A method for achieving spontaneous combustion three-zone division and fire prevention and extinguishment by large-diameter drilling

Abstract

The application discloses a method for realizing self-ignition three-zone division and fire prevention and extinguishment by using a large-diameter drilling hole, and the division method comprises the following steps: drilling a large-diameter hole near a roadway, penetrating through a coal seam and extending to a goaf, and arranging a wall-protecting steel pipe in the large-diameter hole, and a hollow orifice reserved gas extraction hole is arranged in the wall-protecting steel pipe; with the forward advance of the large-diameter hole, a gas extraction rod is extended into the goaf to different depth positions through the orifice reserved gas extraction hole to extract gas; the gas is detected to determine the oxygen concentration at different depth positions, and the first critical position and the second critical position of the goaf are determined based on the oxygen concentration, and the oxygen concentrations of the two positions respectively meet the first oxygen critical point and the second oxygen critical point; and the self-ignition three-zone is divided based on the two critical positions. According to the method, the large-diameter hole drilled near the roadway is directly connected with the goaf and the orifice reserved gas extraction hole is arranged, so that the gas extraction rod can be extended into the goaf to extract gas, and the self-ignition three-zone division and the fire prevention and extinguishment of the goaf are realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of disaster prevention and control of goaf in coal mine, in particular to a method for realizing spontaneous combustion three-zone division and fire prevention and extinguishing by using large-diameter drilling. BACKGROUND

[0002] Mine fire is one of the five major disasters in coal mine, which seriously affects the development speed of China's coal industry, seriously threatens the personal safety of coal mine production personnel, and brings great economic losses to coal enterprises. The mine fire has the outstanding characteristics of fast occurrence, wide range and difficult control. At present, the method for dividing the spontaneous combustion "three-zone" of goaf includes dividing by the size of air leakage wind speed in goaf, the size of temperature rise speed gradient in goaf, and the oxygen concentration between zones. However, the most practical method is to divide by the oxygen concentration through the buried tube in goaf in advance. If the goaf appears spontaneous combustion phenomenon, the goaf fire can be controlled by the fire prevention and extinguishing technologies such as yellow mud grouting, pressure injection of resistance agent, three-phase foam, chemical foam and inert gas injection in goaf.

[0003] The goaf tube monitoring system uses the pre-buried tube in the roadway. As the coal mining face is continuously pushed forward, the pre-buried tube in the goaf enters the deep part of the goaf. The gas sampling in the goaf is analyzed by chromatography through the pre-buried tube by using a vacuum pump. However, it is found in the field that the pre-buried tube is easily broken, scratched, scraped and buried by the falling gangue of the goaf roof, causing the tube to be damaged and leaking, and the vacuum pump gas suction pipeline is easily blocked or interrupted, resulting in inaccurate monitoring data. The large-diameter drilling is constructed in the adjacent roadway, and the steel pipe is placed in the hole. Since the large-diameter drilling is directly connected with the goaf and the steel pipe is placed in the large-diameter drilling, the long-term stability of the large-diameter drilling and the smooth development of the sampling work can be ensured. The gas sampling at different positions in the direction of the goaf working face can be realized by the gas sampling rod of different lengths extending into the goaf. This sampling method is more convenient and flexible. SUMMARY

[0004] The present application provides a method for realizing spontaneous combustion three-zone division and fire prevention and extinguishing by using large-diameter drilling, which can timely and accurately divide the range of spontaneous combustion "three-zone" of goaf by using large-diameter drilling, and proposes a method for preventing and extinguishing fire in goaf, thereby providing accurate basis for controlling goaf fire.

[0005] The present application discloses a method for realizing spontaneous combustion three-zone division by using large-diameter drilling, comprising:

[0006] The large-diameter drilling is constructed in the adjacent roadway, penetrates the coal seam and extends to the goaf, and the steel pipe is arranged in the large-diameter drilling. The steel pipe is provided with a hollow aperture reserved gas sampling hole;

[0007] With the forward advance of the large-diameter borehole, the gas extraction rod extends into the goaf at different depths through the orifice reserved gas extraction hole to extract gas;

[0008] The collected gas is detected to determine the oxygen concentration at different depths of the goaf, and the first critical position and the second critical position of the goaf are determined based on the oxygen concentration, wherein the oxygen concentrations of the first critical position and the second critical position respectively meet the first oxygen critical point and the second oxygen critical point;

[0009] The spontaneous combustion three zones of the goaf are divided based on the first critical position and the second critical position.

