A numerical simulation method and system for underground coal gasification process

Abstract

The application discloses a numerical simulation method and system for a coal underground gasification process and belongs to the technical field of energy development. The method comprises the following steps: constructing a conceptual model of a gasification cavity, a cavity wall and a raw coal three-zone; establishing a kinetic model coupled with five types of chemical reactions (complete oxidation, steam conversion, Boudouard reaction, hydrogen gasification and water gas shift); correlating the porosity change and the cavity wall temperature gradient distribution; realizing the dynamic evolution prediction of a semi-teardrop-shaped gasification cavity through a numerical process of cyclically updating the porosity, marking the cavity, calculating the reaction and outputting the synthesis gas; and generating the cavity shape and the synthesis gas component curve based on a multi-module system (data preparation, numerical calculation, result analysis and visualization). The application solves the problem of insufficient simulation precision of the gasification cavity evolution in the prior art and is suitable for UCG engineering design and safety evaluation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy development and utilization, in particular to a numerical simulation method system for underground coal gasification process, which is used for obtaining the gasification cavity morphology, belongs to the technical field of underground coal gasification process modeling and simulation, has the characteristics of coupled simulation of heat and mass transfer and chemical reaction, and is suitable for engineering design, process optimization and safety evaluation of underground coal process. BACKGROUND

[0002] With the decreasing reserves of conventional fossil energy and the increasing global environmental protection standards, how to realize the efficient and clean utilization of coal resources has become a technical problem to be solved in the energy field. Underground coal gasification (UCG) technology, as a kind of thermo-chemical processing method that can realize in-situ conversion of coal seam by bypassing the traditional mining process, has received widespread attention in recent years. The technology injects gasification agents (such as oxygen, steam or air) into underground coal seams, induces combustion and gasification reactions of coal under controlled geological and operating conditions, and generates combustible synthesis gas containing methane (CH4), hydrogen (H2) and carbon monoxide (CO).

[0003] Hydrogen, as a clean energy carrier with zero carbon emissions and high energy density, is gradually regarded as a substitute for fossil fuels. UCG not only can develop deep or thin coal seam resources that are difficult to access by traditional mining methods, but also can achieve underground storage of part of the pollutants through collaborative operation with geological storage, providing support for carbon dioxide emission reduction.

[0004] However, the underground coal gasification process has significant engineering complexity and multi-physical field coupling characteristics. The dynamic evolution behavior of the underground thermal reactor (gasification cavity) is significantly different from that of the ground gasification device, and its formation and expansion are influenced by multiple factors, including but not limited to: chemical reaction heat release, heat conduction, coal seam crack development, and thermal force spalling of rock, etc.

[0005] Currently, the research methods for UCG process mainly cover three dimensions: experimental research, numerical simulation and field monitoring. In the experimental research, the existing technology studies the influence of operating parameters such as well spacing, gas injection flow rate and temperature on the evolution of cavity morphology through indoor controllable simulation system. The research results show that the gas injection flow rate has a decisive influence on the expansion behavior of the cavity in the axial and radial directions, and the ash content of the coal seam has a restraining effect on the gasification reaction rate and the expansion range of the cavity. Specifically, at low oxygen injection rate, the gasification reaction is mainly concentrated in the local area of the cavity center, while high oxygen flow rate significantly expands the reaction influence range. In addition, coal seam physical parameters such as coal permeability, porosity and rock mechanical strength also play a key role in the dynamic evolution process of the cavity.

[0006] Existing monitoring methods mostly rely on indirect methods to estimate the volume of the cavity, such as back-calculation models based on the change in syngas yield or estimation models based on the coal seam loss on ignition. However, these methods often have large measurement errors and uncertainties when faced with the complex gas flow path and uneven distribution of the reaction zone in the UCG process.

[0007] In terms of mathematical modeling, equilibrium models are the basic tools for modeling the thermodynamic behavior of UCG. Such models assume that the system can reach a state of thermodynamic equilibrium under specific temperature and pressure conditions. Depending on the modeling approach, they can be divided into stoichiometric models and non-stoichiometric models. The former requires the definition of specific reaction paths and imposes constraints on the molar fraction of reactants or products, while the latter determines the composition of syngas based on the Gibbs free energy minimization criterion. This minimization operation can be achieved through direct methods or Lagrange multiplier methods, and is usually based on the assumption that the chemical reaction rate is infinitely fast. Although equilibrium models are computationally efficient, they have natural limitations in simulating the transient changes of reactants and products and the evolution of the cavity geometry.

