A method and system for identifying a composite danger area of a gas-containing goaf under coal-oxygen interaction

Abstract

This application relates to the field of coal mine safety technology, and provides a method and system for identifying complex hazard zones in gas-bearing goafs under the combined effects of coal and oxygen. The method first constructs a multi-field coupled model of "thermal-solid-gas" in the gas-bearing goaf, which includes mutually coupled gas concentration fields, air flow fields, oxygen concentration fields, gas temperature fields, and solid temperature fields. Then, the multi-field coupled model is numerically solved to obtain the spatial distribution characteristics of the temperature field, gas concentration field, and oxygen concentration field within the goaf. Finally, based on preset complex hazard zone identification rules and the superimposed area of ​​the temperature field, gas concentration field, and oxygen concentration field, the goaf is divided into different levels of Class I to Class IV complex hazard zones. This invention, by introducing a gas concentration field, achieves accurate identification of complex hazard zones caused by gas and coal spontaneous combustion, providing key theoretical basis and technical support for the coordinated prevention and control of complex hazards in goafs of high-gas mines.

Description

Technical Field

[0001] This application relates to the field of coal mining technology, and in particular to a method and system for identifying complex hazardous areas in gas-bearing goafs under the combined effects of coal and oxygen. Background Technology

[0002] During the mining process, due to limitations in mining conditions and technology, a small amount of residual coal will inevitably remain in the goaf. Under suitable conditions, this residual coal is bound to spontaneously combust.

[0003] Coal seams with low spontaneous combustion tendency are generally unlikely to spontaneously ignite without external support. Therefore, a certain thickness of coal seam must remain in the goaf, and the coal seam must possess spontaneous combustion characteristics for the coal to have the prerequisite for spontaneous combustion and fire. Moreover, the thickness of the remaining coal seam needs to exceed 0.4m. If the thickness of the remaining coal seam is small, the small amount of remaining coal will be oxidized quickly, and the heat released by its oxidation is unlikely to accumulate to the point that it can cause the coal to enter a stage of intense self-accelerated oxidation. Only when the coal seam reaches a certain thickness can it provide sufficient base material for the heat release of oxidation.

[0004] Furthermore, a continuous supply of oxygen is required for the residual coal. If the residual coal is in an oxygen-deficient environment, there will be insufficient oxygen molecules to support the full combination with carbon molecules, resulting in less exothermic oxidation reaction. Combustion characteristics tend to develop towards oxygen-rich regions. With the help of fresh airflow, the coal body can be kept in an oxygen-rich environment, providing sufficient feedstock for the exothermic oxidation of the residual coal.

[0005] In addition, a suitable thermal environment is required to induce spontaneous combustion of residual coal. Generally, coal has a relatively high ignition point (anthracite). ,bituminous coal ,lignite If the heat released from the oxidation of residual coal continues to dissipate, spontaneous combustion is impossible. However, due to the concealed nature of goaf areas, heat in some goaf areas cannot be dissipated quickly and promptly through heat exchange or conduction, thus accumulating and rising until the temperature exceeds [a certain threshold]. Afterward, the coal body enters a stage of intense oxidation and exothermic reaction, and the rate of temperature increase will accelerate suddenly until the coal body spontaneously combusts. Summary of the Invention

[0006] The purpose of this application is to provide a method and system for identifying complex hazardous areas in gas-bearing goaf areas under the combined action of coal and oxygen, so as to solve or alleviate the problems existing in the prior art.

[0007] To achieve the above objectives, this application provides the following technical solution: This application provides a method for identifying composite hazardous areas in gas-bearing goafs under coal-oxygen combined action, comprising: constructing a thermo-solid-gas multi-field coupling model of the gas-bearing goaf under coal-oxygen combined action; calculating the thermo-solid-gas multi-field coupling model of the gas-bearing goaf under coal-oxygen combined action to determine the distribution areas of high-temperature region, gas concentration field, and oxygen concentration field of the gas-bearing goaf; and identifying and delineating the composite hazardous areas of the goaf based on preset composite hazardous area identification rules and the distribution areas of high-temperature region, gas concentration field, and oxygen concentration field.

[0008] Preferably, the multi-field coupling model includes an interacting single model of gas concentration field, a single model of air flow field, a single model of oxygen concentration field, a single model of gas temperature field, and a single model of solid temperature field, as well as the boundary constraints of each single model.

[0009] The preferred single model for the gas concentration field is: Correspondingly, the boundary constraints for the single model of gas concentration field are: In the formula, In the three-dimensional rectangular coordinate system of the physical model of the gas-bearing goaf area The gas concentration at that location, The molar concentration of gas, For control body The area of ​​the closed boundary surface, The volume enclosed by the closed boundary surface; For the area of ​​the closed boundary surface of the control volume, Gas flow rate at the location; For the area of ​​the closed boundary surface of the control volume, The unit outward normal vector; This represents the proportion of residual coal in solid coal and rock. The volume of gas desorbed per unit mass of residual coal per unit time. This represents the gas molar volume at the corresponding temperature; The apparent density of the residual coal particles; Porosity of coal particles For airflow speed, is the diffusion coefficient constant of gas.

[0010] The preferred single model for the airflow field is: Correspondingly, the boundary constraints for a single airflow model are: In the formula, For control body The area of ​​the closed boundary surface, The volume enclosed by the closed boundary surface; A three-dimensional rectangular coordinate system for the physical model of a gas-bearing goaf. Inner position air pressure; The air permeability coefficient, It is the acceleration due to gravity. The total gas pressure at any point within the goaf. air density; The potential energy of a unit cell. For the area of ​​the closed boundary surface of the control volume, The unit outward normal vector; The thickness of the seepage layer in the goaf. This refers to the angle at which the roof collapses.

[0011] This represents the proportion of residual coal in solid coal and rock. The standard density of methane gas, The volume of gas desorbed per unit mass of coal per unit time; This represents the apparent density of the residual coal particles.

[0012] Preferably, the solution region of the physical model of the gas-containing goaf is divided into grids, and each individual model in the multi-field coupling model is discretized based on the grid division results. The discretization results are then encoded to generate the spontaneous combustion distribution characteristics of the gas-containing goaf.

