Method and system for evolution of coal spontaneous combustion behavior under multi-physics coupling

Abstract

The application relates to the technical field of coal mine safety, and provides a coal spontaneous combustion behavior evolution method and system under multi-physical field coupling. The temperature field of coal body spontaneous combustion changes the volume by affecting the deformation amount, the porosity of the coal body is calculated through the volume, and then the thermal deformation is driven; the thermal deformation influences the water diffusion through the porosity, the residual moisture saturation of the coal body and the liquid phase saturation, and then the water migration is driven in combination with the evaporation rate and the liquid phase saturation; the water migration drives the heat transfer in combination with the evaporation rate, the effective thermal conductivity and the coal oxidation reaction rate, a cycle of "heat transfer-thermal deformation-water-heat transfer" is formed, the "heat-force-water-heat" coupling closed loop during the coal body spontaneous combustion is realized, the two-way coupling of the seepage field, the temperature field and the mechanical field is realized, and the problem that the prediction is inaccurate due to the neglect of thermodynamic deformation and dynamic changes of pores in a traditional model is effectively solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coal mine safety, in particular to a coal spontaneous combustion behavior evolution method and system under multi-physical field coupling. BACKGROUND

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

[0003] Coal is a naturally complex porous organic rock, and its internal pore structure provides a channel for fluid migration and directly determines the storage and transport characteristics of fluids in coal. Temperature is one of the important factors affecting the pore structure of coal, which can significantly affect the water migration and mechanical properties of coal. About 20-40 % of the heat generated during the combustion of coal is consumed in water evaporation, and at the same time, the pore structure also changes, thereby affecting the mass transport and chemical reactions during combustion. SUMMARY

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

[0005] In order to achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0006] The present application provides a coal spontaneous combustion behavior evolution method under multi-physical field coupling, comprising:

[0007] determining the change of the deformation amount of the coal body during spontaneous combustion with time determining the change of the volume of the coal body during spontaneous combustion with time determining the change of the volume of the coal body during spontaneous combustion with time determining the change of the porosity of the coal body during spontaneous combustion with time determining the change of the porosity of the coal body during spontaneous combustion with time determining the change of the porosity of the coal body during spontaneous combustion with time determining the change of the porosity of the coal body during spontaneous combustion with time determining the change of the porosity of the coal body during spontaneous combustion with time determining the change of the porosity of the coal body during spontaneous combustion with time determining the change of the porosity of the coal body during spontaneous combustion with time determining the change of the porosity of the coal body during spontaneous combustion with time determining the change of the porosity of the coal body during spontaneous combustion with time

[0008] determining the change of the porosity of the coal body during spontaneous combustion with time determining the change of the porosity of the coal body during spontaneous combustion with time determining the change of the porosity of the coal body during spontaneous combustion with time determining the change of the porosity of the coal body during spontaneous combustion with time determining the change of the porosity of the coal body during spontaneous combustion with time determining the change of the porosity of the coal body during spontaneous combustion with time determining the change of the porosity of the coal body during spontaneous combustion with time The changes were used to determine the evaporation rate of spontaneous combustion of the coal. Over time Changes;

[0009] 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.

[0010] Preferably, the deformation of the coal body during spontaneous combustion Over time The changes are as follows:

[0011]

[0012] 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 body Time of spontaneous combustion of coal elastic modulus Compared to Poisson The function;

[0013] Volume of coal during spontaneous combustion Over time The changes are as follows:

[0014]

[0015] In the formula, The initial volume of the coal body. Time of spontaneous combustion of coal Total strain tensor The traces.

[0016] Preferably, the porosity of the coal mass at the time of spontaneous combustion of the coal mass with time is given by:

[0017]

[0018] where, is the initial porosity of the coal mass, is the initial volume of the coal mass, is the volume of the coal mass at the time of spontaneous combustion of the coal mass.

