Method for simulating oxidative spontaneous combustion of pressure-bearing loose combustibles based on CFD numerical simulation

Abstract

The invention relates to a CFD numerical simulation-based pressure-bearing loose combustible material oxidation spontaneous combustion simulation method, and belongs to the technical field of combustible material oxidation spontaneous combustion simulation. Physicochemical property testing is carried out on combustible materials, oxidation experiments are carried out on the loose combustible materials under different pressure-bearing conditions, and physical parameters are collected; temperature, gas concentration and pressure parameters of combustible materials are collected in real time, and pressure-bearing oxidation spontaneous combustion parameters are calculated; fitting a function relationship between the oxidation spontaneous combustion parameter and the combustible body temperature; establishing a CFD numerical simulation model of multi-physics field coupling; according to the geometric dimension of the simulation model, dividing calculation grids, setting simulation boundary conditions and initial conditions, and performing CFD numerical simulation calculation; and outputting a three-dimensional dynamic distribution diagram of the temperature field, the heat conductivity coefficient field, the permeability field, the heat release intensity field and the gas concentration field in the simulation process, and analyzing a simulation result to obtain the oxidative spontaneous combustion characteristics of the pressure-bearing loose combustible.

Description

Technical Field

[0001] The invention belongs to the technical field of simulation of oxidation spontaneous combustion of combustibles, and relates to a simulation method of oxidation spontaneous combustion of pressurized loose combustibles based on CFD numerical simulation. Background Art

[0002] The increase in the depth of coal mining has caused coupled mutations in ground stress, ground temperature and coal-rock fragmentation to a certain extent. Due to the influence of coal mining, the coal in the goaf will be successively subjected to the main processes of ground stress, overburden settlement, and stress recovery and compaction in the goaf. Since the coal body in the goaf will continue to break under the action of stress, the surface area of ​​the particles will be increased after breaking, and the mass transfer and heat transfer between the particles and oxygen will be enhanced, which will accelerate the coal-oxygen reaction rate. Studies have shown that the increase in the degree of coal particle fragmentation and the change in grading will make the coal more easily oxidized and make spontaneous combustion more prominent. In addition to the coal mining field, in forest fires, the ignition of forest fallen leaves often occurs under a certain burial depth and pressure. In addition, one of the reasons for the spontaneous combustion and explosion of explosives is that the internal structure and external heat storage environment change under the action of their own gravity. Therefore, the study of the evaluation method of the spontaneous combustion oxidation state of combustibles under pressure is of great significance for preventing fire accidents and ensuring energy security.

[0003] At present, the exploration of the oxidation and spontaneous combustion characteristics of pressurized loose combustibles is mostly based on experimental devices. The invention patent with publication number CN201610176055.7 provides a device for measuring the oxidation and heating characteristic parameters of pressurized coal, which effectively solves the problem of measuring the oxidation and heating characteristic parameters of pressurized coal. The device has a high degree of automation, reliable and stable measurement results, is easy to operate, and has good effects. It can realize the test of the heating and oxidation characteristic parameters of coal under different pressure conditions in a high-pressure atmosphere. The invention patent with publication number CN201610176045.3 can realize the oxidation and heating of the crushed coal sample in a certain pressure difference atmosphere through the coal sample tank, the inlet and outlet parts of the gas path, and the pressurized part of the heating box when the crushed coal body is under pressure or loose state. At the same time, coal sample tanks of different sizes can be used to realize the oxidation and heating characteristic parameter test of the crushed coal body of different sizes under different pressure conditions with a fixed pressure difference. The invention patent with publication number CN201510759269.2 realizes comprehensive control in stress loading, thermal environment control, atmosphere field control, etc., which can make the research on coal spontaneous combustion closer to the multi-field coupling environment where the coal in the actual goaf is located underground, and can simulate the porosity and permeability of the coal in the goaf under different stress states and surrounding rock temperatures. The test device for the evolution of the permeability of the pressurized crushed coal. The invention patent with publication number CN201410625651.X involves a test device for the oxidation characteristics of deep mining-deformed coal bodies, specifically a test device for the spontaneous combustion oxidation characteristics of coal under multiple complex environments of high stress, high temperature, high gas flow pressure, gas concentration and flow, and high-intensity mining deformation. The above invention patents are all for experimental equipment, which are used to experimentally study the oxidation and spontaneous combustion characteristics of pressurized coal bodies. However, the data that can be obtained by experimental equipment in the process of studying the spontaneous combustion of combustibles under pressure oxidation is very limited, and it is impossible to fully understand the distribution of stress field, temperature field, chemical field and gas concentration field of each part of the combustibles under pressure oxidation and spontaneous combustion, so it is impossible to accurately and timely judge the state of spontaneous combustion of combustibles under pressure oxidation, which is of great significance for accurate early warning of spontaneous combustion of combustibles under pressure oxidation. In addition, experimental research requires more time and money. However, there is no report on the simulation method of spontaneous combustion of loose combustibles under pressure oxidation based on CFD numerical simulation. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a simulation method for the oxidation and spontaneous combustion of pressurized loose combustibles based on CFD numerical simulation, in view of the fact that the data obtained by existing experimental equipment is limited and the temporal and spatial distribution characteristics of the oxidation and spontaneous combustion state of pressurized loose combustibles cannot be understood. According to the oxidation and spontaneous combustion characteristics of pressurized loose combustibles, the oxidation and spontaneous combustion state of pressurized loose combustibles can be simply, quickly and accurately evaluated.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A method for simulating oxidation and spontaneous combustion of pressurized loose combustibles based on CFD numerical simulation includes the following steps:

