A method and system for measuring the nitrogen diffusion radius of a goaf nitrogen injection

Abstract

This invention discloses a method and system for determining the nitrogen diffusion radius in a goaf under nitrogen injection, belonging to the field of coal mine safety mining technology. The method includes arranging bundled tube monitoring points on the intake and return air sides of the goaf to monitor the oxygen concentration at each point in real time, and simultaneously recording the working face's advance distance and nitrogen injection process parameters. The nitrogen injection process parameters include the nitrogen injection flow rate and the burial position of the nitrogen injection port. Oxygen concentration data under non-nitrogen injection conditions are extracted, and a functional relationship between oxygen concentration and working face advance distance is established through linear fitting. Based on this functional relationship, the termination position of the heat dissipation zone when the oxygen concentration drops to a first preset threshold is calculated. Oxygen concentration data of the goaf under a specific nitrogen injection flow rate is obtained, and the termination positions of the heat dissipation zone and the oxidation zone after nitrogen injection are determined when the oxygen concentration drops to the first preset threshold. The difference between the termination position of the heat dissipation zone and the termination position of the heat dissipation zone after nitrogen injection is calculated to obtain the nitrogen diffusion radius under that nitrogen injection flow rate.

Description

Technical Field

[0001] This invention belongs to the field of coal mine safety mining technology, specifically relating to a method and system for determining the nitrogen diffusion radius of nitrogen injection in goaf based on the monitoring of the "three zones" of spontaneous combustion in goaf, which is used to optimize the process parameters of nitrogen injection for fire prevention and extinguishing in goaf and improve fire prevention and extinguishing efficiency and safety. Background Technology

[0002] Spontaneous combustion of residual coal in goaf areas is a major safety hazard in coal mining. Nitrogen injection fire prevention and extinguishing technology, which injects inert nitrogen into the goaf area to reduce the oxygen concentration, is a key means of inhibiting coal-oxygen complex reactions. The core effectiveness of this technology largely depends on the diffusion radius of nitrogen in the porous media of the goaf area.

[0003] Currently, in engineering practice, the nitrogen diffusion radius is often determined based on engineering experience or roughly estimated using simple theoretical models. This method has significant drawbacks: First, it fails to consider the complex impacts of actual working conditions such as dynamic face advancement, roof collapse in the goaf, and changes in the air leakage field on gas transport; second, it cannot quantify the impact of different nitrogen injection flow rates on the diffusion effect, leading to unreasonable settings of nitrogen injection process parameters (such as nitrogen injection port location and pipeline spacing). The result is often low nitrogen injection efficiency, either insufficient nitrogen coverage leaving a risk of spontaneous combustion, or excessive nitrogen injection, causing resource waste and economic losses, and even potentially causing safety accidents due to nitrogen leakage to the working face.

[0004] Therefore, there is an urgent need in this field for a method and system that can dynamically and accurately determine the diffusion radius of nitrogen gas injected into the goaf based on field measurement data, so as to realize the quantification, refinement and intelligentization of nitrogen injection fire prevention and extinguishing process. Summary of the Invention

[0005] The primary objective of this invention is to overcome the shortcomings of existing technologies and provide a method for determining the diffusion radius of nitrogen gas injected into goaf areas. This method is based on the theory of dividing goaf areas into three zones and uses measured oxygen concentration data to quantitatively calculate the diffusion radius of nitrogen gas.

[0006] Another objective of this invention is to provide a system for measuring the nitrogen diffusion radius of nitrogen injection in goaf areas to implement the above-mentioned method. This system integrates monitoring, analysis, and control, and can dynamically guide nitrogen injection fire prevention and extinguishing practices.

[0007] To achieve the above objectives, the present invention adopts the following technical solution.

