Coal spontaneous combustion behavior evolution method and system under multi-physics field coupling

Abstract

The invention relates to the technical field of coal mine safety, and provides a coal spontaneous combustion behavior evolution method and system under multi-physics field coupling. According to the method, the volume of a temperature field during spontaneous combustion of a coal body is changed by influencing deformation, the porosity of the coal body is calculated through the volume, and then thermal deformation is driven; the thermal deformation affects moisture diffusion through porosity, residual moisture saturation of the coal body and liquid phase saturation, and then moisture migration is driven by combining the evaporation rate and the liquid phase saturation; moisture migration is combined with the evaporation rate, the effective heat conductivity coefficient and the coal oxidation reaction rate to drive heat transfer, heat transfer-thermal deformation-moisture-heat transfer circulation is formed, a heat-force-water-heat coupling closed loop during spontaneous combustion of the coal body is achieved, bidirectional coupling of a seepage field, a temperature field and a mechanical field is achieved, and the self-ignition performance of the coal body is improved. The problem of prediction misalignment caused by neglecting thermodynamic deformation and pore dynamic change of a traditional model is effectively solved.

Description

Technical Field

[0001] This application relates to the field of coal mine safety technology, and in particular to a method and system for the evolution of coal spontaneous combustion behavior under multi-physics field coupling. Background Technology

[0002] With economic and technological development, global energy demand is rapidly increasing, and coal, as one of the most important fossil fuels, has been widely used in modern industrial production. However, due to the complex physical and chemical properties of coal, spontaneous combustion remains one of the main problems hindering its effective utilization.

[0003] Coal is a complex, porous organic rock whose internal pore structure provides channels for fluid transport and directly determines the storage and transport characteristics of fluids within the coal. Temperature is one of the important factors affecting the pore structure of coal, significantly influencing moisture migration and mechanical properties. During coal combustion, approximately 20-40% of the heat generated is consumed by moisture evaporation, and the pore structure also changes, thus affecting mass transport and chemical reactions during combustion. Summary of the Invention

[0004] The purpose of this application is to provide a method and system for the evolution of coal spontaneous combustion behavior under multi-physics field coupling, so as to solve or alleviate the problems existing in the prior art.

[0005] To achieve the above objectives, this application provides the following technical solution: This application provides a method for the evolution of coal spontaneous combustion behavior under multi-physics coupling, including: Temperature field during spontaneous combustion of coal Over time The changes determine the deformation of the coal body during spontaneous combustion. Over time The changes in volume during spontaneous combustion of the coal were used to determine the volume of the coal. Over time The changes, and through the volume of coal during spontaneous combustion. Over time The changes in porosity during spontaneous combustion of coal were used to determine the porosity of the coal body. Over time Changes; Determine the porosity of coal during spontaneous combustion Remaining water saturation and liquid phase saturation Over time The changes; and based on the equilibrium steam pressure during spontaneous combustion of coal. Liquid phase saturation Over time The changes determine the evaporation rate of spontaneous combustion of the coal. Over time Changes; Based on liquid phase saturation Over time Changes and solid saturation Determine the effective thermal conductivity of coal during spontaneous combustion. Over time The changes; and further, based on the evaporation rate during spontaneous combustion of coal. Effective thermal conductivity Coal oxidation reaction rate Over time Changes in the temperature field of the coal body Make corrections.

[0006] Preferably, the deformation of the coal body during spontaneous combustion Over time The changes are as follows:

[0007] In the formula, The density of the coal body, For divergence operators, This represents the total displacement during coal deformation. For the thermal insulation stress of the coal body, Let be the elastic stiffness tensor of the coal mass. These are the times when the coal spontaneously combusts. The elastic modulus and Poisson's ratio, Time of spontaneous combustion of coal The total strain tensor, For the inelastic strain tensor of the coal body. The volume force of the coal body; The elastic stiffness tensor of coal Time of spontaneous combustion of coal elastic modulus Compared to Poisson The function; Volume of coal during spontaneous combustion Over time The changes are as follows:

[0008] In the formula, The initial volume of the coal body. Time of spontaneous combustion of coal Total strain tensor The traces.

[0009] Preferably, the porosity of the coal during spontaneous combustion Over time The changes are as follows:

[0010] In the formula, The initial porosity of the coal body. The initial volume of the coal body. Time of spontaneous combustion of coal The volume.

