Method for determining spontaneous combustion evolution process of end slope coal of strip mine

Abstract

The invention provides a method for determining the spontaneous combustion evolution process of end slope coal of a strip mine, and belongs to the field of geotechnical engineering geological disaster prevention and control and the field of mine safety and environmental protection. Updating the porosity, the permeability and the range of the combustion space area in the pre-established three-dimensional geologic model by adopting the three-dimensional distribution of the porosity of the bending subsidence zone, the permeability of the fissure zone, the permeability of the caving zone and the porosity of the caving zone in the combustion space area; performing coal fire evolution simulation again according to the updated pre-established three-dimensional geologic model to obtain a coal fire development range, an updated real-time temperature field range and a gas concentration field; and if the combustion cannot be continued, outputting a final coal fire development range and an updated real-time temperature field range. According to the method, the efficiency and accuracy of open-pit mine end slope coal fire treatment are effectively improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of open-pit mining and slope engineering, and particularly relates to a method for determining the evolution process of open-pit mine end-slope coal spontaneous combustion. BACKGROUND

[0002] The end-slope of the open-pit mine stope is the key structure connecting the working slope. After stopping mining, the end-slope may form heat accumulation conditions and induce coal spontaneous combustion. Coal spontaneous combustion can cause sustained combustion of the coal seam, which may lead to serious damage to the rock mass strength and further lead to slope instability. The coal fire propagation model has great practical significance and application value for the design and engineering management of slope engineering. In order to deeply understand the evolution mechanism of coal fire, domestic research has made certain achievements in fire area management and coal fire prediction. Patent CN102176070A discloses a coal fire exploration method based on surface fissures and temperature, which provides evaluation or coal fire prediction information for goaf coal fire prevention and early management based on the fissures and temperature of the surface of the predetermined area. Patent CN117830867A discloses a coal seam fire hazard detection method, which identifies the coal fire hazard area, delineates the fire point position and combustion depth based on the coal seam fire hazard database through multi-source data fusion. Patent CN112540144A discloses a coal fire space evolution process similar simulation test device, which provides a coal fire similar simulation device and method to detect the space evolution and temperature change process of the fire area. Patent CN118362597A discloses a method for determining the coal oxidation heat release intensity of underground coal fire, which quickly estimates the coal oxidation heat release intensity by monitoring the concentration of coal oxidation gas products to prevent and control coal fire disasters. Patent CN118917074A discloses a three-dimensional form evolution simulation method for underground coal fire combustion goaf, which uses remote sensing data, numerical simulation and three-dimensional modeling to inverse the three-dimensional form evolution process of the underground coal fire combustion goaf.

[0003] However, the existing achievements focus more on the evolution law of underground goaf coal spontaneous combustion, but less on the evolution process of open-pit mine end-slope coal spontaneous combustion. Therefore, it is necessary to study this method in order to provide technical support for the design and management of slope engineering. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application provides a method for determining the evolution process of open-pit mine end-slope coal spontaneous combustion.

[0005] In a first aspect, the present application provides a method for determining the evolution process of open-pit mine end-slope coal spontaneous combustion, comprising:

[0006] Step S1: obtaining the coal oxidation kinetic parameters, coal thermophysical properties and mine area geological parameters of the open-pit mine;

[0007] Step S2: input the coal oxidation kinetics parameters, coal thermal physical properties and mine geological parameters into the numerical simulation model;

[0008] Step S3: add the coal spontaneous combustion point in the numerical simulation model according to the field situation;

[0009] Step S4: perform numerical simulation on the numerical simulation model according to the added coal spontaneous combustion point to obtain the real-time temperature field range of the rock stratum in the combustion empty area;

[0010] Step S5: calculate the three-dimensional distribution of the porosity and permeability of the curved subsidence zone, fracture zone and caving zone in the combustion empty area according to the real-time temperature field range of the rock stratum in the combustion empty area;

[0011] Step S6: update the porosity, permeability and range of the combustion empty area in the numerical simulation model according to the real-time temperature field range of the rock stratum and the three-dimensional distribution of the porosity and permeability of the curved subsidence zone, fracture zone and caving zone in the combustion empty area;

[0012] Step S7: perform coal spontaneous combustion evolution process simulation again according to the updated numerical simulation model to obtain the development range of the coal fire, the updated real-time temperature field range and the gas concentration field;

[0013] Step S8: determine whether the combustion can continue according to the updated temperature field range and the coal combustion point;

[0014] Step S9: if the combustion can continue, return to step S5, take the updated temperature field range as the real-time temperature field range, and recalculate the three-dimensional distribution of the porosity of the caving zone;

[0015] Step S10: if the combustion cannot continue, output the final development range of the coal fire and the updated real-time temperature field range.