[0008] A method for determining the diffusion radius of nitrogen gas injected into a goaf, comprising the following steps: S1. Data Acquisition: Bundle tube monitoring points are arranged at 50-meter intervals on the intake and return air sides of the goaf to monitor the oxygen concentration at each monitoring point in real time, and simultaneously record the advancing distance of the working face and the nitrogen injection process parameters; the nitrogen injection process parameters include the nitrogen injection flow rate and the burial position of the nitrogen injection port; S2. Non-nitrogen injection boundary fitting: Extract oxygen concentration data under non-nitrogen injection conditions, establish a functional relationship between oxygen concentration and working face advance distance through linear fitting, and calculate the heat dissipation zone termination position L0 when the oxygen concentration drops to the first preset threshold based on this functional relationship. S3. Nitrogen Injection Boundary Determination: Obtain oxygen concentration data of the goaf area under a specific nitrogen injection flow rate Q1, and determine the termination position L of the post-nitrogen injection heat dissipation zone when the oxygen concentration drops to the first preset threshold. N0 The oxidation zone terminates at position L after nitrogen injection. N1 ; S4. Diffusion radius calculation: Calculate the termination position L0 of the heat dissipation zone and the termination position L of the heat dissipation zone after nitrogen injection. N0 The difference is used to obtain the nitrogen diffusion radius R at the nitrogen injection flow rate Q1. N The calculation formula is: R N = L0-L N0 .

[0009] As a preferred embodiment of the present invention, after step S4, the method further includes: S5. Diffusion radius correction: Based on the actual embedment position L of the nitrogen injection port. inject Regarding the nitrogen diffusion radius R N After correction, the corrected diffusion radius R is obtained. N，adj The corrected formula is: R N，adj = R N + (L0-L) inject ).

[0010] In another preferred embodiment of the present invention, in step S3, oxygen concentration data at another nitrogen injection flow rate Q2 is also obtained, and the termination position L of the post-nitrogen injection oxidation zone corresponding to the oxygen concentration dropping to a second preset threshold is determined. N2 ; In step S4, the diffusion radius R is obtained by calculating the change in the termination position of the oxidation zone after nitrogen injection under different nitrogen injection flow rates. N The calculation formula is: R N =L N1 -L N2 L N1 This represents the termination position of the oxidation zone after nitrogen injection, obtained at a nitrogen injection flow rate of Q1.

[0011] Further, the first preset threshold is an oxygen concentration of 18%, used to define the boundary between the heat dissipation zone and the oxidation zone; the second preset threshold is an oxygen concentration of 5%, used to define the boundary between the oxidation zone and the asphyxiation zone; in step S2, the linear fitting is performed using Origin software, and the fitting formula is... y=a-bx ,in y Oxygen concentration, x To increase the distance, a , b The fitting coefficients are used; the termination position L0 of the heat dissipation strip is calculated by back-calculation. y =18% corresponding to x It's worth it.

[0012] As another preferred embodiment of the present invention, the method for determining the diffusion radius of nitrogen gas injected into the goaf further includes: S6. Release port positioning: Based on the corrected diffusion radius R N，adj Oxidation zone initiation position L under non-nitrogen injection conditions ox，start Determine the location L where nitrogen injection begins at the nitrogen release port. start L start =L ox，start － R N，adj .

[0013] Furthermore, the location L where nitrogen injection begins start It is located 23 to 40 meters inside the goaf.

[0014] As another preferred embodiment of the present invention, the method for determining the diffusion radius of nitrogen gas injected into the goaf further includes: S7. Pipe spacing design: based on the corrected diffusion radius R. N，adj Calculate the laying spacing L of the nitrogen injection pipeline. N The calculation formula is: L N = 2 × R N，adj .

[0015] Furthermore, the laying spacing L of the nitrogen injection pipeline N It ranges from 30 meters to 36 meters.

[0016] As another preferred embodiment of the present invention, the sampling probe of the bundle tube monitoring point is raised more than 1.0 meter above the roadway floor, and an iron protective cover with perforated holes is installed on the sampling probe.