[0011] Preferably, the coal body is saturated with residual moisture during spontaneous combustion. Over time The changes are as follows:

[0012] In the formula, Time of spontaneous combustion of coal porosity; Liquid phase saturation during spontaneous combustion of coal Over time The changes are as follows:

[0013] In the formula, For divergence operators, Time of spontaneous combustion of coal The water diffusion coefficient, Time of spontaneous combustion of coal evaporation rate, ρ is the density of the liquid phase.

[0014] Preferably, the moisture diffusion coefficient during spontaneous combustion of coal is... Over time The changes are as follows:

[0015] In the formula, It is a proportionality constant, and its value is [value missing]. .

[0016] Preferably, the steam pressure is balanced during spontaneous combustion of the coal. Over time The changes are as follows:

[0017] In the formula, All are constants. Time of spontaneous combustion of coal The temperature field.

[0018] Preferably, the effective thermal conductivity during spontaneous combustion of coal is... Over time The changes are as follows:

[0019] In the formula, Let be the thermal conductivity of the coal in a fully saturated state. It is the thermal conductivity of the coal in a completely dry state.

[0020] Preferably, the evaporation rate of coal spontaneous combustion Over time The changes are as follows:

[0021] In the formula, Let be the evaporation rate constant of the liquid phase during spontaneous combustion of coal. The density of the liquid phase is... Time of spontaneous combustion of coal The equilibrium vapor pressure, This is the actual vapor pressure. Time of spontaneous combustion of coal The liquid phase saturation.

[0022] Preferably, according to the formula:

[0023] Temperature field of coal Make corrections; In the formula, For effective density, For effective specific heat capacity, Time of spontaneous combustion of coal The effective thermal conductivity, Time of spontaneous combustion of coal evaporation rate, Time of spontaneous combustion of coal temperature gradient, The latent heat of vaporization of the coal body, Time of spontaneous combustion of coal The heat flux of the oxidation reaction; in,

[0024] In the formula, These are the times when the coal spontaneously combusts. The liquid phase saturation and gas phase saturation, The solid phase saturation of the coal body; These are the liquid phase density, solid phase density, and gas phase density, respectively. Time of spontaneous combustion of coal The liquid relative heat capacity, These are the solid-phase heat capacity and the gas-phase heat capacity, respectively. Time of spontaneous combustion of coal Temperature field; Time of spontaneous combustion of coal The rate of coal oxidation reaction; The enthalpy of reaction per unit mass of the coal; As a pre-exponential factor for coal oxidation, The activation energy of the coal body It is a universal gas constant. This refers to the oxygen concentration inside the coal body during spontaneous combustion.

[0025] This embodiment also provides a coal spontaneous combustion behavior evolution system under multi-physics coupling, which predicts coal spontaneous combustion using any of the above-described methods for coal spontaneous combustion behavior evolution under multi-physics coupling. The system includes: Thermocoupled unit, configured to pass through the temperature field during spontaneous combustion of coal. Over time The changes determine the deformation of the coal body during spontaneous combustion. Over time The changes in volume during spontaneous combustion of the coal were used to determine the volume of the coal. Over time The changes, and through the volume of coal during spontaneous combustion. Over time The changes in porosity during spontaneous combustion of coal were used to determine the porosity of the coal body. Over time Changes; The hydraulic coupling unit is configured to determine the porosity of coal during spontaneous combustion. Remaining water saturation and liquid phase saturation Over time The changes; and based on the equilibrium steam pressure during spontaneous combustion of coal. Liquid phase saturation Over time The changes determine the evaporation rate of spontaneous combustion of the coal. Over time Changes; The hydrothermal coupling unit is configured to adjust according to the liquid phase saturation. Over time Changes and solid saturation Determine the effective thermal conductivity of coal during spontaneous combustion. Over time The changes; and further, based on the evaporation rate during spontaneous combustion of coal. Effective thermal conductivity Coal oxidation reaction rate Over time Changes in the temperature field of the coal body Make corrections.

[0026] Beneficial effects: The method and system for the evolution of coal spontaneous combustion behavior under multi-physics field coupling provided in this application embodiment utilizes the temperature field during coal spontaneous combustion. Over time The changes determine the deformation of the coal body during spontaneous combustion. Over time The changes in volume during spontaneous combustion of the coal were used to determine the volume of the coal. Over time The changes, and through the volume of coal during spontaneous combustion. Over time The changes in porosity during spontaneous combustion of coal were used to determine the porosity of the coal body. Over time The changes; then, the porosity during spontaneous combustion of the coal body was determined. Remaining water saturation and liquid phase saturation Over time The changes, and based on the equilibrium steam pressure during spontaneous combustion of the coal. Liquid phase saturation Over time The changes determine the evaporation rate of spontaneous combustion of the coal. Over time The changes; and further, based on the liquid phase saturation Over time Changes and solid saturation Determine the effective thermal conductivity of coal during spontaneous combustion Over time The changes; finally, based on the evaporation rate during spontaneous combustion of the coal. Effective thermal conductivity Coal oxidation reaction rate Over time Changes in the temperature field of the coal body Make corrections.

