Method for preventing and controlling spontaneous combustion of overlying coal seam goaf in thick coal seam with slicing mining

Abstract

The application discloses a kind of prevention and control methods for spontaneous combustion of overlying coal seam goaf coal in thick coal seam layered mining, and the method comprises the following steps: during overlying coal seam mining, before overlying coal seam working face is closed after mining, during lower layer coal seam tunneling, during lower layer coal seam mining and other different stages, corresponding coal spontaneous combustion prevention and control technology is adopted, a prevention and control system is established, which takes spraying cold storage resistance solution, liquid carbon dioxide injection and nitrogen injection as the core, and combines other fire prevention and extinguishing technologies, to realize continuous and efficient prevention and control of overlying coal seam goaf coal spontaneous combustion target management area.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of prevention and control of coal spontaneous combustion in goaf of overlying coal seam in thick coal seam with sublevel mining, and particularly relates to a method for preventing and controlling coal spontaneous combustion in goaf of overlying coal seam in thick coal seam with sublevel mining. BACKGROUND

[0002] Due to the characteristics of thick coal seam, sublevel mining is usually adopted. During the mining of lower coal seam, the roof and coal body are more likely to be broken under the disturbance of tunneling and coal mining, so that there are a large number of air leakage channels between the upper and lower coal seams. The residual coal in the goaf of the upper coal seam is easily oxidized to form heat accumulation under the long-term effect of air leakage, and eventually develops into a coal spontaneous combustion disaster, which seriously threatens the safety production of the lower coal seam working face.

[0003] At present, the prevention and control of coal spontaneous combustion in thick coal seam mainly focuses on the prevention and treatment of coal spontaneous combustion hazards in the goaf of the working face in the coal seam, such as CN110821552A discloses a comprehensive control method for gas and coal spontaneous combustion in near-horizontal thick coal seam mining. By arranging grouting pipe and gas injection pipe in the air inlet lane of the coal seam mining working face, non-combustible solidified foam is continuously injected into the goaf through the grouting pipe, and then nitrogen is continuously injected into the goaf through the gas injection pipe, thereby achieving the prevention and control of coal spontaneous combustion disaster in the goaf of the working face in the coal seam. However, how to solve the problems such as difficult access and long-term treatment of coal spontaneous combustion in the goaf of the overlying coal seam in the sublevel mining thick coal seam has not been involved. SUMMARY

[0004] The purpose of the present application is to provide a method for preventing and controlling coal spontaneous combustion in the goaf of the overlying coal seam in the sublevel mining thick coal seam, so as to solve the problems such as concealed position, difficult access and long-term treatment of coal spontaneous combustion disaster in the goaf of the overlying coal seam in the thick coal seam.

[0005] To achieve the above-mentioned purpose, the present application provides a method for preventing and controlling coal spontaneous combustion in the goaf of the overlying coal seam in the sublevel mining thick coal seam, comprising the following steps:

[0006] Step 1), during the mining of the overlying coal seam, spray the cold storage and resistance solution in the fault structure area where a large amount of coal is lost to cover the loose residual coal; after the covered residual coal enters the range of 15-10m of the goaf, inject liquid carbon dioxide through the buried pipe to cool and lower the temperature of the loose residual coal area;

[0007] Step 2) after the mining of the overlying coal seam working face is completed, bury the grouting pipe in the upper and lower ports of the stop line before sealing, and inject fly ash slurry or yellow mud slurry into the stop line area after the working face is sealed, with a water-solid ratio of 1:3, so as to block the air leakage channels at the upper and lower ports of the stop line, and block the cracks at the stop line by injecting a sufficient amount of mud slurry;

[0008] Step 3) During the excavation of the lower layer coal seam, when the excavation roadway encounters the upper layer stop line, the roadway is sprayed in full section in advance, the spraying raw material is mortar concrete, the spraying thickness is 100mm-150mm, and the sprayed roadway is manually finished with cement and yellow mud to reduce air leakage; if the stop line and the lower layer roadway have serious air leakage, drill every 3-5m in the stop line section of the transportation roadway, inject cement slurry to block the air leakage channel, and the water-cement ratio is 0.6;

