Numerical simulation method and system for response of spontaneous combustion coal gangue dump to passive cooling of group pipes

Abstract

The invention relates to the technical field of environmental governance and coal gangue mountain fire prevention and extinguishing, in particular to a numerical simulation method and system for response of a spontaneous combustion coal gangue mountain to passive cooling of group pipes, and the method comprises the following steps: building a geometric structure model of the coal gangue mountain according to field actual measurement information of the coal gangue mountain; constructing a coal gangue spontaneous combustion multi-field coupling model according to the field actual measurement information and the geometric structure model of the coal gangue mountain; selecting key physical parameters of temperature change based on the gangue hill initial temperature field information and a gangue spontaneous combustion multi-field coupling model; dividing a numerical simulation grid and numerical simulation time according to the geometric structure model of the coal gangue mountain and the coal gangue spontaneous combustion multi-field coupling model; and simulating the passive cooling application effect of the group tube by combining the geometric structure model, the coal gangue spontaneous combustion multi-field coupling model, the key physical parameters, the numerical simulation grid and the numerical simulation time. According to the method, research is performed through the mathematical model, the spontaneous combustion mechanism of the coal gangue mountain can be known, the heat pipe cooling strategy and scheme are optimized, and the treatment efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of environmental management and fire prevention and extinguishing of coal gangue heaps, and in particular to a numerical simulation method and system for the passive cooling response of a spontaneously combusting coal gangue heap to a group of pipes. Background Art

[0002] Although the current research field of coal gangue spontaneous combustion involves multiple aspects such as spontaneous combustion mechanism, prevention and control strategies, temperature field characteristics and the application of thermal management technology, it is obviously insufficient to use heat pipe technology to achieve effective cooling of spontaneously combusting coal gangue mountains.

[0003] In the complex and changeable field environment, the actual cooling effect and internal mechanism of heat pipes on coal gangue heaps in different temperature zones are still unclear. The numerical simulation study based on the field group pipe test ignored the complex interaction between multiple physical fields such as temperature field, seepage field, and chemical reaction field in the process of analyzing the cooling process of spontaneous combustion coal gangue heaps. Existing analysis technology is difficult to fully reflect the dynamic evolution characteristics of coal gangue heaps during spontaneous combustion. Therefore, a more sophisticated and comprehensive multi-field coupling numerical simulation method is needed to guide field practice, which will help effectively curb the spontaneous combustion of coal gangue heaps and protect the safety of the ecological environment. Summary of the invention

[0004] In view of the defects of existing methods and the shortcomings of practical applications, in order to evaluate the effectiveness of the group management system in controlling the temperature of spontaneously combusting coal gangue heaps in the long term, the present invention carried out simulation prediction, and the long-term change trend of the internal temperature under the optimal arrangement of the group management system, revealing the long-term temperature control effect of the group management technology. A theoretical model was also constructed to provide a solid scientific basis and practical technical reference for the actual spontaneous combustion control of coal gangue heaps, thereby effectively curbing the spontaneous combustion of coal gangue heaps and protecting the safety of the ecological environment. In the first aspect, the present invention provides a numerical simulation method for the response of a spontaneous combustion coal gangue mountain to passive cooling of a group of pipes. The method comprises the following steps: establishing a geometric structure model of the coal gangue mountain based on the field measured information of the coal gangue mountain study area; constructing a multi-field coupling model of spontaneous combustion of coal gangue based on the field measured information and the geometric structure model of the coal gangue mountain; selecting key physical parameters of temperature change based on the initial temperature field information of the coal gangue mountain study area and the multi-field coupling model of spontaneous combustion of coal gangue, dividing different temperature zones, and arranging the group of pipes in a plum blossom shape; dividing the numerical simulation grid and the numerical simulation time based on the geometric structure model of the coal gangue mountain and the multi-field coupling model of spontaneous combustion of coal gangue; and simulating the application effect of passive cooling of the group of pipes in combination with the geometric structure model of the coal gangue mountain, the multi-field coupling model of spontaneous combustion of coal gangue, the key physical parameters, the numerical simulation grid and the numerical simulation time. The present invention establishes a geometric model of the coal gangue mountain according to the temperature information of the gangue mountain study area, and constructs a spontaneous combustion multi-field coupling model based on the geometric model for simulation research, which can improve the simulation accuracy, enhance the management efficiency and safety, and help protect the safety of the ecological environment.

[0005] Optionally, the geometric structure model of the gangue mountain is established based on the field measured information of the gangue mountain study area, including: establishing the geometric structure model of the gangue mountain based on the field measured information, the geometric structure model of the gangue mountain includes a three-dimensional tetrahedral gangue mountain geometric model; dividing the geometric structure model of the gangue mountain in combination with the initial temperature field information of the gangue mountain study area, the geometric structure model of the gangue mountain includes a high temperature zone, a medium temperature zone and a low temperature zone; the high temperature zone, the medium temperature zone and the low temperature zone adopt a plum blossom-shaped arrangement of group pipes. The present invention selects a specific platform and establishes a three-dimensional tetrahedral geometric model based on the temperature field information, which can more accurately reflect the actual terrain and morphology of the gangue mountain, reduce the error caused by the simplification of the model, and can more clearly show the temperature distribution inside the gangue mountain, providing an accurate basis for subsequent temperature control and management.

[0006] Optionally, the multi-field coupling model of spontaneous combustion of coal gangue is constructed according to the field measured information and the geometric structure model of the coal gangue mountain, including: analyzing the coupling relationship between oxygen oxidation reaction, air seepage and temperature field according to the initial temperature field information, the field measured information and the geometric structure model of the coal gangue mountain. The present invention fully considers the interaction relationship between oxygen oxidation reaction, air seepage and temperature field, so that the model can more comprehensively reflect the complex physical and chemical changes in the spontaneous combustion process of coal gangue mountain.

[0007] Optionally, the multi-field coupling model of spontaneous combustion of coal gangue is constructed according to the field measured information and the geometric structure model of the coal gangue mountain, including: establishing the air seepage velocity field balance equation, the oxygen component migration field balance equation and the temperature field transmission balance equation based on the initial temperature field information, the geometric structure model of the coal gangue mountain and the coupling relationship; combining the air seepage velocity field balance equation, the oxygen component migration field balance equation and the temperature field transmission balance equation to obtain the multi-field coupling model of spontaneous combustion of coal gangue. The balance equation established by the present invention can quantitatively analyze the dynamic process of air seepage velocity, oxygen component distribution and temperature change during the spontaneous combustion of coal gangue mountain, which helps to more accurately predict the changing trends and mutual influences of various physical fields during the spontaneous combustion process.

[0008] Optionally, the air seepage velocity field balance equation satisfies the following relationship:

[0009]

[0010] in, represents the simulation result of air seepage velocity field, μ represents the air dynamic viscosity coefficient, k represents the solid permeability, v represents the seepage velocity, P represents the pressure, represents the pressure gradient, ρ g represents air density, g represents gravitational acceleration, T αThe equation of the present invention includes multiple physical parameters, fully considering the interaction and coupling relationship of related parameters, so that the model can more comprehensively reflect the air seepage phenomenon in the spontaneous combustion process of coal gangue pile.

[0011] Optionally, the oxygen component migration field balance equation satisfies the following relationship:

[0012]

[0013] in, represents the simulation result of oxygen component migration field, D represents the air diffusion coefficient, represents the square of oxygen concentration gradient, r represents the reaction rate, e represents the solid porosity, represents the partial derivative of oxygen concentration, represents the partial derivative with time, v represents the seepage velocity, represents the oxygen concentration gradient, c represents the oxygen concentration, A represents the pre-exponential factor, E represents the activation energy, R represents the gas universal constant, and T represents the solid temperature. The equilibrium equation of the present invention includes multiple physical and chemical parameters, so that the model can more comprehensively reflect the oxygen migration phenomenon in the spontaneous combustion process of coal gangue pile.

[0014] Optionally, the temperature field transmission balance equation satisfies the following relationship:

[0015]

[0016] Where, e represents the solid porosity, r represents the reaction rate, ΔH represents the combustion enthalpy change of coal gangue, and ρ g Represents the air density, C g is the specific heat capacity of air, ρ s Represents the density of the solid, C s is the specific heat capacity of the solid, represents the partial derivative of the solid temperature, represents the partial derivative with time, v represents the seepage velocity, represents the gradient, ρ g Represents the air density, C g represents the specific heat capacity of air, T represents the solid temperature, λ s represents the thermal conductivity of the solid, λ g represents the thermal conductivity of air, represents the square of the solid temperature gradient, and Q represents the total cooling capacity of the group of pipes. The temperature field transmission balance equation of the present invention can further reveal the interaction mechanism between temperature, oxygen concentration and air seepage during the spontaneous combustion of coal gangue piles, and provide an important basis for in-depth understanding of the spontaneous combustion mechanism.

[0017] Optionally, the dividing of numerical simulation grids and numerical simulation time according to the geometric structure model of the gangue mountain and the multi-field coupling model of spontaneous combustion of gangue includes: performing tetrahedral grid division according to the geometric structure model of the gangue mountain and obtaining the grid division result of the numerical simulation; setting the simulation calculation time step based on the multi-field coupling model of spontaneous combustion of gangue and obtaining the time stage information of the numerical simulation. The present invention reasonably divides the geometric model, which can reduce the number of unnecessary grids while ensuring the calculation accuracy, thereby reducing the consumption of computing resources.

[0018] Optionally, the combination of the geometric structure model of the gangue mountain, the multi-field coupling model of the gangue spontaneous combustion, the key physical parameters, the numerical simulation grid and the numerical simulation time to simulate the application effect of the passive cooling of the group pipes includes: combining the geometric structure model of the gangue mountain, the key physical parameters, the grid division results and the time step information, carrying out transient numerical simulation of passive cooling of the group pipes of the spontaneous combustion gangue mountain, simulating the application effect of passive cooling of the group pipes, and obtaining the simulation results of the air seepage velocity field, the simulation results of the oxygen component migration field and the temperature field. The present invention comprehensively combines the simulation results of the air seepage velocity field, the oxygen component migration field and the temperature field, and can comprehensively evaluate the influence of the passive cooling measures of the group pipes on the internal temperature distribution, oxygen concentration and seepage velocity of the gangue mountain, and can more accurately reflect the cooling effect, effectively avoiding the limitations of the single factor analysis results.