[0016] The coal oxidation kinetics parameters include the oxidation reaction rate and exothermic characteristics of the coal combustion point at different temperatures;

[0017] The coal thermal physical properties include the thermal conductivity, specific heat capacity and density of the coal;

[0018] The mine geological parameters include the rock stratum thickness of the mine slope, the slope shape of the mine, the porosity, density and thermal conductivity coefficient of each rock stratum of the mine slope.

[0019] The calculation of the three-dimensional distribution of the porosity and permeability of the curved subsidence zone, fracture zone and caving zone in the combustion empty area according to the real-time temperature field range of the rock stratum in the combustion empty area includes:

[0020] Dividing the range of the combustion empty area according to the real-time temperature field range, the coal combustion point and the combustion characteristics;

[0021] A three-dimensional coordinate system is established with the midpoint of the range of the slope top of the combustion air zone as the origin, the length of the strike of the range of the combustion air zone as the x-axis, the length of the tendency of the range of the combustion air zone as the y-axis, and the height of the range of the combustion air zone as the z-axis, and the division ranges of the caving zone, the fractured zone and the curved subsidence zone are calculated according to the three-dimensional coordinate system;

[0022] According to the porosity of the slope surface of the open pit, the porosity of the curved subsidence zone is calculated;

[0023] According to the overburden rock movement law of the open pit, the permeability of the fractured zone and the permeability of the caving zone are calculated;

[0024] The three-dimensional distribution of the porosity of the caving zone is calculated by considering the thermal damage of the tensile strength and the load of the range of the combustion air zone.

[0025] The three-dimensional distribution of the porosity of the caving zone is calculated by considering the thermal damage of the tensile strength and the load of the range of the combustion air zone, including:

[0026] The real-time temperature field range of the combustion air zone rock is segmented and divided according to the height of the range of the combustion air zone;

[0027] According to the segmented and divided temperature, the tensile strength change calculation formula of the rock with the segmented and divided temperature is fitted by using the rock heating tensile experiment, and the rock tensile strength is corrected according to the tensile strength change calculation formula of the rock with the segmented and divided temperature;

[0028] According to the corrected rock tensile strength and the load of the range of the combustion air zone, the subsidence amount of the main roof along the strike mid-axis distribution of the goaf floor is calculated;

[0029] According to the subsidence amount of the main roof along the strike mid-axis distribution of the goaf floor, the three-dimensional distribution of the porosity of the caving zone is calculated.

[0030] The real-time temperature field range of the combustion air zone rock is segmented and divided according to the height of the range of the combustion air zone, and the calculation formula is as follows:

[0031] ;

[0032] Wherein, T is a rock depth temperature correction parameter, z is the height of the range of the combustion air zone, h i (1≤i≤12) is a rock depth range parameter affected by the temperature field, which is determined by the temperature field range calculated by the previous numerical simulation.

[0033] The three-dimensional distribution of the porosity of the caving zone is calculated by considering the thermal damage of the tensile strength and the load of the range of the combustion air zone, including:

[0034] ;

[0035] wherein, T is a different depth rock layer temperature correction parameter, T0 is a mudstone normal temperature, A is a first fitting parameter, B is a second fitting parameter, k0 is an attenuation parameter of the equation, is a corrected rock mass tensile strength, is a mudstone initial tensile strength.

[0036] The corrected basic roof along the goaf floor strike axis distribution subsidence is calculated according to the corrected rock tensile strength and the load of the range of the combustion goaf, and the calculation formula is as follows:

[0037] ;

[0038] wherein, is the corrected basic roof along the goaf floor strike axis distribution subsidence, h d is a direct roof thickness, H is a coal seam height, K p is a direct roof broken rock mass residual broken expansion coefficient, l is a basic roof broken rock length, , is a corrected rock mass tensile strength, q is a load of the range of the combustion goaf.