[0009] Step 4) During the mining of the lower layer coal seam, if the upper layer goaf spontaneous combustion occurs, first, based on the geological data of the thick coal seam layer mining, combined with the detection technology, the area where the overlying coal seam goaf residual coal thickness exceeds 0.4m is determined as the coal spontaneous combustion target control area; secondly, drill holes in the air inlet roadway or air return roadway of the working face of the lower layer coal seam to the coal spontaneous combustion target control area of the overlying coal seam goaf, and the final hole position is located 2.5-4m above the loose residual coal in the target control area, and then the above drilling holes are used to inject cold storage and resistance solution into the target control area; subsequently, after the cold storage and resistance solution in all drilling holes is injected, nitrogen is continuously injected into the target control area through the drilling holes, further driving the cold storage and resistance solution to penetrate into the coal rock body crack and pore structure of the coal spontaneous combustion control area in the overlying coal seam goaf, and expanding the control range of the cold storage and resistance solution to the coal spontaneous combustion; after all the drilling holes complete the nitrogen injection work, liquid carbon dioxide is injected into the target control area through the drilling holes, which rapidly expands and diffuses in the target control area due to the high expansion ratio of liquid carbon dioxide, and at the same time, the target control area is cooled and cooled by the rapid expansion and heat absorption characteristics of liquid carbon dioxide; in addition, the cold storage and resistance solution is frozen and stores cold energy in the overlying coal seam goaf under the action of ultra-low temperature of liquid carbon dioxide, which has the effect of cooling the target control area for a long time; finally, after the drilling holes complete the liquid carbon dioxide injection work, the hole valve is closed to prevent air leakage from the drilling holes; with the continuous advancement of the coal mining face, the above steps are repeated to control the coal spontaneous combustion in the target control area covered by each drilling hole.

[0010] Preferably, the drilling holes in step 4) are all opened at a position 1.8-2.2m above the floor of the working face roadway of the lower layer coal seam, each drilling hole covers a coal spontaneous combustion target control area of the overlying coal seam goaf with a radius of 5m, and the number of actually constructed drilling holes is determined on this basis; the opening interval of each drilling hole is not less than 1.5m.

[0011] Preferably, the hole sealing in step 4) adopts two sealing and two injection, the sealing length is not less than 10m, the distance between the outer bag and the hole is not more than 2m, the whole length is a downhole pipe, the first 3m is a screen pipe, and the rest is a smooth pipe.

[0012] Preferably, the cold storage resistance solution in the step 1) and step 4) is prepared by mixing and stirring high water-absorbing resin, chlorine salt resistance agent, refrigerant, magnesium nitrate hexahydrate and water according to the mass ratio of 5:20:20:10:45.

[0013] Preferably, the high water-absorbing resin is acrylic resin; the chlorine salt resistance agent is one or more combinations of sodium chloride, magnesium chloride and calcium chloride; and the refrigerant is prepared by mixing propylene glycol and glycerol according to the mass ratio of 50:50.

[0014] Preferably, the nitrogen injection time of each borehole in step 4) is not less than 8h, the nitrogen flow is not less than 300m 3 / h, and the purity of nitrogen is higher than 98%.

[0015] Preferably, before the liquid carbon dioxide injection in step 4), the water in the borehole channel should be completely displaced by nitrogen, and the liquid carbon dioxide injection amount of each borehole is not less than 2 tons.

[0016] Further, according to the needs of the spontaneous combustion prevention and control of the coal spontaneous combustion target management area in the overlying coal seam goaf, the borehole can also be repeated step 4) to further prolong the prevention and control period of coal spontaneous combustion.

[0017] Compared with the prior art, the present application has the following beneficial effects:

[0018] 1、The present application realizes the continuous and efficient prevention and control of the coal spontaneous combustion target management area in the overlying coal seam goaf by taking targeted coal spontaneous combustion prevention and control technology during the overlying coal seam mining, before the closure of the overlying coal seam working face, during the excavation of the lower layer coal seam, during the mining of the lower layer coal seam, etc.