[0019] In the second aspect, the present invention also provides a numerical simulation system for the response of a spontaneous combustion coal gangue mountain to the passive cooling of a group of pipes, which can efficiently execute the numerical simulation method for the response of a spontaneous combustion coal gangue mountain to the passive cooling of a group of pipes provided by the present invention, and the system includes an input device, a processor, an output device and a memory, wherein the input device, the processor, the output device and the memory are interconnected, and the memory includes a computer-readable storage medium as described in the first aspect of the present invention, and the memory is used to store a computer program, and the computer program includes program instructions, and the processor is configured to call the program instructions. The system provided by the present invention has a compact structure, strong applicability, and greatly improves the operating efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a flow chart of the numerical simulation method of the passive cooling response of the spontaneous combustion coal gangue mountain to the group pipes of the present invention;

[0021] Figure 2 It is a schematic diagram of the geometric model of the gangue mountain in the numerical simulation method of the spontaneous combustion gangue mountain response to the passive cooling of the group pipes of the present invention;

[0022] Figure 3It is a schematic diagram of the multi-field coupling relationship in the gangue in the numerical simulation method of the spontaneous combustion gangue mountain to the passive cooling response of the group pipes of the present invention;

[0023] Figure 4 It is a schematic diagram of the boundary surface of the second platform of the gangue mountain in the numerical simulation method of the spontaneous combustion gangue mountain to the passive cooling response of the group pipes of the present invention;

[0024] Figure 5 It is a schematic diagram of mesh division of the geometric structure model of the gangue pile in the numerical simulation method of the spontaneous combustion gangue pile to the passive cooling response of the group pipes of the present invention;

[0025] Figure 6 It is a schematic diagram for comparing the measured values ​​and the simulated values ​​in different temperature areas in the numerical simulation method of the spontaneous combustion coal gangue pile to the passive cooling response of the group pipes of the present invention;

[0026] Figure 7 It is a schematic diagram of the internal temperature distribution of a spontaneous combustion gangue pile without heat pipes in 0, 1, 2, 3, 4, and 5 years in the numerical simulation method of the spontaneous combustion gangue pile to the passive cooling response of the group pipes of the present invention;

[0027] Figure 8 It is a schematic diagram of the temperature change of the spontaneous combustion gangue pile after 360 days at different buried depths of the pipe group in the numerical simulation method of the spontaneous combustion gangue pile to the passive cooling response of the pipe group in the present invention;

[0028] Fig. 9 It is a schematic diagram of simulated values ​​of temperature measuring points at different buried depths of a group of pipes in a low temperature zone in the numerical simulation method of the present invention for the response of a spontaneous combustion coal gangue pile to passive cooling of a group of pipes;

[0029] Fig.10 It is a schematic diagram of the temperature change of the spontaneous combustion gangue pile under the optimal arrangement of the group pipes in the numerical simulation method of the spontaneous combustion gangue pile's response to the passive cooling of the group pipes of the present invention for 0, 5, 10, 20 and 30 years of operation;

[0030] Fig.11 It is a schematic diagram of the maximum temperature inside the spontaneous combustion gangue pile changing with time under the action of the group pipe in the numerical simulation method of the spontaneous combustion gangue pile's passive cooling response to the group pipe in the present invention;

[0031] Fig.12 It is a structural schematic diagram of the numerical simulation system of the spontaneous combustion coal gangue mountain to the passive temperature reduction response of the group pipes of the present invention. DETAILED DESCRIPTION

[0032] The specific embodiments of the present invention will be described in detail below. It should be noted that the embodiments described herein are only for illustration and are not intended to limit the present invention. In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present invention. However, it is obvious to those of ordinary skill in the art that these specific details do not need to be adopted to implement the present invention. In other examples, in order to avoid confusing the present invention, known circuits, software or methods are not specifically described.

[0033] The specific embodiments of the present invention will be described in detail below. It should be noted that the embodiments described herein are only for illustration and are not intended to limit the present invention. In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present invention. However, it is obvious to those of ordinary skill in the art that these specific details do not need to be adopted to implement the present invention. In other examples, in order to avoid confusing the present invention, known circuits, software or methods are not specifically described.

[0034] Throughout the specification, references to "one embodiment," "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in conjunction with the embodiment or example is included in at least one embodiment of the present invention. Therefore, the phrases "in one embodiment," "in an embodiment," "an example," or "an example" appearing in various places throughout the specification do not necessarily all refer to the same embodiment or example. In addition, particular features, structures, or characteristics may be combined in one or more embodiments or examples in any suitable combination and / or subcombination. In addition, it should be understood by those of ordinary skill in the art that the figures provided herein are for illustrative purposes and that the figures are not necessarily drawn to scale.

[0035] See also Figure 1 In order to clarify the long-term temperature control effect of the group pipe on the spontaneous combustion of coal gangue heap, the present invention comprehensively simulates and predicts the long-term evolution of the internal temperature of the spontaneous combustion coal gangue heap under the optimal arrangement of the group pipe. On this basis, a model is constructed to provide a theoretical reference for the spontaneous combustion control of coal gangue heap in practice, which is helpful for in-depth analysis of the long-term temperature control ability of the group pipe technology. The present invention provides a numerical simulation method for the passive cooling response of the spontaneous combustion coal gangue heap to the group pipe, and the above numerical simulation method for the passive cooling response of the spontaneous combustion coal gangue heap to the group pipe includes the following steps:

[0036] S1. Establish the geometric structure model of coal gangue pile based on the field measured information of the gangue pile study area; the implementation steps and specific contents are as follows:

[0037] A geometric structure model of a gangue mountain is established based on the field measured information. The geometric structure model of the gangue mountain in the embodiment includes a three-dimensional four-sided gangue mountain geometric model. The geometric structure model of the gangue mountain is divided into a high temperature zone, a medium temperature zone and a low temperature zone in combination with the initial temperature field information of the gangue mountain study area. The high temperature zone, the medium temperature zone and the low temperature zone adopt a plum blossom-shaped arrangement of group pipes, and the specific contents are as follows:

[0038] According to the initial temperature field information of the waste rock heap study area, the waste rock heap study area in the embodiment mainly includes the first platform, the second platform and the third platform. Considering the spontaneous combustion phenomenon of the waste rock heap in the study area, the first platform has been fully spontaneously combusted, the third platform has been partially spontaneously combusted, and the temperature distribution of the second platform is diverse and complicated. In this embodiment, the second platform with significant representativeness is selected for in-depth analysis, that is, the second platform is set as a specific platform in the waste rock heap study area.

[0039] In order to accurately simulate the physical and chemical processes of the second platform, a three-dimensional quadrangular pyramidal gangue mountain geometric model was constructed based on the initial temperature field information of the gangue mountain study area. The above model needs to be designed and improved based on field surveys and basic assumptions. In the three-dimensional quadrangular pyramidal gangue mountain geometric model, the north direction is the positive direction of the x-axis, and specific size parameters are set, including the upper base of 50 meters * 64 meters, the lower base of 60 meters * 64 meters, and the height of 10 meters. At the same time, the slope angle is set to 45 degrees to truly reflect the morphological characteristics of the second platform. In view of the significant cracks on the southeast side of the second platform, a cylindrical channel with a diameter of 1 cm and a height of 10 meters running through the entire model is created at the corresponding position in the geometric model. This channel is connected to the external environment to simulate the impact of cracks on gas flow and temperature distribution.

[0040] In addition, considering that the top of the gangue mountain is covered with a 0.5-meter-thick soil layer, the embodiment sets soil materials in the corresponding area on the top of the geometric model and ensures the continuity of the interface between the soil and the gangue to form a unified union, which helps to more accurately simulate the heat conduction and material exchange processes.

[0041] In terms of temperature distribution area, the embodiment obtains temperature distribution information of different temperature areas based on the initial temperature field information of the waste rock mountain research area, and divides the second platform into high temperature area, medium temperature area and low temperature area. On the other hand, since the temperature in the eastern area of ​​the medium temperature area is abnormally high, reaching or exceeding 200°C, and even reaching 278.9°C at the highest, this part of the area is reclassified as a high temperature area in the geometric model, which can more accurately reflect the actual situation of the platform.

[0042] Based on the temperature data measured on site in the gangue mountain study area, in this embodiment, the geometric model of the three-dimensional four-sided platform gangue mountain is subdivided into three temperature zones: high temperature zone (T>280℃), medium temperature zone (80℃≤T≤280℃), and low temperature zone (T<80℃). For the above three different temperature zone modules, the group pipes are arranged in a plum blossom layout in each temperature zone to optimize the heat conduction efficiency.

[0043] Next, in the constructed three-dimensional tetrahedral coal gangue mountain geometric model, precise boundary conditions are set for each temperature zone, and the physical field parameters of each grid unit, such as temperature and thermal conductivity, are initialized. The above initial values ​​and boundary conditions will serve as the basis for subsequent numerical simulations.

[0044] In order to simulate the passive cooling effect of the gangue heap of spontaneous combustion through the group pipe system, the heat pipe is regarded as an equivalent cold source in the embodiment, and the transient numerical simulation technology is used to simulate the above process. The heat exchange between the heat pipe and the gangue heap, as well as the heat conduction inside the gangue heap, will be considered during the simulation. Finally, by running the numerical simulation program, detailed calculation results will be output, including but not limited to the temperature distribution diagram of each temperature zone, the temperature change curve over time, the heat flow distribution and other key information, which will help to evaluate the cooling effect of the group pipe system in the future and provide a scientific basis for further optimizing the design scheme.

[0045] The three-dimensional four-sided coal gangue mountain geometric model constructed in this embodiment can not only accurately reflect the geometric shape and crack characteristics of the second platform, but also fully consider the complexity of temperature distribution, providing a solid foundation for subsequent numerical simulation and formulation of spontaneous combustion prevention and control strategies. For a schematic diagram of the three-dimensional four-sided coal gangue mountain geometric model, please refer to Figure 2 .

[0046] Furthermore, in the present embodiment, the method for establishing the geometric model of the gangue mountain is only an optional condition of the present invention. In one or some other embodiments, the method for establishing the geometric model can be flexibly adjusted according to the natural conditions and the requirements for model establishment. Since the natural conditions of the gangue mountain, such as the shape, size, and crack distribution, vary from region to region, the use of a flexible modeling method can more accurately reflect the actual conditions of different gangue mountains, and help improve the accuracy and reliability of the simulation results.

[0047] S2. A multi-field coupling model of spontaneous combustion of coal gangue is constructed based on the field measured information of the coal gangue pile study area and the geometric structure model of the coal gangue pile. The specific steps and implementation contents are as follows:

[0048] Firstly, the coupling relationship between oxygen oxidation reaction, air seepage and temperature field is analyzed based on the initial temperature field information of the gangue pile study area, the field measured information and the geometric structure model of the gangue pile. The specific contents are as follows:

[0049] Due to the complex processes occurring inside the gangue heap, especially the oxidation reaction between gangue and oxygen, the dynamics of air seepage in it, and the resulting temperature field changes, a tightly coupled three-field interaction system is formed. For details, please refer to Figure 3 .

[0050] based on Figure 3 It can be seen that in this embodiment, the heat pipe is simplified into a linear cold source, which plays a regulatory role in the overall thermal balance. That is, oxygen passes through the cracks and pores on the surface of the coal gangue mountain, penetrates into the interior in the form of air convection, and undergoes a violent oxidation reaction with the carbonaceous, pyrite and other components rich in the coal gangue. A large amount of heat energy is released in the above process, causing the internal temperature to rise sharply. The increase in temperature not only intensifies the thermal motion of the substances inside the coal gangue, but also triggers the thermal buoyancy effect, that is, under the effect of density difference, hot air rises and cold air sinks, forming an internal and external pressure gradient, which further promotes the accelerated convection entry of external cold air and enhances the heat dissipation capacity of the coal gangue mountain.

[0051] At the same time, the dynamic changes in the temperature field have a significant impact on the oxidation reaction rate. As the temperature rises, the chemical reaction rate accelerates and the oxidation reaction becomes more intense, thereby releasing more heat and forming a positive feedback loop. This cycle not only changes the temperature distribution pattern inside the gangue mountain, but also affects the entire three-field coupling system by affecting the air seepage pattern and the intensity of the oxidation reaction.

[0052] Based on this, it can be seen that the oxidation reaction, air seepage and temperature field in the gangue mountain form a complex and dynamic interaction network. In the above network, the changes in each field will be transmitted to other fields through a specific mechanism, triggering a series of chain reactions, which jointly affect the thermodynamic behavior and spontaneous combustion characteristics of the gangue mountain. Therefore, when studying the spontaneous combustion prevention and control strategy of the gangue mountain, it is necessary to fully consider the multi-field coupling relationship to match accurate and effective prevention and control measures.

[0053] Then, based on the initial temperature field information, the geometric structure model of the gangue mountain and the coupling relationship, the air seepage velocity field balance equation, the oxygen component migration field balance equation and the temperature field transmission balance equation were established; and the multi-field coupling model of gangue spontaneous combustion was obtained by combining the above-mentioned air seepage velocity field balance equation, oxygen component migration field balance equation and temperature field transmission balance equation. The specific contents are as follows:

[0054] In the process of studying the spontaneous combustion of coal gangue, the initial temperature field data, the geometric model of the coal gangue mountain, the multi-field coupling mechanism and other information were analyzed in the embodiment, and COMSOL finite element analysis software was used as a research tool, among which COMSOL has excellent numerical simulation and computing capabilities.