[0013] Preferably, based on the grid partitioning results, the contribution matrix of each individual model is constructed using the interpolation function of each individual model; wherein, The interpolation function for a single model of the gas concentration field is: The interpolation function for a single model of the airflow field is: The interpolation function for a single model of the oxygen concentration field is: The interpolation function for a single model of the gas temperature field is: The interpolation function for a single model of the solid temperature field is: In the formula, These are the vertices of any tetrahedral element within the solution region of the physical model of a gas-bearing goaf; These represent the three directions of the three-dimensional rectangular coordinate system of the physical model of the goaf; For any tetrahedral element The gas concentration value; The vertices of any tetrahedral element are respectively The gas concentration value at the location; For any tetrahedral element air pressure, The vertices of any tetrahedral element are respectively Air pressure at that location; For any tetrahedral element oxygen concentration, The vertices of any tetrahedral element are respectively Oxygen concentration at that location; For any tetrahedral element The gas temperature, The vertices of any tetrahedral element are respectively The gas temperature at that location; For any tetrahedral element solid temperature The vertices of any tetrahedral element are respectively The solid temperature at that location; For control body The volume enclosed by the closed boundary surface; The vertices of the tetrahedral elements The coefficient of the determinant of the contribution of a physical quantity at a given location to the physical quantity at any other location within the unit cell.

[0014] Preferably, the contribution matrix of the single model of gas concentration field is constructed by discretizing the boundary constraints of the single model; wherein, The contribution matrix of the single model for the gas concentration field is: in, and In the formula, The vertices of any tetrahedral element within the solution region of the physical model of a gas-bearing goaf are respectively... gas concentration For tetrahedral elements The contribution of gas concentration; These are constant column vectors; In the three-dimensional rectangular coordinate system of the physical model of the goaf, respectively The velocity component in the direction, Tetrahedral units middle The coefficient of the determinant of the contribution of a physical quantity at a point to a physical quantity at any location within the element. Porosity of coal particles For airflow speed, Let be the gas diffusion coefficient. Tetrahedral units middle The coefficient of the determinant of the contribution of a point physical quantity to a physical quantity at any location within a unit cell; For control body The volume enclosed by the closed boundary surface; This represents the gas molar volume at the corresponding temperature; This represents the proportion of residual coal in solid coal and rock. The volume of gas desorbed per unit mass of residual coal per unit time. This represents the apparent density of the residual coal particles.

[0015] Preferably, the contribution matrix of the single airflow field model is constructed by discretizing the boundary constraints of the single airflow field model; wherein, the contribution matrix of the single airflow field model is: in, and In the formula, The vertices of any tetrahedral element within the solution region of the physical model of a gas-bearing goaf are respectively... air pressure For tetrahedral elements The contribution of air pressure; These are constant column vectors; The air permeability coefficient, It is the acceleration due to gravity. Tetrahedral units middle The coefficient of the determinant of the contribution of a physical quantity at a point to a physical quantity at any location within the element. Tetrahedral units middle The coefficient of the determinant of the contribution of a physical quantity at a point to a physical quantity at any location within a unit cell; air density, The angle of collapse of the roof slab. The standard density of methane gas, The volume of gas desorbed per unit mass of coal per unit time; The apparent density of the coal particles. This represents the proportion of residual coal in solid coal and rock; The density of the gas. This represents the gas molar volume at the corresponding temperature. For control body The volume enclosed by the closed boundary surface.

[0016] Preferably, the spontaneous combustion distribution characteristics of the gas-bearing goaf are used to classify the spontaneous combustion composite hazard zone of the gas-bearing goaf. Among them, the spontaneous combustion distribution characteristics of gas goaf areas include, but are not limited to, gas concentration field distribution, air flow field distribution, oxygen concentration field distribution, gas temperature field distribution, and solid temperature field distribution; gas concentration Oxygen concentration greater than The high-temperature area was identified as a Class I composite hazard area; gas concentration And the oxygen concentration is greater than The area was identified as a Class II composite hazard area; Oxygen concentration greater than The high-temperature area was identified as a Class III composite hazard area; The high-temperature area was identified as a Class IV composite hazard area.

[0017] This embodiment also provides a system for identifying composite hazardous areas in gas-bearing goafs under coal-oxygen combined action. The system uses any of the aforementioned methods for identifying composite hazardous areas in gas-bearing goafs under coal-oxygen combined action to identify spontaneous combustion composite hazardous areas in gas-bearing goafs. The system includes: The model building unit is configured to build a multi-field coupled thermo-solid-gas model of a gas-bearing goaf under the combined action of coal and oxygen. The model solving unit is configured to calculate the thermo-solid-gas multi-field coupling model of the gas-bearing goaf under the combined action of coal and oxygen, and to determine the distribution areas of the high temperature region, gas concentration field and oxygen concentration field of the gas-bearing goaf. The hazard identification unit is configured to identify and delineate the composite hazard areas of the goaf based on preset composite hazard area identification rules, according to the distribution areas of high temperature areas, gas concentration fields, and oxygen concentration fields.

[0018] Beneficial effects: The method and system for identifying composite hazardous areas in gas-bearing goafs under coal-oxygen combined action provided in this application first constructs a "thermal-solid-gas" multi-field coupling model for gas-bearing goafs. This model includes mutually coupled gas concentration fields, air flow fields, oxygen concentration fields, gas temperature fields, and solid temperature fields. Then, the multi-field coupling model is numerically solved to obtain the spatial distribution characteristics of the temperature field, gas concentration field, and oxygen concentration field within the goaf. Finally, based on preset composite hazardous area identification rules and the superposition area of ​​the temperature field, gas concentration field, and oxygen concentration field, the goaf is divided into different levels of Class I to Class IV composite hazardous areas. Therefore, by introducing the gas concentration field, a thermo-solid-gas multi-field coupling model of air flow field, gas concentration field, oxygen concentration field, gas and temperature field of collapsed coal and rock in gas-bearing goaf under coal-oxygen combined action is constructed. The thermo-solid-gas multi-field coupling model of gas-bearing goaf under coal-oxygen combined action is solved and calculated to determine the temperature rise area and gas concentration distribution characteristics of gas-bearing goaf, providing technical support for the evolution law of spontaneous combustion in gas-bearing goaf and the prediction of complex disaster areas. Attached Figure Description