[0019] 2、The present application realizes accurate positioning of the area with high risk of coal spontaneous combustion in the lower coal seam during mining by combining geological data and drilling sampling and other detection technologies, so that the treatment measures can be concentrated in the area where the overlying coal seam goaf residual coal thickness exceeds 0.4m, unnecessary repeated investigation and treatment work can be reduced, efficient use of prevention and control resources can be ensured, and the overall prevention and control effect is improved. In the drilling construction, the opening position of each drill hole is set at a position of 1.8-2.2m above the roadway floor, and each drill hole can cover a coal spontaneous combustion target treatment area with a radius of 5m. This design ensures the accuracy of the injection of the cold storage and inhibition solution, so that the inhibition solution can enter the fissures as much as possible, and the pertinence and effectiveness of coal spontaneous combustion prevention and control are further improved. The drilling spacing is set to be not less than 1.5m, which ensures that the cold storage and inhibition solution can be evenly distributed in the target area, avoiding the problem of insufficient prevention and control range due to too large spacing. In addition, the two-plugging and two-injection sealing method ensures the sealing of the hole, preventing the leakage or loss of the cold storage and inhibition solution; the tightness of the hole enhances the long-term stability of the cold storage and inhibition solution, ensuring that the fire prevention effect can last for a long time.

[0020] 3、The present application uses nitrogen driving mechanism, which utilizes the unique physical properties and action principle of nitrogen to enhance the permeability of the cold storage and inhibition solution in the coal seam fissures and pores. At the same time, compared with CO2 gas injection, the density of nitrogen is smaller than that of air, so nitrogen will move upward, avoiding the problem of downward flow from the drill hole leakage, which is beneficial to long-term storage in the overlying coal seam goaf coal spontaneous combustion target treatment area. By injecting nitrogen into the overlying goaf coal spontaneous combustion target treatment area, using the high-pressure driving effect of nitrogen, the cold storage and inhibition solution can be effectively pushed to penetrate along the fissures and pores of the coal seam, which helps to eliminate the limitation of the permeability of the cold storage and inhibition solution, which is often restricted by the complexity of the pore structure of the coal seam and uneven distribution of fissures, so as to ensure that the cold storage and inhibition solution can cover most of the fissures and pores in the overlying goaf coal spontaneous combustion target treatment area, thereby increasing its contact area with the goaf residual coal and further improving the fire prevention effect. At the same time, nitrogen and cold storage and inhibition solution can synergistically penetrate into the fissures and pores of the overlying goaf coal spontaneous combustion target treatment area, occupying the oxygen space in the fissures and pores, reducing the oxygen concentration in the target treatment area, and thus blocking the oxidation reaction between coal and oxygen. In addition, after the nitrogen is driven, the water in the drill hole is also fully displaced by nitrogen, so that the subsequent continuous injection of liquid CO2 into the drill hole will not cause the phenomenon of pipe blockage, pipe explosion and large amount of CO2 gas leakage in the construction area such as roadway, realizing safe and continuous injection of liquid CO2.

[0021] 4. In this invention, after nitrogen injection is completed in each borehole, liquid CO2 is further injected into the target area through the borehole. Utilizing the low temperature of liquid CO2 (between -56.4℃ and -78℃), its extremely high expansion ratio, and strong heat absorption capacity, liquid CO2 rapidly expands and absorbs a large amount of heat after injection into the target area, lowering the coal seam temperature and effectively inhibiting spontaneous combustion. Furthermore, liquid CO2 not only lowers the coal temperature in the target treatment area of ​​the overlying goaf through direct cooling, but also transfers cold energy to the pre-injected cold-storage inhibitory solution through heat conduction. This allows the cold-storage inhibitory solution to slowly release cold energy within the coal seam, continuously maintaining a low temperature and extending the duration of the control effect. Traditional fire prevention and extinguishing technologies often require frequent reapplication of fire-retardant materials due to short-lived control effects or unstable temperature control. This not only increases costs but may also lead to uncertainty in the effectiveness of the control measures. This invention, however, combines the injection of a long-lasting cold-storage inhibitory solution with liquid CO2, making the control measures more durable and significantly reducing the frequency of material injection. This lowers the cost of controlling spontaneous combustion of coal in underground mines, improving overall safety and economic efficiency. Furthermore, the liquid CO2, after absorbing heat and vaporizing to form CO2 gas, has a higher density than air and migrates towards the floor of the overlying coal seam goaf. Combined with the nitrogen gas injected previously and migrating towards the roof of the overlying coal seam goaf, this achieves full-range inerting of the goaf across its three-dimensional space from top to bottom.