[0010] Further, the large-diameter borehole is obtained by using a large drilling machine to construct in the coal seam, and the diameter ranges from 500 to 800 mm;

[0011] The steel pipe for wall protection has a diameter ranging from 400 to 600 mm, and is used to be deeply inserted into the large-diameter borehole to avoid hole blocking.

[0012] The orifice reserved gas extraction hole has a diameter of 20 mm; the steel pipe for wall protection is provided with a flange plate at one end close to the adjacent roadway, and the flange plate is used to fix the orifice reserved gas extraction hole.

[0013] Further, the gas extraction rod comprises a plurality of single-section pipes connected in sequence, and the length of the single-section pipe is 1.5 m; the vacuum pump is connected to one end of the gas extraction rod close to the adjacent roadway.

[0014] Further, the first oxygen critical point and the second oxygen critical point are respectively 7% and 18% of the oxygen concentration.

[0015] The application further discloses a fire prevention and extinguishing method realized by using the large-diameter borehole, which collects gas from the goaf according to the large-diameter borehole realized spontaneous combustion three zone division method, and the method comprises the following steps:

[0016] The gas extraction rod is deeply inserted into the goaf through the orifice reserved gas extraction hole, the gas is collected through the gas extraction rod, and the temperature of the coal body and the gas composition in the coal body are monitored; if the carbon monoxide concentration in the goaf exceeds the first carbon monoxide critical value; or the temperature of the coal body exceeds the first temperature critical value, it is judged that the goaf will soon catch fire, and the large-diameter borehole needs to be immediately closed;

[0017] The gas injection device starts to inject a specified flow of inert gas into the goaf through the orifice reserved gas extraction hole;

[0018] During the process of injecting inert gas, the temperature of the coal body in the goaf and the change of carbon monoxide gas composition are monitored, if the carbon monoxide gas concentration is monitored to be reduced to below the second carbon monoxide critical value, the flow of the inert gas injection is slowed down, otherwise, the flow of the injection is increased, if the carbon monoxide concentration and the temperature of the coal body are monitored to be respectively within the third carbon monoxide critical value and the second temperature critical value and are basically stable, the injection of the inert gas is stopped.

[0019] Further, the gas injection device comprises a gas injection pump and a high-pressure pipe, the gas injection pump is connected with an inert gas bottle, the gas injection pump is also connected with the high-pressure pipe, the high-pressure pipe is provided with a valve, the high-pressure pipe extends into the goaf along the gas hole reserved in the hole mouth and is used for injecting the inert gas into the goaf.

[0020] Further, the inert gas is nitrogen or carbon dioxide.

[0021] Further, the first carbon monoxide critical value is 50*10 -6 , the first temperature critical value is 40℃, the second carbon monoxide critical value is 10*10 -6 , the third carbon monoxide critical value is 1*10 -6 , and the second temperature critical value is 25℃.

[0022] Further, the expression of the injection flow of the inert gas injected by the gas injection device into the goaf through the gas hole reserved in the hole mouth is as follows:

[0023]

[0024] Wherein, Q n is the nitrogen flow, A is the annual output of the coal mine, γ is the coal density, t is the annual working day, η1 is the pipeline nitrogen conveying efficiency, η2 is the goaf nitrogen injection efficiency, C1 is the average oxygen content in the goaf, and C2 is the fire prevention inerting index of the goaf.

[0025] Further, the method further comprises:

[0026] The continuous observation ensures that the temperature of the fire area after the nitrogen injection is stably maintained at 25℃ and the carbon monoxide gas concentration is reduced to 1*10 -6 Below, the area of the fire area is gradually reduced to 0 to prevent the residual coal in the goaf from re-igniting.

[0027] The present application has at least the following beneficial effects:

[0028] Because of the beam tube commonly used at present, with the caving of the goaf roof in use, the beam tube is easy to be broken, scratched, scraped and buried by the caving gangue, which makes the beam tube break and appear air leakage, and cannot truly collect the gas in the goaf. The present application utilizes the large-diameter drilling adjacent to the roadway, and the wall protection steel pipe is arranged in the hole. Because the large-diameter drilling is directly connected with the goaf, and the wall protection steel pipe is arranged in the large-diameter drilling, the long-term stability of the large-diameter drilling can be ensured. The gas taking hole is reserved through the large-diameter drilling hole, the gas taking rod is extended into the goaf through the gas taking hole, and the vacuum pump is used to extract the gas in the goaf, so that the sampling of the gas in the goaf can be realized, and the division of the spontaneous combustion "three zones" of the goaf can be realized.