[0007] S1: Conduct physical and chemical property tests on combustibles, conduct oxidation experiments on loose combustibles under different pressure conditions, and collect physical parameters;

[0008] S2: Real-time collection of the temperature, gas concentration, and pressure parameters of the combustibles during the experiment, and calculation of the pressure-bearing oxidation and spontaneous combustion parameters of the combustible materials;

[0009] S3: Fitting the functional relationship between oxidation auto-ignition parameters and the temperature of the combustible object;

[0010] S4: Based on the physical and chemical properties of combustibles and initial conditions, combined with experimental data, a multi-physics field coupled CFD numerical simulation model is established;

[0011] S5: Divide the computational grid according to the geometric dimensions of the simulation model, set the simulation boundary conditions and initial conditions, and perform CFD numerical simulation calculations;

[0012] S6: Output the three-dimensional dynamic distribution diagram of the temperature field, thermal conductivity field, permeability field, heat release intensity field and gas concentration field during the simulation process, and analyze the simulation results to obtain the oxidation and spontaneous combustion characteristics of pressurized loose combustibles.

[0013] Further, step S1 specifically includes the following steps:

[0014] Select different combustibles for pretreatment;

[0015] Test the industrial analysis, elemental analysis, density, thermal conductivity, and specific heat capacity of combustibles;

[0016] Carry out pressure oxidation spontaneous combustion experiments on combustibles, configure multi-point temperature sensors, and monitor the temperature in real time at different positions of the reactor; set different pressure conditions, and accurately adjust the gas pressure and flow in the reactor through the gas controller; collect temperature, gas concentration, stress and reaction time in real time;

[0017] The collected data is stored.

[0018] Further, step S2 specifically includes the following steps:

[0019] Preprocess the collected temperature, gas concentration and pressure data;

[0020] Calculate the thermal conductivity, heat release intensity, oxygen consumption rate and gas production rate using the data preprocessed in step S21;

[0021] The kinetic model of oxidation spontaneous combustion was established using the obtained data of thermal conductivity, heat release intensity, oxygen consumption rate and gas production rate.

[0022] The Arrhenius equation or other reaction kinetic models are used to describe the relationship between temperature and reaction rate.

[0023] Further, step S3 specifically includes the following steps:

[0024] Select a suitable mathematical model for preliminary fitting based on data characteristics;

[0025] Calculate the correlation coefficient and root mean square error of the fitting results to evaluate the quality of the fitting effect;

[0026] Use the fitted model to predict new experimental data, compare with the actual measured values, verify the applicability of the model, and select the best model;

[0027] The best model obtained was used to set the initial conditions in the CFD simulation to ensure that the model reflects the effect of temperature changes on the reaction rate during the oxidation auto-combustion process;

[0028] During simulation, the best model is used to adjust parameters in real time.

[0029] Further, step S4 specifically includes the following steps:

[0030] Arrange the basic physical and chemical properties of combustibles, including density, thermal conductivity, specific heat capacity, and reaction heat, as inputs to the CFD model;

[0031] According to the experimental results, the initial conditions of the simulation are set, including the initial temperature, gas concentration, pressure and relative humidity;

[0032] Use CFD software to establish a geometric model of the combustible material to ensure that the geometric shape is consistent with the experimental device; the geometric model includes the particle characteristics of the loose combustible material and the structural characteristics of the pressure environment, taking into account the void ratio and arrangement between different particles;

[0033] Set up fluid mechanics equations and heat conduction equations to simulate the interaction of gas flow and heat transfer;

[0034] Consider the heat exchange between gas and solid particles to ensure that the transfer of reaction heat can be accurately reflected;

[0035] The interaction between reactants and products is considered, and the relationship between reaction rate, temperature and concentration is set to accurately simulate the oxidation self-combustion process.

[0036] Further, in step S4, the equation for the oxidation of combustibles is:

[0037]

[0038] in, vCO represents the stoichiometric coefficients of O2, CO2, and CO, respectively;

[0039] The Arrhenius equation is used to calculate the oxidation rate of combustibles:

[0040]

[0041]

[0042] Where A is the pre-exponential factor; E is the apparent activation energy, kJ / mol; the consumption rate of a specific gas is determined by the following formula:

[0043]

[0044] Where V represents the reaction rate of combustibles or gases, kg / (m 3 ·s); M represents the molar mass of the combustible or gas, kg / mol; the heat released during the oxidation of the combustible is calculated by the following formula:

[0045] Q c =V c ΔH c

[0046] The numerical model is established after comprehensively considering the transfer process of mass, energy, momentum and chemical reactions in the model:

[0047]

[0048] (ρC p ) eff =θ c ρ p C p,c +(1-θ c )ρC p

[0049]