[0027] Therefore, the temperature field during coal spontaneous combustion affects the deformation amount, changes the volume, and calculates the porosity of the coal body through the volume, thereby driving thermal deformation. Thermal deformation determines the moisture diffusion coefficient through porosity, the remaining moisture saturation of the coal body, and the liquid phase saturation, and then drives moisture migration by combining the evaporation rate and the liquid phase saturation. Moisture migration, combined with the evaporation rate, the effective thermal conductivity, and the coal oxidation reaction rate, leads to heat transfer, forming a cycle of "heat transfer-thermal deformation-moisture-heat transfer". This achieves a coupled closed loop of "heat-mechanical-water-heat" during coal spontaneous combustion, realizing the bidirectional coupling of the seepage field, temperature field, and mechanical field, effectively solving the problem of inaccurate predictions caused by neglecting thermodynamic deformation and dynamic changes in pores in traditional models. Attached Figure Description

[0028] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. Wherein: Figure 1 This is a flowchart illustrating a method for the evolution of coal spontaneous combustion behavior under multiphysics coupling, according to some embodiments of this application. Figure 2 This is a logical schematic diagram illustrating the evolution of the mechanical behavior of coal spontaneous combustion under multi-physics coupling according to an embodiment of this application; Figure 3 This is a schematic diagram illustrating the principle of the evolution of coal spontaneous combustion mechanical behavior under multiphysics coupling according to an embodiment of this application; Figure 4 The T2 spectrum of a coal sample under saturation state provided according to an embodiment of this application; Figure 5 The T2 spectrum of a coal sample in a dry state provided according to an embodiment of this application; Figure 6 Coal samples provided according to embodiments of this application A schematic diagram of the remaining water saturation at a given time; Figure 7 A schematic diagram illustrating the setting of boundary conditions for a coal sample according to an embodiment of this application; Figure 8 This is a schematic diagram of coal sample grid division according to an embodiment of this application; Figure 9 This is a schematic diagram comparing the porosity results of coal samples provided according to embodiments of this application in numerical simulation and physical experiments, respectively. Figure 10 This is a schematic diagram illustrating the vertical displacement of a coal sample in numerical simulation and physical experiment, respectively, according to embodiments of this application. Figure 11 This is a schematic diagram showing the horizontal displacement of a coal sample in numerical simulation and physical experiment, respectively, according to embodiments of this application. Figure 12 This is a schematic diagram illustrating the spatial distribution of moisture saturation inside a coal body at different times according to embodiments of this application. Figure 13 This is a schematic diagram illustrating the spatial distribution of coal temperature over time at different heating times according to embodiments of this application. Figure 14 This is a schematic diagram of the total displacement of coal at different temperatures in numerical simulation and physical experiment, according to an embodiment of this application. Figure 15 This is a schematic diagram of a system for the evolution of coal spontaneous combustion behavior under multi-physics coupling, according to some embodiments of this application. Detailed Implementation

[0029] The present application will now be described in detail with reference to the accompanying drawings and embodiments. Various examples are provided by way of explanation and not by way of limitation. In fact, those skilled in the art will understand that modifications and variations can be made to the present application without departing from the scope or spirit of the present application. For example, a feature shown or described as part of one embodiment may be used in another embodiment to produce yet another embodiment. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention should fall within the scope of protection of the embodiments of the present invention.

[0030] Currently, most studies on the thermodynamic behavior of coal spontaneous combustion are conducted at low temperatures, while research on high-temperature conditions is still in its infancy. Although experimental methods are the most direct way to study coal spontaneous combustion, current experimental methods cannot effectively predict the thermodynamic behavior of coal in natural processes. Numerical simulation, with its advantages of visualization and data quantification, can effectively solve these problems in experiments and has become one of the most efficient methods for coal spontaneous combustion research. However, existing numerical simulations of coal thermal effects mainly focus on coal drying and heating, microwave heating, and chemical reactions, lacking research on the entire process of coal spontaneous combustion.