[0019] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. Wherein: Figure 1 This is a flowchart illustrating a method for identifying a complex hazardous area in a gas-bearing goaf under coal-oxygen combined action, according to some embodiments of this application. Figure 2 A schematic diagram of the multi-physics coupling mechanism of spontaneous combustion in a gas-bearing goaf according to some embodiments of this application; Figure 3 This is a schematic diagram of the solution region and boundary of the physical field coupling model for goaf provided according to some embodiments of this application; Figure 4 This is a schematic diagram of the hexahedral element division of the solution region of the physical model of the goaf provided according to some embodiments of this application; Figure 5 This is a schematic diagram of a method for dividing a hexahedral to tetrahedral physical model of a goaf area according to some embodiments of this application; Figure 6 This is a schematic diagram of the tetrahedral element division of the solution region of the physical model of the goaf provided according to some embodiments of this application; Figure 7 This is a schematic diagram of the vertex unit control volume of the physical model mesh of a goaf area provided according to some embodiments of this application; Figure 8 This is a schematic diagram of the control volume of the grid division node W of the physical model of the goaf area according to some embodiments of this application; Figure 9 This is a schematic diagram illustrating the node numbering sequence of the grid unit in the physical model of a goaf area according to some embodiments of this application; Figure 10 This is a schematic diagram of the coordinates of tetrahedral elements in a physical model of a goaf provided according to some embodiments of this application; Figure 11 This is a schematic diagram of the airflow field distribution in the spontaneous combustion distribution characteristics of a gas-bearing goaf according to an embodiment of this application; Figure 12 This is a schematic diagram of the gas concentration field distribution in the spontaneous combustion distribution characteristics of a gas-bearing goaf provided according to an embodiment of this application; Figure 13 A schematic diagram of the three-dimensional distribution of methane at concentrations of 5% and 16% in a methane-containing goaf area provided according to an embodiment of this application; Figure 14 This is a schematic diagram of the oxygen concentration field distribution in the spontaneous combustion distribution characteristics of a gas-bearing goaf according to an embodiment of this application; Figure 15 This is a schematic diagram of the solid temperature field distribution in the spontaneous combustion distribution characteristics of a gas-bearing goaf according to an embodiment of this application; Figure 16 This is a schematic diagram of the gas temperature field distribution in the spontaneous combustion distribution characteristics of a gas-bearing goaf provided according to an embodiment of this application; Figure 17 A schematic diagram illustrating the mechanism of spontaneous combustion of coal and gas outburst disaster in a gas-bearing goaf area according to an embodiment of this application; Figure 18 This is a schematic diagram illustrating the composition of a complex hazard zone within a gas-bearing goaf, according to one embodiment of this application. Figure 19 This is a schematic diagram illustrating the prediction results of a complex hazard zone in a gas-bearing goaf provided according to an embodiment of this application; Figure 20 This is a schematic diagram of a system for identifying a complex hazardous area in a gas-bearing goaf under coal-oxygen combined action, according to some embodiments of this application. Detailed Implementation

[0020] The present application will now be described in detail with reference to the accompanying drawings and embodiments. Various examples are provided by way of explanation and not by way of limitation. In fact, those skilled in the art will understand that modifications and variations can be made to the present application without departing from the scope or spirit of the present application. For example, a feature shown or described as part of one embodiment may be used in another embodiment to produce yet another embodiment. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention should fall within the scope of protection of the embodiments of the present invention.

[0021] Goaf areas are the main sites of coal spontaneous combustion and gas accumulation. The presence of gas in goaf areas affects the process of coal spontaneous combustion. Studying the coupling relationship between coal spontaneous combustion and gas is a prerequisite for understanding the development and evolution of multi-field coupling laws of complex disasters. Therefore, this embodiment provides a method for identifying complex hazard areas in gas-bearing goaf areas under the combined effects of coal and oxygen, such as... Figures 1 to 19 As shown, the method includes: Step S101: Construct a multi-field coupled model of thermo-solid gas in a gas-bearing goaf under the combined action of coal and oxygen.

[0022] The factors that cause spontaneous combustion of residual coal in goaf are interconnected and indispensable. During the mining process, an "O"-shaped ring forms in the goaf. Due to the presence of the "O"-shaped ring, some of the airflow from the intake airway leaks into the goaf. The oxygen carried by the leaked airflow promotes the oxidation and heat release of the residual coal, resulting in different temperatures and volumes of airflow at the intake and return ends. This leads to a pressure difference between the two ends of the goaf, forming an airflow field.

[0023] The oxygen concentration in the leaky airflow changes with gas flow and the oxidation and consumption of residual coal, forming an oxygen concentration field. The heat released by the oxidation of residual coal heats the collapsed coal and air in the goaf, changing the temperature of the collapsed coal and forming a solid temperature field. Convective heat transfer between the collapsed coal and air affects the gas temperature distribution in the goaf, forming a gas temperature field. The heat transfer between the gas temperature field and the collapsed coal further alters the solid temperature distribution, and the gas temperature field and solid temperature field are coupled due to convective heat transfer. The gas temperature field and the flow field are also coupled; gas flow causes changes in the gas temperature distribution, and changes in gas temperature change the gas density, ultimately altering the distribution of various physical quantities in the process.

[0024] Spontaneous combustion in a goaf requires the mutual promotion of air flow field, oxygen concentration field, gas temperature field, and solid temperature field. Only when the air flow makes the oxygen concentration sufficient to continuously generate heat, and the heat storage conditions are good, can the air and fallen coal and rock be heated by heat transfer. Heat is transferred in the solid and gaseous media and continuously accumulates, reaching the conditions for coal spontaneous combustion, which can lead to spontaneous combustion in the goaf.

[0025] The gas in the goaf mainly originates from adjacent seams, the working face, and desorption from residual coal. The amount of gas desorbed from residual coal accounts for a significant proportion of the total gas volume in the goaf. The free gas desorbed from residual coal enters the goaf, forming a gas concentration field. The exothermic oxidation effect of residual coal in the goaf accelerates the rate of gas desorption from coal particles, thus causing changes in the gas concentration field. The presence of this gas concentration field also alters the distribution of the flow field, and the gas flow within the flow field also affects the gas concentration distribution within the goaf.

[0026] The distribution of gas concentration in goaf areas is the result of the interaction of multiple physical quantities, and it is coupled with the airflow field, oxygen concentration field, coal and rock solid temperature field, and air temperature field between coal and rock masses. Changes in the flow field affect the distribution of the gas temperature field, gas concentration field, and oxygen concentration field; air temperature changes air density, affecting the airflow field and altering the temperature of solids (coal and rock); increases or decreases in solid temperature affect the gas desorption rate and oxygen concentration. There is a supply-and-dissipation relationship between the oxygen concentration field and the solid temperature field. The flow of desorbed gas also leads to the renewal of the airflow field distribution, as well as a new round of multi-physical field coupling effects on the oxygen concentration field, coal and rock solid temperature field, and gas temperature field between coal and rock masses.

[0027] In this embodiment, a thermo-solid-gas multi-field coupling model is constructed based on the mutual coupling between the gas concentration field and the air flow field, oxygen concentration field, coal and rock solid temperature field, and the air temperature field between the coal and rock mass. Specifically, the thermo-solid-gas multi-field coupling model includes interacting single models of gas concentration field, air flow field, oxygen concentration field, gas temperature field, and solid temperature field, as well as boundary constraints for each single model.