[0050] Where ρ represents the density of the gas, kg / m 3 ; C p Indicates the constant pressure specific heat capacity of gas, J / (kg·K); (ρC p ) eff It represents the average effective volume heat capacity of solid and gas at constant pressure, J / (m 3 K); is the conduction heat flux, W / m 2 ; represents the velocity vector, m / s; θ c represents the volume fraction of coal, %; λ represents the thermal conductivity, W / (m·K);

[0051]

[0052] Where ε represents the porosity of the combustible; V c Indicates the reaction rate of combustibles, kg / (m 3 ·s); κ represents permeability, m 2 ; μ represents the dynamic viscosity coefficient of the gas, Pa·S; p represents the pressure, Pa; Q br Indicates mass source, kg / (m 3 ·s); ρ b ,ρ c Respectively represent the bulk density and the density of the combustible material, kg / m 3 ;

[0053] The production and consumption of various components in the combustion process are calculated by the following formula:

[0054]

[0055] in: Indicates mass flux, kg / (m 2 ·s);c j Indicates gas concentration, mol / m 3 ; r c represents the median diameter of the combustible particles; D represents the diffusion coefficient of the gas, m 2 / s.

[0056] Further, step S5 specifically includes the following steps:

[0057] Mesh the established geometric model to ensure that the mesh is detailed enough to capture the physical phenomena in the key areas;

[0058] Use structured or unstructured grids and select the appropriate division method according to the characteristics of the flow field;

[0059] Before calculation, perform mesh quality check to evaluate mesh smoothness, deviation and distortion;

[0060] Apply the boundary conditions set in step S4 to the simulation model to ensure that the gas flow rate, temperature, pressure and other conditions are consistent with the actual situation;

[0061] Verify the setup of initial conditions to ensure that all parameters are applied correctly at the start of the simulation.

[0062] Further, step S6 specifically includes the following steps:

[0063] Use the visualization tools of CFD software to generate three-dimensional dynamic distribution diagrams to show the changes in temperature field, gas concentration field and pressure field;

[0064] Generate a cloud diagram to show the changes in temperature, heat release intensity and gas concentration at different locations;

[0065] Make slice diagrams to analyze the distribution of physical quantities in a specific plane;

[0066] Extract key parameters from simulation results and conduct quantitative analysis;

[0067] Analyze the time-varying curves of temperature, gas concentration and other key parameters to identify the critical moments and critical points of the reaction;

[0068] Compare the CFD simulation results with the experimental data obtained in step S1 to evaluate the accuracy and reliability of the model;

[0069] Analyze the possible causes of the existing differences and adjust the model parameters based on the feedback to improve the accuracy of the model;

[0070] Based on the analysis results, the oxidation and spontaneous combustion characteristics of pressurized loose combustibles are summarized, including the spontaneous combustion temperature range, gas release characteristics and reaction rate.

[0071] The beneficial effect of the present invention is that through CFD numerical simulation, key physical parameters such as temperature, gas flow rate, gas concentration and pressure in the spontaneous combustion process of pressurized loose combustibles can be simulated and monitored in real time. Compared with traditional experimental methods, the present invention has the following advantages:

[0072] 1. All-round data collection: The simulation process can obtain multi-physical field data such as stress field, temperature field, gas concentration field and chemical reaction field during the whole process of spontaneous combustion of pressurized loose combustibles;

[0073] 2. Efficient calculation and prediction: Through the coupled calculation of multiple physical fields, the critical point of oxidation spontaneous combustion under different environmental conditions can be quickly predicted, thus improving the accuracy and timeliness of fire warning;

[0074] 3. Cost saving: Compared with traditional experimental equipment and methods, the present invention greatly reduces the experimental cost through simulation means and can be flexibly applied in a variety of complex scenarios.

[0075] The core of the present invention is to use CFD technology, combined with the physical and chemical properties of combustibles, to establish a multi-physical field coupling simulation model that can simulate the oxidation and spontaneous combustion process of pressurized loose combustibles. This simulation model can not only simulate the changes in physical quantities such as temperature field, stress field, and gas flow field, but also simulate the chemical reaction of the interaction between gas and solid, and fully reflect the whole process of spontaneous combustion of combustibles under pressure.

[0076] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0078] Figure 1 A flow chart of a method for simulating oxidation and spontaneous combustion of pressurized loose combustibles based on CFD numerical simulation provided in an embodiment of the present invention;

[0079] Figure 2 It is a self-developed software interface that can be used for the simulation of spontaneous combustion of combustible oxidation after initialization;

[0080] Figure 3 Set the column for parameters;

[0081] Figure 4 It is the fitting curve diagram of coal body porosity and permeability;

[0082] Figure 5 It is the curve diagram of the thermal conductivity of coal under different axial loads;

[0083] Figure 6 It is the fitting curve of oxygen consumption rate under different axial loads;

[0084] Figure 7 The fitting curve of CO generation rate changing with temperature under different axial loads;

[0085] Figure 8 It is the fitting curve of CO2 generation rate changing with temperature under different axial loads;

[0086] Fig. 9 It is the fitting curve diagram of the heat release intensity of coal body changing with temperature under different axial loads;