[0039] The caving zone porosity three-dimensional distribution is calculated according to the corrected basic roof along the goaf floor strike axis distribution subsidence, and the calculation formula is as follows:

[0040] ;

[0041] wherein, is the caving zone porosity three-dimensional distribution, is a porosity change curve on the goaf floor strike axis, dy is a range of the combustion goaf, is the corrected basic roof along the goaf floor strike axis distribution subsidence, h d is a direct roof thickness, H is a coal seam height, φ k is a correlation coefficient function of y, , y is a variable of the range of the combustion goaf.

[0042] In a second aspect, the present application provides a computer program product, comprising a computer program or instructions, which, when executed by a processor, implement the method for determining the evolution process of the open-pit mine end slope coal spontaneous combustion.

[0043] Advantages:

[0044] The application provides a method for determining the evolution process of coal spontaneous combustion in the end slope of an open-pit mine, fills the research gap of the evolution process of coal spontaneous combustion in the end slope of an open-pit mine, effectively improves the efficiency and precision of coal fire treatment in the end slope of an open-pit mine, and helps to understand the objective law of the three-dimensional thermal field of coal fire expansion under complex conditions. The solution of this problem has important significance for the design, safe implementation and early warning of slope engineering. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 The method for determining the evolution process of coal spontaneous combustion in the end slope of an open-pit mine according to the embodiment of the application is a method for determining the evolution process of coal spontaneous combustion in the end slope of an open-pit mine.

[0046] Figure 2 The flowchart of the method for determining the evolution process of coal spontaneous combustion in the end slope of an open-pit mine according to the embodiment of the application is shown in FIG. 1.

[0047] Figure 3 The combustion property curve of coal according to the embodiment of the application is shown in FIG. 2.

[0048] Figure 4 The schematic diagram of the numerical simulation model according to the embodiment of the application is shown in FIG. 3.

[0049] Figure 5 The initial temperature field range diagram of coal spontaneous combustion in a certain open-pit mine according to the embodiment of the application is shown in FIG. 4.

[0050] Figure 6 The schematic diagram of the burning empty area of an open-pit mine according to the embodiment of the application is shown in FIG. 5.

[0051] Figure 7 The schematic diagram of the three-dimensional distribution of the porosity of a caving zone according to the embodiment of the application is shown in FIG. 6.

[0052] Figure 8 The schematic diagram of the first combustion expansion range of a certain open-pit mine according to the embodiment of the application is shown in FIG. 7.

[0053] Figure 9 The schematic diagram of the second combustion expansion range of a certain open-pit mine according to the embodiment of the application is shown in FIG. 8.

[0054] Figure 10 The schematic diagram of the final coal fire development range of a certain open-pit mine according to the embodiment of the application is shown in FIG. 9. DETAILED DESCRIPTION

[0055] The specific embodiments of the application are described in detail below in combination with the drawings and examples.

[0056] The application provides a method for determining the evolution process of coal spontaneous combustion in the end slope of an open-pit mine. The method is based on a COMSOL multi-physical field simulation platform, a numerical simulation model for coal spontaneous combustion in the end slope of an open-pit mine is constructed, and physical processes such as heat conduction, convective heat transfer, oxygen diffusion, coal oxidation reaction kinetics, fluid flow in a porous medium, and three-dimensional distribution of pores in a combustion zone are comprehensively considered. By analyzing the distribution and diffusion law of the temperature field in the coal fire combustion process in stages, the temperature field change of the slope at different time nodes is simulated, and the stage change characteristics of the combustion zone range, porosity and permeability in the coal fire combustion stage are studied. The results show that the method can predict the development process of the coal fire, is simple and efficient, reveals the temperature field evolution characteristics and the range expansion of the combustion zone in the coal fire expansion process, provides a scientific basis and effective reference for dynamic monitoring and prevention and control of the coal fire, and has great practical significance and application value for the design and engineering treatment of the slope engineering.

[0057] Embodiment 1

[0058] The embodiment provides a method for determining the evolution process of coal spontaneous combustion in the end slope of an open-pit mine. In the embodiment, taking a certain open-pit coal mine as an example, the mine geological parameters are obtained, the slope height H is 60 m, the coal seam is nearly horizontal, the thickness is 3.5 m, the slope angle δ is 30°, the strike length is 150 m, the tendency length is 150 m, the immediate roof thickness of the caving zone is 5 m, the basic roof subsidence after the immediate roof subsidence is 2.2 m, the slope surface mudstone swelling coefficient is 1.1, a = 3.1, b = 5.0, and c = 4.0 are selected according to the slope surface overburden lithology, a is the first roof lithology correlation coefficient, b is the second roof lithology correlation coefficient, and c is the third roof lithology correlation coefficient.