[0019] Preferably, the residual moisture saturation of the coal mass at the time of spontaneous combustion of the coal mass with time is given by:

[0020]

[0021] where, is the porosity of the coal mass at the time of spontaneous combustion of the coal mass; Preferably, the liquid phase saturation of the coal mass at the time of spontaneous combustion of the coal mass

[0022] with time is given by:

[0023]

[0024] where, is the divergence operator, is the moisture diffusion coefficient of the coal mass at the time of spontaneous combustion of the coal mass, is the evaporation rate of the coal mass at the time of spontaneous combustion of the coal mass, is the liquid phase density. Preferably, the moisture diffusion coefficient of the coal mass at the time of spontaneous combustion of the coal mass with time is given by:

[0025]

[0026]

[0027] where, is a proportionality constant having a value of .

[0028] Preferably, the equilibrium vapour pressure of the coal mass at the time of spontaneous combustion of the coal mass with time is given by:

[0029]

[0030] where, are constants, ​​​​​​​​​the temperature field of the coal mass as a function of time

[0031] Preferably, the effective thermal conductivity of the coal mass as a function of time

[0032]

[0033] wherein, λ0 is the thermal conductivity of the coal mass in a fully saturated state, λd is the thermal conductivity of the coal mass in a fully dry state.

[0034] Preferably, the evaporation rate of the coal mass as a function of time

[0035]

[0036] wherein, k is the evaporation rate constant of the liquid phase as a function of time, ρ is the liquid phase density, P0 is the equilibrium vapor pressure of the coal mass as a function of time, P is the actual vapor pressure, S0 is the liquid phase saturation as a function of time. Preferably, the temperature field of the coal mass is corrected according to the formula:

[0037]

[0038]

[0039]

[0040] wherein, ρeff is the effective density, Ceff is the effective specific heat capacity, λeff is the effective thermal conductivity of the coal mass as a function of time, k is the evaporation rate of the coal mass as a function of time, ∇T is the temperature gradient of the coal mass as a function of time, L is the latent heat of evaporation of the coal mass, q is the oxidation reaction heat flux of the coal mass as a function of time; wherein,

[0041]

[0042]

[0043] wherein,​​​​​​​​​​​​​ 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,

[0044] These are the solid-phase heat capacity and the gas-phase heat capacity, respectively. Time of spontaneous combustion of coal Temperature field;

[0045] 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.

[0046] 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:

[0047] 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;

[0048] 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;

[0049] The hydrothermal coupling unit is configured to determine the effective thermal conductivity of the coal body at the time of spontaneous combustion of the coal body according to the change of the liquid phase saturation degree over time The hydrothermal coupling unit is configured to determine the effective thermal conductivity of the coal body at the time of spontaneous combustion of the coal body according to the change of the liquid phase saturation degree over time The hydrothermal coupling unit is configured to determine the effective thermal conductivity of the coal body at the time of spontaneous combustion of the coal body according to the change of the liquid phase saturation degree over time The hydrothermal coupling unit is configured to determine the effective thermal conductivity of the coal body at the time of spontaneous combustion of the coal body according to the change of the liquid phase saturation degree over time The hydrothermal coupling unit is configured to determine the effective thermal conductivity of the coal body at the time of spontaneous combustion of the coal body according to the change of the liquid phase saturation degree over time The hydrothermal coupling unit is configured to determine the effective thermal conductivity of the coal body at the time of spontaneous combustion of the coal body according to the change of the liquid phase saturation degree over time

[0050] Beneficial effects:

[0051] In the method and system for evolution of coal spontaneous combustion behavior under multi-physical field coupling provided by the embodiments of the present application, the change of the temperature field of the coal body at the time of spontaneous combustion of the coal body over time is determined, the change of the deformation amount of the coal body at the time of spontaneous combustion of the coal body over time is determined, the change of the volume of the coal body at the time of spontaneous combustion of the coal body over time is determined, the change of the porosity of the coal body at the time of spontaneous combustion of the coal body over time is determined, the change of the porosity of the coal body at the time of spontaneous combustion of the coal body over time is determined, the change of the residual moisture saturation of the coal body at the time of spontaneous combustion of the coal body over time is determined, the change of the liquid phase saturation degree of the coal body at the time of spontaneous combustion of the coal body over time is determined, the change of the evaporation rate of the coal body at the time of spontaneous combustion of the coal body over time is determined, the change of the effective thermal conductivity of the coal body at the time of spontaneous combustion of the coal body over time is determined, and the temperature field of the coal body at the time of spontaneous combustion of the coal body is corrected according to the change of the evaporation rate of the coal body at the time of spontaneous combustion of the coal body, the effective thermal conductivity of the coal body at the time of spontaneous combustion of the coal body, the change of the coal oxidation reaction rate over time. The hydrothermal coupling unit is configured to determine the effective thermal conductivity of the coal body at the time of spontaneous combustion of the coal body according to the change of the liquid phase saturation degree over time The hydrothermal coupling unit is configured to determine the effective thermal conductivity of the coal body at the time of spontaneous combustion of the coal body according to the change of the liquid phase saturation degree over time The hydrothermal coupling unit is configured to determine the effective thermal conductivity of the coal body at the time of spontaneous combustion of the coal body according to the change of the liquid phase saturation degree over time The hydrothermal coupling unit is configured to determine the effective thermal conductivity of the coal body at the time of spontaneous combustion of the coal body according to the change of the liquid phase saturation degree over time The hydrothermal coupling unit is configured to determine the effective thermal conductivity of the coal body at the time of spontaneous combustion of the coal body according to the change of the liquid phase saturation degree over time The hydrothermal coupling unit is configured to determine the effective thermal conductivity of the coal body at the time of spontaneous combustion of the coal body according to the change of the liquid phase saturation degree over time The hydrothermal coupling unit is configured to determine the effective thermal conductivity of the coal body at the time of spontaneous combustion of the coal body according to the change of the liquid phase saturation degree over time The hydrothermal coupling unit is configured to determine the effective thermal conductivity of the coal body at the time of spontaneous combustion of the coal body according to the change of the liquid phase saturation degree over time The hydrothermal coupling unit is configured to determine the effective thermal conductivity of the coal body at the time of spontaneous combustion of the coal body according to the change of the liquid phase saturation degree over time The hydrothermal coupling unit is configured to determine the effective thermal conductivity of the coal body at the time of spontaneous combustion of the coal body according to the change of the liquid phase saturation degree over time The hydrothermal coupling unit is configured to determine the effective thermal conductivity of the coal body at the time of spontaneous combustion of the coal body according to the change of the liquid phase saturation degree over time The hydrothermal coupling unit is configured to determine the effective thermal conductivity of the coal body at the time of spontaneous combustion of the coal body according to the change of the liquid phase saturation degree over time The hydrothermal coupling unit is configured to determine the effective thermal conductivity of the coal body at the time of spontaneous combustion of the coal body according to the change of the liquid phase saturation degree over time The hydrothermal coupling unit is configured to determine the effective thermal conductivity of the coal body at the time of spontaneous combustion of the coal body according to the change of the liquid phase saturation degree over time The hydrothermal coupling unit is configured to determine the effective thermal conductivity of the coal body at the time of spontaneous combustion of the coal body according to the change of the liquid phase saturation degree over time​​​​​​​​​​​​​​​​​​​

[0052] 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

[0053] 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:

[0054] 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.

[0055] 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;

[0056] 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;

[0057] Figure 4 The T2 spectrum of a coal sample under saturation state provided according to an embodiment of this application;

[0058] Figure 5 The T2 spectrum of a coal sample in a dry state provided according to an embodiment of this application;

[0059] Figure 6 Coal samples provided according to embodiments of this application A schematic diagram of the remaining water saturation at a given time;

[0060] Figure 7 A schematic diagram illustrating the setting of boundary conditions for a coal sample according to an embodiment of this application;

[0061] Figure 8 This is a schematic diagram of coal sample grid division according to an embodiment of this application;

[0062] 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.