[0087] Fig.10 This is a comparison of oxygen concentration results and error analysis diagram during the experiment and simulation process;

[0088] Fig.11 This is a diagram showing the change of coal body axial deformation over time during the experiment and numerical simulation process;

[0089] Fig.12 It is the curve diagram of the change of coal body axial deformation with time under different axial loads;

[0090] Fig.13It is the curve diagram of the change of coal body porosity with time under different axial loads;

[0091] Fig.14 It is the curve diagram of coal permeability changing with time under different axial loads;

[0092] Fig.15 This is the trend diagram of the average oxygen consumption rate of coal under different axial loads over time;

[0093] Fig.16 This is the trend diagram of the average temperature of coal body changing with time under different axial loads;

[0094] Fig.17 This is the trend diagram of the average CO concentration of coal body changing with time under different axial loads;

[0095] Fig.18 It is the trend diagram of average CO2 concentration of coal body changing with time under different axial loads;

[0096] Fig.19 This is a graph showing the change trend of the average heat release intensity of coal under different axial loads over time. DETAILED DESCRIPTION

[0097] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0098] It should be noted that the illustrations provided in the following embodiments are only used to illustrate the basic concept of the present invention in a schematic manner. Therefore, the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0099] In the following description, numerous details are discussed to provide a more thorough explanation of the embodiments of the present invention. However, it is obvious to those skilled in the art that the embodiments of the present invention can be implemented without these specific details. In other embodiments, well-known structures and devices are shown in the form of block diagrams rather than in detail to avoid making the embodiments of the present invention difficult to understand.

[0100] See also Figures 1 to 19The present invention provides a method for simulating the oxidation and spontaneous combustion of loose combustibles under pressure based on CFD numerical simulation. The method is a method for simulating the oxidation and spontaneous combustion of loose combustibles under pressure based on CFD numerical simulation. Specifically, the method includes the following specific steps:

[0101] S1. Pressure oxidation spontaneous combustion test of combustible materials, physical and chemical property test of combustibles, oxidation test of loose combustibles under different pressure conditions, collection and monitoring of physical parameters such as axial displacement, permeability, porosity and temperature change;

[0102] In this embodiment, the conditions for the spontaneous combustion of combustibles under pressure oxidation are systematically analyzed. The oxidation conditions of the combustibles need to be strictly controlled during the experiment. The ventilation volume and oxygen concentration during the experiment can be controlled. The test equipment includes a high-precision temperature sensor and a gas analyzer, which can monitor the changes in temperature and gas components during the reaction in real time. The porosity and permeability of the sample after pressure are measured to fully understand the changes in its internal structure under different pressure conditions. These data will serve as an important basis for the input parameters in the subsequent CFD simulation.

[0103] Specifically, different combustibles (such as coal, dead leaves, etc.) are selected to ensure that the samples are representative in terms of physical properties (such as particle size, density). For coal samples, the particle size should be controlled between 1-10 mm. The samples are pretreated and dried in an oven at 70 ° C for 24 hours to remove moisture and ensure that the moisture content of the samples does not exceed 5%. The industrial analysis, elemental analysis, density, thermal conductivity, and specific heat capacity results of the combustibles are tested. Subsequently, a pressure oxidation spontaneous combustion experiment is carried out on the combustibles. Multi-point temperature sensors (such as thermocouples) are configured to monitor the temperature in real time at different positions (top, middle, and bottom) of the reactor. Different pressure conditions are set (such as 0.1MPa, 0.5MPa, 1.0MPa, 1.5MPa, 2MPa), and the gas pressure and flow rate in the reactor are accurately adjusted by the gas controller. Data such as temperature, gas concentration (O2, CO, CO2, etc.), stress, and reaction time are collected in real time, stored using a data acquisition system, and the data acquisition frequency is ensured to reach once per second.

[0104] S2. Calculate the parameters of the pressurized oxidation spontaneous combustion of combustible materials, collect the temperature, gas concentration, pressure and other parameter data of the combustibles in real time during the experiment through sensors, process and analyze these data to obtain key parameters such as thermal conductivity, heat release intensity, oxygen consumption rate and gas production rate;

[0105] Data acquisition requires high-frequency sampling to capture important transient characteristics during the spontaneous combustion process. By correlating the collected temperature, gas concentration, and pressure data with the experimental time series, a kinetic model of the spontaneous combustion reaction can be established. This model can be used to calculate parameters such as thermal conductivity and heat release intensity, thereby providing accurate boundary conditions and initial conditions for subsequent numerical simulations. Specifically, the collected temperature, gas concentration, pressure and other data are processed to remove noise and outliers to ensure the accuracy of the data. The thermal conductivity, heat release intensity, oxygen consumption rate, and gas production rate are calculated from the above data. The kinetic model of oxidative spontaneous combustion is established using the obtained thermal conductivity, heat release intensity, oxygen consumption rate, and gas production rate data. The Arrhenius equation or other reaction kinetic models are used to describe the relationship between temperature and reaction rate for subsequent data analysis and simulation.