[0031] Traditional multi-field coupling in coal spontaneous combustion mainly involves unidirectional coupling between the temperature field and the seepage field. Darcy's law is typically used to describe the gas seepage process, coupled with the Fourier heat conduction equation to simulate temperature field changes. However, this single-phase coupling model only considers the unidirectional effect of temperature on the seepage field and fails to establish an effective reverse mechanism. Some existing models also introduce chemical field coupling, using the heat of oxidation as a fixed source term in the temperature field and calculating the reaction rate using the Arrhenius equation. Such models often simplify the coal pore structure to homogeneous channels, failing to reflect the porous media characteristics of real coal.

[0032] Studies have found that existing models completely ignore the influence of thermal deformation mechanisms, resulting in permeability calculation errors of 50-70%. Furthermore, the prevalence of static porosity assumptions prevents the capture of abrupt porosity changes caused by moisture evaporation during the low-temperature oxidation stage, leading to systematic biases in temperature field simulations. The root cause of these deficiencies lies in the inherent difficulty in characterizing coal pore structure, primarily due to the multi-scale characteristics of coal pores (from nanometer to millimeter). This makes it difficult to establish a unified descriptive framework using continuous medium theory. Coupled with experimental bottlenecks such as the mismatch between micro / nanoscale characterization and macroscopic models, and limitations in high-temperature dynamic measurement technology, the models lack a description of the bidirectional coupling of multiple fields in coal spontaneous combustion (thermal-fluid-mechanical), such as the influence of porosity changes on thermal conductivity and the influence of thermal stress on pore structure. This results in significant deviations between predicted results and actual conditions.

[0033] Based on this, this embodiment incorporates the thermal deformation mechanism and dynamic pore evolution into the multi-field coupling of coal spontaneous combustion, achieving bidirectional coupling of the seepage field, temperature field, and mechanical field, effectively solving the problem of inaccurate predictions caused by neglecting thermodynamic deformation and dynamic changes in pores in traditional models. Figures 1 to 14 As shown, this method for the evolution of coal spontaneous combustion behavior under multiphysics coupling includes: Step S101: Analyzing the temperature field during spontaneous combustion of coal. Over time The changes determine the amount of deformation during spontaneous combustion of the coal. Over time The changes in volume during spontaneous combustion of the coal were used to determine the volume of the coal. Over time The changes, and through the volume of coal during spontaneous combustion. Over time The changes in porosity during spontaneous combustion of coal were used to determine the porosity of the coal body. Over time The changes.

[0034] In this embodiment, the relevant parameters of coal thermal deformation and porosity are obtained through a coal spontaneous combustion pore damage evolution experiment under high temperature conditions. Specifically, fresh large coal samples collected from coal seams in underground coal mines are cored and crushed to obtain coal samples and coal powder particles of different particle sizes. The screened coal samples are then dried in a drying oven for 4 hours.

[0035] In the experiment, the coal sample was first placed in a crucible, completely covered with coal powder particles, and then heated at a high temperature. During the heating process, multiple temperature points were set (e.g., ...). The coal sample was heated for 50 minutes at each temperature point to allow it to reach thermal equilibrium. After heating, the coal sample was allowed to cool naturally in air. Once cooled, the coal sample was placed in a vacuum pressure saturator to... After degassing under pressure for 6 hours and soaking in a negative pressure environment for 20 hours to achieve full saturation, the coal sample was subjected to nuclear magnetic resonance testing to obtain the corresponding T2 spectrum (saturated state T2 spectrum).

[0036] Then, the coal sample was dehydrated using a drying oven and subjected to nuclear magnetic resonance (NMR) testing again to obtain the T2 spectrum of the coal sample in the dry state (dry state T2 spectrum). Finally, the porosity was obtained by inverting the T2 spectrum of the coal sample in the saturated state; the remaining moisture saturation was calculated by combining the saturated state T2 spectrum and the dry state T2 spectrum.

[0037] During the spontaneous combustion of coal, the temperature gradient induces thermal stress, affecting the elastic modulus of the coal. Compared to Poisson It changes non-linearly with temperature. Specifically, according to the formula:

[0038] Determine the elastic modulus of coal during spontaneous combustion. Compared to Poisson With temperature field The nonlinear change; where, These are the elastic moduli of coal in its glassy and rubbery states during spontaneous combustion, respectively. These are Poisson's ratios for the glassy and rubbery states of coal during spontaneous combustion, respectively. The glass transition temperature of the coal. Time during the spontaneous combustion of coal Temperature field, It is a constant, and its value is... .in, All results were obtained through experiments on the evolution of pore damage during spontaneous combustion of coal under high-temperature conditions.