[0063] Figure 10 A schematic diagram of the vertical displacement of a coal sample in numerical simulation and physical experiment, respectively, according to an embodiment of the present application;

[0064] Figure 11 A schematic diagram of the horizontal displacement of a coal sample in numerical simulation and physical experiment, respectively, according to an embodiment of the present application;

[0065] Figure 12 A schematic diagram of the spatial distribution of moisture saturation in coal at different times, according to an embodiment of the present application;

[0066] Figure 13 A schematic diagram of the spatial distribution of temperature in coal at different heating times, according to an embodiment of the present application;

[0067] Figure 14 A schematic diagram of the total displacement of coal at different temperatures in numerical simulation and physical experiment, respectively, according to an embodiment of the present application;

[0068] Figure 15 A schematic diagram of the structure of a system for evolution of coal spontaneous combustion behavior under multi-physical field coupling, according to some embodiments of the present application. DETAILED DESCRIPTION

[0069] The present application will be described in detail below with reference to the accompanying drawings and embodiments. Each example is provided by way of explanation of the present application and is not intended to limit the present application. In fact, those skilled in the art will appreciate that modifications and variations can be made in the present application without departing from the scope or spirit of the present application. For example, features shown or described as part of one embodiment can be used in another embodiment to produce yet another embodiment. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application should fall within the scope of protection of the embodiments of the present application.

[0070] Currently, the thermodynamic behavior of coal spontaneous combustion is mostly studied at low temperatures, and the study under high temperature conditions is not mature. Although experimental methods are the most direct method for studying the process of coal spontaneous combustion, current experimental methods cannot effectively predict the thermodynamic behavior of coal in natural processes; the advantages of visualization and data quantification of numerical simulation can effectively solve these problems in experiments, and have become one of the efficient means for studying coal spontaneous combustion. However, existing numerical simulations of coal thermal effects mostly focus on drying heating, microwave heating and chemical reactions of coal, and lack of research on the whole process of coal spontaneous combustion.

[0071] 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.

[0072] 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.

[0073] 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:

[0074] 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.

[0075] 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.

[0076] 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 process involves heating the coal sample at each temperature point for 50 minutes to allow it to reach thermal equilibrium. After heating, the coal sample is allowed to cool naturally in air. Once cooled, the coal sample is 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).

[0077] 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.

[0078] 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:

[0079]

[0080] 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.

[0081] 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:

[0082]

[0083] 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. 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.

[0084] 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:

[0085]

[0086] 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."

[0087] 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:

[0088]

[0089] In the formula, is the initial porosity of the coal body, is the initial volume of the coal body, is the volume of the coal body at time .

[0090] Step S102, determining the porosity of the coal body at time , the residual moisture saturation of the coal body at time , and the liquid phase saturation of the coal body at time , and determining the change of the evaporation rate of the coal body at time according to the change of the equilibrium vapor pressure of the coal body at time , the liquid phase saturation of the coal body at time .

[0091] The nonlinear change of the elastic modulus and the Poisson's ratio of the coal body at time can be directly determined through the temperature field, but the elastic modulus and the Poisson's ratio cannot directly affect the temperature field, but change the volume of the coal body through the nonlinear change of the elastic modulus and the Poisson's ratio at time , and then affect the porosity of the coal body. The porosity of the coal body determines the "basic capacity" of the coal body to store water, that is, the porosity and the residual moisture saturation of the coal body are in a nonlinear relationship. In the embodiment, the change of the residual moisture saturation of the coal body at time is:

[0092]

[0093] In the formula, is the porosity of the coal body at time ;

[0094] The change of the liquid phase saturation of the coal body at time is:

[0095]

[0096] In the formula, is the divergence operator, is the moisture diffusion coefficient of the coal body at time , is the evaporation rate of the coal body at time , and is the liquid phase density. In the process of the coal body combustion, the thermal deformation affects the moisture diffusion coefficient of the coal body through the porosity, the residual moisture saturation, and the liquid phase saturation. Specifically, the moisture diffusion coefficient of the coal body at time

[0097] ​​​​​The changes are as follows:

[0098]

[0099] In the formula, It is a proportionality constant, and its value is [value missing]. .

[0100] 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.

[0101] 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:

[0102]

[0103] 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:

[0104]

[0105] 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.

[0106] 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.

[0107] 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:

[0108]

[0109] 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.

[0110] 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:

[0111]

[0112] 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.

[0113] in,

[0114]

[0115] 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; respectively liquid phase density, solid phase density and gas phase density; is the temperature field of coal body when time is the specific heat capacity of liquid phase, respectively solid phase specific heat capacity and gas phase specific heat capacity, is the temperature field of coal body when time .