[0106] S3, fitting the relationship between oxidation self-ignition parameters and temperature, and fitting the functional relationship between heat release intensity, oxygen consumption rate and gas production rate and the temperature of the combustible object according to experimental data;

[0107] According to the experimental data, the functional relationship between the heat release intensity, oxygen consumption rate and gas production rate and the temperature of the combustible is fitted to establish a mathematical model of the spontaneous combustion process. The purpose of this step is to clarify the quantitative relationship between temperature and key thermodynamic parameters in the oxidation spontaneous combustion process to ensure the accuracy of the spontaneous combustion process evaluation. Specifically, a suitable mathematical model is selected for fitting according to the data characteristics. Commonly used models include linear regression, polynomial regression, exponential regression and nonlinear regression. For each parameter, a suitable model is selected for preliminary fitting, and a curve of heat release intensity, oxygen consumption rate and gas production rate changing with temperature is fitted. This curve can help further understand the effect of temperature change on the spontaneous combustion reaction rate. Calculate the correlation coefficient (R 2 ) and root mean square error (RMSE) to evaluate the quality of the fitting effect. 2 A value close to 1 indicates a good fitting effect, and a smaller RMSE value indicates a smaller fitting error. The fitting model is used for prediction of new experimental data and compared with the actual measured values ​​to verify the applicability of the model. If the prediction error is large, it is necessary to re-examine the selection of the fitting model and the adjustment of the parameters. The obtained mathematical model is used for the initial condition setting in the subsequent CFD simulation to ensure that the model reflects the effect of temperature changes on the reaction rate during the oxidation self-ignition process. During the simulation process, the model is used to adjust the parameters in real time to improve the accuracy and reliability of the simulation results.

[0108] S4. Establish a CFD numerical simulation model. Based on the physical and chemical properties of the combustibles and initial conditions, combined with experimental data, establish a multi-physical field coupled CFD numerical simulation model. This model not only takes into account the gas-solid two-phase flow, but also needs to simulate heat transfer, mass transfer and chemical reaction processes at the same time. Through the accurate description of the actual physical properties of the combustibles and experimental conditions, it is possible to achieve an accurate simulation of the oxidation and spontaneous combustion process of pressurized loose combustibles.

[0109] Arrange the basic physical and chemical properties of the combustibles, including density, thermal conductivity, specific heat capacity, reaction heat and other parameters, as inputs to the CFD model. Ensure that these parameters can reflect the actual situation and consider the changes under different temperatures and pressures. According to the experimental results, set the initial conditions of the simulation, including initial temperature, gas concentration, pressure and relative humidity. In particular, the setting of oxygen concentration needs to refer to the specific values ​​measured in the experiment to ensure the authenticity of the model. Use CFD software to establish a geometric model of the combustibles to ensure that the geometric shape is consistent with the experimental device. The geometric model should include the particle characteristics of loose combustibles and the structural characteristics of the pressure environment, and consider the porosity and arrangement between different particles. Set fluid mechanics equations (such as the Navier-Stokes equations) and heat conduction equations to simulate the interaction between gas flow and heat transfer. Consider the heat exchange between gas and solid particles to ensure that the transfer of reaction heat can be accurately reflected. Consider the interaction between reactants and products, and set the relationship between reaction rate and temperature and concentration to accurately simulate the oxidation self-ignition process.

[0110] According to the industrial analysis and elemental analysis results of the coal samples used in the experiment, the influence of N and S elements on the coal oxidation products can be ignored. On this basis, combined with previous studies, the chemical reaction kinetics of combustible oxidation was simplified and the equation for combustible oxidation was established:

[0111]

[0112] in, v CO Represent the stoichiometric coefficients of O2, CO2, and CO respectively.

[0113] The Arrhenius equation is used to calculate the oxidation rate of combustibles:

[0114]

[0115] Where: Α is the pre-exponential factor; E is the apparent activation energy, kJ / mol. The consumption rate of a specific gas can be determined by the following formula:

[0116]

[0117] Where: V represents the reaction rate of combustibles or gases, kg / (m3 ·s); M represents the molar mass of the combustible or gas, kg / mol. The heat released during the oxidation of the combustible can be calculated by the following formula:

[0118] Q c =V c ΔH c

[0119] The low-temperature oxidation process of pressurized and crushed combustible objects involves the oxidation of combustibles, the transfer of heat, and the diffusion and movement of gases, and multiple factors are coupled with each other. In CFD numerical simulation, the heat and mass transfer process in the combustible object must establish control equations based on the conservation of mass, energy, and momentum. The numerical model is established after comprehensively considering the transfer process of mass, energy, momentum, and chemical reactions in the model.

[0120]

[0121] (ρC p ) eff =θ c ρ p C p,c +(1-θ c )ρC p

[0122]

[0123] Where: ρ represents the density of the gas, kg / m 3 ; C p Indicates the constant pressure specific heat capacity of gas, J / (kg·K); (ρC p ) eff It represents the average effective volume heat capacity of solid and gas at constant pressure, J / (m 3 K); is the conduction heat flux, W / m 2 ; represents the velocity vector, m / s; θ c represents the volume fraction of coal, %; λ represents the thermal conductivity, W / (m·K).