[0008] To overcome the above shortcomings, kinetic models have been proposed to describe the dynamic process of coal gasification. Typical models include volume reaction models, shrinking core models, and random pore models. In volume reaction models, it is assumed that reactions occur uniformly throughout the entire coke bed region, and the reaction rate is linearly coupled with the specific surface area; the shrinking core model is suitable for spherical coal particles, and the reaction rate is controlled by chemical kinetics, internal diffusion, or external mass transfer processes; the random pore model introduces a pore overlap mechanism to enhance the representation of the structural characteristics of coal samples. However, most of the above kinetic models are limited to one-dimensional analysis frameworks, making it difficult to accurately predict the evolution path of the cavity or reproduce its geometric shape.

[0009] Numerical simulation models have become the most accurate and versatile modeling tools for simulating UCG processes due to their high representation ability in coupling heat, mass, momentum transport processes, and chemical kinetic mechanisms. The main numerical models include packed bed models, channel models, and coal plate models. The packed bed model assumes that gasification mainly occurs in the high-permeability zone between the wellbore composed of coal particles, and its modeling framework integrates mass and energy conservation equations, gas-solid reaction rate equations, and Darcy flow models; the channel model considers that the gasification zone expands along the internal channels of the coal seam, taking into account the lateral diffusion of the gasification agent and the backflow behavior of the product gas, and is suitable for simulating the spatiotemporal evolution of the cavity size and shape; the coal plate model simulates the advancement of multiple reaction fronts, which are divided into dry coal seams, coke zones, ash layers, etc., and is suitable for one-dimensional gasification process modeling under slow heating conditions.

[0010] Overall, although numerical models are superior to equilibrium and dynamic models in terms of accuracy and applicability, their mathematical modeling complexity is high, the computational load is large, and convergence and stability issues are prominent, which still pose significant technical challenges to the development of industrial-grade simulation platforms. Summary of the Invention

[0011] This invention aims to develop a numerical simulation method and system for underground coal gasification processes, addressing technical problems in existing UCG simulation technologies such as incomplete descriptions of chemical reactions, insufficient coupling of thermo-chemical processes, and limited accuracy in simulating the evolution of the gasification chamber and the dynamic behavior of syngas. This invention couples a kinetic model with a thermal model controlled by a temperature gradient. While maintaining the directness and efficiency of the kinetic model, it introduces numerical simulation techniques to effectively capture the evolution of the gasification chamber and the time-varying characteristics of syngas composition. This invention can more realistically reproduce key physical and chemical changes in the UCG process, providing theoretical support for subsequent engineering optimization and control strategies.

[0012] The technical solution of the present invention is as follows:

[0013] A numerical simulation method for underground coal gasification processes includes a UCG conceptual model, a UCG process mathematical model, a numerical solution method, and a UCG process numerical simulation process flow.

[0014] A conceptual model of the underground space during UCG operation, including the gasification chamber, gasification chamber sidewalls, raw coal, and a series of assumptions;

[0015] The UCG mathematical model describes a complex reaction process in UCG that considers chemical reactions, temperature distribution, and changes in physical properties. This model involves five representative chemical reactions modeled across the entire UCG process: complete oxidation, steam reforming, Boudouard reaction, hydrogenation, and water-gas shift reaction. The model also describes the relationship between porosity and solid density in the UCG process, the thermal behavior of the UCG system, the production rate, and the composition of the syngas.

[0016] Numerical solution methods, including a complete set of solution methods for established mathematical models;

[0017] The UCG process numerical simulation workflow involves a multi-module collaborative processing numerical simulation workflow and system, including a data preparation unit, a numerical calculation unit, a result analysis unit, and a visualization generation unit. It can accurately predict the evolution of the gasification chamber and gas composition, dynamically characterize the semi-teardrop-shaped gasification chamber characteristic of UCG, and realize the analysis of the effects of gasification chamber temperature, pressure, water-oxygen ratio, injection rate, temperature gradient, and their anisotropy on UCG efficiency.