[0029] The present application is based on the large-diameter drilling for monitoring the goaf. After the fire occurs in the goaf, the large-diameter drilling is closed, and the inert gas is injected through the high-pressure pipeline, so that the goaf fire can be treated in time.

[0030] The large-diameter drilling can complete the division of the spontaneous combustion "three zones" of the goaf, the treatment of the goaf fire and the extraction of the gas in the goaf, realize the "one hole with multiple uses" of the large-diameter drilling, and further maximize the economic benefits.

[0031] Other beneficial effects of the present application will be described in detail in the specific embodiment part. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0033] Figure 1 It is a large-diameter drilling and goaf structure principle diagram disclosed by the preferred embodiment of the present application.

[0034] Figure 2 It is a position structure diagram of the wall protection steel pipe disclosed by the preferred embodiment of the present application.

[0035] Figure 3 It is a flange structure diagram disclosed by the preferred embodiment of the present application.

[0036] Figure 4 It is a structure principle diagram of the gas taking device disclosed by the preferred embodiment of the present application.

[0037] Figure 5 It is a structure principle diagram of the gas injection device disclosed by the preferred embodiment of the present application.

[0038] Wherein, 1 - goaf, 2 - coal seam, 3 - adjacent roadway, 4 - large diameter borehole, 5 - steel pipe, 6 - hole reserved gas taking hole, 7 - flange, 8 - gas taking rod, 9 - vacuum pump, 10 - inert gas bottle, 11 - gas injection pump, 12 - high pressure pipe, 13 - valve. DETAILED DESCRIPTION

[0039] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work belong to the scope of protection of the present application.

[0040] In view of the problems existing in the prior art, the purpose of the present application is to combine two devices of large diameter borehole and gas sampling equipment, timely and accurately divide the range of goaf spontaneous combustion "three zones", and propose a goaf fire prevention and extinguishing method, to provide accurate basis for treating goaf fire.

[0041] The present application adopts a large diameter borehole gas sampling method to realize goaf spontaneous combustion "three zone" division, which has the advantage that in the closed state of the large diameter borehole, the gas taking rod is inserted into the goaf through the gas taking hole reserved at the large diameter borehole hole, the gas in the goaf is extracted by the vacuum pump to realize the sampling of the gas in the goaf, as shown in Figure 1 .

[0042] The disclosed fire prevention and extinguishing method can continuously inject inert gas into the deep part of the goaf through the high pressure pipe by the gas injection pump in the closed state of the large diameter borehole, and carry out goaf fire extinguishing through the gas taking hole reserved at the large diameter borehole hole. Comprehensive analysis shows that the method of using large diameter borehole gas sampling to divide goaf spontaneous combustion "three zones" and prevent and extinguish fire has strong feasibility and applicability.

[0043] As shown in Figures 1 to 5 , wherein: the adjacent roadway 3 is in surface contact with the coal seam 2, and mainly completes the drilling operation. The large diameter borehole 4 is a hole with a diameter of 500-800 mm drilled by a large drilling machine in the coal seam 2 and penetrating into the goaf 1. The steel pipe 5 with a diameter of 400-600 mm is inserted into the large diameter borehole 4 to ensure the integrity of the large diameter borehole 4 and prevent the coal seam 2 from collapsing and blocking the hole. The hole reserved gas taking hole 6 with a diameter of 20 mm is used to ensure that the gas taking rod 8 can be smoothly inserted into the goaf 1. The flange 7 is used to fix the hole reserved gas taking hole of the large diameter borehole 4. The gas taking rod 8 with a single length of 1.5 m can be inserted into the goaf 1 along the hole reserved gas taking hole 6. The vacuum pump 9 acts on the gas taking rod 8 and is connected with the gas taking rod 8 pipe to extract the internal gas to be measured in the goaf 1.

