coal seam group; 3-U-shaped floor roadway; 4-Extraction pipe; 5-Through-layer borehole; 6-Directional long borehole; 7-Gas migration direction; 8-Intercalation of rock; 9-Fractured area under mining disturbance; 10-Rock block; 11-Residual coal; 12-Hydraulic support; 13-Low-temperature nitrogen box; 14-Flow control valve; 15-No. 1 check valve; 16-Inertia injection pipe; 17-Intelligent three-way switching valve; 18-No. 2 check valve; 19-Extraction branch pipe; 20-Gas intake branch pipe; 21-No. 3 check valve; 22-Automatic chromatography analysis box; 23-Screen pipe; 24-Low-temperature carbon dioxide box. Detailed Implementation

[0034] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. These preferred embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0035] Figure 1 This is a schematic flowchart of a method for the coordinated prevention and control of gas and spontaneous combustion of coal in the whole cycle of layered mining of coal seams at extremely close distances, as disclosed in an embodiment of the present invention. Figure 2 This is a schematic diagram of the layout before upper-layer mining in a method for the coordinated prevention and control of gas and spontaneous combustion of coal in the whole cycle of extremely close-range coal seam layered mining, as disclosed in an embodiment of the present invention. Figure 3 This is a schematic diagram of the upper-layer mining layout in a method for the coordinated prevention and control of gas and spontaneous combustion of coal in the whole cycle of extremely close-range coal seam layered mining, as disclosed in an embodiment of the present invention. Figure 4 This is a schematic diagram of the pre-mining layout of a method for the coordinated prevention and control of gas and spontaneous combustion of coal in the whole cycle of extremely close-range coal seam layered mining, as disclosed in an embodiment of the present invention. Figure 5 This is a schematic diagram of the layout in the lower layer mining stage of a method for the coordinated prevention and control of gas and spontaneous combustion of coal in the whole cycle of extremely close coal seam layer mining, as disclosed in an embodiment of the present invention. Figure 6 This is a schematic diagram of the cross-layer borehole layout for a method for the coordinated prevention and control of gas and spontaneous combustion of coal in the whole cycle of extremely close-range coal seam layered mining, as disclosed in an embodiment of the present invention. Figure 7 This is a schematic diagram of the directional long borehole layout for a method of coordinated prevention and control of gas and spontaneous combustion of coal in extremely close-range coal seam layered mining throughout the entire life cycle, as disclosed in an embodiment of the present invention. The method of coordinated prevention and control of gas and spontaneous combustion of coal in extremely close-range coal seam layered mining throughout the entire life cycle disclosed in the present invention specifically includes the following five steps.

[0036] S1: Delineate the upper and lower working faces of the coal seam group. Construct a U-shaped floor roadway 3 in the lower part of the coal seam group, and construct cross-sea boreholes 5 along the roof of the floor roadway 3 towards the upper coal seam group. Before the upper layer mining, the final position of cross-sea borehole 5 is located at the roof of the upper layer of the coal seam group. During the upper layer mining, the final position of cross-sea borehole 5 that has not entered the upper layer goaf is located at the roof of the upper coal seam, and the final position of cross-sea borehole 5 that has entered the upper layer goaf is located at the floor of the upper coal seam. During the lower layer mining, the final position of cross-sea borehole 5 that has not entered the lower layer goaf is located at the floor of the upper coal seam, and the final position of cross-sea borehole 5 that has entered the lower layer goaf is located at the floor of the lower coal seam. Construct directional long boreholes 6 towards the upper part of the coal seam group. The number of boreholes is determined based on the predicted gas emission intensity and single-hole gas extraction concentration during the mining period.

[0037] S2: Before the upper layer mining, the bottom roadway 3 is not sealed. The cross-layer borehole 5 is connected to the extraction pipe 4 for negative pressure extraction. The extraction negative pressure is set to 15-20KPa. The high negative pressure extraction system is used to quickly reduce the gas content of the coal seam group. At the same time, the gas in the upper and lower layers of the coal seam group is extracted until the gas concentration in the upper layer drops to the set threshold to ensure that the gas extraction of the working face meets the standard.