[0022] 5. The cold storage inhibitory solution used in this invention mainly comprises superabsorbent resin, chloride salt inhibitor, refrigerant, magnesium nitrate hexahydrate, and water. Among them, the chloride salt inhibitor (sodium chloride, magnesium chloride, calcium chloride) is widely used in current underground applications and has a good effect on inhibiting coal spontaneous combustion. The refrigerant is a mixture of propylene glycol and glycerol. The freezing point of the propylene glycol solution can reach about -50°C, and the freezing point of the glycerol solution can reach about -40°C. By adding appropriate concentrations of propylene glycol and glycerol, the freezing point of the cold storage inhibitory solution can be lowered to below -20°C. Moreover, the chloride salt inhibitor also lowers the freezing point of the solution. The lower freezing point makes the inhibitory solution have better cold storage capacity under the same conditions, which helps to absorb more liquid CO2 and release it gradually in the future, thus prolonging the cooling time of the target area for coal spontaneous combustion control in the overlying goaf. Acrylic superabsorbent resin is non-toxic and harmless, and has the function of repeatedly releasing and absorbing water. When it is prepared into an inhibitory solution with other components, it exists in the form of water-absorbing small particles. After being injected into loose coal, it can effectively adhere to the pore structure of the coal. The particle shape can also block the cracks in the coal. Especially after reacting with high-cold liquid CO2, it forms hard ice particles similar to "ice crystals", which can play an excellent role in blocking cracks and pores and prevent the oxidation of oxygen with the active structure on the surface of coal. Meanwhile, propylene glycol and glycerol are surfactants that can effectively reduce the surface tension of water, which helps the cold storage inhibitory solution to better penetrate and diffuse into the pores and fissures of the coal body in the target treatment area of ​​spontaneous combustion in the overlying goaf, thereby enhancing the wetting and cooling effect on the coal body. When the coal oxidation temperature rises to between 70-90℃, magnesium nitrate hexahydrate will absorb heat and gradually lose its water of crystallization, and at 400℃, it will absorb heat and decompose into magnesium oxide. Both the process of losing water of crystallization and the endothermic decomposition process can absorb the heat released by the oxidation of the coal body in the target treatment area of ​​spontaneous combustion, thereby reducing the coal temperature and further enhancing the inhibitory effect on spontaneous combustion. Detailed Implementation

[0023] This invention provides a method for preventing spontaneous combustion of coal in the goaf of an overlying coal seam during layered mining. By adopting targeted coal spontaneous combustion prevention and control technologies at different stages, such as during the mining of the overlying coal seam, before the overlying coal seam working face is closed after mining, during the tunneling of the lower coal seam, and during the mining of the lower coal seam, the method can achieve continuous and efficient prevention and control of spontaneous combustion of coal in the target area of ​​the overlying coal seam goaf.

[0024] The specific steps are as follows:

[0025] Step 1) During the mining of the overlying coal seam, accelerate the advance and reduce the amount of coal lost in the goaf. Spray a cold storage and inhibition solution in areas such as fault structures where there is a lot of coal loss to cover the loose coal residue. After the covered coal residue enters the goaf area within 15-10m, inject liquid CO2 through buried pipes to cool down the loose coal residue area.