[0044] The gas in the inert gas bottle 10 can use N2, CO2, etc., and is connected with the gas injection pump 11 pipe, which is used for fire extinguishing in the goaf 1. The gas injection pump 11 acts on the high-pressure pipe 12 and is connected with the high-pressure pipe 12 pipe, which is used for filling inert gas into the goaf 1. The high-pressure pipe 12 extends into the goaf 1 along the preformed gas taking hole 6, which is used for transporting inert gas in the goaf 1. The valve 13 is connected with the high-pressure pipe 12 pipe, which is used for controlling the flow of inert gas and whether to fill inert gas.

[0045] In order to solve the problem of dividing the spontaneous combustion "three zones" and treating the fire in the goaf 1, the present application provides a method for dividing the spontaneous combustion "three zones" and preventing and extinguishing fire by using a large-diameter borehole 4, which comprises the following steps:

[0046] Firstly, the large-diameter borehole 4 is constructed in the adjacent roadway 3 of the goaf 1, and the wall protection steel pipe 5 is placed in the borehole after the construction is completed.

[0047] Secondly, the gas taking rod 8 is extended into the goaf 1 through the preformed gas taking hole 6, the gas in the goaf 1 is extracted by the vacuum pump 9, and the sampling of the gas in the goaf 1 and the testing of the oxygen concentration are realized.

[0048] Thirdly, the large-diameter borehole 4 is continuously advanced, the second step is repeated, and two critical points of the oxygen concentration of 7% and 18% in the goaf 1, i.e. the first oxygen critical point and the second oxygen critical point, are found, the distances of the detection points of the large-diameter borehole 4 entering the goaf 1 are determined, the spontaneous combustion "three zones" relationship of the goaf 1 is clearly divided, and the operation is stopped.

[0049] Fourthly, the gas taking rod 8 is deeply extended into the goaf 1 through the preformed gas taking hole 6, the gas is collected by the gas taking rod 8, and the temperature of the coal body and the gas composition in the coal body in each area are monitored. If the CO concentration in the goaf 1 exceeds 50×10 -6 (i.e. the first carbon monoxide critical value) or the temperature exceeds 40℃ (i.e. the first temperature critical value), it indicates that the goaf 1 will soon catch fire, and the large-diameter borehole 4 needs to be immediately closed.

[0050] Fifthly, the valve 13 is started, the inert gas is continuously injected into the deep part of the goaf 1 by the gas injection pump 11 through the high-pressure pipe 12, and the fire extinguishing in the goaf 1 is performed.

[0051] The determination of the nitrogen injection amount mainly considers the following factors: ① the oxygen concentration in the working face air inlet flow is above 19%; ② the oxygen concentration in the oxidation zone of the goaf 1 is within 10%; ③ the CO in the goaf 1 or the upper corner of the working face is easy to accumulate, and the nitrogen injection amount should be increased. The reference formula (1) of the nitrogen injection flow in the goaf 1 is as follows:

[0052]

[0053] wherein Q n is the nitrogen flow rate, m 3 / h; A is the annual output of the coal mine, t; γ is the density of coal, t / m 3 ; t is the working days per year, d; η1 is the nitrogen pipeline injection efficiency; η2 is the nitrogen injection efficiency of the goaf 1; C1 is the average oxygen content of the goaf 1; and C2 is the fire prevention inertization index of the goaf 1.

[0054] In the sixth step, the temperature of the coal body and the CO (carbon monoxide) gas composition of the region are monitored during the injection of the inert gas for fire extinguishing, and the nitrogen injection flow rate is taken as the reference. If the CO gas concentration is reduced to 10×10 -6 (the second carbon monoxide critical value) or less, the nitrogen injection flow rate is reduced, otherwise the nitrogen injection flow rate is increased. If the temperature of the coal body and the CO gas composition of the goaf 1 reach 25℃ (the second temperature critical value) and 1×10 -6 (the third carbon monoxide critical value) and are basically stable, the region is determined as a safe region for coal spontaneous combustion, and the injection of the inert gas for fire extinguishing into the region is stopped. The temperature of the fire zone after the nitrogen injection is continuously observed to ensure that the temperature is stably maintained at 25℃ and the CO gas concentration is reduced to 1×10 -6 The area of the fire zone is gradually reduced to 0 to prevent the re-ignition of the residual coal in the goaf.

[0055] In the seventh step, the valve 13 is closed after the fire extinguishing is completed, and the fire control work of the goaf 1 is completed.

[0056] Through the above method, the oxygen in the goaf 1 is collected by the gas collecting rod 8 and the vacuum pump 9 to divide the "three-zone" range, and the inert gas is injected into the goaf 1 by the drill hole to control the goaf fire.