[0055] In this embodiment, COMSOL software was used to simulate the dynamic temperature change process of the gangue mountain without heat pipe intervention and under the cooling effect of group pipes. In the absence of heat pipes, the natural temperature increase trend during the spontaneous combustion process was observed, as well as the accelerated oxidation reaction and enhanced air convection caused by it. Under the cooling effect of group pipes, the control effect of different group pipe arrangements on the temperature distribution inside the gangue mountain was evaluated, as well as the influence of the above effects on the process, speed and range of spontaneous combustion.

[0056] In this embodiment, in order to construct a multi-field coupling model that can comprehensively reflect the complex interaction between oxidation reaction, air seepage and temperature field in the process of spontaneous combustion of coal gangue, the air seepage velocity field balance equation, the oxygen component migration field balance equation and the temperature field transmission balance equation are further established. Through the above equations, we can have a deeper understanding of the internal mechanism of the spontaneous combustion phenomenon and predict its development trend.

[0057] In an optional embodiment, the establishment conditions of the multi-field coupling model of gangue spontaneous combustion are set in advance, and the specific contents are as follows:

[0058] In view of the complex three-dimensional non-steady-state characteristics of temperature changes inside the spontaneous combustion coal gangue pile and the complex phase change process involved in heat transfer inside the heat pipe, this embodiment adopts a series of reasonable assumptions in the model establishment stage to simplify the model to ensure the effectiveness and feasibility of the calculation.

[0059] In this embodiment, the direct impact of solar radiation on the surface of the gangue mountain is ignored: it is assumed that the surface gangue is not significantly affected by the change of solar radiation energy to simplify the thermal boundary conditions.

[0060] Internal homogeneity and isotropy assumption of coal gangue: Coal gangue is regarded as a homogeneous and isotropic porous medium, which facilitates the application of unified physical parameters for numerical simulation and ignores the influence of its internal heterogeneous characteristics on the heat transfer process.

[0061] Idealized treatment of gas flow: Assuming that the gas flow inside the gangue pile is incompressible and follows the ideal gas law, the fluid dynamics equations are simplified to facilitate the calculation of changes in fluid temperature and pressure.

[0062] Uniformity of external gas flow: It is assumed that the gas flow in the external environment of the gangue mountain is uniform and consistent, which reduces the complexity of boundary conditions and improves the solvability of the model.

[0063] Solid-gas temperature consistency: It is assumed that the solid matrix inside the gangue and the gas in the voids reach thermal equilibrium, that is, the temperatures of the two are the same, in order to simplify the energy transfer equation.

[0064] Ignore the effect of moisture on the spontaneous combustion process: temporarily ignore the potential impact of the evaporation and condensation of moisture inside the gangue on the spontaneous combustion reaction kinetics and heat transfer, in order to focus on the main thermophysical processes.

[0065] Physical properties of coal gangue are constant: During the simulation, it is assumed that the thermal physical and transport parameters of coal gangue, such as thermal conductivity and specific heat capacity, do not change with temperature in order to facilitate numerical solution.

[0066] Simplification of heat pipe equivalent cold source: The heat pipe is regarded as an equivalent cold source with constant cooling capacity, and heat is exchanged with coal gangue through heat conduction. The details of its internal phase change are ignored to simplify the complexity of the model.

[0067] Heat pipe heat balance assumption: It is assumed that the heat absorbed by the evaporation section of the heat pipe is exactly equal to the heat released by the condensation section, maintaining the dynamic balance of heat inside the heat pipe and ensuring the accurate reflection of the cooling effect of the heat pipe in the simulation.

[0068] The above assumptions not only ensure the rationality of the numerical simulation, but also simplify the calculation process of the model, allowing more focus on studying the essential laws of temperature changes inside the spontaneous combustion coal gangue pile and the effectiveness evaluation of the heat pipe cooling technology.

[0069] In another optional embodiment, the air seepage velocity field balance equation is established in combination with the above preset conditions.

[0070] When analyzing air seepage inside coal gangue heaps, although the standard Darcy's law is widely applicable to low-speed fluid flow in porous media, its applicability is limited when facing special media such as coal gangue with large particle size and potential high airflow shear force. In order to more accurately capture the fluid dynamics characteristics in complex environments, the Brinkman equation is used as an analysis tool in the embodiment. As an extension of Darcy's law, the above Brinkman equation not only considers the pressure gradient driven flow in porous media, but also incorporates the effect of viscous shear force on fluid momentum, thereby effectively describing the kinetic energy dissipation phenomenon caused by viscous shear.

[0071] In addition, considering that the temperature increase inside the spontaneous combustion coal gangue mountain will significantly change the air density and thus produce a thermal buoyancy effect, the above physical phenomenon should not be ignored in the process of establishing the equation. In order to reasonably introduce the influence of thermal buoyancy on the seepage field, the Boussinesq hypothesis is introduced in the embodiment. This hypothesis can only consider the influence of density changes caused by temperature changes on fluid movement while keeping other physical parameters of the fluid such as viscosity and thermal conductivity unchanged. Based on this, the problem is simplified and the key characteristics of the thermal buoyancy effect are retained, making the simulation results closer to the actual situation.

[0072] By combining the Brinkman equation and the Boussinesq hypothesis, the momentum balance process of the air seepage velocity field inside the gangue pile can be described more comprehensively and accurately, providing a solid theoretical basis for subsequent numerical simulation and spontaneous combustion risk assessment.

[0073] The above Boussinesq assumption satisfies the following relationship:

[0074]

[0075] Among them, F 热浮力 represents the thermal buoyancy generated by the temperature rise inside the gangue pile, ρ g represents air density, g represents gravitational acceleration, T α represents the atmospheric temperature and T represents the solid temperature.

[0076] Furthermore, based on the Boussinesq hypothesis, the equilibrium equation of the air seepage velocity field is established, and the following relationship is satisfied:

[0077]

[0078] in, represents the simulation result of air seepage velocity field, μ represents the air dynamic viscosity coefficient, k represents the solid permeability, v represents the seepage velocity, P represents the pressure, represents the pressure gradient, ρ g represents air density, g represents gravitational acceleration, T α represents the atmospheric temperature and T represents the solid temperature.

[0079] The above equation is a momentum balance equation for the air seepage velocity field inside a spontaneous combustion coal gangue mountain established by combining the Boussinesq hypothesis and the Brinkman equation, that is, it refers to the air seepage velocity field balance equation of the embodiment. The above equation comprehensively considers factors such as the permeability of the porous medium, the viscosity of the fluid, the pressure gradient, and the thermal buoyancy effect under the action of gravity.

[0080] The simulation result of the air seepage velocity field is the second-order spatial derivative of the seepage velocity of the seepage velocity field, that is, the Laplace operator acts on the velocity field, which can directly represent the rate of change or curvature of the velocity field in space, and thus reflects the momentum balance result.

[0081] Among them, the air dynamic viscosity coefficient, solid permeability, and seepage velocity can describe the velocity gradient caused by the resistance of the porous medium, that is, the resistance encountered by the fluid when flowing in the porous medium is proportional to the velocity.

[0082] In the Boussinesq hypothesis, except for the density which changes with temperature, other physical parameters such as viscosity and thermal conductivity are considered constants. When the solid temperature is higher than the atmospheric temperature, the air density decreases, generating an upward buoyancy; otherwise, a downward force is generated, which reflects the influence of density differences caused by temperature changes on fluid flow.

[0083] In another optional embodiment, an oxygen component migration field balance equation is established in combination with the above-mentioned preset conditions.

[0084] As a complex porous media system, the migration of oxygen inside coal gangue heap is a dynamic equilibrium process involving convection, diffusion, migration driven by temperature gradient, and consumption or generation by chemical reactions.

[0085] In the pore network of coal gangue heaps, oxygen is transported mainly through two modes: infiltration, i.e. convection, and molecular diffusion. The infiltration is driven by the pressure gradient in the pores, while the molecular diffusion is caused by the concentration gradient. The above two mechanisms jointly determine the distribution and flow rate of oxygen in the pore space.

[0086] In any given micro-volume unit, according to the law of conservation of mass, the rate of change of oxygen mass is equal to the mass flow rate of oxygen entering through the boundary of the micro-element minus the mass flow rate leaving, plus or minus the change in oxygen mass due to chemical reactions such as spontaneous combustion, oxidation reactions, etc.

[0087] Due to the complex and changeable pore structure of coal gangue heaps, factors such as pore size, shape, and connectivity will affect the migration of oxygen. Larger pores are conducive to convection, while small pores rely more on diffusion. In addition, the roughness of the pore wall and adsorption characteristics will also affect the flow resistance and effective diffusion coefficient of oxygen.

[0088] Chemical reactions inside the gangue heap, such as spontaneous combustion and oxidation reactions of coal, will consume or generate oxygen. The rate of the relevant chemical reactions is closely related to the oxygen concentration, temperature, pressure, and the properties of the reactants. Therefore, when describing the equilibrium equation of the oxygen migration field, the effect of the chemical reaction rate on the change of oxygen concentration must be considered.

[0089] In the embodiment, according to the law of conservation of mass in porous media heat and mass transfer, the initial equilibrium equation of the oxygen component migration field satisfies the following relationship:

[0090]

[0091] in, represents the simulation result of oxygen component migration field, D represents the air diffusion coefficient, c represents the oxygen concentration, e represents the solid porosity, represents the partial derivative of oxygen concentration, represents the partial derivative of time, t represents time, v represents the seepage velocity, represents the oxygen concentration gradient, and r represents the reaction rate.

[0092] In the embodiment, the Arrhenius law can be used to represent the reaction rate of oxidation inside the gangue pile, and satisfies the following relationship:

[0093]

[0094] Among them, r represents the reaction rate, c represents the oxygen concentration, A represents the pre-exponential factor, E represents the activation energy, R represents the gas universal constant, and T represents the solid temperature.

[0095] By bringing the reaction rate of the internal oxidation of the gangue mountain into the initial equilibrium equation of the oxygen component migration field, the equilibrium equation of the oxygen component migration field of the embodiment can be obtained, and the following relationship is satisfied:

[0096]

[0097] in, represents the simulation result of oxygen component migration field, D represents the air diffusion coefficient, represents the square of oxygen concentration gradient, r represents the reaction rate, e represents the solid porosity, represents the partial derivative of oxygen concentration, represents the partial derivative with time, v represents the seepage velocity, represents the oxygen concentration gradient, c represents the oxygen concentration, A represents the pre-exponential factor, E represents the activation energy, R represents the gas universal constant, and T represents the solid temperature.

[0098] In another optional embodiment, a temperature field transmission balance equation is established in combination with the above preset conditions.

[0099] In the heat transfer analysis of porous media, due to the complex geological conditions of coal gangue heaps, the embodiment assumes that the solid coal gangue body and the gas phase seepage air have reached a thermal equilibrium state at a microscopic or local scale. This means that in any given micro-area, the temperature difference between the coal gangue particles and the surrounding flowing air can be ignored, and they are regarded as having the same temperature. The above assumption simplifies the complexity of the heat transfer process, and then the solid phase and the gas phase can be treated as a unified porous medium system with a single temperature.

[0100] Based on the above assumptions of local thermal equilibrium, the heat transfer process in porous media can be described by a comprehensive heat balance equation. This equation not only takes into account the heat conduction caused by the temperature gradient inside the solid phase, but also covers the contribution of gas phase flow, i.e., heat convection, to heat transfer. The equation takes into account the thermal conductivity of the solid phase material, the flow characteristics of the gas phase such as flow velocity and temperature distribution, and the pore structure parameters of the porous media such as porosity and permeability, so as to more comprehensively reflect the heat transfer mechanism in the porous media of coal gangue heaps.

[0101] Ignoring surface thermal radiation, the heat transfer of porous media in coal gangue piles can be described by a heat balance equation based on the local thermal equilibrium assumption. The balance equation comprehensively considers the heat conduction and heat convection between the solid phase and the gas phase, providing strong technical support for understanding and predicting the temperature distribution and heat transfer process inside coal gangue piles.