[0018] In the above technical solution, the description of the three different sub-processes running by UCG is as follows:

[0019] First, the gasifying agent is injected into the cavity through the injection well. Then, a chemical reaction occurs in the gasification cavity, which is composed of the gasification cavity, the gasification cavity wall and the deposits. At this time, the raw coal undergoes transformations such as pyrolysis and gasification. The stress field in the gasification cavity wall changes, which in turn promotes the development of cracks and the stripping of coal seams. Finally, the syngas produced in the gasification process is discharged through the production well.

[0020] A conceptual model of the UCG's underground space operation, in which...

[0021] It includes three parts: the gasification chamber, the gasification chamber sidewalls, and the raw coal, as shown in the attached document. Figure 1 As shown, the dark gray grid at the bottom represents the gasification chamber, the darker gray grid around the gasification chamber represents the sidewall of the gasification chamber, and the light gray grid represents the raw coal.

[0022] The relevant model assumptions, among which,

[0023] The temperatures in the gasification chamber and the raw coal zone are known and uniformly distributed. The temperature at the gasification chamber wall is non-uniformly distributed with a constant temperature gradient. The multiphase and multicomponent free flow in the gasification chamber, the porous medium flow at the gasification chamber wall, and the coupling effect at the interface are ignored. Assuming constant and uniform pressure, homogeneous and heterogeneous reactions occur at the gasification chamber wall, while homogeneous reactions occur inside the gasification chamber. A chemical reaction kinetic model is used to describe the chemical reaction process, considering the porosity changes caused by solid consumption during the chemical reaction.

[0024] In the above technical solution, this method proposes a description of five representative chemical reactions to model the entire UCG process, including:

[0025] The complete oxidation reaction of coal (R1), in which,

[0026] Coal in the strata mixes with injected oxidant at high underground temperatures to induce a strong oxidation reaction. Solid carbon reacts with gaseous oxygen molecules on its surface to form gaseous product CO2.

[0027] The steam reforming reaction (R2) involves the following:

[0028] Solid coal components react with gasifying agents (such as steam, oxygen, or CO2) to produce combustible gases;

[0029] The Boudouard reaction (R3), in which...

[0030] This process is a highly reversible gas-solid heterogeneous reaction, and its reaction direction is significantly related to the system temperature. Under low temperature conditions, it tends to generate CO2, while under high temperature conditions, it promotes CO generation.

[0031] Hydrogenation reaction (R4), in which,

[0032] In this process, hydrogen reacts with solid carbon at high temperature to produce methane. This reaction is a solid-gas heterogeneous reaction, which is often limited by the gas diffusion rate, the carbon solidification reactivity and the temperature field distribution of the vaporization chamber.

[0033] Water-gas shift reaction (R5).

[0034] The mathematical modeling of the chemical reaction in the above technical solution includes:

[0035] The reaction process of coal combustion is as follows: ;

[0036] in, For chemical reaction rate, The interphase mass transfer coefficient is... It is the mole fraction;

[0037] The interphase mass transfer coefficient is: ,in, Indicates particle size, Indicates porosity. Indicates the apparent gas flow rate. , Indicates the first The concentration of the gaseous components, Indicates the first The molar heat capacity of each gas component It represents the kinetic viscosity of a gas and is a function of temperature and pressure;

[0038] ;

[0039] in, This indicates the density of charcoal. Indicates the pressure in the vaporization chamber. Defined as , and These represent the solid temperature and the fluid temperature, respectively. Take 1, therefore equal ;

[0040] The steam reforming reaction is as follows: ;

[0041] Among them, subscript Represents water components;

[0042] for: ;

[0043] Boudouard's reaction is: ;

[0044] for: ;

[0045] The hydrogenation reaction is as follows: ;

[0046] for: ;

[0047] The water-gas shift reaction is as follows: ;

[0048] for: , The concentration of water gas. This represents the concentration of carbon monoxide.

[0049] In the above technical solution, the chemical consumption of solid carbon leads to changes in porosity and a decrease in solid density.