[0059] A method for determining the evolution process of coal spontaneous combustion in the end slope of an open-pit mine, and the specific process is as shown in Figure 1 、 Figure 2 , which comprises the following steps.

[0060] Step S1: obtaining the coal oxidation kinetics parameters, the coal thermal physical properties and the mine geological parameters of the open-pit mine.

[0061] In the embodiment, the coal oxidation kinetics parameters include the oxidation reaction rate and the heat release characteristics of the coal ignition point at different temperatures, the coal thermal physical properties include the thermal conductivity, the specific heat capacity and the density of the coal, and the mine geological parameters include the rock layer thickness, the slope form, the porosity and the permeability of the mine.

[0062] The oxidation reaction rate and heat release characteristics of the coal sample at different temperatures are determined by a programmed temperature experiment (such as thermogravimetric analysis and differential scanning calorimetry), and the thermal conductivity, specific heat capacity and density of the coal are obtained by a laboratory thermal physical property testing device (such as a laser flash instrument).

[0063] Specifically, a thermal gravimetric-differential thermal experiment is performed on a coal sample of a certain open-pit mine to obtain a TG-DTG-DSC (Thermogravimetric-Differential Scanning Calorimetry) curve of the coal sample as shown in Figure 3 wherein TG (Thermogravimetric Analysis), DTG (Differential Thermogravimetry) and DSC (Differential Scanning Calorimetry) are plotted in the same graph, and the coal ignition point and the oxidation reaction rate and heat release characteristics of the coal sample at different temperatures are determined according to the TG-DTG-DSC curve of the coal sample. It can be observed from the image that the coal sample loses weight rapidly after the temperature reaches 370°, and therefore 370° is determined as the temperature criterion for judging the burning-out of the coal seam. It can also be observed that the heat release intensity of the coal sample increases with the increase of the coal temperature, and the function of the oxidation heat generation power of the coal with respect to the temperature is fitted as follows: The thermal conductivity, specific heat capacity and other thermal physical parameters of the coal sample are obtained by a laser flash instrument experiment, and the rock stratum thickness, slope shape, density, porosity and permeability and other mine geological parameters are obtained from mine data. The parameters obtained by the experiment are shown in Table 1.

[0064] In this embodiment, based on the results of previous geological exploration and geotechnical physical and mechanical tests, the geotechnical physical and mechanical parameters used in numerical simulation are shown in Table 1.

[0065] Table 1 Geotechnical physical and mechanical parameter table

[0066] ;

[0067] Step S2: input the coal oxidation kinetic parameters, coal thermal physical properties and mine geological parameters into the numerical simulation model;

[0068] Step S3: according to the site conditions, add the coal spontaneous ignition point to the exposed coal seam in the numerical simulation model;

[0069] In this embodiment, a numerical simulation model is established based on the aforementioned experimental data and geological parameters of the mining area. Using the COMSOL multiphysics simulation platform, a numerical model considering convective heat transfer, oxygen diffusion, and coal oxidation reaction is established. Based on the site conditions, a coal auto-ignition point is added to the slope surface. The initial temperature field range of the slope is obtained based on the numerical simulation results. The combustion zone is then divided according to the temperature field range, the coal's ignition point, and combustion characteristics. The combustion zone is approximated as a rectangular extension, with the side length of the rectangle denoted as d. x The side with the tendency is d y .

[0070] In this implementation example, a numerical simulation model was established based on the experimental data in Table 1 and the geological parameters of the mining area. According to the site conditions, a coal spontaneous combustion point was added to the slope surface. The coal spontaneous combustion point is a rectangle 14m long and 7m wide on the coal seam outcrop surface. The numerical simulation physical model is as follows: Figure 4 , Figure 4 In the middle, H III H represents the height of the coal seam caving zone. II H is the height of the fracture zone, L is the coal seam height, L is the slope strike length, d is the slope dip length, and θ is the slope angle. The numerical simulation parameters are set as shown in Table 2.

[0071] Table 2. Calculation parameters of the numerical simulation model;

[0072] ;

[0073] The initial temperature field range of coal spontaneous combustion on the slope was obtained based on the numerical simulation results, as follows: Figure 5 The combustion zone is divided according to the temperature field range and the ignition point and combustion characteristics of coal, such as... Figure 6 As shown.

[0074] Step S4: Simulate the coal fire evolution of the numerical simulation model based on the added coal auto-ignition point to obtain the real-time temperature field range of the rock strata in the combustion zone.