[0039] During the spontaneous combustion of coal, the temperature gradient induces thermal stress, which causes deformation of the coal. Specifically, the amount of deformation during spontaneous combustion of coal... Over time The changes are as follows:

[0040] In the formula, The density of the coal body, For divergence operators, Time during coal deformation The total displacement; For the thermal insulation stress of the coal body, Let be the elastic stiffness tensor of the coal mass. These are the times when the coal spontaneously combusts. The elastic modulus and Poisson's ratio, Time of spontaneous combustion of coal The total strain tensor, For the inelastic strain tensor of the coal body. The volume force of the coal body; The elastic stiffness tensor of coal Time of spontaneous combustion of coal elastic modulus Compared to Poisson The function.

[0041] Thermal stress causes deformation of the coal body, which in turn changes its volume. Specifically, this changes the volume of the coal body during spontaneous combustion. Over time The changes are as follows:

[0042] In the formula, The initial volume of the coal body. Time of spontaneous combustion of coal Total strain tensor The traces. Therefore, by using temperature-induced mechanical response, a " "Driven by thermal deformation of coal body, this lays the foundation for multi-field bidirectional coupling driven by thermal deformation during spontaneous combustion of coal body."

[0043] During spontaneous combustion of coal, the nonlinear changes in the elastic modulus and Poisson's ratio over time can be directly determined through the temperature field. However, the elastic modulus and Poisson's ratio do not directly affect the temperature field; rather, they alter the coal volume through their nonlinear changes over time. These volume changes cause changes in the coal's porosity. Specifically, the porosity during spontaneous combustion of coal... Over time The changes are as follows:

[0044] In the formula, The initial porosity of the coal body. The initial volume of the coal body. Time of spontaneous combustion of coal The volume.

[0045] Step S102: Determine the porosity of the coal during spontaneous combustion. Remaining water saturation and liquid phase saturation Over time The changes, and based on the equilibrium steam pressure during spontaneous combustion of the coal. Liquid phase saturation Over time The changes determine the evaporation rate of spontaneous combustion of the coal. Over time The changes.

[0046] During spontaneous combustion of coal, the nonlinear changes in the elastic modulus and Poisson's ratio over time can be directly determined through the temperature field. However, the elastic modulus and Poisson's ratio do not directly affect the temperature field; rather, they alter the coal volume through their nonlinear changes over time, thereby affecting the coal porosity. The porosity of the coal determines its "basic capacity" for water storage; that is, porosity has a nonlinear relationship with the residual water saturation of the coal. In this embodiment, the residual water saturation during spontaneous combustion of the coal is... Over time The changes are as follows:

[0047] In the formula, Time of spontaneous combustion of coal porosity; Liquid phase saturation during spontaneous combustion of coal Over time The changes are as follows:

[0048] In the formula, For divergence operators, Time of spontaneous combustion of coal The water diffusion coefficient, Time of spontaneous combustion of coal evaporation rate, ρ is the density of the liquid phase.

[0049] During the spontaneous combustion of coal, thermal deformation affects the moisture diffusion coefficient of the coal through porosity, residual moisture saturation, and liquid phase saturation. Specifically, the moisture diffusion coefficient during spontaneous combustion of coal... Over time The changes are as follows:

[0050] In the formula, It is a proportionality constant, and its value is [value missing]. .

[0051] In this embodiment, the thermal stress during coal spontaneous combustion causes changes in coal volume, which in turn affects the dynamic evolution of porosity. By controlling the residual moisture saturation to influence the moisture diffusion coefficient, a positive transmission of "thermal deformation-porosity-moisture" is achieved. Simultaneously, based on the mediating effect of thermal deformation during media spontaneous combustion, the temperature field serves as the heat source, and thermal-mechanical positive coupling is completed through the amount of media deformation; thermal deformation induces changes in coal volume, and the coal properties (effective thermal conductivity) are updated through solid-state heat transfer, completing thermal-mechanical reverse coupling.

[0052] Thermal deformation affects the evaporation rate by regulating the moisture diffusion coefficient through porosity, thereby driving moisture migration. Specifically, firstly, the equilibrium steam pressure during coal self-ignition... Over time The changes are as follows:

[0053] In the formula, All are constants, where, , Time of spontaneous combustion of coal The temperature field. Then, the evaporation rate of spontaneous combustion of the coal. Over time The changes are as follows:

[0054] In the formula, Let be the evaporation rate constant of the liquid phase during spontaneous combustion of coal. The density of the liquid phase is... Time of spontaneous combustion of coal The equilibrium vapor pressure, This is the actual vapor pressure. Time of spontaneous combustion of coal The liquid phase saturation.