[0050] The change in solid density is quantified using solid mass balance, where:

[0051] ;

[0052] in, Here is the molar mass of coke; For the reaction The stoichiometric coefficient of medium coke, For time, For the reaction The rate of chemical reaction.

[0053] In the above technical solution, the relationship between porosity and solid density during the UCG process is as follows:

[0054] ;

[0055] Where the subscript 0 indicates the initial condition, Porosity This is the density of the solid.

[0056] In the above technical solution, the thermal field is described by pre-defining a uniform temperature distribution inside the cavity and a non-uniform temperature distribution on the cavity wall.

[0057] The non-uniform distribution is characterized by a preset temperature gradient, which can be constant or variable. For a variable gradient, the temperature gradient varies with the distance between the target point and the cavity wall interface, thus providing a more accurate representation of the thermal behavior of the system, where:

[0058] ;

[0059] Among them, T cavity This represents the cavity temperature, and dis represents the shortest distance from the point of interest to the cavity-wall interface.

[0060] The above technical solution proposes a numerical calculation method for a UCG mathematical model, including:

[0061] Initialize the simulation parameters and predefine the gasification cavity grid in the geological model. At each time step, update the porosity and mark the gasification cavity grid (cells with porosity equal to 1 or exceeding a predetermined threshold).

[0062] Identify the cells adjacent to the vaporization chamber, calculate the temperature of the non-vaporization chamber mesh to identify the vaporization chamber wall mesh, update the component concentration in the vaporization chamber with the newly injected vaporizing agent, and determine the total pore volume of the vaporization chamber.

[0063] Furthermore, the specific numerical calculation method is as follows: initialize simulation parameters; set the step size n=n+1; update porosity and mark the cavity grid; identify the cells adjacent to the cavity; calculate the temperature of the non-cavity grid and identify the cavity wall grid; update the gasification cavity component concentration and total pore volume, determine the chemical reaction rate in the cavity and cavity wall grid, update the solid phase density; determine the synthesis gas production rate and composition.

[0064] In the above technical solution, it is assumed that the components are uniformly distributed inside and on the gasification chamber wall. Based on the kinetic model, the chemical reaction rates in the cavity and cavity wall grid are determined, the solid phase density is updated, and the productivity and composition of the syngas are determined, including:

[0065] The production rate is calculated, where:

[0066] ;

[0067] The total amount of the i-th gas is determined based on the reaction results, V tot C0 represents the total pore volume of the vaporization chamber, and C0 represents the gas phase concentration at a predetermined chamber pressure and temperature. Indicates the first The total amount of each gas Indicates a time step;

[0068] The composition of syngas is calculated, where:

[0069] ;

[0070] After producing syngas, the first The concentration of the gas is calculated, where:

[0071] .

[0072] The above technical solution proposes a numerical simulation process for UCG processes, specifically involving a numerical simulation method and system based on multi-module collaborative processing, including a data preparation unit, a numerical calculation unit, a result analysis unit, and a visualization generation unit. It can accurately predict the evolution of the gasification chamber and gas composition, dynamically characterize the semi-teardrop-shaped gasification chamber characteristic of UCG, and realize the analysis of the effects of gasification chamber temperature, pressure, water-oxygen ratio, injection rate, temperature gradient, and their anisotropy on UCG efficiency.

[0073] In the above technical solution, the data preparation unit receives raw data from experimental tests, field monitoring, or user input, performs data cleaning and normalization processing, sets initial conditions, boundary conditions, physical property parameters, and numerical format parameters according to the needs of numerical simulation, and generates a standardized input dataset that meets the calculation requirements.

[0074] The above technical solution can obtain the two-dimensional and three-dimensional evolution process of gasification cavity, porosity and formation temperature during UCG, and can visualize the three-dimensional evolution process of semi-teardrop-shaped gasification cavity during UCG.

[0075] In the above technical solution, an analytical process is established to analyze the effects of cavity temperature, water-oxygen ratio, injection rate, and temperature gradient on the UCG process.

[0076] A numerical simulation system for underground coal gasification processes is provided, which uses the above-mentioned numerical simulation method to dynamically adjust the gasifying agent injection parameters to improve syngas yield.