[0017] In addition, the present invention provides a system for measuring the diffusion radius of nitrogen gas injected into a goaf, which is used to implement the above-mentioned method for measuring the diffusion radius of nitrogen gas injected into a goaf. The measuring system includes a bundle tube monitoring subsystem, a gas sampling and analysis subsystem, a data acquisition and processing subsystem, and a nitrogen injection control subsystem. The bundled tube monitoring subsystem includes multiple bundled tube monitoring points deployed on the air intake and return sides of the goaf, PE pipes for protecting the bundled tubes, perforated protective covers installed on the sampling probes of the bundled tube monitoring points, and dust filters at the ends of the bundled tube monitoring points, for collecting gas samples inside the goaf. The gas sampling and analysis subsystem is connected to the bundled tube monitoring subsystem via pipelines, and includes a negative pressure sampler for extracting gas samples and a gas chromatograph for performing component analysis on the gas samples. The data acquisition and processing subsystem is communicatively connected to the gas sampling and analysis subsystem. It is used to record and store the working face advance, air volume and nitrogen injection parameters, and has a built-in processing module. The processing module is configured to perform the following calculations: fit the heat dissipation zone boundary under non-nitrogen injection conditions based on oxygen concentration data and calculate the heat dissipation zone or oxidation zone boundary under nitrogen injection conditions, and calculate the nitrogen diffusion radius based on the change in boundary position. The nitrogen injection control subsystem is communicatively connected to the data acquisition and processing subsystem, and includes a nitrogen injection pipeline, control valves, and a controller. The controller is configured to receive the diffusion radius calculated by the data acquisition and processing subsystem or the nitrogen injection parameters determined based on the radius, and control the opening and closing position of the nitrogen injection port or adjust the nitrogen injection flow rate accordingly.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: The method and system for determining the diffusion radius of nitrogen gas injected into a goaf provided by this invention have the following significant advantages: (1) Quantification and precision: By fitting and back-calculating on-site measured data, the extensive mode that relies on experience has been completely changed, and the accuracy and reliability of nitrogen injection have been significantly improved, providing a scientific basis for fire prevention and extinguishing decisions.

[0019] (2) Strong dynamic adaptability: The method proposed in this invention can adjust the diffusion radius calculation results and nitrogen injection parameters in real time according to changes in working face advance, nitrogen injection flow rate, geological conditions, etc., to adapt to complex downhole environments.

[0020] (3) High practical value in engineering: The measurement results can directly and quantitatively guide the precise positioning of nitrogen injection ports and the optimization design of pipeline spacing, improve the fire prevention and extinguishing effect from the source, reduce the risk of spontaneous combustion, and ensure safe production.

[0021] (4) System integration and intelligence: The system proposed in this invention constitutes a complete "monitoring-analysis-decision-control" closed loop, realizing the automated and intelligent management of the nitrogen injection fire prevention and extinguishing process in the goaf, which greatly improves work efficiency and safety. Attached Figure Description

[0022] Figure 1This is a schematic flowchart of a method for determining the diffusion radius of nitrogen gas injected into a goaf, provided by an embodiment of the present invention.

[0023] Figure 2 This is a schematic block diagram of a nitrogen diffusion radius measurement system for nitrogen injection in a goaf area, provided in an embodiment of the present invention.

[0024] Figure 3 This is a fitting curve of the termination position of the heat dissipation zone in the goaf under non-nitrogen injection conditions in an embodiment of the present invention.

[0025] Figure 4 This is a graph showing the change in oxygen concentration in the goaf under nitrogen injection conditions with the advance distance in an embodiment of the present invention.

[0026] The diagram is labeled as follows: 1- Measurement system for nitrogen diffusion radius of nitrogen injection in goaf; 101- Bundle tube monitoring subsystem; 102- Gas sampling and analysis subsystem; 103- Data acquisition and processing subsystem; 104- Nitrogen injection control subsystem. Detailed Implementation

[0027] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0028] The present invention Figure 1 The complete workflow from data acquisition, non-nitrogen-injected boundary fitting, nitrogen-injected boundary determination to diffusion radius calculation is clearly demonstrated; refer to Figure 1 The present invention provides a method for determining the diffusion radius of nitrogen gas injected into a goaf, comprising the following steps: S1. Data Acquisition: Bundle tube monitoring points are arranged at 50-meter intervals on the intake and return air sides of the goaf to monitor the oxygen concentration at each monitoring point in real time, and simultaneously record the advancing distance of the working face and the nitrogen injection process parameters; the nitrogen injection process parameters include at least the nitrogen injection flow rate and the burial position of the nitrogen injection port; S2. Non-nitrogen injection boundary fitting: Extract oxygen concentration data under non-nitrogen injection conditions, establish a functional relationship between oxygen concentration and working face advance distance through linear fitting, and calculate the heat dissipation zone termination position L0 when the oxygen concentration drops to the first preset threshold based on this functional relationship. S3. Nitrogen Injection Boundary Determination: Obtain oxygen concentration data of the goaf area under a specific nitrogen injection flow rate Q1, and determine the termination position L of the post-nitrogen injection heat dissipation zone when the oxygen concentration drops to the first preset threshold. N0 The oxidation zone terminates at position L after nitrogen injection. N1 ; S4. Diffusion radius calculation: Calculate the termination position L0 of the heat dissipation zone and the termination position L of the heat dissipation zone after nitrogen injection. N0 The difference is used to obtain the nitrogen diffusion radius R at the nitrogen injection flow rate Q1. N The calculation formula is: R N = L0-L N0 .