[0124] The accumulation of broken combustible particles is a porous medium, and the flow process of gas between combustible objects can be regarded as a porous medium seepage process. The kinetic energy of the fluid comes from the fluid velocity, pressure and gravity of the driving fluid, and this process can be described by the Brinkman equation. In addition, the flow rate of the fluid through the porous medium is related to the permeability characteristics, pressure distribution and viscosity of the porous medium. Based on the assumption in this study that the combustible object is an isotropic uniform porous medium, the fluid flow process between coal bodies can be expressed by the equation:

[0125]

[0126] Where: ε represents the porosity of the combustible; V c Indicates the reaction rate of combustibles, kg / (m 3 ·s); κ represents permeability, m 2 ; μ represents the dynamic viscosity coefficient of the gas, Pa·S; p represents the pressure, Pa; Q br Indicates mass source, kg / (m 3 ·s); ρ b ,ρ c Respectively represent the bulk density and the density of the combustible material, kg / m 3 .

[0127] The production and consumption of various components in the combustion process are calculated by the following formula:

[0128]

[0129] in: Indicates mass flux, kg / (m 2 ·s);c j Indicates gas concentration, mol / m 3 ; r c represents the median diameter of the combustible particles; D represents the diffusion coefficient of the gas, m 2 / s.

[0130] S5, CFD numerical simulation calculation, divide the calculation grid according to the geometric size of the simulation model, set the simulation boundary conditions and initial conditions, and perform CFD numerical simulation calculation;

[0131] According to the geometric dimensions of the simulation model, the computational grid is divided, the simulation boundary conditions and initial conditions are set, and CFD numerical simulation calculations are performed. Based on experimental data and actual working conditions, the CFD numerical simulation model adopts a multi-physics field coupling model, taking into account multiple factors such as gas-solid two-phase flow, heat conduction, and chemical reactions to ensure the accuracy and reliability of the simulation results. By simulating the oxidation and spontaneous combustion process of combustibles under different pressure conditions, key thermodynamic and kinetic data, including temperature fields and gas concentration fields, are obtained. Appropriate grid division techniques, such as structured grids or unstructured grids, are required to ensure a balance between computational accuracy and computational efficiency. At the same time, appropriate turbulence models and chemical reaction models are selected to ensure the correct description of turbulence effects and combustion reactions during the simulation process. Through simulation calculations, the temperature distribution and gas concentration distribution at each moment are obtained to analyze the temperature and concentration changes in different regions during the spontaneous combustion process.

[0132] Specifically, determine the CFD software to be used and ensure that the software supports the required multi-physics field coupling and chemical reaction simulation. Mesh the established geometric model to ensure that the mesh is detailed enough to capture the physical phenomena in the key areas. Use structured or unstructured grids and select the appropriate division method according to the characteristics of the flow field. Before calculation, perform a grid quality check to evaluate parameters such as grid smoothness, deviation, and distortion to ensure that the grid quality meets the calculation requirements. Apply the boundary conditions set in step S4 to the simulation model to ensure that conditions such as gas flow rate, temperature, and pressure are in line with the actual situation. Verify the setting of initial conditions to ensure that all parameters (such as gas concentration, temperature, etc.) are correctly applied at the beginning of the simulation.

[0133] S6. Analysis of the simulation results of oxidation spontaneous combustion characteristics, output of the three-dimensional dynamic distribution diagram of the temperature field, thermal conductivity field, permeability field, heat release intensity field and gas concentration field during the simulation process, and analysis of the simulation results to obtain the oxidation spontaneous combustion characteristics of pressurized loose combustibles. The simulation results output includes temperature cloud map, thermal conductivity cloud map, permeability cloud map, heat release intensity cloud map and gas flow rate cloud map, and the results can be used to evaluate the oxidation spontaneous combustion state of pressurized loose combustibles in real time.

[0134] Specifically, the visualization tools built into the CFD software are used to generate a three-dimensional dynamic distribution diagram to show the changes in the temperature field, gas concentration field, and pressure field. A change cloud map is generated to show the changes in temperature, heat release intensity, and gas concentration at different locations. A slice diagram is made to analyze the distribution of physical quantities in a specific plane to more intuitively observe the characteristics of the reaction zone. Key parameters such as maximum temperature, maximum gas concentration, and maximum reaction rate are extracted from the simulation results for quantitative analysis. The time-varying curves of temperature, gas concentration, and other key parameters are analyzed to identify the critical moments and critical points of the reaction. The CFD simulation results are compared with the experimental data obtained in step S1 to evaluate the accuracy and reliability of the model. For the differences that exist, possible causes are analyzed, and the model parameters are adjusted based on feedback to improve the accuracy of the model. Based on the analysis results, the oxidation and spontaneous combustion characteristics of pressurized loose combustibles are summarized, including the spontaneous combustion temperature range, gas release characteristics, and reaction rate.

[0135] In the above embodiments, the description's reference to "this embodiment" indicates that a particular feature, structure, or characteristic described in conjunction with the embodiment is included in at least some embodiments, but not necessarily all embodiments. Multiple occurrences of "this embodiment" do not necessarily all refer to the same embodiment.