[0077] Beneficial effects:

[0078] 1. Breakthrough in the accuracy of gasification chamber evolution prediction:

[0079] By constructing a three-zone conceptual model of "gasification chamber-chamber wall-raw coal" and combining it with a porosity dynamic update mechanism, a precise dynamic simulation of the semi-teardrop-shaped gasification chamber morphology was achieved, and the prediction error of the chamber boundary was better than that of the traditional model.

[0080] 2. Innovation in thermo-chemical coupling mechanism:

[0081] A coupling framework was established between five types of chemical reaction kinetic equations (complete oxidation, steam conversion, Boudouard reaction, hydrogenation, and water-gas shift) and a temperature gradient control model to solve the prediction bias of syngas components caused by neglecting heterogeneous reactions in the cavity walls in existing technologies.

[0082] 3. Improved computational efficiency and engineering applicability:

[0083] The design employs a cyclical process of "porosity update → cavity marking → reaction calculation". By marking the gasification cavity boundary using a grid, the amount of unnecessary calculations is reduced, and the simulation speed is improved compared to traditional methods, providing real-time data support for optimizing on-site injection schemes.

[0084] 4. Enhanced ability to prevent and control safety risks:

[0085] By accurately simulating the heat transfer process of the cavity wall using a temperature gradient model, the diffusion range of the high-temperature zone can be predicted, and the risk of coal seam collapse can be warned in advance, providing a key theoretical tool for the safety assessment of UCG projects. Attached Figure Description

[0086] Figure 1 : Schematic diagram of the UCG conceptual model structure.

[0087] Figure 2 UCG numerical calculation flowchart.

[0088] Figure 3 : Overall flowchart of the UCG numerical simulation method.

[0089] Figure 4 : Three-dimensional evolution diagram of the semi-teardrop-shaped vaporization cavity.

[0090] Figure 5 : Dynamic evolution curve of syngas components. Detailed Implementation

[0091] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. However, the following embodiments are only for explaining the present invention, and the scope of protection of the present invention should include all the contents of the claims. Moreover, through the description of the following embodiments, those skilled in the art can fully implement all the contents of the claims of the present invention.

[0092] Example 1:

[0093] This embodiment aims to describe in detail a numerical simulation method and system for underground coal gasification processes, including: a UCG conceptual model, a UCG mathematical model, a numerical solution method, and a numerical simulation process.

[0094] (1) UCG conceptual model:

[0095] UCG operation can be divided into three distinct sub-processes. First, the gasifying agent is injected into the gasification chamber through an injection well. Subsequently, a chemical reaction occurs within the gasification chamber, its walls, and the coal fragments. During this process, the raw coal undergoes pyrolysis and gasification, altering the stress field within the chamber walls and promoting fracture development and coal seam exfoliation. Finally, the syngas produced during the gasification process is discharged through a production well. This invention simplifies the underground space into three parts: the gasification chamber, the chamber walls, and the raw coal. Figure 1 As shown, the dark gray grid at the bottom represents the gasification chamber, the darker gray grid around the gasification chamber represents the sidewall of the gasification chamber, and the light gray grid represents the raw coal.

[0096] The model makes the following assumptions: the temperatures in the gasification chamber and the raw coal zone are known and uniformly distributed; the temperature at the gasification chamber wall is non-uniformly distributed with a constant temperature gradient; the multiphase and multicomponent free flow within the gasification chamber, the porous medium flow at the gasification chamber wall, and the coupling effect at the interface are ignored; the pressure is assumed to be constant and uniform; homogeneous and heterogeneous reactions occur at the gasification chamber wall, while homogeneous reactions occur inside the gasification chamber; a chemical reaction kinetic model is used to describe the chemical reaction process; and the porosity change caused by solid consumption during the chemical reaction process is considered.

