Methods to ensure safe mining of working faces in shallow, closely spaced coal seam groups under old fire zones

Abstract

This invention relates to the field of fire prevention, specifically to a method for ensuring the safe mining of a working face in the old fire zone of a shallowly buried, closely spaced coal seam group. The method includes the following steps: S100 – Excavating the mining face of the lower coal group of the shallowly buried, closely spaced coal seam group. After the mining face is arranged, multiple sets of observation-venting holes are drilled into the old fire zone in the intake airway, return airway, and cut-out of the lower coal group. S200 – Before mining the working face, multiple sets of surface nitrogen injection-grouting holes are drilled from the ground towards the old fire zone, located directly above the working face and between the intake and return airways. S300 – Before mining the working face, liquid nitrogen is injected into the old fire zone through the surface nitrogen injection-grouting holes. The injection of liquid nitrogen extinguishes any potential fire sources in the old fire zone, inertes the goaf, and balances the pressure difference between the goaf and the ground. After the S400 degassing is completed, the working face is back-mined. Mud is injected into the old fire zone from the surface nitrogen injection-grouting hole until the surface nitrogen injection-grouting hole is located above the goaf suffocation zone. The mud is then used to seal the fractures in the stope.

Description

Technical Field

[0001] This invention relates to the field of fire prevention, specifically to a method for ensuring safe mining of working faces in shallow, closely spaced coal seam groups under old fire zones. Background Technology

[0002] For working faces in shallow, closely spaced coal seam mining, the shallow burial depth of the coal seam leads to the collapse and deformation of the overlying strata after mining, forming a vertically conductive gas-conducting zone that connects to the surface. Since mines typically use negative pressure ventilation, a pressure difference exists between the surface and underground, exacerbating air leakage into the goaf and making the goaf highly susceptible to spontaneous combustion. After spontaneous combustion occurs in the overlying coal seam, sealing and other fire extinguishing measures are necessary. However, even after the fire is extinguished, large amounts of toxic and harmful gases such as CO and CH4 remain in the goaf of the upper coal group. When the lower coal seam is mined, secondary collapse and damage to the overlying strata can easily form new air leakage channels between the lower goaf, the upper goaf (old fire zone), and the surface. This can cause large amounts of toxic and harmful gases from the old fire zone to surge into the working face, significantly increasing the risk of spontaneous combustion in the goaf and potentially triggering major disasters. Currently, pressure equalization ventilation at the working face is commonly used to prevent toxic and harmful gases from the old fire zone from entering the lower working face. However, pressure equalization ventilation is a complex technical and management task. If not properly controlled, it may not only fail to achieve the desired fire prevention and extinguishing effect but could also trigger a fire, causing serious consequences. Therefore, it is urgent to propose a new prevention and control method to ensure the safe mining of working faces in shallowly buried, closely spaced coal seam groups under old fire zones. Summary of the Invention

[0003] This invention addresses the problem of gas inrush from the overlying old fire zone in shallow, closely spaced coal seams entering the lower working face, causing excessive levels of toxic and harmful gases and spontaneous combustion in the goaf. It provides a method to ensure safe mining of the working face beneath the old fire zone in shallow, closely spaced coal seams.

[0004] The present invention adopts the following technical solution: a method for ensuring safe mining of working faces in the old fire zone of shallow buried coal seam groups, comprising the following steps.

[0005] S100 – The mining face for the lower coal seam group of shallowly buried, closely spaced coal seams. After the mining face is arranged, multiple sets of observation-venting holes are drilled into the old fire zone in the lower coal seam intake roadway, return roadway, and opening cut. Thermocouples are inserted to measure the temperature at different locations in the old fire zone. Gas samples are taken to analyze the gas composition at different locations in the old fire zone. The observation-venting holes are used to determine whether spontaneous combustion of coal still exists in the old fire zone. After the test is completed, all observation-venting holes are closed.

[0006] Before the S200 working face is mined, multiple sets of surface nitrogen injection-grouting holes are drilled from the ground towards the old fire area, located directly above it in the middle of the intake and return airways.

[0007] Before the S300 working face is mined, liquid nitrogen is injected into the old fire zone through the nitrogen injection-grouting hole on the ground. The injection of liquid nitrogen is used to extinguish any potential fire sources in the old fire zone, inertate the goaf, and balance the pressure difference between the goaf and the ground.

[0008] After the S400 degassing is completed, the working face is back-mined. Mud is injected into the old fire zone from the surface nitrogen injection-grouting hole until the surface nitrogen injection-grouting hole is above the goaf suffocation zone. The mud is then used to seal the fractures in the stope.