[0029] Specifically, after step S4, the method further includes: S5. Diffusion radius correction: Based on the actual embedment position L of the nitrogen injection port. inject Regarding the nitrogen diffusion radius R N After correction, the corrected diffusion radius R is obtained. N，adj The corrected formula is: R N，adj = R N + (L0-L) inject ).

[0030] Specifically, in step S3, oxygen concentration data at another nitrogen injection flow rate Q2 is also acquired, and the termination position L of the post-nitrogen injection oxidation zone corresponding to when the oxygen concentration drops to a second preset threshold is determined. N2 ; In step S4, the diffusion radius R is obtained by calculating the change in the termination position of the oxidation zone after nitrogen injection under different nitrogen injection flow rates. N The calculation formula is: R N =L N1 -L N2 L N1 This represents the termination position of the oxidation zone after nitrogen injection, obtained at a nitrogen injection flow rate of Q1.

[0031] Specifically, the first preset threshold is an oxygen concentration of 18%, used to define the boundary between the heat dissipation zone and the oxidation zone; the second preset threshold is an oxygen concentration of 5%, used to define the boundary between the oxidation zone and the asphyxiation zone; in step S2, the linear fitting is performed using Origin software, and the fitting formula is... y=a-bx ,in y Oxygen concentration, x To increase the distance, a , b The fitting coefficients are used; the termination position L0 of the heat dissipation strip is calculated by back-calculation. y =18% corresponding to x It's worth it.

[0032] Specifically, the method for determining the diffusion radius of nitrogen gas injected into the goaf also includes: S6. Release port positioning: Based on the corrected diffusion radius R N，adj Oxidation zone initiation position L under non-nitrogen injection conditions ox，start Determine the location L where nitrogen injection begins at the nitrogen release port.start L start =L ox，start － R N，adj The location where nitrogen injection begins, L start This is located 23 to 40 meters inside the goaf, ensuring that nitrogen effectively covers the starting area of ​​the oxidation zone.

[0033] Specifically, the method for determining the diffusion radius of nitrogen gas injected into the goaf also includes: S7. Pipe spacing design: based on the corrected diffusion radius R. N，adj Calculate the laying spacing L of the nitrogen injection pipeline. N The calculation formula is: L N = 2 × R N，adj The laying spacing L of the nitrogen injection pipeline N The spacing is 30 to 36 meters. To enhance the coverage effect, the actual spacing can be appropriately reduced, such as using 30 meters, to accommodate the spontaneous combustion characteristics of coal seams.

[0034] Specifically, the sampling probe of the bundle tube monitoring point is raised more than 1.0 meter above the roadway floor, and an iron protective cover with perforated holes is installed on the sampling probe.

[0035] The present invention Figure 4 The changes in oxygen concentration curves under nitrogen injection and non-nitrogen injection conditions were exemplarily compared, visually demonstrating the forward shift of the heat dissipation zone termination position (i.e., L). N0 < L0).