[0075] Step S5: Based on the real-time temperature field range of the rock strata in the combustion zone, calculate the three-dimensional distribution of porosity in the tortuous subsidence zone, permeability in the fracture zone, permeability in the collapse zone, and porosity in the collapse zone in the combustion zone.

[0076] In this embodiment, obtaining the real-time temperature field range is only the initial step. The focus is on simulating the development range of the coal fire and the updated real-time temperature field range. Simulating the development range of the coal fire is not easy due to the special conditions of open-pit mine slopes, and existing methods cannot meet the requirements. In this embodiment, a three-dimensional coordinate system is established with the midpoint of the overlying strata slope top of the combustion zone as the origin O, dividing the area into three zones. Figure 6 As shown. The range of the combustion zone is determined based on the temperature field distribution. Combining the masonry beam theory and the pyrolysis characteristics of coal and rock, the three-dimensional porosity distribution of the combustion zone is calculated.

[0077] The three-dimensional distribution of the porosity of the curved subsidence zone, the permeability of the fractured zone, the permeability of the caving zone, and the porosity of the caving zone in the combustion and emptying zone is calculated according to the real-time temperature field range of the combustion and emptying zone rock stratum, comprising:

[0078] Step S5.1: dividing the range of the combustion and emptying zone according to the real-time temperature field range, the combustion point of the coal, and the combustion characteristics;

[0079] Step S5.2: establishing a three-dimensional coordinate system with the midpoint position of the slope top in the range of the combustion and emptying zone as the origin, the strike length in the range of the combustion and emptying zone as the x-axis, the tendency length in the range of the combustion and emptying zone as the y-axis, and the height in the range of the combustion and emptying zone as the z-axis, and calculating the division range of the caving zone, the fractured zone, and the curved subsidence zone according to the three-dimensional coordinate system;

[0080] Step S5.3: calculating the porosity of the curved subsidence zone according to the slope surface porosity of the open pit;

[0081] In this embodiment, the fractures of the curved subsidence zone are usually not through, but are mostly closed fractures or micro-fractures, and the gas passing performance is limited. The curved subsidence zone is mainly curved deformation. Therefore, the porosity of the curved subsidence zone is consistent with the slope surface porosity.

[0082] Step S5.4: calculating the permeability of the fractured zone and the permeability of the caving zone according to the overburden strata movement law of the open pit;

[0083] First, according to the overburden strata movement law, the coal seam caving zone height H III and the fractured zone height H II are calculated:

[0084] (1);

[0085] (2);

[0086] wherein H is the coal seam height, W Ⅱ is the subsidence amount of the immediate roof after caving, K p is the caving rock swelling coefficient, α is the coal seam inclination angle, a is the first roof lithology related coefficient, b is the second roof lithology related coefficient, and c is the third roof lithology related coefficient. In this embodiment, according to the overburden strata movement law of the open pit, the coal seam caving zone height H III = 13m and the fractured zone height H II = 18m are calculated by the calculation formulas (1) and (2).

[0087] The permeability of the fractured zone is much greater than the permeability of the rock stratum itself, so the smoke and oxygen mainly exchange through the fractured zone. According to the parallel plate model, the fractured zone permeability k l can be represented as:

[0088] (3);

[0089] where ρ f is the fluid density, with the unit of kg / m 3 ; g is the gravity acceleration; j is the fracture width, j = C s Z; C s is the proportional coefficient, taking 0.003-0.015; Z is the fracture depth, ; E is the elastic modulus of rock-soil, with the unit of MPa; ε is the horizontal deformation value, with the unit of mm / m; ρ r is the bulk density of stratum, with the unit of kN / m 3 ; v is the Poisson's ratio.

[0090] The calculation of the permeability of caving zone: when the mudstone roof is subjected to high temperature, the mechanical parameters of mudstone will change greatly, leading to the development of mudstone pores and fissures, affecting the breaking length of mudstone roof, and further affecting the porosity distribution of caving zone.

[0091] (4);

[0092] where φ is the porosity of broken rock.

[0093] (5);

[0094] Therefore, the porosity variation curve on the strike axis (y = 0) of goaf floor is represented by the following formula:

[0095] (6);

[0096] where according to the masonry beam theory:

[0097] (7);

[0098] where, is the porosity variation curve on the strike axis of goaf floor; h d is the immediate roof thickness; H is the seam height; w(y = 0) is the subsidence of main roof along the strike axis of goaf floor; K p is the residual dilatancy coefficient of broken rock mass of immediate roof; l is the length of broken rock block of main roof. .σ b is the tensile strength of rock-soil, q is the load of the range of combustion zone.