[0009] In step S100, all observation-exhaust ports are equipped with pressure gauges, flow control valves, and air intake valves.

[0010] In step S100, the interval between the observation and exhaust ports located in the intake air roadway and the return air roadway is 80-100m, and the interval between the observation and exhaust ports located in the cut-out is 40-60m.

[0011] In step S200, the ground nitrogen injection-grouting holes and the observation-exhaust holes in the intake and return air channels are kept consistent, with an interval of 80-100m.

[0012] The specific process of step S300 is as follows: During the nitrogen injection process, some observation-venting holes are kept open. The gas in the old fire zone is driven in stages through the observation-venting holes and discharged to the next coal mining face. The toxic and harmful gases in the old fire zone are discharged into the return air roadway by the working face ventilation and then discharged from the mine. Various gas concentration sensors are installed in the return air roadway of the working face. The exhaust volume of the observation-venting holes is adjusted in combination with the concentration of various gases to prevent the gas concentration in the working face from exceeding the limit during the exhaust process. When the environment in the old fire zone meets the specified opening conditions, nitrogen injection into the goaf is stopped and all observation-venting holes are sealed. The cooling and exhaust process of the old fire zone is completed.

[0013] In step S400, the ground nitrogen injection-grouting hole is injected into the old fire zone 20-30m after the working face.

[0014] Compared with existing technologies, this invention drills observation and venting holes in the working face roadway and cut-out into the old fire zone; and drills a row of surface nitrogen injection and grouting holes directly above the working face into the old fire zone. By injecting liquid nitrogen, potential fire sources in the old fire zone are extinguished, the goaf is inertized, and the pressure difference between the goaf and the surface is balanced. This preemptively discharges toxic and harmful gases into the next coal face, and the working face ventilation system removes these gases from the mine, preventing their intrusion into the working face during the next coal face mining. After nitrogen injection is stopped, the working face is mined. Once the surface nitrogen injection and grouting holes lag behind the working face by 20-30m, slurry is injected into the old fire zone using these existing holes, achieving multiple uses for a single hole and saving costs. Grouting is stopped when the nitrogen injection and grouting holes are located above the goaf suffocation zone. By injecting grout into the old fire zone, the air leakage channels between the lower coal goaf, the upper coal goaf (old fire zone), and the ground surface were effectively sealed, preventing spontaneous combustion in the goaf and thus ensuring the safe mining of the working face below the old fire zone. Attached Figure Description

[0015] Figure 1 This is a three-dimensional layout diagram to ensure safe mining of the working face in the old fire zone of shallowly buried coal seam group;

[0016] Figure 2 This is a schematic diagram of the nitrogen injection-grouting holes and observation-venting holes in the goaf of the upper coal seam group of shallowly buried, closely spaced coal seams;

[0017] In the diagram: 1-Ground Nitrogen Injection Hole #1 - Ground Nitrogen Injection Hole #2 - Ground Nitrogen Injection Hole #2 - Ground Nitrogen Injection Hole #3 - Ground Nitrogen Injection Hole #3 - Ground Nitrogen Injection Hole #4 - Ground Nitrogen Injection Hole #4 - Ground Nitrogen Injection Hole #5 - Ground Nitrogen Injection Hole #5 - Ground Nitrogen Injection Hole #6 - Ground - Ground - 8-Pressure Gauge - 9-Observation Hole #15 - Exhaust Hole - 10-Protective Coal Pillar - 11-Gas Intake Valve - 12-Flow Control Valve - 13-Observation Hole #14 - Exhaust Hole - 14-Observation Hole #13 - Exhaust Hole - 15-Observation Hole #12 - Exhaust Hole - 16-Observation Hole #11 - Exhaust Hole - 14-Observation Hole #13 - Exhaust Hole - 15-Observation Hole #12 - Exhaust Hole - 16-Observation Hole #11 - Exhaust Hole - 14-Observation Hole #14 - Exhaust Hole - 15-Observation Hole #12 - Exhaust Hole - 16-Observation Hole #11 - Exhaust Hole - 14-Observation Hole #15 ... Holes; 17-10# observation - vent hole; 18-9# observation - vent hole; 19-8# observation - vent hole; 20-7# observation - vent hole; 21-6# observation - vent hole; 22-5# observation - vent hole; 23-4# observation - vent hole; 24-3# observation - vent hole; 25-2# observation - vent hole; 26-1# observation - vent hole; 27-collapsed rock in the upper coal goaf; 28-intake airway of the lower coal; 29-cut-out of the lower coal; 30-return airway of the lower coal; 31-sealed connecting roadway. Detailed Implementation

[0018] The following is a detailed description of a method for ensuring safe mining of a working face in the old fire zone of a shallowly buried, closely spaced coal seam group, with reference to the accompanying drawings.