[0116] is the coal oxidation reaction rate when time ; is the unit mass reaction enthalpy of coal body; is the coal oxidation pre-exponential factor, , is the activation energy of coal body, , is the universal gas constant, is the internal oxygen concentration of coal body when time .

[0117] Here, the liquid phase saturation and the gas phase saturation change with time during the coal spontaneous combustion process, and the solid phase saturation is a fixed value. The saturation of the solid phase can be obtained by the initial porosity obtained by experiment, and then the gas phase saturation can be obtained by the initial liquid phase saturation.

[0118] In a specific example, according to the size of the coal sample in the coal spontaneous combustion pore damage evolution experiment under high temperature conditions, a 2D geometric model matched therewith is established. The initial porosity of the coal sample is 11%, and the initial temperature of the coal sample ; according to the formula:

[0119]

[0120] the initial water content of the coal sample and the initial volume fraction of water (i.e. the initial liquid phase saturation ) are determined.

[0121] The upper boundary and the right boundary of the coal body in the 2D geometric model are set as the boundary conditions of heat flux, free deformation, water evaporation, heat evaporation, etc.; the heat variable enters the coal body from the outside world, and the free deformation, water evaporation and heat evaporation diffuse from the coal body to the outside world; the lower boundary of the coal body is set as the boundary conditions of solid boundary constraint and thermal insulation; and the left boundary of the coal body is set as the boundary condition of axisymmetric boundary.

[0122] The 2D geometric model is divided into triangles of any shape, and the grid is analyzed for skewness. The closer the skewness is to 1, the higher the quality of the grid. After the model is calculated, the porosity parameters and displacement parameters measured by experiments are used to verify the model results. The evolution of porosity with temperature during the coal spontaneous combustion process is shown, and the porosity increases with the increase of temperature.

[0123] At the initial stage of coal spontaneous combustion, the fluid in the pore is mainly liquid water, and there is only a small amount of gas phase. Further increase of the temperature of the coal body increases the evaporation rate, which leads to the increase of the internal pressure of the coal, and the liquid water will boil and evaporate at high temperature. During the heating process of the coal, the temperature first rises from the two sides and the top of the coal, and gradually transfers to the central region. The higher temperature at the two sides and the top forms a certain thermal stress, which causes the sample to deform from the vicinity of these regions.

[0124] The deformation of the coal under the heating condition is thermal shrinkage. In the initial state, the coal body has no deformation and high compactness. With the increase of temperature, cracks and pores begin to appear on the surface of the coal. When the temperature exceeds the glass transition temperature, the cracks and pores of the coal body increase, and the bending is caused by uneven heating.

[0125] Therefore, by constructing a thermal deformation as a link, the thermal deformation mechanism and dynamic pore evolution are incorporated into the multi-field coupling model of coal spontaneous combustion, the constitutive relationship of temperature-thermal strain-porosity is established, the closed-loop coupling mechanism of "heat transfer-thermal deformation-pore change-water migration-heat transfer" is covered, the full coupling dynamic evolution of flow field, temperature field and mechanical field in the process of coal spontaneous combustion is realized, and the problem of inaccurate prediction caused by ignoring the thermal deformation and dynamic pore change in the traditional model is solved, which provides theoretical support for the prevention and control of coal spontaneous combustion.

[0126] As shown in Figure 15 , the embodiment also provides a coal spontaneous combustion behavior evolution system under multi-physical field coupling. The coal spontaneous combustion is predicted by using the coal spontaneous combustion behavior evolution method under multi-physical field coupling of any one of the above embodiments. The system comprises:

[0127] A thermal coupling unit 1501 is configured to determine the deformation of the coal body during spontaneous combustion of the coal body by the change of the temperature field of the coal body during spontaneous combustion of the coal body over time, determine the change of the volume of the coal body during spontaneous combustion of the coal body over time, determine the change of the volume of the coal body during spontaneous combustion of the coal body over time, determine the change of the volume of the coal body during spontaneous combustion of the coal body over time, determine the change of the volume of the coal body during spontaneous combustion of the coal body over time, determine the change of the volume of the coal body during spontaneous combustion of the coal body over time, determine the change of the volume of the coal body during spontaneous combustion of the coal body over time, determine the change of the volume of the coal body during spontaneous combustion of the coal body over time, determine the change of the volume of the coal body during spontaneous combustion of the coal body over time, determine the change of the volume of the coal body during spontaneous combustion of the coal body over time, determine the change of the volume of the coal body during spontaneous combustion of the coal body over time,

[0128] 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 were used to determine the evaporation rate of spontaneous combustion of the coal. Over time Changes;

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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 evolution of coal spontaneous combustion behavior under multi-physical field coupling, characterized in that, Comprising: determining the deformation of the coal mass upon self-ignition of the coal mass by the temperature field over time determining the deformation of the coal mass upon self-ignition of the coal mass by the change in volume over time over time determining the volume of the coal mass upon self-ignition of the coal mass by the change in volume over time over time determining the porosity of the coal mass upon self-ignition of the coal mass by the change in volume over time over time determining the porosity of the coal mass upon self-ignition of the coal mass by the change in volume over time over time determining the porosity of the coal mass upon self-ignition of the coal mass by the change in volume over time 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; wherein, according to the formula: ； Temperature field of coal body correction is made; 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; ； wherein respectively liquid saturation and gas saturation at time of coal spontaneous combustion, is the solid saturation of coal; respectively liquid density, solid density and gas density; respectively liquid specific heat capacity and gas specific heat capacity at time of coal spontaneous combustion, Cp, respectively, the solid and gas specific heat capacities, is the time of coal spontaneous combustion temperature field; is the coal oxidation reaction rate when the coal body is self-ignited; is the coal oxidation reaction rate when the coal body is self-ignited; is the unit mass reaction enthalpy of the coal body; is the coal oxidation pre-exponential factor, is the activation energy of the coal body, is the universal gas constant, is the internal oxygen concentration of the coal body when the coal body is self-ignited.

2. The method of claim 1, wherein, Deformation of coal body during spontaneous combustion over time is: ； 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 body at the time of spontaneous combustion over time is: ； wherein is the initial volume of the coal body, is the time of self-ignition of the coal body is the total strain tensor is the trace.

3. The method of claim 1, wherein, Porosity of coal body at spontaneous combustion over time is: ； wherein is the initial porosity of the coal body, is the initial volume of the coal body, is the volume of the coal body at time of spontaneous combustion.

4. The method of claim 1, wherein, remaining moisture content of the coal body at the time of spontaneous combustion over time is: ； wherein time for coal spontaneous combustion porosity of the pores; Liquid saturation during spontaneous combustion of coal over time is: ； wherein is the divergence operator, is the time to spontaneous combustion of the coal body is the moisture diffusion coefficient, is the time to spontaneous combustion of the coal body is the evaporation rate, is the liquid phase density.

5. The method of claim 4, wherein, Water diffusion coefficient of coal body during spontaneous combustion over time is: ； wherein is a proportionality constant, taking values .

6. The method of claim 1, wherein, Equilibrium vapor pressure of coal during spontaneous combustion over time is: ； wherein are constants, is the temperature field of the coal body at the time of spontaneous combustion of coal.

7. The method of claim 1, wherein, Effective thermal conductivity of coal during spontaneous combustion over time is: ； wherein is the thermal conductivity of the coal body in a fully saturated state, is the thermal conductivity of the coal body in a fully dry state.

8. The method of claim 1, wherein, Evaporation rate of coal spontaneous combustion over time is: ； wherein is the evaporation rate constant of the liquid phase at the time of spontaneous combustion of the coal body, is the density of the liquid phase, is the equilibrium vapor pressure at the time of spontaneous combustion of the coal body, is the actual vapor pressure, is the actual vapor pressure, is the liquid phase saturation at the time of spontaneous combustion of the coal body, is the liquid phase saturation at the time of spontaneous combustion of the coal body.

9. A system for evolution of coal spontaneous combustion behavior under multi-physical field coupling, characterized in that, The system comprises: The system comprises: 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 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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