[0099] (8);

[0100] where γ is the bulk density of rock-soil, and δ is the slope angle.

[0101] Step S5.5: Calculate the porosity three-dimensional distribution of the caving zone, including:

[0102] Step S5.5.1: Segmentally divide the real-time temperature field range of the goaf rock stratum according to the height of the range of the goaf, and the calculation formula is as follows:

[0103] (9);

[0104] Wherein, T is the temperature correction parameter of the rock stratum at different depths, and z is the height of the range of the goaf.

[0105] In this embodiment, the rock stratum is divided into zones according to the previous temperature field distribution, and the z coordinate is introduced for description.

[0106] Step S5.5.2: According to the segmented temperature, the tensile strength change calculation formula of the rock stratum with the segmented temperature is obtained by using the rock temperature rise tensile experiment fitting, and the tensile strength of the rock is corrected according to the tensile strength change calculation formula of the rock stratum with the segmented temperature, and the calculation formula is as follows:

[0107] (10);

[0108] Wherein, T is the temperature correction parameter of the rock stratum at different depths, is the corrected tensile strength of the rock mass, is the initial tensile strength of the mudstone.

[0109] Step S5.5.3: According to the corrected tensile strength of the rock and the load of the range of the goaf, the corrected subsidence amount of the basic roof along the goaf floor strike central axis distribution is calculated, and the calculation formula is as follows:

[0110] (11);

[0111] Wherein, is the corrected subsidence amount of the basic roof along the goaf floor strike central axis distribution, h d is the thickness of the immediate roof, H is the height of the coal seam, K p is the residual crushing and swelling coefficient of the broken rock mass of the immediate roof, l is the length of the broken rock mass of the immediate roof, , is the corrected tensile strength of the rock mass, and q is the load of the range of the goaf.

[0112] Step S5.5.4: According to the corrected subsidence amount of the basic roof along the goaf floor strike central axis distribution, the porosity three-dimensional distribution of the caving zone is calculated, and the calculation formula is as follows:

[0113] (12);

[0114] wherein, is the three-dimensional distribution of porosity of the caving zone, the implementation result of the embodiment is as shown in Figure 7 , is the porosity variation curve on the central axis of the goaf floor strike, dy is the length of the inclined side of the combustion goaf, is the corrected subsidence amount of the basic roof along the central axis of the goaf floor strike, h d is the immediate roof thickness, H is the coal seam height, φ k is the correlation coefficient function of y, the correlation coefficient function of y coordinate is introduced according to the “O” ring theory k to describe the porosity variation in the inclined direction, , y is the variable of the length of the inclined side in the range of the combustion goaf.

[0115] According to the Kozeny-Carman relationship between permeability and porosity and the research results of Hoek and Bray on the Kozeny-Carman relationship:

[0116] (13);

[0117] wherein, k is the permeability of the caving zone, the unit is μm 2 ; φ is the porosity of the caving zone; F s is the shape coefficient; s is the tortuosity; S gv is the surface area of the particles contained in the unit mass medium; k0 is the reference permeability, which can be taken as 10 3 μm 2 .

[0118] Step S6: updating the porosity, permeability and range of the combustion goaf in the numerical simulation model according to the real-time temperature field range of the rock stratum and the three-dimensional distribution of the porosity of the curved subsidence zone, the permeability of the fractured zone, the permeability of the caving zone and the porosity of the caving zone in the combustion goaf;

[0119] Step S7: performing coal fire evolution simulation again according to the updated numerical simulation model to obtain the development range of the coal fire, the updated real-time temperature field range and the gas concentration field;

[0120] Step S8: judging whether the combustion can continue according to the updated temperature field range and the ignition point of the coal;

[0121] In the embodiment, the model parameters such as the porosity, permeability, combustion goaf range in the numerical simulation model are updated. Based on the updated multi-physical field model, numerical simulation is performed to solve the characteristic field range in the combustion goaf, including the updated real-time temperature field range and the gas concentration field characteristic distribution, such as Figure 8The updated real-time temperature field range and the coal ignition point are used to determine whether the combustion can be maintained.