[0019] A method for ensuring safe mining of working faces in the old fire zone of shallowly buried, closely spaced coal seams includes the following steps.

[0020] S100 is a shallow-buried, closely spaced coal seam mining face. After the working face layout is completed, observation and venting holes are drilled into the old fire zone in the intake airway 28, return airway 30, and cut-out 29. Thermocouples are inserted to measure the temperature at different locations in the old fire zone. Gas samples are taken through the gas sampling valve 11 to analyze the gas composition at different locations in the fire zone. The observation and venting holes are used to determine whether spontaneous combustion of coal still exists in the old fire zone. After the test is completed, all observation and venting holes are closed. All observation and venting holes are equipped with a pressure gauge 8, a flow control valve 12, and a gas sampling valve 11.

[0021] Before the S200 working face is mined, nitrogen injection-grouting holes 1, 2, 3, 4, 5, and 6 are drilled from the ground surface towards the old fire area at the position between the intake and return airways directly above it.

[0022] Before the S300 working face is mined, liquid nitrogen is injected into the old fire zone through the No. 1 nitrogen injection-grouting hole 1 on the ground. The injection of liquid nitrogen extinguishes any potential fire sources in the old fire zone, inertizes the goaf, and balances the pressure difference between the goaf and the ground. During the nitrogen injection process, the No. 1 observation-exhaust hole 26 and No. 2 observation-exhaust hole 25 in the intake and return airways on both sides, as well as the adjacent No. 3 observation-exhaust hole 24 and No. 4 observation-exhaust hole 23, are kept open. The remaining observation-exhaust holes are closed. The gas in the old fire zone is discharged to the next coal mining face through the observation-exhaust holes in the intake airway 28 and return airway 30. The toxic and harmful gases in the old fire zone are discharged into the return airway through the working face ventilation, and then discharged from the mine. Once the environment within the old fire zone measured by observation holes #1 and #2 meets the opening conditions stipulated in the "Coal Mine Safety Regulations," nitrogen injection into surface nitrogen injection hole #1 will cease, and liquid nitrogen will be injected into the old fire zone from surface nitrogen injection hole #2. While injecting liquid nitrogen into the old fire zone from surface nitrogen injection hole #2, keep observation holes #3 (24), #4 (23), and adjacent observation holes #5 (22) and #6 (21) in the intake and return airways on both sides unobstructed. Close the remaining observation holes to displace the gas from the old fire zone. Continue injecting nitrogen into surface nitrogen injection hole #2 until the environment within the old fire zone measured by observation holes #3 and #4 meets the opening conditions stipulated in the "Coal Mine Safety Regulations." Then, stop injecting nitrogen into surface nitrogen injection hole #2 and inject liquid nitrogen into the old fire zone from surface nitrogen injection hole #3. Repeat the above steps to grade and expel toxic and harmful gases from the old fire zone until all observation and exhaust ports measure that the environment within the old fire zone meets the opening conditions stipulated in the "Coal Mine Safety Regulations," at which point nitrogen injection into the goaf is stopped. Install gas concentration sensors for O2, CH4, CO, CO2, and H2 in the return airway of the working face. Adjust the exhaust volume of the observation and exhaust ports based on the concentrations of O2, CH4, CO, CO2, and H2 to prevent the gas concentration at the working face from exceeding the limit during exhaust. After all surface nitrogen injection and grouting ports stop injecting nitrogen into the goaf, seal all observation and exhaust ports. The cooling and exhaust process of the old fire zone is complete.

[0023] After the S400 degassing is completed, the working face is back-mined. When the No. 6 nitrogen injection-grouting hole 6 on the surface lags behind the working face by 20-30m, grouting begins from the No. 6 nitrogen injection-grouting hole 6 into the old fire zone. Grouting stops when the No. 6 nitrogen injection-grouting hole 6 is above the goaf asphyxiation zone. Then, when the No. 5 nitrogen injection-grouting hole 5 on the surface lags behind the working face by 20-30m, grouting begins from the No. 5 nitrogen injection-grouting hole 5 into the old fire zone. Grouting stops when the No. 5 nitrogen injection-grouting hole 5 is above the goaf asphyxiation zone. The above steps are repeated, sequentially injecting grout from the No. 6 nitrogen injection-grouting hole 6 to the No. 1 nitrogen injection-grouting hole 1 into the old fire zone to seal the stope fractures.