[0028] After coal seam mining is completed, most goaf areas experience roof collapse, forming a fractured coal and rock zone. Due to the numerous pores in this fractured zone, airflow from the intake ventilation roadway carries gas released from the coal face and adjacent coal seams into the goaf. Most of the gas in the coal face is transported out of the mine with the coal mining, while the remaining coal continues to desorb gas into the goaf. In this embodiment, free gas in the fractures and gas desorbed from the remaining coal are the main gas sources in the goaf. A single model of the gas concentration field within the gas-bearing goaf is constructed, specifically as follows: In the formula, any infinitesimal element within the solution region of the physical model of a gas-bearing goaf is defined as the control volume. control body It is closed, and the area of ​​the closed boundary surface is The volume enclosed by the boundary surface is , The molar concentration of gas; For the area of ​​the closed boundary surface of the control volume, Gas flow rate at the location; For the area of ​​the closed boundary surface of the control volume, The unit outward normal vector; This represents the proportion of residual coal in solid coal and rock. The volume of gas desorbed per unit mass of residual coal per unit time. This represents the gas molar volume at the corresponding temperature; The apparent density of the residual coal particles; Porosity of coal particles For airflow speed, is the diffusion coefficient constant of gas.

[0029] In a specific example, a physical model of a gas-bearing goaf is constructed, with the intersection of the mining face roadway and the goaf as the origin of the coordinate system. (point), vertically upwards is The axis extends towards the rear of the goaf. The shaft, along the working surface, is Axis. Define the physical model of the goaf. These are the solution boundaries for the gas flow field, methane concentration field, oxygen concentration field, and coal-rock inter-gas temperature field, respectively. The boundary is the front boundary of the actual goaf area; The boundary is the height boundary of the goaf, i.e., the roof. The boundary is the bottom boundary of the goaf. The boundary is the depth boundary of the goaf. The boundaries are the left and right sides of the goaf.

[0030] For the front boundary of the goaf Affected by the angle of collapse The influence is divided into two intersecting planes with one side. This boundary surface is in direct contact with the airflow at the working surface. The upper and lower parts have different airflow pressures and directions, and are divided into an upper boundary. and lower boundary The wind flows from the upper boundary Inflow, from the lower boundary Outflow.

[0031] At the same time, define The outer boundary of the solid temperature field on both sides due to the heat transfer around the goaf. (Extending beyond the actual goaf area) The boundary extends towards the protective coal pillar, thus extending the boundary. Updated to include the front boundary of the actual goaf plus the front boundaries of the coal pillars on both sides. Updated to include the actual roof boundary of the goaf plus the roof boundaries of the coal pillars on both sides. Updated to include the actual floor boundary of the goaf plus the floor boundaries of the coal pillars on both sides. Updated to the deep boundary of the actual goaf plus the deep boundary of the coal pillars on both sides.

[0032] As the working face advances, the goaf moves forward continuously, and the physical model of the goaf moves accordingly. The physical quantities at each coordinate point within the physical model change dynamically with space, meaning the physical model of the goaf is an unsteady-state model. In this embodiment, we define that each coordinate point within the physical model moves at the same speed as the working face, and the physical model is relatively stationary relative to the working face, thus transforming the unsteady-state problem of the actual goaf into a steady-state problem.

[0033] A single model of gas concentration field has Six boundary faces, in the absence of external gas sources in the goaf, the upper boundary The gas concentration is 0, at the lower boundary. The methane concentration at the working face is approximately equal to the methane concentration at the working face, meaning the methane diffusion flux perpendicular to the working face is 0. There is no air leakage at the boundary surface, and the gas diffusion flux is 0; deep boundary surface of the goaf. The amount of gas entering per unit area per unit time outside the boundary surface Due to the influence of the gas, the deep coal and rock in the goaf, which is far from the working face, are gradually compacted, and gas desorption is slow; the left and right boundary surfaces of the goaf There was also no air leakage, and the gas diffusion flux was 0. Therefore, boundary constraints for a single model of the gas concentration field were constructed: In the formula, A three-dimensional rectangular coordinate system for the physical model of a gas-bearing goaf. Inner position The gas concentration.

[0034] In this embodiment, the flow field distribution in the goaf is affected by three factors: airflow, the influx of gas from the desorbed residual coal, and density changes caused by temperature variations. The effects of these three factors on the goaf flow field can be represented by controlling for changes in gas mass within the goaf, thus constructing a single airflow model. Specifically, the single airflow model is as follows: In the formula, For control body The area of ​​the closed boundary surface, The volume enclosed by the closed boundary surface; The air permeability coefficient, It is the acceleration due to gravity. The total gas pressure at any point within the goaf. air density; The potential energy of a unit cell. For the area of ​​the closed boundary surface of the control volume, The unit outward normal vector; This represents the proportion of residual coal in solid coal and rock. The standard density of methane gas, The volume of gas desorbed per unit mass of coal per unit time; This represents the apparent density of the residual coal particles.

[0035] In the flow field model Of the six boundary surfaces, the boundary The airflow pressure is measured directly. The airflow pressure at the boundary is calculated by measuring the gas flow excess per unit length. Here, gas from deep within the void will pass through the boundary. The solution domain of the physics model is flooded into the boundary. The amount of gas entering a unit area per unit time is ;definition There is no gas exchange between the boundary surface and the outside, meaning the air leakage is zero. Therefore, the boundary constraints for a single airflow field model are constructed: In the formula, A three-dimensional rectangular coordinate system for the physical model of a gas-bearing goaf. Inner position air pressure; The thickness of the seepage layer in the goaf. The top plate is the corner.

[0036] In this embodiment, the oxygen concentration field in the goaf, the gas temperature field between coal and rock, and the solid temperature field of coal and rock are not directly affected by the gas concentration field. A single model of the oxygen concentration field in the goaf is established based on Fick's law and the law of conservation of mass, and a single model of the temperature field in the goaf is established based on Fourier's law and the law of conservation of energy. Specifically, the single model of the oxygen concentration field in the goaf is as follows: Correspondingly, the boundary constraints for the single model of oxygen concentration field are: In the formula, For control body The area of ​​the closed boundary surface, The volume enclosed by the closed boundary surface; For the area of ​​the closed boundary surface of the control volume, Gas flow rate at the location; For the area of ​​the closed boundary surface of the control volume, The unit outward normal vector; Porosity of coal particles; For airflow speed, Let be the diffusion coefficient constant of oxygen. for The oxygen consumption rate per unit volume at any given time is a function representing the oxygen consumption rate per unit volume. A three-dimensional rectangular coordinate system for the physical model of a gas-bearing goaf. Inner position oxygen concentration; This represents the molar concentration of oxygen.

[0037] In a specific example, based on coal spontaneous combustion simulation experiments, it was determined that... oxygen consumption rate function per unit volume at any given time ,have: In the formula, The gas flow rate along the axial direction of the coal sample container during the coal spontaneous combustion simulation experiment. The oxygen concentration of the fresh airflow in the coal spontaneous combustion simulation experiment. Let be the cross-sectional area of ​​the coal sample container along the axial direction. The height of the coal sample in the coal sample container. The porosity of the coal sample. These are the inlet oxygen concentration and outlet oxygen concentration of the coal sample container, respectively.