[0055] Step S103: Based on liquid phase saturation Over time Changes and solid saturation Determine the effective thermal conductivity of coal during spontaneous combustion. Over time The changes; and further, based on the evaporation rate during spontaneous combustion of coal. Effective thermal conductivity Coal oxidation reaction rate Over time Changes in the temperature field of the coal body Make corrections.

[0056] In this embodiment, coal deformation leads to the reconstruction of the coal's pore structure, causing the effective thermal conductivity of the coal to dynamically adjust with porosity and liquid phase saturation, forming a reverse feedback loop of "thermal deformation-heat transfer." Specifically, the effective thermal conductivity of the coal during spontaneous combustion... Over time The changes are as follows:

[0057] In the formula, Let be the thermal conductivity of the coal in a fully saturated state. is the thermal conductivity of the coal in a completely dry state. Wherein, All results were obtained through experiments on the evolution of pore damage during spontaneous combustion of coal under high-temperature conditions.

[0058] Thermal deformation affects the evaporation rate by modulating the moisture diffusion coefficient through porosity, thereby driving moisture migration. Moisture migration alters the effective thermal conductivity through liquid phase saturation and, by combining the evaporation rate and the coal oxidation reaction rate, modifies the coal body temperature field. Specifically, according to the formula:

[0059] Temperature field of coal Make corrections; in the formula, For effective density, For effective specific heat capacity, Time of spontaneous combustion of coal The effective thermal conductivity, Time of spontaneous combustion of coal evaporation rate, Time of spontaneous combustion of coal temperature gradient, The latent heat of vaporization of the coal body, Time of spontaneous combustion of coal The heat flux of the oxidation reaction.

[0060] in,

[0061] In the formula, These are the times when the coal spontaneously combusts. The liquid phase saturation and gas phase saturation, The solid phase saturation of the coal body; These are the liquid phase density, solid phase density, and gas phase density, respectively. Time of spontaneous combustion of coal The liquid relative heat capacity, These are the solid-phase heat capacity and the gas-phase heat capacity, respectively. Time of spontaneous combustion of coal The temperature field.

[0062] Time of spontaneous combustion of coal The rate of coal oxidation reaction; The enthalpy of reaction per unit mass of the coal; As a pre-exponential factor for coal oxidation, , The activation energy of the coal body , It is a universal gas constant. This refers to the oxygen concentration inside the coal body during spontaneous combustion.

[0063] Here, liquid phase saturation and gas phase saturation The solid phase saturation changes over time during the spontaneous combustion of coal. This is a fixed value. The initial porosity obtained experimentally can be used to determine the saturation of the solid phase. Then, the gas phase saturation can be obtained from the initial liquid phase saturation.

[0064] In a specific example, a matching 2D geometric model is established based on the coal sample size from a high-temperature coal spontaneous combustion pore damage evolution experiment. The initial porosity of the coal sample is used as a reference. The initial temperature of the coal sample was 11%. According to the formula:

[0065] Determine the initial moisture content of the coal sample. and the initial volume fraction of water (i.e., initial liquid phase saturation) ).

[0066] In the 2D geometric model, the upper and right boundaries of the coal body are set as boundary conditions such as heat flux, free deformation, water evaporation, and thermal evaporation. The heat variable enters the coal body from the outside, while free deformation, water evaporation, and thermal evaporation diffuse from the coal body to the outside. The lower boundary of the coal body is set as a solid boundary constraint and a thermal insulation boundary condition, and the left boundary of the coal body is set as an axisymmetric boundary condition.

[0067] The 2D geometric model was divided into triangles of arbitrary shape, and the mesh was analyzed for skewness; a skewness closer to 1 indicates higher mesh quality. After model calculation, the porosity and displacement parameters obtained from experiments were used to verify the model results. The results show the evolution of porosity with temperature during coal spontaneous combustion, with porosity increasing as temperature rises.

[0068] In the initial stage of coal spontaneous combustion, the fluid in the pores is mainly liquid water with very little gas. Further increases in coal temperature lead to a higher evaporation rate, causing an increase in internal pressure, which in turn causes the liquid water to boil and evaporate at high temperatures. During the heating process, the temperature initially rises from the sides and top of the coal, gradually moving towards the center. The higher temperatures at the sides and top create thermal stress, causing the sample to deform from these areas.