[0057] The technical solutions of the present application are described in detail through two embodiments as follows:

[0058] Embodiment one

[0059] Referring to Figure 1 , Figure 2 , Figure 3 , Figure 4 , the embodiment discloses a method for dividing the spontaneous combustion "three-zone" of a goaf by a large-diameter drill hole, which specifically comprises the following steps.

[0060] The spontaneous combustion "three-zone" is divided by the oxygen concentration between the zones. The oxygen concentration in the heat dissipation zone is high, usually greater than 18%; the oxygen concentration in the oxidation zone is 7% to 18%; and the oxygen concentration in the suffocation zone is less than 7%.

[0061] In the vicinity of roadway 3, a large-diameter borehole 4 is constructed, and after construction is completed, a protective arm steel pipe 5 is placed underneath to ensure smooth development of the sampling work, and by extending the gas sampling rod 8 into the goaf 1 to different lengths, gas sampling at different positions in the working face direction of the goaf 1 can be achieved, and this sampling method is more convenient and flexible.

[0062] After waiting for the large-diameter borehole 4 to enter the goaf 1, the gas sampling rod 8 is inserted into the goaf 1 through the orifice reserved gas sampling hole 6, the vacuum pump 9 is started, the gas inside the goaf 1 is collected, and oxygen concentration analysis is performed.

[0063] The large-diameter borehole 4 is continuously advanced, and step 3 is repeated until two positions with oxygen concentrations of 18% and 7% inside the goaf 1 are found, the distance of the detection point of the large-diameter borehole 4 into the goaf 1 is determined, and the spontaneous combustion "three-zone" relationship is clearly divided, and the operation is stopped.

[0064] Example Two

[0065] Referring to Figure 1 , Figure 2 , Figure 3 and Figure 5 , a method for goaf fire prevention and extinguishment using a large-diameter borehole is as follows:

[0066] The gas sampling rod 8 is inserted into the goaf 1 through the orifice reserved gas sampling hole 6, gas is collected through the gas sampling rod 8, and the temperature of the coal body and the gas composition in the coal body are monitored. If the CO concentration in the goaf 1 exceeds 50x10-6 or the temperature exceeds 40℃, it indicates that the goaf is about to catch fire, and the large-diameter borehole 4 needs to be immediately closed.

[0067] The valve 13 is started, and the inert gas is continuously injected into the deep part of the goaf 1 through the high-pressure pipe 12 by the gas injection pump 11, and the goaf is extinguished. The determination of the nitrogen injection amount mainly considers the following factors: ① the oxygen concentration in the working face intake air flow is above 19%; ② the oxygen concentration in the oxidation zone of the goaf is within 10%; ③ CO is prone to accumulate in the upper corner of the goaf or the working face, so the nitrogen injection amount should be increased. The nitrogen injection flow rate of the goaf is determined with reference to formula (1):

[0068]

[0069] In the formula, Q n is the nitrogen flow rate, m 3 / h; A is the annual coal production, taken as 3000000t; γ is the coal density, taken as 1.31t / m 3 ; t is the annual working days, taken as 300d; η1 is the pipeline nitrogen conveying efficiency, taken as 0.9; η2 is the goaf nitrogen injection efficiency, taken as 0.65; C1 is the average oxygen content in the goaf, taken as 20.9%; C2 is the goaf fire prevention inertization index, taken as 7%.

[0070] Substitute the parameters of a certain mine into equation (1) to calculate the nitrogen injection flow rate Q of the goaf n = 1080 m 3 / h.

[0071] During the injection of the inert gas for fire extinguishing, monitor the temperature of the coal body and the change of the CO gas composition in the area. If the CO gas concentration is reduced to 10 x 10 -6 below, the nitrogen injection flow rate can be reduced, otherwise, the nitrogen injection flow rate should be increased. If the temperature of the coal body and the CO gas composition in the goaf reach 25℃ and 1 x 10 -6 below and are basically stable, the area is determined as a safe area for coal spontaneous combustion, and the injection of the inert gas for fire extinguishing into the area is stopped. The temperature of the fire area after the nitrogen injection is continuously observed to ensure that the temperature is stably maintained at 25℃, and the CO gas concentration is reduced to 1 x 10 -6 below. The area of the fire area is gradually reduced to 0 to prevent the re-ignition of the residual coal in the goaf.