[0038] In this embodiment, the single model of the gas temperature field is: In the formula, For control body The area of ​​the closed boundary surface, The volume enclosed by the closed boundary surface; For the area of ​​the closed boundary surface of the control volume, Gas flow rate at the location; For the area of ​​the closed boundary surface of the control volume, The unit outward normal vector; To control the convective heat transfer coefficient between the gas and solid coal / rock within the body, To control the surface area for convective heat transfer between the gas and solid coal / rock within the body, To control the temperature of the solid coal and rock inside the body, To control the temperature of the gas between the coal and rock within the body; The thermal conductivity is measured in terms of air density. Porosity of coal particles To control the specific heat capacity of the gas between coal and rock within the body, To control the thermal conductivity of the gas between coal and rock within the body.

[0039] Correspondingly, the boundary constraints for a single model of the gas temperature field are: In the formula, coordinates Temperature function of the gas at the boundary.

[0040] The single model for the temperature field of a solid is: In the formula, For control body The area of ​​the closed boundary surface, The volume enclosed by the closed boundary surface; For the area of ​​the closed boundary surface of the control volume, The unit outward normal vector; To control the convective heat transfer coefficient between the gas and solid coal / rock within the body, To control the surface area for convective heat transfer between the gas and solid coal / rock within the body, To control the temperature of the solid coal and rock inside the body, To control the thermal conductivity of the gas between coal and rock within the body; This refers to controlling the heat released by the oxidation reaction of residual coal within the body per unit time. To control the thermal conductivity of the solid coal and rock skeleton within the body, To control the density of coal and rock solids within the body, To control the specific heat capacity of the solid coal and rock skeleton within the body. For flow rate, Porosity of coal particles This refers to the angle at which the roof collapses.

[0041] Correspondingly, the boundary constraints for a single model of the solid temperature field are: In the formula, coordinates Temperature function of the gas at the boundary.

[0042] Step S102: Calculate the thermo-solid-gas multi-field coupling model of the gas-bearing goaf under the combined action of coal and oxygen to determine the distribution areas of the high-temperature region, gas concentration field, and oxygen concentration field of the gas-bearing goaf.

[0043] In this embodiment, the solution region of the physical model of the gas-bearing goaf is divided into a regular and orderly grid by meshing. First, the grid is divided into hexahedral elements: because the porosity distribution in the goaf conforms to… "Ring features, in a three-dimensional Cartesian coordinate system" In In terms of direction, the deeper the goaf along the depth direction, the higher the compaction degree, the smaller the change in physical quantities, and the sparser the unit division; in In terms of direction, the left and right sides of the goaf are " "The large-pore region of the ring shape is subject to more external disturbances, resulting in greater changes in physical quantities and a denser unit division; in" The directional changes are relatively uniform, and the units are evenly divided.

[0044] By using the three intersecting lateral faces of the hexahedron as the bases of the tetrahedron, from The point (the common vertex of the three intersecting lateral faces of the hexahedron) is used to divide the hexahedron into tetrahedrons. Each lateral face can be divided into two tetrahedrons. The hexahedron can be divided into 6 independent tetrahedrons in total. In this way, a finite control volume with no overlap is obtained.

[0045] For any tetrahedral element within the solution region, the element control volumes at all four vertices pass through the tetrahedral centroid. Furthermore, a plane parallel to the base corresponding to that vertex divides the tetrahedral element into smaller tetrahedrons. For example, a tetrahedral element... That is, the vertex The unit control body of the first vertex can be obtained in the same way as the unit control bodies of the other vertices.

[0046] For any node within the solution region, the composition of its physical quantities by adjacent tetrahedral elements constitutes a "contribution" to that node. Tetrahedral elements that contribute to that node are considered control elements of that node and are thus said to be associated with it. For example, for any node within the solution region... There are 24 tetrahedral units surrounding it, and the enclosed space formed by these 24 tetrahedral units is called a node. The associated region, for nodes within the associated region By synthesizing all control units, a node can be obtained. The control body, namely An enclosed space.

[0047] In this embodiment, a three-layer numbering system is used to associate the coordinates of the vertices of tetrahedral and hexahedral elements with the coordinates of the overall nodes. The bottom layer numbering is the overall numbering of the solution region. First, for the temperature field of the non-solid skeleton, starting from number 0 along... Axial direction encoding to Number( for (number of layers in the axial direction), then turn The second column of numbers is numbered from bottom to top along the axis, i.e., from... Number to Number, along Shaft-to- The last node of the first layer (numbered as) ( for (Number of layers in the axial direction)). First layer numbering complete, then turn... Number the nodes in the second layer along the axis, continuing until the last node in the solution domain is reached (numbered as...). ( for (Number of layers in the axial direction). Then, for the temperature field of the solid skeleton, there is the protective coal pillar boundary on the right. Renumber the location.

[0048] The middle layer is numbered using hexahedral element numbers. Based on the number of layers divided in three directions, the total number of hexahedral elements is... ,definition The hexahedral element containing the point is the first... The numbering sequence is consistent with the underlying numbering, and the final numbering reaches... The six vertices inside the hexahedral element are numbered sequentially as follows: Here, the vertices of each hexahedron are distinguished by a two-dimensional array [hexahedron number, vertex number].

[0049] The top layer is numbered using the tetrahedral element numbering system, and the four internal vertices are numbered sequentially as follows: Associating all vertices within each numbered hexahedron with their corresponding global coordinates, and then associating the vertices of the tetrahedron with the vertices of the hexahedron. For any node within the solution region... Nodes are determined through a three-level numbering system. The control volume region is used to solve the control volume.

[0050] In this embodiment, based on the mesh generation results of the physical model, each individual model in the multi-field coupling model is discretized. Specifically, the integral of the node control volume is transformed into a "contribution" matrix to the vertex of the unit control volume through the interpolation function of each individual model. That is, the contribution matrix of each individual model is constructed. By synthesizing the contributions of all unit control volumes to the common vertex, the discretization of each individual model under multi-field coupling is achieved.

[0051] For a single model of gas concentration field, within the solution area of ​​the physical model of the goaf, an arbitrary tetrahedral element is placed in a three-dimensional rectangular coordinate system. The gas concentration value in the tetrahedral element is along... The axis changes linearly, and the gas concentration value Gas concentration values ​​at the four vertices of the tetrahedral unit Indicates. That is: In the formula, For control body The volume enclosed by the closed boundary surface; These are the vertices of any tetrahedral element within the solution region of the physical model of a gas-bearing goaf; These represent the three directions of the three-dimensional rectangular coordinate system of the physical model of the goaf; For any tetrahedral element The gas concentration value; The vertices of any tetrahedral element are respectively The gas concentration value at the location; The vertices of the tetrahedral elements The coefficient of the determinant of the contribution of a physical quantity (gas concentration) at a given location to the physical quantity (gas concentration) at any other location within the unit cell.