[0102] The above temperature field transmission balance equation satisfies the following relationship:

[0103]

[0104] Where, e represents the solid porosity, r represents the reaction rate, ΔH represents the combustion enthalpy change of coal gangue, and ρ g Represents the air density, C g is the specific heat capacity of air, ρ s Represents the density of the solid, C s is the specific heat capacity of the solid, represents the partial derivative of the solid temperature, represents the partial derivative with time, v represents the seepage velocity, represents the gradient, ρ g Represents the air density, C g represents the specific heat capacity of air, T represents the solid temperature, λ s represents the thermal conductivity of the solid, λ g represents the thermal conductivity of air, It represents the square of solid temperature gradient, and Q represents the total cooling capacity of the tube group.

[0105] In the complex environment of the spontaneous combustion coal gangue mountain, the carbonaceous substances in the coal gangue react with oxygen to undergo oxidation. The above chemical process is not only the source of heat release, but also a key factor in driving the dynamic changes of multiple physical fields in the system. In an optional embodiment, the heat released for each mole of oxygen consumed refers to the enthalpy change ΔH, which constitutes the main part of the heat source term inside the system. This heat source term directly depends on the distribution of oxygen concentration, because oxygen is a necessary condition for the oxidation reaction, and the change in its concentration directly affects the rate of heat generation.

[0106] At the same time, the migration process of oxygen in the porous media of coal gangue heaps is also significantly affected by the temperature field. As the oxidation reaction proceeds, the release of heat causes the local temperature to rise, which in turn changes the physical properties of the gas such as density, viscosity, and flow characteristics, thereby affecting the diffusion and convection speed of oxygen. Therefore, the oxygen consumption term in the oxygen migration field is expressed as a function of temperature, reflecting the feedback effect of temperature on the oxygen migration process.

[0107] In order to more comprehensively describe the multi-field coupling model of gangue spontaneous combustion, it is necessary to organically combine the above heat source terms, oxygen migration equations and temperature field equations, construct the interdependence between air velocity, oxygen concentration and temperature, and realize the dynamic coupling relationship between the three physical fields. That is, changes in air velocity will affect the diffusion and convection of oxygen, and then affect the size and distribution of heat source terms; and changes in heat source terms will lead to the redistribution of temperature fields, which will have new effects on oxygen migration. This interactive cycle constitutes the core of the multi-field coupling model of gangue spontaneous combustion, and provides strong technical support for understanding and predicting the physical and chemical processes inside the spontaneous combustion gangue mountain.

[0108] In the complex thermal environment of the spontaneous combustion waste rock pile, the heat pipe, as an efficient heat conduction element, can effectively transfer the heat from the internal high-temperature area to the external low-temperature environment. The heat transfer process can be decomposed into two key stages, as follows:

[0109] The first stage is heat conduction and phase change in the evaporation section. The evaporation section of the heat pipe goes deep into the gangue mountain and directly contacts the high-temperature gangue mountain. In this stage, the heat accumulated in the gangue mountain is efficiently transferred to the working fluid in the evaporation section of the heat pipe by heat conduction. With the continuous input of heat, the working fluid is heated to the boiling point and undergoes a phase change from liquid to gas. The above process is accompanied by the release of a large amount of latent heat. This phase change process greatly enhances the heat transfer efficiency and enables the high-temperature heat in the gangue mountain to be quickly extracted.

[0110] The second stage is the convection heat dissipation of the condensation section. The condensation section of the heat pipe is located outside the spontaneous combustion waste rock mountain and is in direct contact with the relatively low temperature external environment. In the condensation section, the gaseous working fluid gradually loses energy due to the decrease in temperature and re-condenses into liquid. The heat released in the above process is mainly dissipated to the external environment through convection heat exchange with the surrounding air. Since convection heat exchange has a high heat transfer coefficient, the condensation section of the heat pipe can quickly release the internal heat to the outside world, thereby maintaining the temperature gradient inside the heat pipe and ensuring the continuous heat transfer process.

[0111] Based on the above content, it can be seen that the heat transfer process of the heat pipe inside the spontaneous combustion waste rock pile is a complex process that integrates heat conduction, phase change heat transfer and convection heat transfer. Through the synergistic effect of two key stages, the heat pipe realizes the rapid and efficient transfer of high-temperature heat in the spontaneous combustion waste rock pile to the external environment, which is of great significance for controlling the temperature of the spontaneous combustion waste rock pile and slowing down the spontaneous combustion process.

[0112] The heat transfer performance of a heat pipe is measured by its heat transfer amount, which is directly affected by the temperature difference and thermal resistance between the evaporation section and the condensation section. Specifically, the heat transfer amount is proportional to the temperature difference and inversely proportional to the thermal resistance. It can be further understood that when the temperature difference increases, the heat pipe can transfer more heat; and when the thermal resistance decreases, that is, when the heat conduction inside the heat pipe and the heat dissipation outside are smoother, more heat can be transferred under the same temperature difference.

[0113] Therefore, the heat transfer of the heat pipe satisfies the following relationship:

[0114]

[0115] Among them, Q represents the heat transfer of the heat pipe, ΔT represents the temperature difference between the heat dissipation sections, and R represents the thermal resistance. The above relationship expression reveals the interaction between the two key parameters in the heat pipe design. In order to obtain higher heat transfer, the temperature difference between the evaporation section and the condensation section can be increased, and the total thermal resistance of the heat pipe system can be reduced at the same time to optimize the thermal resistance and make full use of the temperature difference, thereby achieving efficient and reliable heat transfer.

[0116] In the heat transfer process of the heat pipe, if the heat transfer resistance between the evaporation section and the coal gangue and the heat transfer resistance of the condensation section and the external environment are taken into account, the total thermal resistance needs to satisfy the following relationship:

[0117] R=R a +R b

[0118] Where R represents the total thermal resistance, R a Represents the heat transfer resistance between the evaporation section and the coal gangue, R b It represents the thermal resistance of the convective heat exchange between the condensing section and the external environment. Based on this, it can be seen that the total thermal resistance is composed of the heat transfer resistance of the evaporation section and the convective heat transfer resistance of the condensing section, which emphasizes that when heat is transferred in the heat pipe, it is not just a single thermal resistance that needs to be overcome, but the cumulative effect of multiple thermal resistances.

[0119] In the heat transfer process of the heat pipe, if the average temperature of the evaporation section and the average temperature of the external environment in contact with the condensation section, as well as the sum of the total thermal resistance of the heat pipe and the thermal resistance of the condensation section are known, then the incremental cooling capacity of the heat pipe from the initial moment to a specific moment, that is, the heat transferred from the high temperature end to the low temperature end of the heat pipe during this period of time, satisfies the following relationship:

[0120]

[0121] Where dQ(t) represents the cooling capacity increment of the heat pipe from the initial time to the specific time t, T m Indicates the average temperature of the evaporation section of the heat pipe, T air Indicates the average temperature of the external environment that the condensation section contacts, R a Represents the heat transfer resistance between the evaporation section and the coal gangue, R b It represents the thermal resistance of convective heat transfer between the condensation section and the external environment.

[0122] By integrating the above cooling capacity increment calculation formula, the instantaneous cooling capacity of the heat pipe at a specific time t can be obtained, and the following relationship is satisfied:

[0123]

[0124] Furthermore, if the total working time of the heat pipe is τ, the total cooling capacity of the heat pipe is:

[0125]

[0126] In this embodiment, the heat pipe in the evaporation section is generalized as a linear cold source, which has a high heat conduction capacity and can continuously and evenly absorb and remove heat from the interior of the spontaneous combustion waste rock pile. In order to simplify the analysis, it is assumed that the thermal conductivity of this linear cold source is consistent with the actual thermal conductivity of the heat pipe evaporation section. This means that no matter what phase change and transmission process the heat undergoes inside the heat pipe, the amount of heat that is ultimately removed from the interior of the spontaneous combustion waste rock pile is equivalent to the effect that can be achieved by a solid linear cold source with the same thermal conductivity.

[0127] The linear cold source model emphasizes its sustainability and efficiency. It can not only quickly absorb heat from the high-temperature area of ​​the spontaneous combustion waste rock pile, but also continuously transfer this heat to the external environment at a stable rate, thereby effectively reducing the temperature inside the spontaneous combustion waste rock pile and preventing or slowing down the occurrence of the spontaneous combustion process.

[0128] Although the heat pipe itself is a heat transfer element containing a working medium and a complex structure, in the simplified model of the embodiment, its evaporation section is regarded as being composed of solid materials, which facilitates the use of solid heat conduction theory to analyze its heat transfer performance. It also simplifies the calculation and analysis process, thereby providing an intuitive and effective method to analyze and evaluate the application effect of heat pipes in the treatment of spontaneous combustion waste rock piles.

[0129] Finally, the multi-field coupling model of gangue spontaneous combustion is obtained based on the balance equation of air seepage velocity field, oxygen component migration field and temperature field transmission. When constructing the multi-field coupling model, it is considered that the change of air velocity will affect the migration of oxygen components and the distribution of temperature; the change of oxygen concentration will affect the rate of spontaneous combustion reaction and the generation of heat; and the change of temperature will affect the physical properties of air and the rate of chemical reaction. In the embodiment, the balance equations of the above three physical fields are solved jointly, and the interaction and mutual influence between air velocity, oxygen concentration and temperature are comprehensively considered, so as to achieve close coupling between multiple physical fields, so that the multi-field coupling model of gangue spontaneous combustion can more accurately describe the complex phenomena in the process of gangue spontaneous combustion.

[0130] Furthermore, the method of constructing a multi-field coupling model of spontaneous combustion of coal gangue in this embodiment is only an optional condition of the present invention. In one or some other embodiments, the method of establishing the multi-field coupling model can be changed according to the coupling relationship between the numerical simulation target and the multi-physical field. Different coal gangue accumulations have different physical, chemical and geometric properties. The above characteristics will directly affect the multi-physical field coupling behavior during the spontaneous combustion process. Adjusting the modeling method according to the specific situation can ensure that the model more accurately reflects the actual spontaneous combustion process, thereby improving the accuracy of prediction and simulation.

[0131] S3. Based on the initial temperature field information of the gangue mountain study area and the multi-field coupling model of gangue spontaneous combustion, the key physical parameters of temperature change are selected. The specific implementation steps and related contents are as follows:

[0132] When constructing a multi-field coupling model of gangue spontaneous combustion, it is crucial to set the model parameters reasonably and accurately to ensure that the simulation results reflect the actual temperature changes and the behavior of other physical fields as realistically as possible. In this embodiment, the key physical parameters of temperature change are selected based on the initial temperature field information of the gangue mountain study area.

[0133] The field test data in the gangue mountain study area directly measures and records key parameters, such as air density, thermal properties of coal gangue such as thermal conductivity, specific heat capacity, and characteristics such as porosity and particle size distribution. The relevant field data provide the most direct and realistic reference for setting model parameters.

[0134] In an optional embodiment, due to field test condition limitations or cost considerations, it may not be possible to directly obtain all required parameter information. In this case, it is necessary to refer to the empirical coefficients or formulas widely used in the industry. The correlation coefficients and formulas are based on long-term practice and a large amount of data accumulation, and have certain representativeness and applicability.

[0135] At the same time, in order to make up for the shortcomings of field tests and empirical coefficients, the embodiments also extensively consulted academic literature in related fields at home and abroad, especially research results that have been successfully applied to similar scenarios or problems.

[0136] Based on this, this embodiment scientifically and rationally selects the key physical parameters of temperature change based on the field test data, initial temperature field information, and empirical coefficients of the gangue mountain study area, which not only ensures the accuracy and reliability of the model parameters, but also improves the authenticity and credibility of the simulation results, providing strong support for the subsequent spontaneous combustion coal gangue mountain management and monitoring work.

[0137] In the embodiments, please refer to Table 1 for key physical parameter information of temperature change.

[0138] Table 1 Key physical parameters and numerical settings

[0139]

[0140]

[0141] In order to further ensure that the simulation results can truly and effectively reflect the actual temperature changes and other physical field behaviors of the spontaneous combustion of coal gangue, the solution conditions of the multi-field coupling model of spontaneous combustion of coal gangue are set in advance in this embodiment. The pre-set solution conditions are the boundary and basis of the model solution, which helps to ensure the accuracy and authenticity of the simulation results. The specific contents are as follows:

[0142] 1. The initial conditions mainly include temperature initial conditions, wind speed initial conditions and oxygen concentration initial conditions.