[0122] Step S9: If the combustion can be maintained, return to step S5, use the updated temperature field range as the initial real-time temperature field range, and recalculate the three-dimensional distribution of the porosity of the caving zone.

[0123] In this embodiment, it can be understood that whether the combustion can be maintained refers to whether the combustion can continue to burn deep, because the combustion will continue to develop along the strike on both sides. After the heat source temperature is removed, the combustion-free zone can maintain the temperature. The three-dimensional distribution of the porosity of the caving zone is recalculated, and the reacquired combustion expansion range is as shown in FIG. 6. Figure 9

[0124] Step S10: If the combustion cannot be maintained, output the final development range of the coal fire and the updated real-time temperature field range.

[0125] In this embodiment, it is determined that the combustion-free zone cannot maintain the temperature after the heat source temperature is removed, and the final development range of the coal fire is output as shown in FIG. 7. Figure 10 After the heat source temperature is removed, the temperature in the deep part of the combustion-free zone cannot be maintained, and decreases to 120 degrees Celsius after 50 days. The temperature expands along the strike on both sides. Therefore, the range at this time is the final combustion range.

[0126] Embodiment 2

[0127] This embodiment provides a computer program product, which includes a computer program or instructions. When the computer program or instructions are executed by a processor, the computer program or instructions realize the method for determining the evolution process of the coal spontaneous combustion at the end slope of the open pit mine.

[0128] Based on such understanding, the technical solution of the present application or the part of the technical solution that essentially contributes to the prior art or the part of the technical solution can be embodied in the form of a computer program product.

[0129] Each of the embodiments in the present application is described in a progressive manner, and the same or similar parts of each of the embodiments can be referred to each other. Each of the embodiments mainly describes the differences from other embodiments.

[0130] The protection scope of the present application is not limited to the above-described embodiments. Obviously, those skilled in the art can make various modifications and changes to the present disclosure without departing from the scope and spirit of the present disclosure. If these modifications and changes belong to the scope of the equivalent technology of the present disclosure, the present disclosure also includes these modifications and changes.​

Claims

1. A method for determining the spontaneous combustion evolution process of coal at the end of an open-pit mine, characterized in that, include: Step S1: Obtain coal oxidation kinetic parameters, coal thermophysical properties, and geological parameters of the mining area in the open-pit mine; Step S2: Input the coal oxidation kinetic parameters, coal thermophysical properties, and mining area geological parameters into the numerical simulation model; Step S3: Add the coal auto-ignition point to the numerical simulation model based on the site conditions; Step S4: Perform numerical simulation on the numerical simulation model based on the added coal auto-ignition point to obtain the real-time temperature field range of the rock strata in the combustion zone. Step S5: Based on the real-time temperature field range of the rock strata in the combustion zone, calculate the three-dimensional distribution of porosity and permeability in the curved subsidence zone, fracture zone, and collapse zone in the combustion zone; Step S6: Update the porosity, permeability, and range of the combustion zone in the numerical simulation model based on the real-time temperature field range of the rock strata and the three-dimensional distribution of porosity and permeability in the bent subsidence zone, fracture zone, and collapse zone in the combustion zone. Step S7: Simulate the coal spontaneous combustion evolution process again based on the updated numerical simulation model to obtain the development range of the coal fire, the updated real-time temperature field range, and the gas concentration field. Step S8: Determine whether combustion can continue based on the updated temperature field range and the ignition point of coal; Step S9: If combustion can continue, return to step S5, use the updated temperature field range as the real-time temperature field range, and recalculate the three-dimensional porosity distribution of the collapse zone. Step S10: If combustion cannot be sustained, output the final range of coal fire development and the updated real-time temperature field range.

2. The method for determining the spontaneous combustion evolution process of coal at the end of an open-pit mine according to claim 1, characterized in that, The coal oxidation kinetic parameters include: the oxidation reaction rate and exothermic characteristics of coal at different temperatures; The thermal physical properties of coal include: thermal conductivity, specific heat capacity, and density. The geological parameters of the mining area include: the thickness of the rock strata on the mining area slope, the slope morphology, the porosity, density, and thermal conductivity of each rock stratum on the mining area slope.