[0052] Similarly, the interpolation function for a single model of the airflow field is: In the formula, For any tetrahedral element air pressure, The vertices of any tetrahedral element are respectively Air pressure at that location.

[0053] The interpolation function for a single model of the oxygen concentration field is: In the formula, For any tetrahedral element oxygen concentration, The vertices of any tetrahedral element are respectively Oxygen concentration at that location.

[0054] The interpolation function for a single model of the gas temperature field is: In the formula, For any tetrahedral element The gas temperature, The vertices of any tetrahedral element are respectively The gas temperature at that location.

[0055] The interpolation function for a single model of the solid temperature field is: In the formula, For any tetrahedral element solid temperature The vertices of any tetrahedral element are respectively The solid temperature at that location.

[0056] in, The vertices of the tetrahedral elements The coefficient of the determinant of the contribution of a physical quantity at a given location to the physical quantity at any other location within the unit cell; it should be noted that the meaning of a physical quantity differs in different individual models, and in each individual model, it corresponds to gas concentration, oxygen concentration, air pressure, gas temperature, and solid temperature, respectively.

[0057] Each is a tetrahedral element The vertex of In a three-dimensional rectangular coordinate system The coordinates in the diagram.

[0058] In this embodiment, within the gas concentration field, a tetrahedral element is randomly selected. Through discretization of the boundary constraints of the single model of the gas concentration field, the contribution matrix of the single model of the gas concentration field is constructed, as follows: in, and In the formula, The vertices of any tetrahedral element within the solution region of the physical model of a gas-bearing goaf are respectively... gas concentration For tetrahedral elements The contribution of gas concentration; These are constant column vectors; In the three-dimensional rectangular coordinate system of the physical model of the goaf, respectively The velocity component in the direction, Tetrahedral units middle The coefficient of the determinant of the contribution of the gas concentration at a point to the gas concentration at any location within the unit cell. Porosity of coal particles For airflow speed, Let be the gas diffusion coefficient. Tetrahedral units middle The coefficient of the determinant of the contribution of point gas concentration to the gas concentration at any location within the unit cell; For control body The volume enclosed by the closed boundary surface; This represents the gas molar volume at the corresponding temperature; This represents the proportion of residual coal in solid coal and rock. The volume of gas desorbed per unit mass of residual coal per unit time. This represents the apparent density of the residual coal particles.

[0059] Similarly, by discretizing the boundary constraints of the single airflow field model, the contribution matrix of the single airflow field model is constructed; whereby the contribution matrix of the single airflow field model is: in, and In the formula, The vertices of any tetrahedral element within the solution region of the physical model of a gas-bearing goaf are respectively... air pressure For tetrahedral elements The contribution of air pressure; These are constant column vectors; The air permeability coefficient, It is the acceleration due to gravity. Tetrahedral units middle The coefficient of the determinant of the contribution of the air pressure at a point to the air pressure at any location within the element. Tetrahedral units middle The coefficient of the determinant of the contribution of the air pressure at a point to the air pressure at any location within the unit cell; air density, The angle of collapse of the roof slab. The standard density of methane gas, The volume of gas desorbed per unit mass of coal per unit time; The apparent density of the coal particles. This represents the proportion of residual coal in solid coal and rock; The density of the gas. This represents the gas molar volume at the corresponding temperature. For control body The volume enclosed by the closed boundary surface.

[0060] Simultaneously, the individual models and boundary conditions corresponding to the oxygen concentration field, gas temperature field, and solid temperature field are discretized to construct the contribution matrices of the individual models for the oxygen concentration field, gas temperature field, and solid temperature field, where: The contribution matrix of the single model for the oxygen concentration field is: in, In the formula, The vertices of any tetrahedral element within the solution region of the physical model of a gas-bearing goaf are respectively... oxygen concentration For tetrahedral elements The contribution of oxygen concentration; for The rate of oxygen consumption per unit volume at any given time.

[0061] The contribution matrix of the single model of the gas temperature field is: in, In the formula, The vertices of any tetrahedral element within the solution region of the physical model of a gas-bearing goaf are respectively... gas temperature For tetrahedral elements The contribution of gas temperature.

[0062] The volume enclosed by the closed boundary surface. It is the acceleration due to gravity. Tetrahedral units middle The coefficient of the determinant of the contribution of a physical quantity at a point to the physical quantity at any location within the element. In the three-dimensional rectangular coordinate system of the physical model of the goaf, respectively The velocity component in the direction, Let be the unit normal vector on the boundary surface of the control volume, pointing outwards. The thermal conductivity of the gas between solid particles is denoted as . The density of the gas, For the specific heat of the gas, The convective heat transfer coefficient is... To control the surface area of ​​convective heat transfer between solid particles and gas within the body, This is the solid temperature.

[0063] Solid temperature field: in, In the formula, The vertices of any tetrahedral element within the solution region of the physical model of a gas-bearing goaf are respectively... gas temperature For tetrahedral elements The solid temperature contribution; The volume enclosed by the closed boundary surface. Tetrahedral units middle The coefficient of the determinant of the contribution of a physical quantity at a point to the physical quantity at any location within the element. Let be the unit normal vector on the boundary surface of the control volume, pointing outwards. For airflow speed, The density of the solid particles, The specific heat of solid particles. The convective heat transfer coefficient is... This refers to the surface area of ​​solid particles within the body that undergo convective heat transfer with gas.

[0064] After discretizing the multi-field coupled model, the discretized multi-field coupled model is solved based on the Jacobi iteration rule. First, relevant constants, variables, and matrix arrays are defined, the grid and nodes of the solution region are divided and represented, the corresponding initial and boundary conditions are arranged, and the coefficient matrix of the discrete model is initialized.

[0065] Next, the coefficient matrix is ​​assigned values ​​based on the contribution matrices of each physical field obtained by discretization. The contribution matrix is ​​then used as the coefficient matrix for solving the physical quantities at the nodes. Each node in the solution region searches all tetrahedral elements and retains the control volume elements with non-zero coefficient matrices for contribution synthesis. The node equations are solved through an iterative function to obtain the distribution data of each physical field.