[0143] Initial temperature conditions: In the embodiment, representative and timely data points are selected, that is, the temperature data of the surface and internal layers of the gangue mountain actually monitored on May 12, 2020 are used as the initial temperature value of the model. The above settings ensure that the simulation process is close to the actual environmental conditions at that time from the beginning, laying a solid foundation for the subsequent temperature change prediction.

[0144] Initial wind speed conditions: In order to reflect the typical climatic conditions in the gangue mountain area, the initial wind speed is set to 2 m / s in the embodiment. The above value is set based on the analysis of historical meteorological data and the wind conditions in the area where the gangue mountain is located, which is conducive to simulating the initial seepage state of the area under the action of the natural wind field.

[0145] Initial conditions of oxygen concentration: Taking into account the sensitivity of the spontaneous combustion process of coal gangue to oxygen concentration, the initial oxygen concentration is set to 9.375 mol / m3 in the embodiment. This value not only conforms to the conventional concentration range of oxygen in the atmosphere, but also fully considers the influence of the internal pore structure of the coal gangue mountain on oxygen diffusion, and provides a reasonable starting point for simulating the dynamic changes of oxygen distribution and consumption during spontaneous combustion.

[0146] 2. Boundary conditions mainly involve comprehensive consideration of environmental complexity and model simplification.

[0147] In practical applications, gangue heaps and their surrounding environment are complex and changeable. When constructing a multi-field coupling model of spontaneous combustion of gangue to simulate its spontaneous combustion process, in order to maintain the feasibility and computational efficiency of the model, it is necessary to simplify and make assumptions to a certain extent.

[0148] In this embodiment, the gangue mountain is not only exposed to the changing atmospheric environment, but also closely connected with the surrounding geological bodies, forming a multi-interface interactive system. Among them, the upper surface and the windward side of the slope of the gangue mountain are often covered with a layer of loess, which is like a natural barrier, protecting the gangue below from direct wind and rain erosion, and serving as a medium for the exchange between the atmosphere and the internal environment of the gangue. However, in the model, it is approximately assumed that the changes in the external environment on the above interface are consistent in all directions to simplify the simulation and calculation process.

[0149] In addition, the three sides of the gangue mountain are connected to the gangue mountain with a lower degree of spontaneous combustion, and the mountain is in different stages of spontaneous combustion, which has a complex impact on the heat conduction, oxygen supply and other processes of the central gangue mountain. However, in the model process, the above sides are regarded as boundaries with similar physical and chemical properties to reduce the complexity and calculation of the model.

[0150] As for the bottom of the gangue heap, it is usually in close contact with the soil, and the heat exchange and water migration on this interface also have an important influence on the spontaneous combustion process of the gangue heap. In the model, attention will be paid to the physical properties of this interface, such as thermal conductivity and permeability, to more accurately simulate the impact of the bottom boundary conditions on the internal physical field of the gangue heap.

[0151] For details, please see Figure 4 ,based on Figure 4 It can intuitively display the main interaction interfaces between the gangue dump and the surrounding environment, as well as the simplifications and assumptions made in the modeling process, and further understand the complexity of the gangue dump environment and the necessity and rationality of model simplification.

[0152] In an optional embodiment, the specific content of the temperature field boundary condition is as follows:

[0153] In the temperature field simulation of the gangue mountain, its upper surface and the windward side of the slope constitute the key interface in direct contact with the surrounding air. The heat exchange on the above interface is mainly achieved through the convection heat transfer mechanism, that is, the heat transfer caused by the temperature difference between the gangue surface and the air flowing over it. This type of boundary condition is usually classified as the third type of boundary condition in thermodynamics, which involves three key parameters: solid surface temperature, fluid temperature, and the convection heat transfer coefficient between the two.

[0154] The upper surface and windward side of the gangue mountain slope will experience air flow with different temperatures, humidity and wind speeds under the influence of the natural environment. Changes in external conditions will directly affect the intensity of convective heat transfer between the gangue surface and the air. In order to accurately simulate the above process, the third type of boundary conditions are set, and the following relationship is satisfied:

[0155]

[0156] Among them, n represents the direction of the boundary normal, λ represents the thermal conductivity of the coal gangue pile surface, represents the solid temperature gradient, h represents the surface convection heat transfer coefficient, T 0 represents the initial temperature and T represents the solid temperature.

[0157] The remaining boundaries are considered as adiabatic boundaries and satisfy the following relationship:

[0158]

[0159] Among them, λ represents the thermal conductivity of the coal gangue pile surface, represents the solid temperature gradient.

[0160] In another optional embodiment, the specific content of the air seepage velocity field boundary condition setting is as follows:

[0161] In the process of constructing the air seepage velocity field equilibrium equation, the boundary conditions were carefully set according to the specific environmental conditions of the study area.

[0162] The seepage velocity on the windward side of the slope is set. In view of the fact that the windward side of the slope is directly affected by the external environmental wind speed, its seepage velocity is set to match the annual average wind speed in the area, that is, 2 m / s, to further reflect the direct driving effect of the external environmental wind speed on the air flow inside the coal gangue mountain.

[0163] The upper surface outlet boundary conditions are set. The upper surface of the gangue mountain is regarded as the outlet of gas flow, which means that the gas generated by spontaneous combustion of gangue can be freely released to the external environment. In the process of model establishment, the above boundary conditions are classified as the second type of boundary conditions, that is, the boundary conditions with known flow direction. Here, it is assumed that the gas flow on the upper surface is not hindered by anything and is completely driven by internal pressure.

[0164] Zero flux boundaries are set for the sides and bottom. For the sides and bottom boundaries of the gangue mountain, it is assumed that the air seepage velocity is zero, that is, there is no obvious gas exchange on this interface. The above setting is mainly based on the following considerations: the sides are usually in contact with the gangue mountain with a low degree of spontaneous combustion, and the gas flow between them is relatively weak; while the bottom may have low gas permeability due to soil compaction or the presence of groundwater. Therefore, in the multi-field coupling model of gangue spontaneous combustion, the above interface is simplified to a zero flux boundary, that is, the air seepage velocity is 0 m / s.

[0165] By reasonably setting the boundary conditions of the air seepage velocity field in the gangue pile, the internal air flow can be simulated more accurately, and then its influence on the spontaneous combustion process can be analyzed. In addition, factors such as the roughness, humidity, color of the gangue surface and the flow state of the air will affect the convective heat transfer coefficient. Therefore, when setting the model parameters, these practical factors should be fully considered to ensure the accuracy and reliability of the simulation results.

[0166] In another optional embodiment, the specific contents of the boundary condition setting of the oxygen concentration migration field are as follows:

[0167] In the process of simulating the migration of oxygen concentration inside the gangue mountain, it is necessary to clearly set the boundary conditions according to the characteristics of oxygen entering the gangue mountain with air infiltration. The windward side of the gangue mountain is directly exposed to the external environment and is the main channel for oxygen to enter the gangue mountain. The oxygen concentration is set to the oxygen concentration value in the external environment on this interface. The above setting is based on measured data or oxygen concentration under standard atmospheric conditions. In the embodiment, such boundary conditions are set as the first type of boundary conditions, that is, boundary conditions of known material concentration on the boundary.

[0168] The upper surface of the gangue mountain serves as the outlet for gas flow. The oxygen flow on it is driven by internal pressure and affected by the external wind field, but it is in a free flow state as a whole. The specific value of oxygen concentration is not directly set on this interface, but it is assumed that the diffusion flux caused by the oxygen concentration gradient is proportional to the surface normal velocity, that is, it follows Fick's law. In the embodiment, such boundary conditions are set as the second type of boundary conditions, that is, the boundary conditions of the material flux or flux gradient on the known boundary.

[0169] By reasonably setting the boundary conditions of the oxygen concentration migration field in the gangue pile, the migration process of oxygen inside the gangue pile can be simulated more accurately, and then its influence on the spontaneous combustion process can be analyzed.

[0170] The second type of boundary conditions mentioned above need to satisfy the following relationship:

[0171]

[0172] Where n represents the direction of the boundary normal, D i represents the diffusion coefficient of the fluid on the surface of the gangue pile, Represents the oxygen concentration gradient on the surface of the coal gangue pile.

[0173] The remaining boundaries are zero flux boundaries, and the following relationship is satisfied:

[0174]

[0175] Among them, dc represents the integral of oxygen concentration, dn represents the integral in the direction of boundary normal, and s represents the remaining boundary of the gangue mountain.

[0176] Furthermore, the method for setting key physical parameters and fixed solution conditions in the present embodiment is only an optional condition of the present invention. In one or some other embodiments, the method for setting physical parameters and fixed solution conditions can be adjusted according to the simulation requirements of the numerical simulation method and the actual environmental conditions. Different coal gangue mountains, different geographical locations and climatic conditions will affect the characteristics of physical processes such as oxygen concentration migration, air seepage velocity and temperature field. By adjusting the physical parameters and fixed solution conditions, it can be ensured that the simulation model is closer to the actual situation, thereby improving the applicability of the simulation results.

[0177] S4. Divide the numerical simulation grid and numerical simulation time according to the geometric structure model of coal gangue mountain and the multi-field coupling model of coal gangue spontaneous combustion. The specific steps and related contents are as follows:

[0178] Firstly, the geometric structure model of the gangue mountain is divided into tetrahedral meshes, and the mesh division results of the numerical simulation are obtained. The specific implementation contents are as follows:

[0179] First, the grid division strategy and implementation are carried out.

[0180] To ensure the accuracy and computational efficiency of the numerical simulation, the geometric structure model of the gangue mountain is meshed based on the finite element method in the embodiment. The meshing process is dominated by tetrahedral meshes, which aims to capture the complex spatial forms and potential physical field changes. Special attention should be paid to high-temperature and medium-temperature areas. The meshes in key areas are further refined manually to ensure higher computational accuracy in areas with intense thermal activity.

[0181] Then, mesh composition and quality assessment are performed.

[0182] The meshing results can be found in Figure 5 ,based on Figure 5It can be seen that there are a total of 117,522 tetrahedral units, which constitute the basic framework of the geometric model and effectively cover the main part of the coal gangue mountain. In addition, in order to enhance the simulation ability of boundary effects and special geometric features, 22,953 prism units, 13,962 triangle units, and 1,014 quadrilateral units are introduced. The overall grid system in the embodiment consists of 140,475 units, forming a highly integrated computing network.

[0183] At the same time, in this embodiment, the unit quality parameters are strictly controlled to ensure the stability and accuracy of the model calculation. The minimum unit quality in the embodiment reaches 0.05023, showing that a certain calculation efficiency can be maintained even in the mesh refinement area; the average unit quality is 0.6894, reflecting the high quality characteristics of the overall mesh. The mesh volume ratio is optimized to 1.386×10 -5 , which ensures the uniformity of the volume between grids and is conducive to the accurate transmission of the physical field. The total volume of the grid is 35,200m 3 , which can accurately reflect the actual volume of the coal gangue mountain.

[0184] Finally, the geometric shape function and linear unit selection are performed.

[0185] In order to simplify the calculation process and maintain high calculation accuracy, the linear unit is selected as the order of the geometric shape function in the embodiment. The linear unit has been widely used in various numerical simulations due to its simple calculation and good convergence. The application of the linear unit in this model can not only improve the calculation efficiency, but also further ensure the continuity and accuracy of the physical field simulation.

[0186] The grid division strategy and implementation details adopted in this embodiment provide a solid data foundation and calculation framework for the numerical simulation of coal gangue mountain, and lay an important foundation for subsequent physical field analysis and research.

[0187] Then, the simulation calculation time stage is set based on the multi-field coupling model of gangue spontaneous combustion, and the time stage information of numerical simulation is obtained. The specific contents are as follows:

[0188] The calculation process and stages of the model are set based on the multi-field coupling model of gangue spontaneous combustion. In this embodiment, the transient calculation mode is adopted, and the physical field changes of the gangue mountain in different time periods are simulated by the transient solver. The entire calculation process is divided into four key stages. Each stage sets the time unit, calculation time limit, and time step for specific research objectives to ensure the accuracy and timeliness of the simulation results.