[0069] Coal deformation under heating conditions manifests as thermal shrinkage; initially, the coal body is undeformed and has high density; as the temperature rises, cracks and pores begin to appear on the coal surface; when the temperature exceeds the glass transition temperature, the cracks and pores in the coal body increase, and bending occurs due to uneven heating.

[0070] Therefore, by constructing a multi-field coupled model of coal spontaneous combustion with thermal deformation as the link, the thermal deformation mechanism and dynamic porosity evolution are incorporated into the model. The constitutive relationship of temperature-thermal strain-porosity is established, covering the closed-loop coupling mechanism of "heat transfer-thermal deformation-porosity change-moisture migration-heat transfer". This realizes the fully coupled dynamic evolution of the flow field, temperature field and mechanical field during coal spontaneous combustion, and solves the problem of inaccurate prediction caused by neglecting thermodynamic deformation and dynamic changes in porosity in traditional models. This provides theoretical support for the prevention and control of coal spontaneous combustion.

[0071] like Figure 15 As shown, this embodiment also provides a coal spontaneous combustion behavior evolution system under multi-physics coupling, which uses the coal spontaneous combustion behavior evolution method under multi-physics coupling of any of the above embodiments to predict coal spontaneous combustion. The system includes: Thermocouple unit 1501 is configured to pass through the temperature field during spontaneous combustion of coal. Over time The changes determine the deformation of the coal body during spontaneous combustion. Over time The changes in volume during spontaneous combustion of the coal were used to determine the volume of the coal. Over time The changes, and through the volume of coal during spontaneous combustion. Over time The changes in porosity during spontaneous combustion of coal were used to determine the porosity of the coal body. Over time Changes; The hydraulic coupling unit 1502 is configured to determine the porosity of coal during spontaneous combustion. Remaining water saturation and liquid phase saturation Over time The changes; and based on the equilibrium steam pressure during spontaneous combustion of coal. Liquid phase saturation Over time The changes determine the evaporation rate of spontaneous combustion of the coal. Over time Changes; The hydrothermal coupling unit 1503 is configured to adjust according to the liquid phase saturation. Over time Changes and solid saturation Determine the effective thermal conductivity of coal during spontaneous combustion. Over time The changes; and further, based on the evaporation rate during spontaneous combustion of coal. Effective thermal conductivity Coal oxidation reaction rate Over time Changes in the temperature field of the coal body Make corrections.

[0072] The coal spontaneous combustion behavior evolution system under multi-physics field coupling provided in this embodiment can realize the steps and processes of the coal spontaneous combustion behavior evolution method under multi-physics field coupling in any of the above embodiments, and achieve the same technical effect, which will not be described in detail here.

[0073] In the description of this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0074] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for the evolution of coal spontaneous combustion behavior under multi-physics coupling, characterized in that, include: Temperature field during spontaneous combustion of coal Over time The changes determine the deformation of the coal body during spontaneous combustion. Over time The changes in volume during spontaneous combustion of the coal were used to determine the volume of the coal. Over time The changes, and through the volume during spontaneous combustion of coal. Over time The changes in porosity during spontaneous combustion of coal were used to determine the porosity of the coal. Over time Changes; Determine the porosity of coal during spontaneous combustion Remaining water saturation and liquid phase saturation Over time The changes; and based on the equilibrium steam pressure during spontaneous combustion of coal. Liquid phase saturation Over time The changes were used to determine the evaporation rate of spontaneous combustion of the coal. Over time Changes; Based on liquid phase saturation Over time Changes and solid saturation Determine the effective thermal conductivity of coal during spontaneous combustion. Over time The changes; and further, based on the evaporation rate during spontaneous combustion of coal. Effective thermal conductivity Coal oxidation reaction rate Over time Changes in the temperature field of the coal body Make corrections.

2. The method according to claim 1, characterized in that, Deformation of coal during spontaneous combustion Over time The changes are as follows: ； In the formula, The density of the coal body, For divergence operators, This represents the total displacement during coal deformation. For the thermal insulation stress of the coal body, Let be the elastic stiffness tensor of the coal mass. These are the times when the coal spontaneously combusts. The elastic modulus and Poisson's ratio, Time of spontaneous combustion of coal The total strain tensor, For the inelastic strain tensor of the coal body. For the volume forces of the coal body; The elastic stiffness tensor of coal Time of spontaneous combustion of coal elastic modulus Compared to Poisson The function; Volume of coal during spontaneous combustion Over time The changes are as follows: ； In the formula, The initial volume of the coal body. Time of spontaneous combustion of coal Total strain tensor The traces.