[0036] Figure 2 The diagram illustrates the connections and data interaction relationships between the four subsystems of this invention: the bundle tube monitoring subsystem 101, the gas sampling and analysis subsystem 102, the data acquisition and processing subsystem 103, and the nitrogen injection control subsystem 104. Combined with... Figure 2As shown, the present invention provides a system for measuring the nitrogen diffusion radius of nitrogen injected into a goaf, used to implement the above-mentioned method for measuring the nitrogen diffusion radius of nitrogen injected into a goaf. The system 1 for measuring the nitrogen diffusion radius of nitrogen injected into a goaf includes a bundle tube monitoring subsystem 101, a gas sampling and analysis subsystem 102, a data acquisition and processing subsystem 103, and a nitrogen injection control subsystem 104. The bundle tube monitoring subsystem 101 includes multiple bundle tube monitoring points deployed on the air intake and return sides of the goaf, PE pipes for protecting the bundle tubes, and perforated protective covers installed on the sampling probes of the bundle tube monitoring points and dust filters at the ends of the bundle tube monitoring points, used to collect gas samples from inside the goaf. The gas sampling and analysis subsystem 102 is connected to the bundle tube monitoring subsystem 101 through pipelines and includes a negative pressure sampler for extracting gas samples and a data acquisition and processing subsystem for... A gas chromatograph for component analysis of gas samples; the data acquisition and processing subsystem 103, communicatively connected to the gas sampling and analysis subsystem 102, is used to record and store the working face advance, air volume, and nitrogen injection parameters, and has a built-in processing module configured to perform the following calculations: fitting the heat dissipation zone boundary under non-nitrogen injection conditions based on oxygen concentration data and calculating the heat dissipation zone or oxidation zone boundary under nitrogen injection conditions, and calculating the nitrogen diffusion radius based on the change in boundary position; the nitrogen injection control subsystem 104, communicatively connected to the data acquisition and processing subsystem 103, includes a nitrogen injection pipeline, control valves, and a controller, the controller being configured to receive the diffusion radius calculated by the data acquisition and processing subsystem 103 or the nitrogen injection parameters determined based on the radius, and control the opening and closing position of the nitrogen injection port or adjust the nitrogen injection flow rate accordingly.

[0037] The negative pressure sampler is a CFZ-22(A) portable mine negative pressure sampler, which extracts gas samples from the goaf by connecting to a pre-embedded bundle tube. It can effectively solve the shortcomings of low efficiency and slow speed of manual gas extraction. The gas chromatograph is a GC-4085 gas chromatograph, which can quickly analyze major components (complete gas detection within 4 minutes) and quickly analyze trace gas components (complete detection of C2H4, C2H2, CO2, and CO within 8 minutes).

[0038] Example: This example uses the "Application Example of the 1309 Fully Mechanized Longwall Mining Face of Dananhu No. 1 Mine of State Grid Energy Hami Coal and Power Co., Ltd." as background, and applies the method and system of the present invention.

[0039] 1. Method Implementation Process S1: Data Acquisition Four bundled tube monitoring points were set up at 50-meter intervals in both the intake and return airways of the 1309 fully mechanized longwall face, for a total of eight bundled tube monitoring points. The sampling probes of the bundled tube monitoring points were raised more than 1.0 meter above the roadway floor and equipped with perforated iron protective covers. Gas samples were extracted daily using a CFZ-22(A) type negative pressure sampler, and the oxygen concentration was analyzed using a GC-4085 type gas chromatograph. The daily advance rate and air volume (approximately 2200 m³ / min) of the working face were recorded simultaneously. The daily advance rate of the working face is shown in Table 1-1 below.

[0040] Table 1-1 Daily Advancement Speed ​​Statistics of Working Face

[0041]

[0042] Record nitrogen injection parameters: Nitrogen injection begins on day 14, with an initial flow rate of Q1 = 225 m³ / h, and the nitrogen injection port is buried at position L. inject =25m; after 35 days, the flow rate increases to Q2=310 m³ / h.

[0043] S2: Non-nitrogen injection boundary fitting Extract the non-nitrogen-injected oxygen concentration data up to day 14, such as the early data from measuring point #3 in the lower corner. Use Origin software to perform linear fitting to obtain the function: y = 20.73759 － 0.06702 x (Corrected coefficient of determination R) 2 =0.85437), such as Figure 3 As shown; Figure 3 An illustrative example demonstrates how to perform linear fitting on non-nitrogen injection data using Origin software to obtain the formula. y =20.73759 － 0.06702 x And the process of calculating L0=40.8m in reverse.

[0044] Let y=18, and calculate the termination position of the heat dissipation zone under non-nitrogen injection conditions, L0=40.8m.

[0045] S3 & S4: Determination of Nitrogen Injection Boundary and Calculation of Diffusion Radius (Method 1) Obtain oxygen concentration data at a nitrogen injection flow rate Q1 = 225 m³ / h to determine the termination position L of the heat dissipation belt. N0 = 38.6m (see Table 1-2 below, measuring point 3 at the lower corner).

[0046] Table 1-2 Range of the three zones of spontaneous combustion at various measuring points in the goaf.

[0047]

[0048] Calculate the nitrogen diffusion radius: R N = L0-L N0 = 40.8-38.6 = 2.2m.