[0038] S3: In the upper-layer backfilling, for every fifteen groups of cross-layer boreholes 5 adjacent to the bottom roadway 3, one borehole is retained and connected to a smart three-way switching valve 17. The interfaces are respectively connected to a low-temperature nitrogen tank 13 and an extraction pipe 4. The remaining boreholes are removed from the extraction pipe 4 and the bottom extraction roadway is sealed. Negative pressure extraction is carried out at the roadway entrance. Each directional long borehole 6 is connected to a smart three-way switching valve 17. The interfaces are respectively connected to a low-temperature carbon dioxide tank 24 and an extraction pipe 4. The smart three-way switching valves 17 of the cross-layer boreholes 5 and directional long boreholes 6 are routinely connected to the extraction pipe 4 for gas extraction. The negative pressure of extraction in the bottom extraction roadway and directional long boreholes 6 is 5-8 kPa. A low negative pressure extraction system is selected to reduce air leakage in the goaf. The negative pressure of extraction in the retained cross-layer boreholes 5 is maintained at 15-20 kPa to enhance the gas sampling detection range near the end of the cross-layer boreholes 5. Each extraction pipe leads out a gas sampling branch pipe 20 and connects to an automatic chromatographic analysis box 22. A smart valve is installed at the branch pipe opening, and the valve automatically opens daily. The system initiates sampling and analysis of the extracted gas to determine the composition of spontaneous combustion indicator gases, methane, oxygen, etc. After sampling, the valve automatically closes. When the CO concentration is detected to be greater than 10 ppm or C2H2 and C2H4 are present, the intelligent three-way switching valve 17 of the cross-layer borehole 5 in the area automatically connects to the low-temperature carbon dioxide tank 24, and the intelligent three-way switching valve 17 of the directional long borehole 6 in the area automatically connects to the low-temperature nitrogen tank 13. Through the cooling and buoyancy effect of low-temperature nitrogen and the cooling and settling effect of low-temperature carbon dioxide, the inert gas eventually converges in the residual coal area, reducing the oxygen concentration in the target area to the asphyxiation zone. At the same time, the extraction negative pressure of the adjacent boreholes is reduced to 6-10 kPa, and the number of daily sampling and analysis is increased to 3 times. When the oxygen and indicator gas concentrations in the target area are simultaneously restored to the safe range for 8 hours, the intelligent three-way switching valve 17 automatically connects to the extraction pipe 4, and the extraction negative pressure of the adjacent boreholes is restored to the initial value.

[0039] S4: Before the lower layer mining, the negative pressure of the bottom roadway 3 is reduced to 3-5 kPa. On the basis of low negative pressure mining, the negative pressure of the mining is further reduced to reduce air leakage in the upper layer goaf, extract the residual gas in the lower layer of the coal seam group, and eliminate the potential risk of gas accumulation.

[0040] S5: During the lower-level mining, stop negative pressure extraction, conduct normal borehole gas extraction and testing, and coordinate with ventilation to control residual gas and prevent local gas accumulation. If the gas concentration in a certain area exceeds 10%, the intelligent three-way switching valve 17 of the target area cross-layer borehole 5 is connected to the extraction pipe 4 for gas extraction until the gas concentration in the extraction pipe 4 is lower than 3%. If the spontaneous combustion index gas concentration of the cross-layer borehole 5 or the directional long borehole 6 in a certain area exceeds the threshold, it indicates that there is a risk of spontaneous combustion of coal in the coal seam group composite goaf. Low-temperature nitrogen is injected into the target area cross-layer borehole 5 and low-temperature carbon dioxide is injected into the directional long borehole 6 to achieve precise inerting and eliminate the risk of spontaneous combustion of coal in the composite goaf. If the sampling results of the same borehole show that the gas concentration and the spontaneous combustion index gas concentration both exceed the threshold, the intelligent three-way switching valve 17 of the target area borehole is still connected to the low-temperature nitrogen box 13 or the low-temperature carbon dioxide box 24 to prioritize the elimination of the risk of spontaneous combustion of coal.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the method of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the method described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions 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 synergistically preventing and controlling gas and coal spontaneous combustion in the whole cycle of component layer mining of close distance coal seams, characterized in that, Includes the following steps: S1: Delineate the upper and lower working faces of the coal seam group. Construct a U-shaped bottom roadway in the lower part of the coal seam group, and construct cross-layer boreholes along the top of the bottom roadway to the upper coal seam group. The initial and final borehole positions of the cross-layer boreholes are located at the top of the upper layer of the coal seam group. Construct directional long boreholes to the upper part of the coal seam group. The number of boreholes is determined based on the predicted gas emission intensity and the gas extraction concentration of a single borehole during the mining period. S2: Before the upper layer is mined, the bottom roadway is not closed. The cross-layer borehole is connected to the extraction pipe for negative pressure extraction. At the same time, the gas in the upper and lower layers of the coal seam is extracted until the gas concentration in the upper layer drops to the set threshold. S3: In the upper-layer backfilling, for every fifteen groups of cross-layer boreholes adjacent to the bottom roadway, one borehole is connected to a smart three-way switching valve. The interfaces are respectively connected to a cryogenic nitrogen tank and an extraction pipe. The remaining boreholes are removed from the extraction pipes and the bottom roadway is sealed. Negative pressure extraction is carried out at the roadway entrance. Each directional long borehole is connected to a smart three-way switching valve, with the interfaces respectively connected to a cryogenic carbon dioxide tank and an extraction pipe. The smart three-way switching valves of the cross-layer boreholes and directional long boreholes are routinely connected to the extraction pipes for gas extraction. Each extraction pipe leads out a gas extraction branch pipe and connects to an automatic chromatographic analysis box. A smart valve is installed at the branch pipe opening. The valve automatically opens daily to sample and analyze the components of spontaneous combustion indicator gases, methane, oxygen, etc. in the extracted gas. After sampling, the valve automatically closes. If monitoring... When the spontaneous combustion index gas in a certain area of ​​the goaf exceeds the threshold, the intelligent three-way switching valve of the cross-layer borehole in that area automatically connects to the low-temperature carbon dioxide tank, and the intelligent three-way switching valve of the directional long borehole in that area automatically connects to the low-temperature nitrogen tank. Through the cooling and buoyancy effect of low-temperature nitrogen and the cooling and settling effect of low-temperature carbon dioxide, the inert gas eventually gathers in the residual coal area, reducing the oxygen concentration in the target area to the asphyxiation zone. At the same time, the extraction negative pressure of the adjacent borehole is reduced to 6-10 kPa, and the number of daily sampling and analysis is increased to 3 times. When the oxygen and index gas concentrations in the target area are simultaneously restored to the safe range for 8 hours, the intelligent three-way switching valve automatically connects to the extraction pipe, and the extraction negative pressure of the adjacent borehole is restored to the initial value. S4: Before the lower layer mining, the negative pressure of the bottom roadway is reduced to the set value, and the residual gas in the lower layer of the coal seam is extracted to eliminate the potential risk of gas accumulation. S5: During the lower layer mining, stop negative pressure extraction, conduct normal drilling and gas extraction, and coordinate with ventilation to control residual gas and prevent local gas accumulation. If the concentration of spontaneous combustion indicator gas in a certain area of ​​the cross-layer borehole or directional long borehole exceeds the threshold, it indicates that there is a risk of spontaneous combustion of coal in the coal seam group composite goaf. By injecting low-temperature nitrogen into the cross-layer borehole in the target area and injecting low-temperature carbon dioxide into the directional long borehole, precise inerting is achieved to eliminate the risk of spontaneous combustion of coal in the composite goaf.