[0189] Phase 1: Model identification and verification phase.

[0190] Time unit: day (d);

[0191] Calculation period: from May 2020 to May 2021, a total of 360 days;

[0192] Time step: 1 day;

[0193] Setting the time step of Phase I is conducive to the preliminary identification and verification of the model, ensuring that the model can accurately reflect the physical field change characteristics of the gangue mountain in the short term and provide a reliable basis for subsequent research.

[0194] Phase 2: Prediction of spontaneous combustion coal gangue heap without heat pipe.

[0195] Time unit: day (d);

[0196] Calculation period: extended from May 2020 to May 2025, covering 5 years;

[0197] Time step: Keep it as 1 day;

[0198] Without the intervention of heat pipes, the temperature and other physical field evolution trends of the gangue mountain in the next five years are predicted, and its spontaneous combustion risk and stability in its natural state are evaluated.

[0199] Phase 3: Optimizing the heat pipe burial depth.

[0200] Time unit: day (d);

[0201] Calculation period: Again, focus on May 2020 to May 2021, a period of 360 days;

[0202] Time step: maintain the precision of 1 day;

[0203] By adjusting the burial depth of the heat pipe, the influence of different burial depths on the temperature control effect of the coal gangue mountain is explored to optimize the heat pipe layout and achieve the best cooling effect.

[0204] Stage 4: Prediction of the temperature evolution of spontaneous combustion coal gangue heap under the action of group management.

[0205] Time unit: year(a);

[0206] Calculation timeframe: Long-term outlook, extending from May 2020 to May 2050, a total of 30 years;

[0207] Time step: adjusted to 1 year;

[0208] Under the intervention of the group pipe, that is, multiple heat pipes working in coordination, the temperature evolution trend of the coal gangue mountain in the next thirty years is predicted, the long-term cooling effect and stability are evaluated, and a scientific basis is provided for the long-term management and governance of the coal gangue mountain.

[0209] Through the gradual deepening and refinement of the above four stages, the multi-field coupling model of gangue spontaneous combustion can comprehensively and systematically simulate the physical field changes of gangue heaps under different conditions, providing strong support for research and decision-making in related fields.

[0210] In an optional embodiment, model identification is performed on the multi-field coupling model of spontaneous combustion of coal gangue, and the specific implementation content is as follows:

[0211] In order to verify the reliability of the simulation results of the multi-field coupling model of gangue spontaneous combustion, data comparison and error analysis methods were adopted in the embodiment.

[0212] Verification strategy and implementation,In order to scientifically evaluate the accuracy of the numerical simulation results, two groups of temperature monitoring points were selected in the high temperature zone, medium temperature zone and low temperature zone of the gangue mountain, totaling six monitoring points. The above monitoring points are representative and can reflect the temperature change trend of each region. Subsequently, the actual measurement data of different monitoring points were collected from May 2020 to May 2021, a period of 360 days, and compared in detail with the temperature prediction values ​​of the numerical simulation during the same period.

[0213] Then, we conducted comparative analysis and chart display, and discussed the use of data processing and visualization technology to draw a comparison chart between the measured values ​​and simulated values ​​of the temperature monitoring points. For details, please see Figure 6 , Figure 6 It intuitively shows the difference and consistency of different temperature zones in different time periods. Based on this, it not only reflects the changing trend of temperature in high temperature zone, medium temperature zone and low temperature zone, but also helps to identify the error source and distribution characteristics of the data.

[0214] After completing the comparative analysis, a systematic error calculation was performed on the measured and simulated values ​​of the monitoring points in different temperature zones, and the results are summarized in Table 2.

[0215] Table 2 Error analysis table of measured values ​​and simulated values ​​after 360 days of operation of heat pipe

[0216]

[0217] Table 2 lists in detail the measured temperature, simulated temperature and the error percentage between the two at each monitoring point in the high temperature zone, medium temperature zone and low temperature zone after 360 days. By analyzing the above error data, it can be found that the numerical simulation can capture the changing characteristics of the temperature field of the coal gangue mountain as a whole, especially in the medium temperature zone and low temperature zone, where the simulated value is consistent with the measured value. However, in the high temperature zone, due to the more complex heat exchange process and the influence of various factors, there is a certain degree of deviation in the simulation results. In view of the above deviations, the possible sources of error are further discussed, and corresponding improvement measures and future research directions are proposed. Through scientific verification strategies, chart display and error analysis, the reliability of the multi-field coupling model of coal gangue spontaneous combustion in the prediction of the temperature field of coal gangue mountain can be effectively verified, and it provides strong support for subsequent research and application.

[0218] based on Figure 6 As shown in Table 2, in the three temperature ranges (high temperature zone, medium temperature zone, and low temperature zone), the temperature measured values ​​and simulated values ​​of the temperature measuring points show a high degree of consistency, and the errors are all controlled within a small range. For key temperature measuring points such as T218, T219, T232, T234, T228, and T245, the absolute error and relative error are effectively controlled: the error in the high temperature zone is the smallest, with an absolute error of no more than ±4.3°C and a relative error of no more than 0.95%; the error in the medium temperature zone is slightly larger, but the absolute error is still within ±4.6°C, and the relative error does not exceed 2.38%; while the low temperature zone shows a relatively high accuracy, with a relative error of no more than 2.45%, although its absolute error range is slightly smaller, at ±1.9°C. From the simulation effect point of view, the low temperature zone performed best, followed by the high temperature zone, and finally the medium temperature zone. However, the relative errors of the three were strictly controlled within 2.45%, and the absolute errors were uniformly limited to ±4.6℃, which fully verified the rationality and accuracy of the multi-field coupling model of coal gangue spontaneous combustion and its key physical parameters.

[0219] The multi-field coupling model of spontaneous combustion of coal gangue can accurately simulate the dynamic changes of the temperature field of passive cooling of heat pipes inside the spontaneous combustion coal gangue mountain. The reasons for the slight difference between the measured value and the simulated value are as follows: First, the thermal physical parameters and environmental parameters of coal gangue used in numerical simulation are difficult to fully and accurately reflect the actual situation due to the limitations of measurement conditions and means; second, the temperature change inside the spontaneous combustion coal gangue mountain is indeed a highly complex three-dimensional non-steady-state process, and the phase change heat transfer mechanism inside the heat pipe is particularly complex. Reasonable assumptions were made in the modeling process to simplify the calculation, which inevitably introduced errors; third, the complexity of field conditions, such as fluctuations in uncontrollable factors such as wind speed and humidity, will also affect the measured results. The multi-field coupling model of spontaneous combustion of coal gangue established in this implementation has sufficient accuracy and reliability, and can be used for the simulation and prediction of the temperature field of passive cooling of spontaneous combustion gangue mountain, providing strong support for actual engineering.

[0220] S5. Combining the geometric structure model of coal gangue mountain, the multi-field coupling model of coal gangue spontaneous combustion, key physical parameters, numerical simulation grid and numerical simulation time, the application effect of group pipe passive cooling is simulated. The implementation steps and related contents are as follows:

[0221] Combined with the above-mentioned coal gangue mountain geometric structure model, key physical parameters, grid division results and time step information, a transient numerical simulation of passive cooling of the spontaneous combustion coal gangue mountain group pipes was carried out. The application effect of passive cooling of the group pipes was simulated, and the simulation results of air seepage velocity field, oxygen component migration field and temperature field were obtained.

[0222] In an optional embodiment, a simulation scheme is designed based on the above steps and related contents and numerical simulation results are obtained.

[0223] 1. Design a systematic simulation plan.

[0224] In order to explore the dynamic evolution characteristics of the temperature field inside the spontaneous combustion gangue mountain, this embodiment adopts a series of systematic simulation schemes. First, without the intervention of heat pipes, the natural evolution process of the internal temperature of the gangue mountain within 1 to 5 years is simulated to provide basic data for subsequent comparative analysis.

[0225] Subsequently, in order to optimize the arrangement of heat pipes in different temperature zones of the gangue mountain, the optimal arrangement spacing of heat pipes in the high temperature zone, medium temperature zone and low temperature zone was determined to be 3 meters, 4 meters and 5 meters respectively based on the results of the on-site group pipe test. In the numerical simulation process, a plum blossom arrangement was adopted, and heat pipes were configured according to the above spacing. The total buried depth of heat pipes was uniformly set to 3.5 meters, of which 1.5 meters were exposed in the air. A total of 320 heat pipes were arranged, with 220 in the high temperature zone, 86 in the medium temperature zone, and 14 in the low temperature zone.

[0226] Based on the temperature peak depth information obtained from the previous field tests in the gangue heap study area, it can be known that the high temperature zone is 5 meters deep, the medium temperature zone is 7 meters deep, the low temperature zone is 8 meters deep, and the heat pipe is buried at a depth of 3.5 meters, which can still affect the temperature of the deeper layer of 8 meters. We further simulated the impact of different heat pipe burial depths of 3.5 meters, 4 meters, 5 meters, and 6 meters, where the condensation section is 1.5 meters, on the internal temperature of the gangue heap. The time step was set to 1 day, and the changes in the internal temperature of the gangue heap at different burial depths within 360 days were analyzed in detail, in order to find the optimal burial depth of the group pipes in each temperature zone.

[0227] Finally, after determining the optimal burial depth of the heat pipe group, in order to evaluate its effect on the long-term temperature control of the gangue heap, the time step was set to 1 year, and the long-term evolution of the internal temperature of the gangue heap under the optimal arrangement of the heat pipe group was simulated in the next 0 years, i.e. the current state, 5 years, 10 years, 20 years and 30 years. The above series of simulation schemes can fully reveal the effectiveness and durability of the heat pipe cooling technology. The specific simulation schemes are shown in Table 3.

[0228] Table 3 Numerical simulation scheme information table

[0229]

[0230] 2. Numerical simulation results.

[0231] 2.1 Study the temperature changes of spontaneous combustion waste rock pile without heat pipe.

[0232] The internal temperature of the spontaneous combustion gangue heap is dynamically studied based on the condition of no heat pipe. In order to understand the natural evolution mechanism of the internal temperature of the spontaneous combustion gangue heap without heat pipe intervention, a numerical simulation is performed for the second platform area in the embodiment. The simulation covers the temperature field changes from the initial state to the next 5 years, please refer to Figure 7 and through Figure 7 It can intuitively display the relevant changes. Figure 7 The southeast corner of the second platform is set as the coordinate origin, with the positive direction of the x-axis pointing to the north, the positive direction of the y-axis pointing to the west, and the z-axis pointing vertically upward to the surface of the coal gangue mountain.

[0233] The yz section diagram can clearly observe the temperature distribution and changes of the second platform in the east-west direction; similarly, the zx section diagram reveals the temperature distribution characteristics in the north-south direction and its evolution over time. The above series of section diagrams not only show the complex structure of the temperature field inside the gangue mountain, but also reveal the laws and trends of temperature changes in different time periods, which helps to better understand the spontaneous combustion process of the gangue mountain and provide a scientific basis for the subsequent design of heat pipe cooling strategies.

[0234] based on Figure 7 The evolution law of high temperature area in spontaneous combustion coal gangue heap can be analyzed.

[0235] Without intervention, the high-temperature area of ​​the spontaneous combustion gangue mountain was initially concentrated on the slope. However, as time went on, the high-temperature area not only gradually penetrated into the coal gangue mountain, but also showed a significant expansion trend in space, and its shape gradually evolved into an ellipsoid. The core driving force of this evolution was the continuous increase in the temperature inside the high-temperature area, which accelerated the transfer speed of heat and expanded the scope of high temperature influence. Specifically, after five years of natural development, the high-temperature center point shifted about 10 meters to the southeast from the original slope position.