[0026] Step 2) After the working face of the overlying coal seam is mined, the grouting pipes are embedded in the upper and lower ports of the stopping line before being closed, and a large amount of fly ash slurry or yellow mud slurry is injected into the area of the stopping line after the working face is closed, with a water-solid ratio of 1:3, so as to block the air leakage channel of the upper and lower ports of the stopping line, and the gap at the stopping line is blocked by injecting a sufficient amount of mud slurry;

[0027] Step 3) During the excavation of the lower layer coal seam, the damage to the roof is minimized, and full-face spraying is performed on the roadway in advance when the upper layer stopping line is encountered during the excavation of the roadway, the spraying material is mortar concrete, the spraying thickness is 100mm-150mm, and the spraying is followed by manual cement and yellow mud troweling to reduce air leakage; if the stopping line and the lower layer roadway have serious air leakage, drilling can be performed every 3-5m in the stopping line segment of the transportation roadway, and cement slurry is injected to block the air leakage channel, with a water-cement ratio of 0.6;

[0028] Step 4) During the mining of the lower layer coal seam, if the upper layer goaf spontaneous combustion is encountered, first, based on the geological data of the thick coal seam layer mining, combined with the detection technology, the area where the thickness of the overlying coal seam goaf is more than 0.4m is determined as the coal spontaneous combustion target control area; secondly, drilling is performed in the air intake roadway or the air return roadway of the lower layer coal seam to the coal spontaneous combustion target control area of the upper layer goaf, and the final hole position is located 2.5-4m above the loose coal in the target control area, and the above-mentioned drilling is used to inject the cold storage and resistance solution into the target control area; then, after the cold storage and resistance solution of all the drillings is injected, nitrogen is continuously injected into the target control area through the drillings, further driving the cold storage and resistance solution to penetrate into the crack and pore structure of the coal rock body in the coal spontaneous combustion control area of the overlying goaf, and expanding the control range of the cold storage and resistance solution to the coal spontaneous combustion; after the nitrogen injection work of all the drillings is completed, liquid carbon dioxide is injected into the target control area through the drillings, which rapidly expands and diffuses in the target control area due to its high expansion ratio, and at the same time, the target control area is cooled and cooled by its rapid expansion and heat absorption characteristics; in addition, the cold storage and resistance solution is stored in the overlying goaf under the action of the ultra-low temperature of the liquid carbon dioxide, which has the effect of cooling the target control area for a long time; finally, after the liquid carbon dioxide injection work of the drillings is completed, the hole valve is closed to prevent air leakage; with the continuous advancement of the coal mining face, the above steps are repeated to control the coal spontaneous combustion in the target control area covered by the drillings.

[0029] The application will be further described in conjunction with the examples.

[0030] Implementation background: a mine has 15-17 The coal seam geological structure is relatively simple, but the coal seam is thick, and the layer-by-layer mining method is adopted, and the interval between the upper and lower layers is only 1.0m. 15-17 -1208 上The working face mainly recovers the upper sublevel coal seam, which has been recovered in 2020. At present, the mine is recovering the lower coal seam of the Yijia 15-17 -1208 下 The working face, due to the close interval between the upper and lower sublevels, is in the Yijia 15-17 -1208 下 During the recovery process of the working face, the roof is severely broken, and there is a situation of air leakage from the lower sublevel working face to the goaf of the upper sublevel working face, which leads to the Yijia 15-17 -1208 上 The residual coal in the goaf of the working face has been in a state of air leakage for a long time. In early October 2023, the CO2 concentration in the sealed detection of the return air roadway of the Yijia 15-17 -1208 上 reached 120 ppm, indicating that spontaneous combustion occurred in the goaf of the overlying coal seam. In order to effectively inhibit the coal spontaneous combustion disaster in the goaf of the overlying coal seam, by using the nitrogen injection pipeline pre-buried in the Yijia 15-17 -1208 上 air inlet roadway, a large-scale inerting was carried out, which made the CO concentration in the sealed monitoring place of the return air roadway of the Yijia 15-17 -1208 上 gradually decreased to 35 ppm, but after the nitrogen injection stopped, the CO concentration in the monitoring place gradually increased to more than 120 ppm. This is because after the nitrogen injection, only inerting and oxygen reduction were achieved, but the high temperature point was not cooled, so the coal spontaneous combustion fire area in the goaf was not effectively eliminated and controlled, which seriously affected the normal recovery of the Yijia 15-17 -1208 下 working face of the lower sublevel. In order to efficiently prevent and control the coal spontaneous combustion disaster in the goaf of the Yijia 15-17 -1208 上 working face of the overlying coal seam, the mine adopts a control method for preventing and controlling the spontaneous combustion of coal in the goaf of the overlying coal seam in the layered mining of thick coal seam. Since the mine has completed the mining of the overlying coal seam, the closure of the Yijia