2. The method for full-cycle coordinated prevention and control of gas and coal spontaneous combustion in component layer mining of close distance coal seams according to claim 1, characterized in that, In step S1, during the upper-layer mining, the final borehole of the cross-layer borehole that did not enter the upper-layer goaf is located on the roof of the upper-layer coal seam, and the final borehole of the cross-layer borehole that entered the upper-layer goaf is located on the floor of the upper-layer coal seam. During the lower-layer mining, the final borehole of the cross-layer borehole that did not enter the lower-layer goaf is located on the floor of the upper-layer coal seam, and the final borehole of the cross-layer borehole that entered the lower-layer goaf is located on the floor of the lower-layer coal seam.

3. The method for full-cycle coordinated prevention and control of gas and coal spontaneous combustion in component layer mining of close distance coal seams according to claim 1, characterized in that, In step S1, the vertical distance between the U-shaped bottom roadway and the lower layer bottom plate of the coal seam group is 10-15m. The final position of the directional long borehole is located in the fracture zone of the goaf. The height of the fracture zone is determined according to the actual field measurement. The vertical or horizontal distance between the final positions of adjacent boreholes is 5m.

4. The method for full-cycle coordinated prevention and control of gas and coal spontaneous combustion in component layer mining of close distance coal seams according to claim 1, characterized in that, In step S2, before the upper layer is mined, the negative pressure of the cross-layer drilling extraction is set to 15-20 kPa, and a high negative pressure extraction system is used to quickly reduce the gas content of the coal seam group.

5. The method for coordinated prevention and control of gas and spontaneous combustion of coal in the whole cycle of layered mining of extremely close coal seams as described in claim 1, characterized in that, In step S3, the negative pressure of the bottom roadway and the directional long borehole extraction is 5-8 kPa. A low negative pressure extraction system is selected to reduce air leakage in the goaf. The negative pressure of the cross-layer borehole extraction is maintained at 15-20 kPa to enhance the gas extraction detection range in the area near the end of the cross-layer borehole.

6. The method for full-cycle coordinated prevention and control of gas and coal spontaneous combustion in component layer mining of close distance coal seams according to claim 1, characterized in that, In step S3, the indicator gases are specifically CO, C2H2, and C2H4, and the threshold is set to a CO concentration greater than 10 ppm or the presence of C2H2 and C2H4 in the test.

7. The method for full-cycle coordinated prevention and control of gas and coal spontaneous combustion in component layer mining of close distance coal seams according to claim 1, characterized in that, In step S4, before the lower layer mining, the negative pressure setting for the bottom roadway sealing and extraction is 3-5 kPa. Based on the low negative pressure extraction, the extraction negative pressure is further reduced to reduce air leakage in the upper layer goaf.

8. The method for full-cycle coordinated prevention and control of gas and coal spontaneous combustion in component layer mining of close distance coal seams according to claim 1, characterized in that, In step S5, during the lower-level mining, if the gas concentration in a certain area exceeds 10%, the intelligent three-way switching valve of the target area through-layer drilling is connected to the extraction pipe for gas extraction until the gas concentration in the extraction pipe is lower than 3%.

9. The method for full-cycle coordinated prevention and control of gas and coal spontaneous combustion in component layer mining of close distance coal seams according to claim 1, characterized in that, In step S5, if the gas concentration and the concentration of the spontaneous combustion indicator gas both exceed the threshold in the same borehole sampling results, the intelligent three-way switching valve of the target area borehole is still connected to the low-temperature nitrogen box or the low-temperature carbon dioxide box to prioritize the elimination of coal spontaneous combustion hazards.

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