[0072] After the fire extinguishing is completed, the valve 13 is closed, and the operation is stopped.

[0073] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited to this. Any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A method for self-ignition three-zone division using a large-diameter borehole, characterized by, The method comprises the following steps: A large-diameter drill hole is drilled along the axial direction of the adjacent roadway, through the coal seam and extending to the goaf, and a steel pipe is arranged in the large-diameter drill hole, and a hollow orifice reserved gas extraction hole is arranged in the steel pipe; With the continuous drilling of the large-diameter drill hole along the axial direction of the adjacent roadway, the gas extraction rod is inserted into the goaf at different depths through the orifice reserved gas extraction hole to extract gas; The collected gas is detected to determine the oxygen concentration at different depths of the goaf, and the first critical position and the second critical position of the goaf are determined based on the oxygen concentration, wherein the oxygen concentrations of the first critical position and the second critical position respectively meet the first oxygen critical point and the second oxygen critical point; The spontaneous combustion three-zone of the goaf is divided based on the first critical position and the second critical position; The large-diameter drill hole is drilled in the coal seam by using a large drilling machine, and the diameter ranges from 500 mm to 800 mm; The steel pipe has a diameter ranging from 400 mm to 600 mm, and is used to be deeply inserted into the large-diameter drill hole to avoid hole blocking; The orifice reserved gas extraction hole has a diameter of 20 mm, and the end of the steel pipe close to the adjacent roadway is provided with a flange plate for fixing the orifice reserved gas extraction hole.

2. The method of self-ignition three-zone delineation with a large diameter borehole according to claim 1, characterized in that, The gas extraction rod comprises a plurality of single-section pipes connected in sequence, and each single-section pipe has a length of 1.5 m; and a vacuum pump is connected to the end of the gas extraction rod close to the adjacent roadway.

3. The method of claim 1, wherein the method is implemented by using a large diameter drill hole. The first oxygen critical point and the second oxygen critical point respectively refer to oxygen concentrations of 7% and 18%.

4. A method for extinguishing a fire, implemented with a large diameter borehole, characterized in that, The method for collecting gas from the goaf by using the large-diameter drill hole to divide the spontaneous combustion three-zone according to any one of claims 1 to 3 comprises the following steps: The gas extraction rod is deeply inserted into the goaf through the orifice reserved gas extraction hole, the gas is collected by the gas extraction rod, and the temperature of the coal body and the gas composition in the coal body are monitored; if the carbon monoxide concentration in the goaf exceeds the first carbon monoxide critical value, or the temperature of the coal body exceeds the first temperature critical value, it is judged that the goaf will soon catch fire, and the large-diameter drill hole needs to be immediately closed; The gas injection device starts to inject a specified flow of inert gas into the goaf through the orifice reserved gas extraction hole; During the injection of the inert gas, the change of the temperature of the coal body and the carbon monoxide gas composition in the goaf is monitored; if the carbon monoxide gas concentration is monitored to be reduced to below the second carbon monoxide critical value, the flow of the inert gas injection is slowed down, otherwise, the flow of the inert gas injection is increased; if the carbon monoxide concentration and the temperature of the coal body are monitored to be within the third carbon monoxide critical value and the second temperature critical value respectively and are basically stable, the injection of the inert gas is stopped.

5. The fire prevention method with large diameter drilling according to claim 4, characterized in that, The gas injection device comprises a gas injection pump and a high-pressure pipe, the gas injection pump is connected with an inert gas bottle, the gas injection pump is further connected with the high-pressure pipe, the high-pressure pipe is provided with a valve, and the high-pressure pipe extends into the goaf along the orifice reserved gas extraction hole to inject the inert gas into the goaf.

6. The fire prevention method by using a large diameter borehole according to claim 4, wherein The inert gas is nitrogen or carbon dioxide.

7. The fire prevention method by large diameter drilling according to claim 4, wherein The expression of the injection flow of the inert gas injected by the gas injection device into the goaf through the orifice reserved gas extraction hole is as follows: ； wherein Q n is the nitrogen flow rate, A is the annual production of the coal mine, γ is the coal density, t is the annual working days, η1 is the pipeline nitrogen delivery efficiency, η2 is the goaf nitrogen injection efficiency, C1 is the average oxygen content in the goaf, and C2 is the fire prevention inerting index of the goaf.

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