[0031] Step 1) Based on the geological data of the layered mining of thick coal seam, the area where the residual coal thickness in the goaf of the Yijia 15-17 -1208 上 working face of the overlying coal seam exceeds 0.4 m is determined, and the length range of the target control area of coal spontaneous combustion is determined to be 25 m and the width range is 15 m through drilling sampling analysis and other methods.

[0032] Step 2) Since the target area is close to the return air roadway position of the Yijia 15-17 -1208 下 working face of the lower sublevel, the Yijia 15-17 -1208下 The return airway of the working face is upwardly overlying the goaf, and the drilling is performed in the goaf. During the drilling, the drilling opening is made at a position 1.8 m above the floor of the roadway. Each drilling can cover a coal spontaneous combustion danger area of a radius of 5 m in the goaf, and 8 drillings are made in the goaf overlying the working face. The drilling opening spacing of each drilling is 2 m. A centralizer with the same diameter as the drill bit is used in the drilling. During the drilling into the roof rock, a high rotation speed and slow advancement are maintained to reduce the drilling trajectory deviation. Two sealing and two injection are used for the hole sealing, the hole sealing length is 12 m, the outer bag is 1.5 m away from the hole opening, the whole process is under the iron pipe, the first 3 m uses a screen pipe, and the light pipe is used outside the screen pipe. The final hole position is 4 m above the loose residual coal in the target treatment area;

[0033] Step 3), after the opening of each drilling, the drilling is used to inject the long-acting coal spontaneous combustion inhibition and cold storage solution into the coal spontaneous combustion target treatment area overlying the working face goaf, which can effectively absorb heat, reduce the temperature of the coal seam, prevent the entry of oxygen and reduce the risk of coal spontaneous combustion. During the injection, the cold storage and inhibition solution penetrates into the fissure and pore structure of the target treatment area through the drilling, covering the target area.

[0034] The long-acting coal spontaneous combustion inhibition and cold storage solution used in the embodiment is prepared by mixing and stirring high water absorption resin, chlorine salt inhibitor, refrigerant, magnesium nitrate hexahydrate and water according to a mass ratio of 5:20:20:10:45. First, 20% of the chlorine salt inhibitor is taken according to the mass ratio, and the chlorine salt inhibitor is magnesium chloride. Then, 20% of the refrigerant is taken, and the refrigerant is prepared by mixing propylene glycol and glycerol according to a mass ratio of 50:50. 10% of magnesium nitrate hexahydrate and 5% of high water absorption acrylic acid resin are taken, and 45% of water is used as a solvent. The above components are fully dissolved. Under the action of the stirrer, continuous stirring is carried out for 10-20 minutes to ensure that all components are completely dissolved and uniformly mixed to obtain a stable cold storage and inhibition solution. Under the action of propylene glycol and glycerol, the freezing point of the cold storage and inhibition solution is reduced to below -20℃. The lower freezing point makes the inhibition solution have better cold storage capacity under the same conditions, which helps to absorb more cold energy of liquid CO2, store cold energy by freezing in the coal spontaneous combustion target treatment area, and gradually and slowly release the absorbed cold energy after the oxidation and heating of the coal body, thereby prolonging the cooling time of the residual coal in the goaf.

[0035] Step 4), after the cold storage and inhibition solution in each drilling is injected, nitrogen is continuously injected into the coal spontaneous combustion target treatment area overlying the working face goaf through the drilling. The injection time is 8 h, the nitrogen flow is 500 m 3 / h, and the purity of the injected nitrogen is 98.5%. The nitrogen further drives the cold storage and inhibition solution to penetrate into the fissure and pore structure of the loose residual coal in the target treatment area, thereby expanding the control range of the cold storage and inhibition solution on coal spontaneous combustion.