[0136] In the above-described embodiments, although the invention has been described in conjunction with specific embodiments of the invention, many substitutions, modifications, and variations of these embodiments will be apparent to those of ordinary skill in the art based on the foregoing description. For example, other storage structures (e.g., dynamic RAM (DRAM)) may use the embodiments discussed. Embodiments of the invention are intended to encompass all such substitutions, modifications, and variations that fall within the broad scope of the appended claims.

[0137] This embodiment further provides a computer-readable storage medium on which a computer program is stored. When the program is executed by a processor, any one of the methods in this embodiment is implemented.

[0138] This embodiment also provides an electronic terminal, including: a processor and a memory;

[0139] The memory is used to store a computer program, and the processor is used to execute the computer program stored in the memory, so that the terminal executes any one of the methods in this embodiment.

[0140] The computer-readable storage medium in this embodiment can be understood by ordinary technicians in this field: all or part of the steps of implementing the above-mentioned method embodiments can be completed by hardware related to the computer program. The aforementioned computer program can be stored in a computer-readable storage medium. When the program is executed, the steps of the above-mentioned method embodiments are executed; and the aforementioned storage medium includes: ROM, RAM, magnetic disk or optical disk and other media that can store program codes.

[0141] The electronic terminal provided in this embodiment includes a processor, a memory, a transceiver and a communication interface. The memory and the communication interface are connected to the processor and the transceiver and complete communication with each other. The memory is used to store computer programs, the communication interface is used to communicate, and the processor and the transceiver are used to run computer programs so that the electronic terminal executes each step of the above method.

[0142] In this embodiment, the memory may include a random access memory (RAM), and may also include a non-volatile memory (non-volatile memory), such as at least one disk memory.

[0143] The above-mentioned processor can be a general-purpose processor, including a central processing unit (CPU), a network processor (NP), etc.; it can also be a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components.

[0144] The present invention can be used in many general or special computing system environments or configurations, such as personal computers, server computers, handheld or portable devices, tablet devices, multiprocessor systems, microprocessor-based systems, set-top boxes, programmable consumer electronic devices, network PCs, minicomputers, mainframe computers, distributed computing environments including any of the above systems or devices, and the like.

[0145] The present invention may be described in the general context of computer-executable instructions executed by a computer, such as program modules. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform specific tasks or implement specific abstract data types. The present invention may also be practiced in distributed computing environments where tasks are performed by remote processing devices connected through a communication network. In a distributed computing environment, program modules may be located in local and remote computer storage media, including storage devices.

[0146] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A method for simulating the oxidation and spontaneous combustion of pressurized loose combustibles based on CFD numerical simulation, characterized by: The following steps are involved: S1: Conduct physical and chemical property tests on combustibles, conduct oxidation experiments on loose combustibles under different pressure conditions, and collect physical parameters; S2: Real-time collection of the temperature, gas concentration, and pressure parameters of the combustibles during the experiment, and calculation of the pressure-bearing oxidation and spontaneous combustion parameters of the combustible materials; S3: Fitting the functional relationship between oxidation auto-ignition parameters and the temperature of the combustible object; S4: Based on the physical and chemical properties of combustibles and initial conditions, combined with experimental data, a multi-physics field coupled CFD numerical simulation model is established; S5: Divide the computational grid according to the geometric dimensions of the simulation model, set the simulation boundary conditions and initial conditions, and perform CFD numerical simulation calculations; S6: Output the three-dimensional dynamic distribution diagram of the temperature field, thermal conductivity field, permeability field, heat release intensity field and gas concentration field during the simulation process, and analyze the simulation results to obtain the oxidation and spontaneous combustion characteristics of pressurized loose combustibles.

2. The method for simulating oxidation and spontaneous combustion of pressurized loose combustibles based on CFD numerical simulation according to claim 1 is characterized in that: Step S1 specifically includes the following steps: Select different combustibles for pretreatment; Test the industrial analysis, elemental analysis, density, thermal conductivity, and specific heat capacity of combustibles; Carry out pressure oxidation spontaneous combustion experiments on combustibles, configure multi-point temperature sensors, and monitor the temperature in real time at different positions of the reactor; set different pressure conditions, and accurately adjust the gas pressure and flow in the reactor through the gas controller; collect temperature, gas concentration, stress and reaction time in real time; S14: Store the collected data.

3. The method for simulating oxidation and spontaneous combustion of pressurized loose combustibles based on CFD numerical simulation according to claim 1 is characterized in that: Step S2 specifically includes the following steps: Preprocess the collected temperature, gas concentration and pressure data; Calculate the thermal conductivity, heat release intensity, oxygen consumption rate and gas production rate using the data preprocessed in step S21; The kinetic model of oxidation spontaneous combustion was established using the obtained data of thermal conductivity, heat release intensity, oxygen consumption rate and gas production rate. The Arrhenius equation or other reaction kinetic models are used to describe the relationship between temperature and reaction rate.