[0049] S5: Diffusion radius correction According to the nitrogen injection port position L inject =25m, correction needed: R N，adj = R N + (L0-L) inject ) = 2.2 + (40.8-25) = 18.0m.

[0050] This is the equivalent diffusion radius considering the actual nitrogen injection location at a nitrogen injection flow rate of 225 m³ / h.

[0051] In addition, the diffusion radius can be calculated based on the change in the termination position of the oxide zone (example of method two). Obtain the termination position L of the oxidation zone at Q1=225 m³ / h. N1 = 91.6m (oxygen concentration = 5%).

[0052] Obtain the termination position L of the oxidation zone at Q2=310 m³ / h. N2 = 74.2m.

[0053] Calculate the diffusion radius: R N = L N1 -L N2 = 91.6-74.2 = 17.4m.

[0054] This result is similar to the result after the correction of Method 1 (18.0m), and R can be finally taken as... N，adj ≈ 18m, which is the typical diffusion radius for low-flow nitrogen injection under the conditions of this mine.

[0055] Engineering parameters determined Release port positioning: Oxidation zone start position L ox，start ≈L0 = 40.8m, starting position of nitrogen injection L start =L ox，start － R N，adj = 40.8 － 18 = 22.8m; For safety reasons, nitrogen injection will begin when the nitrogen injection port is buried 23-40m into the goaf.

[0056] Pipe spacing design: L N = 2×R N，adj = 2×18 = 36m; Given that the No. 3 coal seam is a coal seam that is prone to spontaneous combustion, in order to strengthen the cover, the actual laying spacing is 30m.

[0057] The specific configuration of the system of the present invention in this mine is as follows: Bundle tube monitoring subsystem 101: Eight bundle tube monitoring points are arranged as described in step S1 to form a monitoring network.

[0058] Gas sampling and analysis subsystem 102: Gas samples are drawn to the ground monitoring station through a pre-set bundled tube, and the GC-4085 gas chromatograph performs automatic analysis and uploads the data.

[0059] Data acquisition and processing subsystem 103: This is an industrial computer running dedicated software. This software automatically receives and stores data such as gas concentration, propulsion rate, and nitrogen injection parameters. Its built-in processing module automatically executes the calculation process from S2 to S5, outputting the diffusion radius R in real time. N，adj .

[0060] Nitrogen injection control subsystem 104: Its controller is connected to the data processing subsystem. When the controller receives the signal that "the nitrogen injection port burial depth has reached 23m" and calculates R... N，adj When the nitrogen flow rate reaches 18m, the solenoid valve of the corresponding branch will automatically open to start nitrogen injection. When a change in nitrogen injection flow rate is detected, the system can automatically recalculate the diffusion radius and optimize the pipeline switching strategy.

[0061] The application of this embodiment demonstrates that the method and system of the present invention can successfully and accurately determine the nitrogen diffusion radius in complex on-site environments, and directly transform scientific research results into efficient engineering practices, significantly improving the fire prevention and extinguishing safety level of the 1309 fully mechanized mining face.