[0036] Step 5), after each borehole is completed, the water in the borehole channel is determined to be completely expelled by nitrogen, and liquid CO2 is further injected into the goaf of the overlying working face through the borehole, the amount of liquid CO2 injected into each borehole is 2 tons, the liquid CO2 is rapidly expanded and diffused in the target treatment area by virtue of the high expansion ratio of the liquid CO2, and the target treatment area is cooled and cooled by the rapid expansion heat absorption characteristics of the liquid CO2; in addition, the cold storage and inhibition solution is frozen and stores cold in the coal spontaneous combustion target treatment area of the overlying goaf under the action of the ultra-low temperature of the liquid CO2, and has the effect of cooling the target treatment area for a long time;

[0037] Step 6), after the liquid CO2 injection work of each borehole is completed, the valve is immediately closed to ensure that the borehole is sealed to avoid gas leakage and reduce the control effect. When closing the valve, the sealing condition of each borehole is comprehensively checked to ensure that the sealing components such as the valve and the pipeline connection are not loose or damaged, so as to prevent the injection medium from leaking or external air from entering the borehole, which affects the cooling effect of the liquid CO2 and the stability of the cold storage and inhibition solution. At the same time, the injection amount, injection pressure and sealing time of each borehole are recorded to form a systematic construction file for subsequent monitoring and maintenance. After the borehole is sealed, the surrounding area of the borehole is detected to confirm that the sealing effect is good and there is no gas emission phenomenon, so as to ensure the integrity and continuity of the entire control system.

[0038] Step 7), as the coal mining face advances, steps 1) to 6) are repeated to control the coal spontaneous combustion in the target treatment area covered by each borehole.

[0039] In addition, according to the needs of the overlying goaf coal spontaneous combustion control, the formed borehole continues to repeat steps 3) to 7), thereby further prolonging the coal spontaneous combustion control period.

[0040] After the coal spontaneous combustion prevention and control method for the overlying goaf of the thick coal seam is proposed, for the area where the residual coal thickness of the overlying goaf exceeds 0.4m, the precise drilling and injection of the cold storage and inhibition solution are adopted, and the nitrogen driving and liquid CO2 refrigeration long-acting cooling method is adopted, so that the coal spontaneous combustion hazard of the overlying goaf of the thick coal seam is effectively controlled, and the coal spontaneous combustion hazard of the overlying goaf of the thick coal seam is effectively controlled. 15-17 -1208 上 The CO concentration gradually decreases and stabilizes at 0ppm at the return airway closed monitoring point, indicating that the overlying goaf of the thick coal seam has been effectively controlled. 15-17 -1208 上 The residual coal oxidation and high temperature hazard in the goaf of the working face are effectively inhibited, thereby completely eliminating the coal spontaneous combustion disaster in the overlying goaf of the upper layer, and also ensuring the safety of the lower layer. 15-17 -1208 下The working face mining process is not affected by the overlying goaf coal spontaneous combustion, and the final lower layer has been 15-17 -1208 下 The working face safely completes all the mining work and realizes safe closure, and during this period, the coal seam working face goaf of the upper and lower layers does not have any coal spontaneous combustion high temperature hidden danger.

[0041] The above is only the preferred embodiment of the present application, it should be noted that for those skilled in the art, without departing from the principles of the present application, can make a number of improvements and refinements, these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method for preventing spontaneous combustion of coal in the goaf of an overlying coal seam during layered mining of thick coal seams, characterized in that, The specific steps are as follows: Step 1) During the mining of the overlying coal seam, a cold storage and inhibition solution is sprayed in the fault structure area with a large amount of lost coal to cover the loose residual coal. After the covered residual coal enters the goaf area within 15-10m, liquid carbon dioxide is injected through buried pipes to cool the loose residual coal area. The cold storage and inhibition solution is prepared by mixing and stirring superabsorbent resin, chloride salt inhibitor, coolant, magnesium nitrate hexahydrate and water in a mass ratio of 5:20:20:10:

45. The superabsorbent resin is acrylic resin, the chloride salt inhibitor is one or more combinations of sodium chloride, magnesium chloride and calcium chloride, and the coolant is a mixture of propylene glycol and glycerol in a mass ratio of 50:

50. Step 2) Before the overlying coal seam working face is closed after mining is completed, grouting pipes are buried at the upper and lower ends of the stop mining line in advance. After the working face is closed, fly ash slurry or yellow mud slurry is injected into the stop mining line area with a water-solid ratio of 1:3 to seal the air leakage channels at the upper and lower ends of the stop mining line. Step 3) During the excavation of the lower coal seam, when the roadway encounters the upper mining stop line, the roadway should be sprayed with grout in advance. The grout material is mortar concrete, and the thickness of the grout is 100mm-150mm. After spraying, the surface should be manually plastered with cement and yellow mud to reduce air leakage. If there is serious air leakage between the mining stop line and the lower roadway, drill every 3-5m in the mining stop section of the transport roadway and inject cement grout to seal the air leakage channels. The water-cement ratio is 0.

6. Step 4): During the mining of the lower coal seam, if spontaneous combustion occurs in the goaf, firstly, based on the geological data of the layered mining of thick coal seams and combined with detection technology, determine the area where the thickness of the residual coal in the goaf of the overlying coal seam exceeds 0.4m as the target area for coal spontaneous combustion control. Secondly, drill holes in the intake or return airway of the working face of the lower coal seam to the target area for coal spontaneous combustion control in the goaf of the upper coal seam. The final hole position is located 2.5-4m above the loose residual coal in the target area. A cold-storage inhibitory solution is injected into the target area through these holes. Subsequently, after all the holes have been filled with the cold-storage inhibitory solution, nitrogen is continuously injected into the target area through the holes to further drive the cold-storage inhibitory solution to penetrate into the cracks and pores of the coal and rock mass in the goaf of the overlying coal seam, expanding the control range of the cold-storage inhibitory solution for coal spontaneous combustion. After all the holes have been filled with nitrogen, liquid carbon dioxide is injected into the target area through the holes, utilizing the high expansion rate of liquid carbon dioxide. The carbon dioxide rapidly expands and diffuses within the target treatment area, simultaneously cooling the area by absorbing heat during its rapid expansion. Furthermore, the cold-storing inhibitory solution, under the ultra-low temperature effect of liquid carbon dioxide, freezes and stores cold energy in the overlying coal seam goaf, achieving a long-term cooling effect on the target treatment area. Finally, after the drilling is completed with liquid carbon dioxide injection, the borehole valve is closed to prevent leakage. As the coal face advances, the above steps are repeated to control spontaneous combustion of coal in the target treatment area covered by each borehole. During the drilling process, boreholes are drilled at a position 1.8-2.2m on the floor of the working face roadway of the lower coal seam. Each borehole covers a 5m radius target treatment area for spontaneous combustion of coal in the overlying coal seam goaf, and the actual number of boreholes is determined based on this. The spacing between each borehole is no less than 1.5m. Sealing is done with two plugs and two injections, with a sealing length of no less than 10m. The outer bag is no more than 2m from the borehole opening. Iron pipes are used throughout the entire process, with a screen pipe for the first 3 meters and a smooth pipe for the remaining length.

2. The method for preventing spontaneous combustion of coal in the goaf of an overlying coal seam during layered mining according to claim 1, characterized in that, In step 4), the nitrogen injection time for each borehole shall not be less than 8 hours, and the nitrogen flow rate shall not be less than 300 m³ / h. 3 / h, nitrogen purity is higher than 98%.

3. The method for preventing spontaneous combustion of coal in the goaf of an overlying coal seam during layered mining according to claim 1, characterized in that, Before injecting liquid carbon dioxide as described in step 4), ensure that the water in the borehole channel has been completely displaced by nitrogen gas, and that the amount of liquid carbon dioxide injected into each borehole is not less than 2 tons.

4. The method for preventing spontaneous combustion of coal in the goaf of an overlying coal seam during layered mining according to claim 1, characterized in that, Based on the needs of spontaneous combustion prevention and control in the target area of ​​coal spontaneous combustion in the overlying coal seam goaf, repeat step 4) to further extend the prevention and control period of coal spontaneous combustion.