4. The method for simulating oxidation and spontaneous combustion of pressurized loose combustibles based on CFD numerical simulation according to claim 1 is characterized in that: Step S3 specifically includes the following steps: Select a suitable mathematical model for preliminary fitting based on data characteristics; Calculate the correlation coefficient and root mean square error of the fitting results to evaluate the quality of the fitting effect; Use the fitted model to predict new experimental data, compare with the actual measured values, verify the applicability of the model, and select the best model; The best model obtained was used to set the initial conditions in the CFD simulation to ensure that the model reflects the effect of temperature changes on the reaction rate during the oxidation auto-combustion process; During simulation, the best model is used to adjust parameters in real time.

5. The method for simulating oxidation and spontaneous combustion of pressurized loose combustibles based on CFD numerical simulation according to claim 1 is characterized in that: Step S4 specifically includes the following steps: Arrange the basic physical and chemical properties of combustibles, including density, thermal conductivity, specific heat capacity, and reaction heat, as inputs to the CFD model; According to the experimental results, the initial conditions of the simulation are set, including the initial temperature, gas concentration, pressure and relative humidity; Use CFD software to establish a geometric model of the combustible material to ensure that the geometric shape is consistent with the experimental device; the geometric model includes the particle characteristics of the loose combustible material and the structural characteristics of the pressure environment, taking into account the void ratio and arrangement between different particles; Set up fluid mechanics equations and heat conduction equations to simulate the interaction of gas flow and heat transfer; Consider the heat exchange between gas and solid particles to ensure that the transfer of reaction heat can be accurately reflected; The interaction between reactants and products is considered, and the relationship between reaction rate, temperature and concentration is set to accurately simulate the oxidation self-combustion process.

6. The method for simulating oxidation and spontaneous combustion of pressurized loose combustibles based on CFD numerical simulation according to claim 5 is characterized in that: In step S4, the equation for the oxidation of combustibles is: in, v CO Represent the stoichiometric coefficients of O2, CO2, and CO respectively; The Arrhenius equation is used to calculate the oxidation rate of combustibles: Where A is the pre-exponential factor; E is the apparent activation energy, kJ / mol; the consumption rate of a specific gas is determined by the following formula: Where V represents the reaction rate of combustibles or gases, kg / (m 3 ·s); M represents the molar mass of the combustible or gas, kg / mol; the heat released during the oxidation of the combustible is calculated by the following formula: Q c =V c ΔH c The numerical model is established after comprehensively considering the transfer process of mass, energy, momentum and chemical reactions in the model: (ρC p ) eff =θ c r p C p,c +(1-θ c )ρC p Where ρ represents the density of the gas, kg / m 3 ; C p Indicates the constant pressure specific heat capacity of gas, J / (kg·K); (ρC p ) eff It represents the average effective volume heat capacity of solid and gas at constant pressure, J / (m 3 K); is the conduction heat flux, W / m 2 ; represents the velocity vector, m / s; θ c represents the volume fraction of coal, %; λ represents the thermal conductivity, W / (m·K); Where ε represents the porosity of the combustible; V c Indicates the reaction rate of combustibles, kg / (m 3 ·s); κ represents permeability, m 2 ; μ represents the dynamic viscosity coefficient of the gas, Pa·S; p represents the pressure, Pa; Q br Indicates mass source, kg / (m 3 ·s); ρ b ,ρ c Respectively represent the bulk density and the density of the combustible material, kg / m 3 ; The production and consumption of various components in the combustion process are calculated by the following formula: in: Indicates mass flux, kg / (m 2 ·s);c j Indicates gas concentration, mol / m 3 ; r c represents the median diameter of the combustible particles; D represents the diffusion coefficient of the gas, m 2 / s.

7. The method for simulating oxidation and spontaneous combustion of pressurized loose combustibles based on CFD numerical simulation according to claim 1 is characterized in that: Step S5 specifically includes the following steps: Mesh the established geometric model to ensure that the mesh is detailed enough to capture the physical phenomena in the key areas; Use structured or unstructured grids and select the appropriate division method according to the characteristics of the flow field; Before calculation, perform mesh quality check to evaluate mesh smoothness, deviation and distortion; Apply the boundary conditions set in step S4 to the simulation model to ensure that the gas flow rate, temperature, pressure and other conditions are consistent with the actual situation; Verify the setup of initial conditions to ensure that all parameters are applied correctly at the start of the simulation.

8. The method for simulating oxidation and spontaneous combustion of pressurized loose combustibles based on CFD numerical simulation according to claim 1 is characterized in that: Step S6 specifically includes the following steps: Use the visualization tools of CFD software to generate three-dimensional dynamic distribution diagrams to show the changes in temperature field, gas concentration field and pressure field; Generate a cloud diagram to show the changes in temperature, heat release intensity and gas concentration at different locations; Make slice diagrams to analyze the distribution of physical quantities in a specific plane; Extract key parameters from simulation results and conduct quantitative analysis; Analyze the time-varying curves of temperature, gas concentration and other key parameters to identify the critical moments and critical points of the reaction; Compare the CFD simulation results with the experimental data obtained in step S1 to evaluate the accuracy and reliability of the model; Analyze the possible causes of the existing differences and adjust the model parameters based on the feedback to improve the accuracy of the model; Based on the analysis results, the oxidation and spontaneous combustion characteristics of pressurized loose combustibles are summarized, including the spontaneous combustion temperature range, gas release characteristics and reaction rate.

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