3. The method according to claim 1, characterized in that, Porosity of coal during spontaneous combustion Over time The changes are as follows: ； In the formula, The initial porosity of the coal body. The initial volume of the coal body. Time of spontaneous combustion of coal The volume.

4. The method according to claim 1, characterized in that, The remaining moisture in the coal body during spontaneous combustion is saturated. Over time The changes are as follows: ； In the formula, Time of spontaneous combustion of coal porosity; Liquid phase saturation during spontaneous combustion of coal Over time The changes are as follows: ； In the formula, For divergence operators, Time of spontaneous combustion of coal The water diffusion coefficient, Time of spontaneous combustion of coal evaporation rate, ρ is the density of the liquid phase.

5. The method according to claim 1, characterized in that, Moisture diffusion coefficient during spontaneous combustion of coal Over time The changes are as follows: ； In the formula, It is a proportionality constant, and its value is [value missing]. .

6. The method according to claim 1, characterized in that, Balanced steam pressure during spontaneous combustion of coal Over time The changes are as follows: ； In the formula, All are constants. Time of spontaneous combustion of coal The temperature field.

7. The method according to claim 1, characterized in that, Effective thermal conductivity of coal during spontaneous combustion Over time The changes are as follows: ； In the formula, Let be the thermal conductivity of the coal in a fully saturated state. The thermal conductivity of the coal in a completely dry state.

8. The method according to claim 1, characterized in that, Evaporation rate of spontaneous combustion of coal Over time The changes are as follows: ； In the formula, Let be the evaporation rate constant of the liquid phase during spontaneous combustion of coal. The density of the liquid phase is... Time of spontaneous combustion of coal The equilibrium vapor pressure, This is the actual vapor pressure. Time of spontaneous combustion of coal The liquid phase saturation.

9. The method according to claim 1, characterized in that, According to the formula: ； Temperature field of coal Make corrections; In the formula, For effective density, For effective specific heat capacity, Time of spontaneous combustion of coal The effective thermal conductivity, Time of spontaneous combustion of coal evaporation rate, Time of spontaneous combustion of coal temperature gradient, The latent heat of vaporization of the coal body, Time of spontaneous combustion of coal The heat flux of the oxidation reaction; in, ； In the formula, These are the times when the coal spontaneously combusts. The liquid phase saturation and gas phase saturation, The solid phase saturation of the coal body; These are the liquid phase density, solid phase density, and gas phase density, respectively. Time of spontaneous combustion of coal The liquid relative heat capacity, These are the solid-phase heat capacity and the gas-phase heat capacity, respectively. Time of spontaneous combustion of coal Temperature field; Time of spontaneous combustion of coal The rate of coal oxidation reaction; The enthalpy of reaction per unit mass of the coal; As a pre-exponential factor for coal oxidation, The activation energy of the coal body It is a universal gas constant. This refers to the oxygen concentration inside the coal body during spontaneous combustion.

10. A system for the evolution of coal spontaneous combustion behavior under multi-physics coupling, characterized in that, The method for predicting coal spontaneous combustion using the multiphysics field coupling evolution of coal spontaneous combustion behavior as described in any one of claims 1-9, the system comprising: Thermocoupled unit, configured to pass through the temperature field during spontaneous combustion of coal. Over time The changes determine the deformation of the coal body during spontaneous combustion. Over time The changes in volume during spontaneous combustion of the coal were used to determine the volume of the coal. Over time The changes, and through the volume during spontaneous combustion of coal. Over time The changes in porosity during spontaneous combustion of coal were used to determine the porosity of the coal. Over time Changes; The hydraulic coupling unit is configured to determine the porosity of coal during spontaneous combustion. Remaining water saturation and liquid phase saturation Over time The changes; and based on the equilibrium steam pressure during spontaneous combustion of coal. Liquid phase saturation Over time The changes were used to determine the evaporation rate of spontaneous combustion of the coal. Over time Changes; The hydrothermal coupling unit is configured to adjust according to the liquid phase saturation. Over time Changes and solid saturation Determine the effective thermal conductivity of coal during spontaneous combustion. Over time The changes; and further, based on the evaporation rate during spontaneous combustion of coal. Effective thermal conductivity Coal oxidation reaction rate Over time Changes in the temperature field of the coal body Make corrections.

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