[0236] There are multiple reasons for the above phenomenon: First, the cracks on the slopes of the gangue mountain provide channels for air flow, allowing outside air to more easily penetrate into the interior of the gangue mountain, especially in high-temperature areas. Due to the high temperature, a significant air pressure difference is formed with the outside world. The air pressure difference further promotes the acceleration of air infiltration speed, providing sufficient oxygen support for the spontaneous combustion process of coal gangue.

[0237] Secondly, the continuous spontaneous combustion of gangue requires the consumption of a certain amount of combustible materials. On the slope, due to the long-term effect of the spontaneous combustion process, the combustible materials are gradually consumed, causing the spontaneous combustion intensity in this area to gradually weaken. On the contrary, the interior of the gangue mountain contains more abundant combustible materials. When the relevant materials are ignited under the action of oxygen, they push the high-temperature center point to gradually move inward.

[0238] It can be further known that the evolution of high-temperature areas in spontaneously combusting coal gangue piles is a complex and dynamic process, which is affected by multiple factors such as air infiltration, distribution of combustible materials and heat transfer. This implementation not only helps to understand the spontaneous combustion mechanism of coal gangue piles, but also provides an important reference for the subsequent formulation of effective governance strategies.

[0239] 2.2 The influence of heat pipe burial depth on the temperature change of spontaneous combustion waste rock pile is studied.

[0240] The effect of heat pipe burial depth on the temperature control effect inside the spontaneous combustion gangue heap is explored. In order to systematically evaluate the specific impact of the key parameter of heat pipe burial depth on the temperature control effect inside the spontaneous combustion gangue heap, and optimize the group pipe layout strategy in different temperature zones accordingly, a series of targeted numerical simulation experiments were carried out in the embodiment.

[0241] In the experiment, four different heat pipe burial depths of 3.5 meters, 4 meters, 5 meters and 6 meters were set, and the temperature changes inside the gangue heap under each burial depth were recorded in detail. In order to intuitively display the relevant change information, the temperature distribution diagrams of the inside of the gangue heap in the yz direction and zx direction at different burial depths were drawn. For details, please refer to Figure 8 , Figure 8 It not only reveals the specific form of the temperature field in three-dimensional space, but also clearly shows the obvious adjustment of the temperature distribution inside the coal gangue mountain as the buried depth of the heat pipe changes.

[0242] pass Figure 8 The influence mechanism of heat pipe burial depth on the internal temperature field of spontaneous combustion waste rock pile can be further explained.

[0243] exist Figure 8In (i), the temperature distribution diagrams of the yz and zx sections reveal the unique morphology of the high-temperature area and its expansion trend. The high-temperature area is hump-shaped, and the expansion speed in the x direction, that is, in the direction of wind, is significantly faster than that in the y direction, indicating that air flow and infiltration are more significant in the x direction, which promotes the rapid transfer of heat. At the same time, the high-temperature area tends to form an ellipsoid as a whole, further proving the close connection between air flow and temperature distribution. The high-temperature area near the slope is directly related to the accelerated air infiltration speed, which causes the high-temperature area to continuously move into the interior of the coal gangue mountain along the x direction.

[0244] exist Figure 8 From (ii) to (v), we can observe the changes in the temperature inside the gangue mountain after a certain period of operation at different heat pipe burial depths. First, the low-temperature zone shows a stable temperature state at different burial depths and is almost unaffected by the heat pipe, indicating that the heat exchange efficiency in the low-temperature zone is low or the heat source is far away from the action range of the heat pipe. For the medium-temperature zone and the high-temperature zone, as the burial depth of the heat pipe increases, the heat source area gradually decreases, and the temperature also shows a downward trend. In particular, when the burial depth reaches 6 meters, the peak of the heat source in the high-temperature zone is significantly reduced, which shows that the deep buried heat pipe has obvious effects in controlling the expansion of high temperature and reducing the intensity of the heat source. However, it is worth noting that even at a deeper burial depth, the high-temperature zone still exists and the temperature is still high, suggesting the need for continuous monitoring and further control measures.

[0245] The buried depth of heat pipes is one of the key factors affecting the temperature distribution and changes inside the spontaneous combustion waste rock pile. Through reasonable buried depth design, the expansion of the high temperature area can be effectively controlled and its temperature level can be reduced, thus providing strong support for the spontaneous combustion prevention and control of coal waste rock piles. At the same time, it is also necessary to realize that relying solely on heat pipe technology may not completely eliminate the high temperature area, so it is necessary to combine other control measures to achieve a more comprehensive prevention and control effect.

[0246] Furthermore, the multi-dimensional analysis of the influence of heat pipe burial depth on the time-varying temperature characteristics of spontaneous combustion waste rock pile is as follows:

[0247] Based on the monitoring data of the temperature measuring points T218 and T219 in the high temperature zone, T232 and T234 in the medium temperature zone, and T228 and T245 in the low temperature zone, for an in-depth discussion of the buried depths of the group pipes at 3.5 meters, 4 meters, 5 meters, and 6 meters, please refer to Fig. 9 The temperature of the above-mentioned temperature measurement points changes with time within 360 days, based on Fig. 9 The results are presented intuitively, and the drop, cooling rate and cooling ratio of each temperature measuring point are quantitatively evaluated. The specific results are summarized in Table 4.

[0248] Table 4 Temperature variation information of temperature measuring points at different buried depths of group pipes

[0249]

[0250]

[0251] Graphical analysis of temperature time-varying characteristics

[0252] based on Fig. 9 As shown in Table 4, heat pipe systems with different burial depths can effectively reduce the temperature of each temperature measuring point, but there are significant differences in the degree of influence and time effectiveness. With the increase of burial depth, the temperature drop trend of each temperature measuring point becomes more obvious, especially in the high temperature area and the medium temperature area. The cooling curves of the temperature measuring points T218 and T219 in the high temperature area are relatively steep, indicating that the above areas respond more quickly to the heat pipe system; while the temperature measuring points in the medium temperature area and the low temperature area show a relatively gentle cooling trend, indicating that their temperature control process is relatively long.

[0253] Quantitative evaluation of cooling range, cooling rate and cooling rate

[0254] Table 4 lists in detail the temperature drop at each temperature measurement point within 360 days. The results show that as the heat pipe burial depth increases, the temperature drop at the same temperature measurement point gradually increases, especially in high temperature areas, where the heat pipe system with a burial depth of 6 meters shows greater cooling potential than the shallow buried system.

[0255] The cooling rate reflects how fast the temperature drops. Analysis shows that the cooling rate of the temperature measuring points in the high temperature zone is generally higher than that in the medium and low temperature zones, and the cooling rate of each temperature measuring point increases with the increase in burial depth. This shows that the deep buried heat pipe system can transfer heat more efficiently, thereby accelerating the temperature drop process.

[0256] The cooling rate is one of the important indicators to measure the efficiency of the heat pipe system. The data in Table 4 show that at different burial depths, the cooling rate in the high temperature area is generally higher, while the cooling rate in the low temperature area is relatively lower. This reflects that the heat pipe system has a higher energy transfer efficiency in the high temperature area, and also shows that the temperature control in the medium and low temperature areas requires a longer time and a more complicated process.

[0257] Through in-depth analysis and quantitative evaluation of data from different temperature measurement points, it can be seen that the buried depth of heat pipes is one of the key factors affecting the temperature control effect of spontaneous combustion waste rock piles. Deep buried heat pipe systems can more effectively reduce the temperature in high-temperature areas, accelerate the heat transfer process, and improve the overall cooling efficiency. However, for different temperature zones and specific conditions, it is necessary to further optimize the heat pipe layout strategy and operating parameters to achieve the best governance effect.

[0258] Furthermore, combined with Fig. 9 The relevant information in Table 4 is analyzed, and the specific contents are as follows;

[0259] according to Fig. 9Combined with the relevant data in Table 4, we can conduct an in-depth analysis on the cooling effect of heat pipes buried at different temperature zones, high temperature zone, medium temperature zone and low temperature zone in the spontaneous combustion waste rock pile.

[0260] Among them, the cooling effect in the high temperature area is significant, and the burial depth is the key factor:

[0261] In the high-temperature area, heat pipes with different burial depths significantly reduced the temperature of the measuring points T218 and T219. In particular, when the heat pipe burial depth reached 6 meters, the temperature drop at the two measuring points was the largest, reaching 77.3°C and 74.1°C, respectively. Compared with the burial depth of 3.5 meters, the drop was 43.2°C and 37.1°C higher, respectively. At the same time, the heat pipe with a burial depth of 6 meters showed the highest cooling rate (0.21°C / d) and cooling rate (0.14% and 0.15%, respectively), indicating that the burial depth has a decisive role in the cooling effect in the high-temperature zone. The greater the burial depth, the more significant the cooling effect.

[0262] The cooling effect in the medium temperature zone is positively correlated with the burial depth, but there is a marginal effect:

[0263] In the medium temperature area, the increase in the buried depth of the heat pipe also brought about a significant cooling effect. The drop in the temperature measuring points T232 and T234 increased with the increase in the buried depth, especially at the burial depth of 5 meters and 6 meters, the two drops were similar, with a small difference, showing a certain marginal effect. Despite this, the heat pipe with a buried depth of 6 meters still showed advantages in cooling rate and cooling rate, indicating that the buried depth is still important for the cooling effect in the medium temperature zone, but after reaching a certain depth, the effect improvement tends to be flat.

[0264] The cooling effect in low temperature areas is limited, and the influence of burial depth is small:

[0265] In the low temperature area, due to the low initial temperature, the cooling effect of the heat pipe burial depth on the temperature measurement points T228 and T245 is relatively limited. Although each burial depth has achieved a certain degree of cooling, the difference in the reduction is not large, especially the change between 3.5 meters and 6 meters is more subtle. This shows that in the low temperature area, the influence of the heat pipe burial depth on the temperature is weak, mainly because the heat conduction efficiency is low in the low temperature environment and the initial temperature is close to the ambient temperature.

[0266] In summary, the choice of heat pipe burial depth should be different for different temperature zones of spontaneous combustion waste rock heap. In the low temperature zone, due to the limited cooling effect, it is recommended to choose a shallower burial depth (such as 3.5 meters) to save costs; in the medium temperature zone, considering the positive correlation between the cooling effect and the burial depth and the marginal effect, the recommended burial depth is 5 meters; and in the high temperature zone, in order to pursue the best cooling effect, it is recommended to use a deeper burial depth (such as 6 meters). The above analysis and conclusions provide a scientific guiding basis for the application of heat pipe cooling technology in spontaneous combustion waste rock heaps.

[0267] 2.3 Study the simulation of the dynamic evolution of the temperature field of spontaneous combustion waste rock pile.

[0268] In-depth analysis of the long-term evolution mechanism of the temperature field of the spontaneous combustion coal gangue mountain under the optimal arrangement of group pipes. In order to deeply explore the impact of group pipes on the dynamic evolution of the temperature field of the spontaneous combustion coal gangue mountain under the optimal arrangement strategy, the embodiment simulates the situation where the group pipes are arranged at a specific spacing and burial depth in the high temperature zone, medium temperature zone, and low temperature zone of different temperature zones, and observes the temperature field changes on a time scale of up to 30 years. By setting the time step to 1 year, the temperature field evolution of the two platforms at five key time points of 0 years, 5 years, 10 years, 20 years and 30 years are recorded in detail, and the corresponding schematic diagram is drawn. Please refer to Fig.10 and Fig.11 .

[0269] Dynamic evolution of the spatial distribution of temperature field.

[0270] like Fig.10 As shown in the figure, the temperature distribution diagrams in the yz and zx directions clearly reveal the evolution characteristics of the temperature field under the action of the group pipe. Five years after the initial operation of the group pipe, the high temperature area was significantly controlled and there was no phenomenon of moving inward, which shows the effectiveness of the group pipe in blocking the conduction of heat sources. As time goes by, the shallow high temperature area cools down rapidly, while the low temperature area remains relatively stable, and the deep temperature of the medium temperature area also decreases significantly. By 10 years, the high temperature area at the slope has been significantly reduced, the temperature curve of the zx profile has changed from a double peak to a single peak, the area of ​​the high temperature area has been greatly reduced, and the deep temperature has generally decreased. After 20 years, the temperature of the medium temperature zone and the low temperature zone tends to be consistent, and the high temperature area is further reduced to a few point-like areas in the deep. Finally, at the end of the 30-year simulation period, the shallow temperature of the gangue mountain generally dropped below 100°C, and only a very small range of high temperature concentration points existed in the deep, showing the significant governance effect under the long-term action of the group pipe.