[0062] It is understood that, although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for determining the diffusion radius of nitrogen gas injected into a goaf, characterized in that: Includes the following steps: S1. Data Acquisition: Bundle tube monitoring points are arranged at 50-meter intervals on the intake and return air sides of the goaf to monitor the oxygen concentration at each monitoring point in real time, and simultaneously record the advancing distance of the working face and the nitrogen injection process parameters; the nitrogen injection process parameters include the nitrogen injection flow rate and the burial position of the nitrogen injection port; S2. Non-nitrogen injection boundary fitting: Extract oxygen concentration data under non-nitrogen injection conditions, establish a functional relationship between oxygen concentration and working face advance distance through linear fitting, and calculate the heat dissipation zone termination position L0 when the oxygen concentration drops to the first preset threshold based on this functional relationship. S3. Nitrogen Injection Boundary Determination: Obtain oxygen concentration data of the goaf area under a specific nitrogen injection flow rate Q1, and determine the termination position L of the post-nitrogen injection heat dissipation zone when the oxygen concentration drops to the first preset threshold. N0 The oxidation zone terminates at position L after nitrogen injection. N1 ; In step S3, oxygen concentration data at another nitrogen injection flow rate Q2 is also acquired to determine the termination position L of the post-nitrogen injection oxidation zone when the oxygen concentration drops to the second preset threshold. N2 ; The first preset threshold is an oxygen concentration of 18%, used to define the boundary between the heat dissipation zone and the oxidation zone; the second preset threshold is an oxygen concentration of 5%, used to define the boundary between the oxidation zone and the asphyxiation zone; in step S2, the linear fitting is performed using Origin software, and the fitting formula is... y=a-bx ,in y Oxygen concentration, x To increase the distance, a , b The fitting coefficients are used; the termination position L0 of the heat dissipation strip is calculated by back-calculation. y =18% corresponding to x Worth it; S4. Diffusion radius calculation: Calculate the termination position L0 of the heat dissipation zone and the termination position L of the heat dissipation zone after nitrogen injection. N0 The difference is used to obtain the nitrogen diffusion radius R at the nitrogen injection flow rate Q1. N The calculation formula is: R N = L0-L N0 ; In step S4, the diffusion radius R is obtained by calculating the change in the termination position of the oxidation zone after nitrogen injection under different nitrogen injection flow rates. N The calculation formula is: R N =L N1 -L N2 L N1 The termination position of the oxidation zone after nitrogen injection is obtained at nitrogen injection flow rate Q1; S5. Correction for nitrogen diffusion radius at nitrogen injection flow rate Q1: based on the actual burial position L of the nitrogen injection port. inject Regarding the nitrogen diffusion radius R N After correction, the corrected diffusion radius R is obtained. N，adj The corrected formula is: R N，adj = R N + (L0-L) inject ); S6. Release port positioning: Based on the corrected diffusion radius R N，adj Oxidation zone initiation position L under non-nitrogen injection conditions ox，start Determine the location L where nitrogen injection begins at the nitrogen release port. start L start =L ox，start － R N，adj ; S7. Pipe spacing design: based on the corrected diffusion radius R. N，adj Calculate the laying spacing L of the nitrogen injection pipeline. N The calculation formula is: L N = 2 × R N，adj .

2. The method for determining the diffusion radius of nitrogen gas injected into a goaf area according to claim 1, characterized in that: The location where nitrogen injection begins L start It is located 23 to 40 meters inside the goaf.

3. The method for determining the diffusion radius of nitrogen gas injected into a goaf area according to claim 1, characterized in that: The laying spacing L of the nitrogen injection pipeline N It ranges from 30 meters to 36 meters.

4. The method for determining the diffusion radius of nitrogen gas injected into a goaf area according to claim 1, characterized in that: The sampling probe of the bundle tube monitoring point is raised more than 1.0 meter above the roadway floor, and a perforated protective cover is provided on the outer sleeve of the sampling probe.

5. A system for determining the diffusion radius of nitrogen gas injected into a goaf, characterized in that: The method for determining the nitrogen diffusion radius of nitrogen injection in the goaf area according to any one of claims 1 to 4; the determination system includes a bundle tube monitoring subsystem, a gas sampling and analysis subsystem, a data acquisition and processing subsystem, and a nitrogen injection control subsystem; The bundled tube monitoring subsystem includes multiple bundled tube monitoring points deployed on the air intake and return sides of the goaf, PE pipes for protecting the bundled tubes, perforated protective covers installed on the sampling probes of the bundled tube monitoring points, and dust filters at the ends of the bundled tube monitoring points, for collecting gas samples inside the goaf. The gas sampling and analysis subsystem is connected to the bundled tube monitoring subsystem via pipelines, and includes a negative pressure sampler for extracting gas samples and a gas chromatograph for performing component analysis on the gas samples. The data acquisition and processing subsystem is communicatively connected to the gas sampling and analysis subsystem. It is used to record and store the working face advance, air volume and nitrogen injection parameters, and has a built-in processing module. The processing module is configured to perform the following calculations: fit the heat dissipation zone boundary under non-nitrogen injection conditions based on oxygen concentration data and calculate the heat dissipation zone or oxidation zone boundary under nitrogen injection conditions, and calculate the nitrogen diffusion radius based on the change in boundary position. The nitrogen injection control subsystem is communicatively connected to the data acquisition and processing subsystem, and includes a nitrogen injection pipeline, control valves, and a controller. The controller is configured to receive the diffusion radius calculated by the data acquisition and processing subsystem or the nitrogen injection parameters determined based on the radius, and control the opening and closing position of the nitrogen injection port or adjust the nitrogen injection flow rate accordingly.

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