3. The method for determining the spontaneous combustion evolution process of coal at the end of an open-pit mine according to claim 1, characterized in that, The calculation of the three-dimensional distribution of porosity and permeability in the tortuous subsidence zone, fracture zone, and collapse zone within the combustion zone, based on the real-time temperature field range of the rock strata in the combustion zone, includes: The range of the combustion zone is defined based on the real-time temperature field range, the ignition point of coal, and the combustion characteristics. A three-dimensional coordinate system is established with the midpoint of the slope top in the range of the combustion zone as the origin, the strike length in the range of the combustion zone as the x-axis, the dip length in the range of the combustion zone as the y-axis, and the height in the range of the combustion zone as the z-axis. The division range of the collapse zone, the fissure zone and the bending subsidence zone is calculated based on the three-dimensional coordinate system. Calculate the porosity of the tortuous subsidence zone based on the porosity of the open-pit mine slope; Based on the movement pattern of the overlying strata in the open-pit mine, the permeability of the fracture zone and the permeability of the caving zone are calculated. Considering the thermal damage to tensile strength and the load within the combustion zone, the three-dimensional porosity distribution of the collapse zone is calculated.

4. The method for determining the spontaneous combustion evolution process of coal at the end of an open-pit mine according to claim 3, characterized in that, The calculation of the three-dimensional porosity distribution of the collapse zone, considering the thermal damage to tensile strength and the load within the combustion zone, includes: The real-time temperature field range of the rock strata in the combustion zone is segmented according to the height of the combustion zone. Based on the segmented temperature, a calculation formula for the change of tensile strength with the segmented temperature is obtained by fitting a rock heating tensile test. The tensile strength of the rock is then corrected based on the calculation formula for the change of tensile strength with the segmented temperature. Based on the corrected rock tensile strength and the load of the goaf area, the subsidence of the corrected basic roof along the centerline of the goaf floor is calculated. Based on the subsidence distribution along the centerline of the corrected basic top edge of the goaf floor, the three-dimensional porosity distribution of the caving zone is calculated.

5. The method for determining the spontaneous combustion evolution process of coal at the end of an open-pit mine according to claim 4, characterized in that, The real-time temperature field range of the rock strata in the combustion zone is segmented according to the height of the combustion zone, and the calculation formula is as follows: ； Where T is the temperature correction parameter for rock strata at different depths, z is the height of the combustion zone, and h i (1≤i≤12) represents the range of rock strata depth affected by the temperature field, which is determined by the temperature field range calculated in the previous numerical simulation.

6. The method for determining the spontaneous combustion evolution process of coal at the end of an open-pit mine according to claim 4, characterized in that, The tensile strength is calculated based on the segmented temperature range using a rock heating tensile test fitting method. The rock tensile strength is then corrected according to this formula, which is as follows: ； Where T represents the temperature correction parameter for rock strata at different depths, T0 represents the ambient temperature of mudstone, A represents the first fitting parameter, B represents the second fitting parameter, and k0 represents the attenuation parameter of the equation. The corrected tensile strength of the soil and rock mass. This represents the initial tensile strength of the mudstone.

7. The method for determining the spontaneous combustion evolution process of coal at the end of an open-pit mine according to claim 4, characterized in that, Based on the corrected rock tensile strength and the load of the goaf area, the subsidence of the corrected basic roof along the strike of the goaf floor centerline is calculated, and the calculation formula is as follows: ； in, h represents the subsidence distribution along the centerline of the goaf floor after correction. d H is the immediate roof thickness, H is the coal seam height, and K is the thickness of the immediate roof. p l represents the residual fragmentation coefficient of the directly fractured rock mass, and l represents the length of the basic fractured rock block. , q represents the corrected tensile strength of the soil and rock mass, and q represents the load within the combustion zone.

8. The method for determining the spontaneous combustion evolution process of coal at the end of an open-pit mine according to claim 4, characterized in that, The three-dimensional porosity distribution of the caving zone is calculated based on the subsidence distribution along the central axis of the corrected basic roof along the strike of the goaf floor. The calculation formula is as follows: ； in, The porosity three-dimensional distribution of the collapse zone. This is the porosity variation curve along the strike centerline of the goaf floor, where dy is the dip side length of the goaf. h represents the subsidence distribution along the centerline of the goaf floor after correction. d H is the immediate roof thickness, H is the coal seam height, and φ is the thickness of the immediate roof. k The correlation coefficient function of y y is a variable representing the inclination length within the range of the combustion zone.

9. A computer program product, comprising a computer program or instructions, characterized in that, When the computer program or instructions are executed by the processor, they implement the method for determining the spontaneous combustion evolution process of coal at the end of an open-pit mine as described in any one of claims 1 to 8.

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