[0066] Then, iterative calculations are performed, and physical quantities are corrected based on coupling relationships. Initial values ​​are assigned to all physical field coefficient arrays and nodal physical quantities before iteration; the influence of gas desorption on the flow field can be achieved by assigning values ​​to the pressure coefficient array. After assignment, the first multi-physics solution begins, calling the Jacobi iteration module to obtain the nodal values ​​of each physical field. At this point, because the temperature changes with iteration, the residual coal gas desorption rate and gas density are corrected. Simultaneously, the coefficient matrix is ​​updated, and the pressure field and gas concentration field obtained in the next iteration will redistribute as the temperature increases, thus completing the multi-field coupled solution of the air flow field, gas concentration field, oxygen concentration field, and temperature field.

[0067] The error of the node physical quantities obtained through continuous iteration and calculation is constantly reduced compared with the previous numerical value. When the iteration error is less than 0.01 or the number of iterations increases to the target number of iterations, the calculation ends and the distribution characteristics of the multi-physical field of the goaf are obtained, including the distribution of air flow field, gas concentration field, oxygen concentration field, solid temperature field, and gas temperature field.

[0068] Step S103: Based on the preset rules for identifying composite hazardous areas, and according to the distribution areas of high-temperature areas, gas concentration fields, and oxygen concentration fields, identify and delineate the composite hazardous areas of the goaf. In this embodiment, the composite danger zones in goafs are identified based on the distribution characteristics of multiple physical fields in the goaf. To prevent disasters primarily caused by spontaneous combustion of coal during the formation of goafs, it is necessary to analyze the changes in parameters such as temperature and gas within the goaf, predict and delineate danger zones, and understand their evolution characteristics.

[0069] In goaf areas, under the coupled effects of multiple factors, the exothermic oxidation of residual coal can lead to spontaneous combustion, and the flow of high-concentration methane can cause methane exceedance hazards. Once these two hazards are under suitable conditions, a combined hazard of methane explosion can easily occur. In this embodiment, a methane concentration of... Areas between certain thresholds, areas with oxygen concentrations greater than 12%, and areas prone to spontaneous combustion due to high temperatures are considered high-risk areas for combined gas and coal spontaneous combustion disasters. Among these, gas concentration... Oxygen concentration greater than High temperature (greater than) The area was identified as a Class I composite hazard area; gas concentration And the oxygen concentration is greater than The area was designated as a Class II composite hazard area; the oxygen concentration was greater than [missing information]. The high-temperature areas were classified as Class III composite hazard areas; the high-temperature areas were classified as Class IV composite hazard areas, as shown in Table 1: Table 1. Classification of Composite Hazard Zones in Gas-Bearing Goaf Areas In a Class I complex hazardous area, characterized by the superposition of oxygen concentration, gas concentration, and high temperature zones, there is a dual risk of coal spontaneous combustion and gas explosion. Temperature within this area should be a key monitoring focus; any abnormal temperature should prompt immediate implementation of corresponding cooling and fire prevention measures.

[0070] In a Class II composite hazard zone, two areas of oxygen and methane concentration that meet certain conditions overlap, primarily consisting of the remaining area with methane concentrations between 5% and 16%. Within this zone, there is a risk of methane exceeding limits at the working face and upper corners. Furthermore, if high temperatures spread to this area, the accumulated heat can easily transform it into a Class I composite hazard zone. Due to its proximity to the working face, this zone is prone to unsafe factors from production machinery and unsafe acts by personnel, making it susceptible to ignition sources and potentially leading to methane explosions.

[0071] In the three-category composite hazard zone, which is the superposition zone of the 12% oxygen concentration zone and the high temperature zone, the risk of spontaneous combustion of coal is high. Due to the increase in air leakage or the unreasonable implementation of extraction measures on the return air side, the gas concentration boundary will shift backward, and the three-category composite hazard zone will easily evolve into a one-category composite hazard zone.

[0072] The fourth category of composite hazard zones covers the remaining high-temperature areas, where there is only the risk of spontaneous combustion of coal. Only when the boundaries of oxygen concentration and gas concentration both shift backward can this area potentially evolve into a first-category composite hazard zone.

[0073] Therefore, by analyzing the distribution of gas concentration field, air flow field, oxygen concentration field, gas temperature field and solid temperature field in the goaf, the range of high-temperature zone with potential spontaneous combustion risk was identified; and the goaf composite hazard zone was divided with the temperature field as the core, providing a basis for understanding the evolution law of spontaneous combustion under gas desorption of residual coal in the goaf and the prevention and control of composite disasters.

[0074] like Figure 20 As shown, this embodiment also provides a system for identifying composite hazardous areas in gas-bearing goafs under coal-oxygen combined action. The system uses the method described in any of the above embodiments for identifying composite hazardous areas in gas-bearing goafs under coal-oxygen combined action to identify spontaneous combustion composite hazardous areas in gas-bearing goafs. The system includes: Model building unit 201 is configured to build a thermo-solid-gas multi-field coupling model of a gas-bearing goaf under the combined action of coal and oxygen; Model solver 202 is configured to calculate the thermo-solid-gas multi-field coupling model of gas-bearing goaf under the combined action of coal and oxygen, and determine the distribution areas of high temperature region, gas concentration field and oxygen concentration field of gas-bearing goaf. The hazard identification unit 203 is configured to identify and delineate the composite hazard areas of the goaf based on the preset composite hazard area identification rules, according to the distribution areas of high temperature areas, gas concentration fields, and oxygen concentration fields.

[0075] The coal-oxygen combined action gas-bearing goaf complex hazard area identification system of this embodiment can realize the steps and process of the coal-oxygen combined action gas-bearing goaf complex hazard area identification method of any of the above embodiments, and achieve the same technical effect, which will not be repeated here.

[0076] In the description of this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0077] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for identifying composite hazardous areas in gas-bearing goaf areas under the combined effects of coal and oxygen, characterized in that, include: Construct a multi-field coupled thermo-solid-gas model for gas-bearing goaf under the combined action of coal and oxygen; A multi-field coupled thermo-solid-gas model of a gas-bearing goaf under the combined action of coal and oxygen was calculated to determine the high-temperature region, gas concentration field, and oxygen concentration field distribution region of the gas-bearing goaf. Based on the preset rules for identifying complex hazardous areas, the complex hazardous areas of the goaf are identified and delineated according to the distribution areas of high temperature areas, gas concentration fields, and oxygen concentration fields.

2. The method according to claim 1, characterized in that, The multi-field coupling model includes interacting single models of gas concentration field, air flow field, oxygen concentration field, gas temperature field, and solid temperature field, as well as the boundary constraints of each single model.