[0271] Quantitative analysis of maximum temperature variation over time.

[0272] Fig.11 It intuitively shows the downward trend of the maximum temperature inside the coal gangue mountain over time. Fig.11 It can be seen that the maximum temperature decreases year by year, and has dropped below 280°C after 30 years. The above changes indicate that under the continuous action of the group pipes, the spontaneous combustion of the coal gangue mountain in the study area has been effectively controlled, the high-temperature area has almost disappeared, and only a small amount of medium-temperature area remains in the deep part, which fully proves the effectiveness of the group pipe layout strategy, which not only successfully prevents the spread of internal heat sources, but also significantly reduces the overall temperature level of the coal gangue mountain.

[0273] Based on this, it can be seen that a reasonable group pipe layout strategy can effectively control the evolution of the temperature field of the spontaneous combustion coal gangue mountain, inhibit the expansion of the high-temperature area, and gradually reduce the temperature level of the entire coal gangue mountain, thereby providing an important theoretical basis and technical support for the prevention and control of spontaneous combustion of coal gangue mountain.

[0274] In an optional embodiment, a comprehensive analysis is performed on a numerical simulation method of the response of a spontaneous combustion coal gangue pile to passive cooling of a group of pipes.

[0275] In this embodiment, based on the second platform of the spontaneous combustion coal gangue mountain of Yinying Coal Mine, a "heat-fluid-chemical" multi-field coupling model for this type of mountain was constructed, which refers to the multi-field coupling model of heat conduction, fluid flow and chemical reaction. Through this model, the influence of the group pipe layout and its burial depth on the long-term evolution of the temperature field inside the gangue mountain was deeply explored, and the cooling effect of the group pipe under the optimal layout strategy was simulated.

[0276] Comparing the model prediction results with the measured data of the group pipe test, it was found that the simulation errors of the temperature measurement points in the high temperature zone, medium temperature zone and low temperature zone of each temperature zone were kept at a low level. The maximum absolute error did not exceed 4.6℃, and the maximum relative error was only 2.45%, indicating that the model can accurately simulate the dynamic changes of the temperature field during the passive cooling process of the heat pipe inside the spontaneous combustion coal gangue mountain.

[0277] The natural evolution characteristics of the temperature field inside the spontaneous combustion gangue mountain are analyzed. The high temperature points inside the spontaneous combustion gangue mountain gradually move inward over time, the area of ​​the high temperature zone gradually expands, and the temperature spreads faster in the horizontal direction than in the vertical direction, forming an ellipsoidal high temperature area. At the same time, the higher the temperature inside the gangue mountain, the faster the heat transfer speed, which further aggravates the expansion of the high temperature zone.

[0278] Then, the cooling effect of the group pipes was analyzed. Group pipes with different burial depths showed significant differences in cooling effects. In the high temperature zone, the group pipes with a burial depth of 6 meters had the best cooling effect and the largest cooling amplitude. The cooling rate and cooling rate were significantly higher than those of the shallowly buried group pipes. In the medium temperature zone, the group pipes with burial depths of 5 meters and 6 meters showed similar excellent cooling performance, while the low temperature zone was less affected by the burial depth of the group pipes. Based on the above analysis, it was concluded that the optimal burial depth of the group pipes in the high temperature zone was 6 meters, 5 meters in the medium temperature zone, and 3.5 meters in the low temperature zone, which provided a scientific basis for the arrangement of group pipes in actual projects.

[0279] Under the optimal arrangement of the group pipes, the 30-year evolution of the temperature field inside the spontaneous combustion gangue mountain was simulated. Based on the results, it can be seen that the group pipes effectively controlled the conduction of the internal heat source, the high-temperature area did not move inward significantly, the shallow high-temperature area cooled significantly, and the low-temperature area remained relatively stable. As time went by, the area of ​​the high-temperature area gradually shrank, and the deep temperature also dropped significantly. After 30 years, there were only a very small range of high-temperature concentration points inside the gangue mountain, and the overall temperature level was significantly reduced, effectively curbing the development of spontaneous combustion.

[0280] The numerical simulation method of the response of a spontaneously combusted coal gangue mountain to the passive cooling of a group of pipes proposed in this embodiment not only verifies the accuracy and effectiveness of the thermal-fluid-chemical multi-field coupling model, but also deeply reveals the influence mechanism of the group pipe arrangement and its burial depth on the evolution process of the internal temperature field of a spontaneously combusted coal gangue mountain, providing important theoretical support and technical reference for the treatment of spontaneously combusted coal gangue mountains.

[0281] See also Fig.12 In an optional embodiment, the present invention further provides a numerical simulation system for the passive cooling response of a spontaneously combusted coal gangue mountain to a group of pipes, the numerical simulation system for the passive cooling response of a spontaneously combusted coal gangue mountain to a group of pipes comprises a processor, an input device, an output device and a memory, the processor, the input device, the output device and the memory are interconnected, wherein the memory is used to store a computer program, the computer program comprises program instructions, the processor is configured to call the program instructions, and execute the specific steps of the numerical simulation method for the passive cooling response of a spontaneously combusted coal gangue mountain to a group of pipes and the related embodiments provided by the present invention. The numerical simulation system for the passive cooling response of a spontaneously combusted coal gangue mountain to a group of pipes of the present invention has a complete structure and is objectively stable.

[0282] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and description of the present invention. .

Claims

1. A numerical simulation method for the passive cooling response of a spontaneously combusted coal gangue mountain to a group of pipes, characterized in that: The steps include: The geometric structure model of coal gangue dump is established based on the field measured information of the gangue dump study area; Constructing a multi-field coupling model of spontaneous combustion of coal gangue according to the field measured information and the geometric structure model of the coal gangue mountain; Based on the initial temperature field information of the gangue heap study area and the multi-field coupling model of spontaneous combustion of coal gangue, the key physical parameters of temperature change are selected; According to the geometric structure model of the gangue mountain and the multi-field coupling model of spontaneous combustion of gangue, the numerical simulation grid and the numerical simulation time are set; The application effect of passive cooling of the group pipes is simulated by combining the geometric structure model of the coal gangue mountain, the multi-field coupling model of coal gangue spontaneous combustion, the key physical parameters, the numerical simulation grid and the numerical simulation time.

2. The numerical simulation method of the spontaneous combustion coal gangue pile to the passive cooling response of the group pipes according to claim 1 is characterized in that: The geometric structure model of the gangue mountain is established based on the field measured information of the gangue mountain study area, including: A geometric structure model of a coal gangue mountain is established based on the field measured information of the coal gangue mountain study area, wherein the geometric structure model of the coal gangue mountain includes a three-dimensional four-sided platform coal gangue mountain geometric model; Dividing the geometric structure model of the gangue mountain according to the initial temperature field information of the gangue mountain study area, the geometric structure model of the gangue mountain includes a high temperature area, a medium temperature area and a low temperature area; The high temperature zone, the medium temperature zone and the low temperature zone adopt a plum blossom-shaped arrangement of tube groups.

3. The numerical simulation method of the spontaneous combustion coal gangue pile to the passive cooling response of the group pipes according to claim 1 is characterized in that: The step of constructing a multi-field coupling model of spontaneous combustion of coal gangue according to the field measured information and the geometric structure model of the coal gangue mountain includes: The coupling relationship between oxygen oxidation reaction, air seepage and temperature field is analyzed based on the initial temperature field information, the on-site measured information and the geometric structure model of the coal gangue mountain.

4. The numerical simulation method of the spontaneous combustion coal gangue pile to the passive cooling response of the group pipes according to claim 3 is characterized in that: The step of constructing a multi-field coupling model of spontaneous combustion of coal gangue according to the field measured information and the geometric structure model of the coal gangue mountain includes: Based on the initial temperature field information, the geometric structure model of the coal gangue mountain and the coupling relationship, an air seepage velocity field balance equation, an oxygen component migration field balance equation and a temperature field transmission balance equation are established; The multi-field coupling model of spontaneous combustion of coal gangue is obtained by combining the air seepage velocity field balance equation, the oxygen component migration field balance equation and the temperature field transmission balance equation.

5. The numerical simulation method of the spontaneous combustion coal gangue pile to the passive cooling response of the group pipes according to claim 4 is characterized in that: The air seepage velocity field balance equation satisfies the following relationship: in, represents the momentum balance result of the air seepage velocity field inside the spontaneous combustion coal gangue pile, μ represents the air dynamic viscosity coefficient, k represents the solid permeability, v represents the seepage velocity, P represents the pressure, ρ g represents air density, g represents gravitational acceleration, T α represents the atmospheric temperature and T represents the solid temperature.

6. The numerical simulation method for the response of spontaneous combustion coal gangue heap to passive cooling of pipe groups according to claim 4 is characterized in that: The oxygen component migration field balance equation satisfies the following relationship: Where D is the air diffusion coefficient, represents the square of oxygen concentration gradient, r represents the reaction rate, e represents the solid porosity, represents the partial derivative of oxygen concentration, represents the partial derivative with time, v represents the seepage velocity, represents the oxygen concentration gradient, c represents the oxygen concentration, A represents the pre-exponential factor, E represents the activation energy, R represents the gas universal constant, and T represents the solid temperature.

7. The numerical simulation method for the response of spontaneous combustion coal gangue heap to passive cooling of pipe groups according to claim 4 is characterized in that: The temperature field transmission balance equation satisfies the following relationship: Where, e represents the solid porosity, r represents the reaction rate, ΔH represents the combustion enthalpy change of coal gangue, and ρ g Represents the air density, C g is the specific heat capacity of air, ρ s Represents the density of the solid, C s is the specific heat capacity of the solid, represents the partial derivative of the solid temperature, represents the partial derivative with time, v represents the seepage velocity, represents the gradient, ρ g Represents the air density, C g represents the specific heat capacity of air, T represents the solid temperature, λ s represents the thermal conductivity of the solid, λ g represents the thermal conductivity of air, It represents the square of solid temperature gradient, and Q represents the total cooling capacity of the tube group.

8. The numerical simulation method for the response of spontaneous combustion coal gangue heap to passive cooling of pipe groups according to claim 1 is characterized in that: The dividing of numerical simulation grids and numerical simulation time according to the geometric structure model of the gangue mountain and the multi-field coupling model of spontaneous combustion of gangue includes: Performing tetrahedral mesh division according to the geometric structure model of the coal gangue mountain and obtaining mesh division results of numerical simulation; The simulation calculation time step is set based on the multi-field coupling model of coal gangue spontaneous combustion, and the time stage information of the numerical simulation is obtained.

9. The numerical simulation method for the response of spontaneous combustion coal gangue heap to passive cooling of pipe groups according to claim 8, characterized in that: The simulation of the passive cooling application effect of the group pipes by combining the geometric structure model of the coal gangue mountain, the multi-field coupling model of coal gangue spontaneous combustion, the key physical parameters, the numerical simulation grid and the numerical simulation time includes: Combined with the geometric structure model of the gangue mountain, the key physical parameters, the grid division results and the time step information, a transient numerical simulation of passive cooling of the spontaneous combustion gangue mountain pipe group is carried out, the application effect of the passive cooling of the pipe group is simulated, and the simulation results of the air seepage velocity field, the oxygen component migration field and the temperature field are obtained.

10. Numerical simulation system of the response of spontaneous combustion coal gangue heap to passive cooling of group pipes, characterized in that: The system includes a processor, an input device, an output device and a memory, wherein the processor, the input device, the output device and the memory are interconnected, wherein the memory is used to store a computer program, the computer program includes program instructions, and the processor is configured to call the program instructions to execute the numerical simulation method of the passive cooling response of a spontaneous combustion coal gangue mountain to a group of pipes as described in any one of claims 1 to 9.

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