[0024] like Figure 1 , 2As shown, the nitrogen injection-grouting hole drilled directly above the working face, in the middle of the intake and return roadways, is mainly used to compress the gas in the old fire zone from the middle to the observation-venting hole in the intake and return airway, and then discharge it into the lower mining face, thus utilizing the working face ventilation to remove it from the mine. Flow control valves are installed in the observation-venting hole to regulate the exhaust volume and prevent the gas concentration at the working face from exceeding the limit during the exhaust process. After the cooling and exhaust process of the old fire zone is completed, mining begins. Existing nitrogen injection-grouting holes are used to inject mud into the old fire zone 20-30m behind the working face, effectively sealing the mining area fractures and achieving multiple uses for a single hole, saving costs. Through these measures, safe mining of the working face below the old fire zone of the shallowly buried, closely spaced coal seam group is achieved.

[0025] Finally, it should be noted that the above description is only the technical solution of the present invention and does not limit it. Any modifications, improvements, or equivalent substitutions made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for ensuring safe mining of working faces beneath old fire zones in shallowly buried, closely spaced coal seam groups, characterized in that: Includes the following steps, S100 ~ Excavation of the lower coal seam group of shallow buried close-range coal mining face. After the mining face is arranged, multiple sets of observation-venting holes are drilled into the old fire zone in the lower coal intake air roadway (28), return air roadway (30) and opening cut (29). Thermocouples are inserted to measure the temperature at different locations in the old fire zone. Gas samples are taken to analyze the gas composition at different locations in the old fire zone. The observation-venting holes are used to determine whether there is still coal spontaneous combustion in the old fire zone. After the test is completed, all observation-venting holes are closed. Before the S200 working face is mined, multiple sets of ground nitrogen injection-grouting holes are drilled from the ground towards the old fire area, located directly above it in the middle of the intake and return airways. Before the S300 working face is mined, liquid nitrogen is injected into the old fire zone through the nitrogen injection-grouting hole on the ground. The injection of liquid nitrogen is used to extinguish any possible fire sources in the old fire zone, inertize the goaf, and balance the pressure difference between the goaf and the ground. During nitrogen injection, some observation and venting holes are kept open. Gases in the old fire zone are graded and driven out through these holes and discharged to the next coal face. The working face ventilation is used to discharge toxic and harmful gases from the old fire zone into the return airway and then out of the mine. Various gas concentration sensors are installed in the return airway of the working face. The exhaust volume of the observation and venting holes is adjusted according to the concentration of various gases to prevent the gas concentration at the working face from exceeding the limit during the exhaust process. When the environment in the old fire zone meets the specified opening conditions, nitrogen injection into the goaf is stopped, and all observation and venting holes are sealed. The cooling and exhaust process of the old fire zone is then completed. After the S400 degassing is completed, the working face is back-mined. Mud is injected into the old fire zone from the surface nitrogen injection-grouting hole until the surface nitrogen injection-grouting hole is above the goaf suffocation zone. The mud is then used to seal the fractures in the stope.

2. The method for ensuring safe mining of the working face beneath the old fire zone of a shallowly buried, closely spaced coal seam group according to claim 1, characterized in that: In step S100, all observation-exhaust ports are equipped with pressure gauges (8), flow control valves (12), and air intake valves (11).

3. The method for ensuring safe mining of the working face beneath the old fire zone of a shallowly buried, closely spaced coal seam group according to claim 1, characterized in that: In step S100, the interval between the observation and exhaust holes located in the inlet air duct (28) and the return air duct (30) is 80-100m, and the interval between the observation and exhaust holes located in the cut-out eye is 40-60m.

4. The method for ensuring safe mining of the working face beneath the old fire zone of a shallowly buried, closely spaced coal seam group according to claim 3, characterized in that: In step S200, the ground nitrogen injection-grouting hole and the observation-exhaust hole in the intake and return air duct are kept consistent and spaced 80-100m apart.

5. The method for ensuring safe mining of the working face beneath the old fire zone of a shallowly buried, closely spaced coal seam group according to claim 1, characterized in that: In step S400, the nitrogen injection-grouting hole on the ground lags behind the working face by 20-30m before injecting mud into the old fire zone.

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