3. The method according to claim 2, characterized in that, The single model for the gas concentration field is: Correspondingly, the boundary constraints for the single model of gas concentration field are: In the formula, In the three-dimensional rectangular coordinate system of the physical model of the gas-bearing goaf area The gas concentration at that location, The molar concentration of gas, For control body The area of ​​the closed boundary surface, The volume enclosed by the closed boundary surface; For the area of ​​the closed boundary surface of the control volume, Gas flow rate at the location; For the area of ​​the closed boundary surface of the control volume, The unit outward normal vector; This represents the proportion coefficient of residual coal in solid coal rock types. The volume of gas desorbed per unit mass of residual coal per unit time. This represents the gas molar volume at the corresponding temperature; The apparent density of the residual coal particles; Porosity of coal particles For airflow speed, is the diffusion coefficient constant of gas.

4. The method according to claim 2, characterized in that, The single model of the airflow field is: Correspondingly, the boundary constraints for a single airflow model are: In the formula, For control body The area of ​​the closed boundary surface, The volume enclosed by the closed boundary surface; A three-dimensional rectangular coordinate system for the physical model of a gas-bearing goaf. Inner position air pressure; The air permeability coefficient, It is the acceleration due to gravity. The total gas pressure at any point within the goaf. air density; The potential energy of a unit cell. For the area of ​​the closed boundary surface of the control volume, The unit outward normal vector; The thickness of the seepage layer in the goaf. The angle of collapse of the roof slab; This represents the proportion of residual coal in solid coal and rock. The standard density of methane gas, The volume of gas desorbed per unit mass of coal per unit time; This represents the apparent density of the residual coal particles.

5. The method according to claim 1, characterized in that, The solution region of the physical model of the gas-bearing goaf is divided into grids, and each individual model in the multi-field coupling model is discretized based on the grid division results. The discretization results are then encoded to generate the spontaneous combustion distribution characteristics of the gas-bearing goaf.

6. The method according to claim 5, characterized in that, Based on the grid partitioning results, the contribution matrix of each individual model is constructed using the interpolation function of each individual model; among which, The interpolation function for a single model of the gas concentration field is: The interpolation function for a single model of the airflow field is: The interpolation function for a single model of the oxygen concentration field is: The interpolation function for a single model of the gas temperature field is: The interpolation function for a single model of the solid temperature field is: In the formula, These are the vertices of any tetrahedral element within the solution region of the physical model of a gas-bearing goaf; These represent the three directions of the three-dimensional rectangular coordinate system of the physical model of the goaf; For any tetrahedral element The gas concentration value; The vertices of any tetrahedral element are respectively The gas concentration value at the location; For any tetrahedral element air pressure, The vertices of any tetrahedral element are respectively Air pressure at that location; For any tetrahedral element oxygen concentration, The vertices of any tetrahedral element are respectively Oxygen concentration at that location; For any tetrahedral element The gas temperature, The vertices of any tetrahedral element are respectively The gas temperature at that location; For any tetrahedral element solid temperature The vertices of any tetrahedral element are respectively The solid temperature at that location; For control body The volume enclosed by the closed boundary surface; The vertices of the tetrahedral elements The coefficient of the determinant of the contribution of a physical quantity at a given location to the physical quantity at any other location within the unit cell.

7. The method according to claim 6, characterized in that, By discretizing the boundary constraints of a single model of the gas concentration field, the contribution matrix of the single model of the gas concentration field is constructed; where, The contribution matrix of the single model for the gas concentration field is: in, and In the formula, The vertices of any tetrahedral element within the solution region of the physical model of a gas-bearing goaf are respectively... gas concentration For tetrahedral elements The contribution of gas concentration; These are constant column vectors; In the three-dimensional rectangular coordinate system of the physical model of the goaf, respectively The velocity component in the direction, Tetrahedral units middle The coefficient of the determinant of the contribution of a physical quantity at a point to a physical quantity at any location within the element. Porosity of coal particles For airflow speed, Let be the gas diffusion coefficient. Tetrahedral units middle The coefficient of the determinant of the contribution of a point physical quantity to a physical quantity at any location within a unit cell; For control body The volume enclosed by the closed boundary surface; This represents the gas molar volume at the corresponding temperature; This represents the proportion of residual coal in solid coal and rock. The volume of gas desorbed per unit mass of residual coal per unit time. This represents the apparent density of the residual coal particles.

8. The method according to claim 6, characterized in that, By discretizing the boundary constraints of a single airflow field model, the contribution matrix of the single airflow field model is constructed; whereby the contribution matrix of the single airflow field model is: in, and In the formula, The vertices of any tetrahedral element within the solution region of the physical model of a gas-bearing goaf are respectively... air pressure For tetrahedral elements The contribution of air pressure; These are constant column vectors; The air permeability coefficient, It is the acceleration due to gravity. Tetrahedral units middle The coefficient of the determinant of the contribution of a physical quantity at a point to a physical quantity at any location within the element. Tetrahedral units middle The coefficient of the determinant of the contribution of a physical quantity at a point to a physical quantity at any location within a unit cell; air density, The angle of collapse of the roof slab. The standard density of methane gas, The volume of gas desorbed per unit mass of coal per unit time; The apparent density of the coal particles. This represents the proportion of residual coal in solid coal and rock; The density of the gas. This represents the gas molar volume at the corresponding temperature. For control body The volume enclosed by the closed boundary surface.

9. The method according to claim 1, characterized in that, Based on the distribution characteristics of spontaneous combustion in gas-bearing goaf areas, spontaneous combustion composite hazard zones are delineated in gas-bearing goaf areas; Among them, the spontaneous combustion distribution characteristics of gas goaf areas include, but are not limited to, gas concentration field distribution, air flow field distribution, oxygen concentration field distribution, gas temperature field distribution, and solid temperature field distribution; gas concentration Oxygen concentration greater than The high-temperature area was identified as a Class I composite hazard area; gas concentration And the oxygen concentration is greater than The area was identified as a Class II composite hazard area; Oxygen concentration greater than The high-temperature area was identified as a Class III composite hazard area; The high-temperature area was identified as a Class IV composite hazard area.

10. A system for identifying complex hazardous areas in gas-bearing goaf areas under the combined effects of coal and oxygen, characterized in that, The method for identifying composite hazardous areas in gas-bearing goafs under coal-oxygen combined action as described in any one of claims 1-9 is used to identify spontaneous combustion composite hazardous areas in gas-bearing goafs. The system comprises: The model building unit is configured to build a multi-field coupled thermo-solid-gas model of a gas-bearing goaf under the combined action of coal and oxygen. The model solving unit is configured to calculate the thermo-solid-gas multi-field coupled model of a gas-bearing goaf under the combined action of coal and oxygen, and to determine the high-temperature region, gas concentration field, and oxygen concentration field distribution region of the gas-bearing goaf. The hazard identification unit is configured to identify and delineate the composite hazard areas of the goaf based on preset composite hazard area identification rules, according to the distribution areas of high temperature areas, gas concentration fields, and oxygen concentration fields.

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