[0097] (2) UCG mathematical model:

[0098] This invention relates to a method for describing complex reaction processes that consider chemical reactions, temperature distribution, and changes in physical properties. This method models the entire UCG process using five representative chemical reactions, as listed in Table 1. Reactions R1 to R4 are heterogeneous reactions, occurring both on the inner surface (i.e., the cavity wall) and within the cavity space. Homogeneous reactions refer to reactions where reactants and products are in different phases (e.g., gas-solid, gas-liquid). The reaction rate is controlled by interfacial mass transfer, the distribution of surface active sites, and local temperature changes, exhibiting strong spatial distribution characteristics and wall dependence. R1 represents the complete oxidation of coal, in which coal in the formation mixes with injected oxidant at high underground temperatures, resulting in a strong oxidation reaction. Solid carbon reacts with gaseous oxygen molecules on its surface to form the gaseous product CO2. This process exhibits significant interfacial control characteristics, with the combustion rate controlled by factors such as gas diffusion, formation temperature, and surface activity. R2 represents the steam reforming reaction, in which solid coal components react with a gasifying agent (such as steam, oxygen, or CO2) to produce combustible gas. This process is essentially a combination of a series of heterogeneous reactions, and the gas composition is closely related to the operating temperature, the type of gasifying agent, and the reactivity of the coal. R3 represents the Boudouard reaction, a highly reversible gas-solid heterogeneous reaction whose reaction direction is significantly related to the system temperature. Under low temperatures, it tends to produce CO2, while under high temperatures, it promotes CO production. In actual coal gasification and pyrolysis systems, the reduction reaction participates in the regulation of gas composition and the optimization of carbon conversion efficiency. R4 represents the hydrogenation reaction, in which hydrogen reacts with solid carbon under high temperatures to produce methane. This reaction is a solid-gas heterogeneous reaction, often limited by the gas diffusion rate, the activity of carbon fixation reactivity, and the temperature field distribution in the gasification chamber. R5 represents the water-gas shift reaction, a homogeneous reaction that occurs only within the chamber.

[0099] The above-described reaction couples the heat and mass transfer behavior within the system with the changes in physical properties caused by the chemical reaction during the reaction process, enabling a precise description of the dynamic evolution of the reaction system within the cavity. This method allows for the systematic analysis and process optimization of multi-field coupled behavior in complex UCG reaction systems.

[0100] Table 1 Chemical Reactions in UCG

[0101]

[0102] In this invention, the kinetic model is used for mathematical modeling of chemical reactions. The complete oxidation reaction of coal is as follows:

[0103] (1)

[0104] in, For chemical reaction rate, The interphase mass transfer coefficient is... The mole fraction is defined as follows:

[0105] (2)

[0106] (3)

[0107] in, Indicates particle size; Indicates porosity; Indicates apparent gas velocity; , Indicates the first The concentration of the gaseous components, Indicates the first The molar heat capacity of each gas component; It represents the dynamic viscosity of a gas and is a function of temperature and pressure. It is expressed as follows:

[0108] (4)

[0109] in, Indicates the density of charcoal; Indicates the pressure in the vaporization chamber; Defined as , and These represent the solid temperature and the fluid temperature, respectively. In this invention... Take 1, therefore equal The steam vaporization reaction formula is as follows:

[0110] (5)

[0111] Among them, subscript Represents water components; It is expressed as follows:

[0112] (6)

[0113] The Boudouard reaction is given by the following equation:

[0114] (7)

[0115] in, Written as:

[0116] (8)

[0117] The hydrogenation reaction is as follows:

[0118] (9)

[0119] in, Written as:

[0120] (10)

[0121] The water-gas shift reaction is as follows:

[0122] (11)

[0123] in, Written as:

[0124] (12)

[0125] The chemical consumption of solid-phase carbon leads to changes in porosity and a decrease in solid density. Solid mass balance is used to quantify changes in solid density.

[0126] (13)

[0127] in, Here is the molar mass of coke; For the reaction The stoichiometric coefficient of medium-density coke. The relationship between porosity and solid density during the UCG process is defined as follows:

[0128] (14)

[0129] Here, the subscript 0 indicates the initial conditions. The thermal field is described by predefining a uniform temperature distribution within the cavity and a non-uniform temperature distribution on the cavity walls. The non-uniform distribution is characterized by a preset temperature gradient, which can be constant or variable. For a variable gradient, the temperature gradient varies with the distance between the target point and the cavity wall interface, thus allowing for a more accurate representation of the thermal behavior of the system.

[0130] (15)

[0131] in, Indicates the cavity temperature; This represents the shortest distance from the research point to the interface between the cavity and its wall.

[0132] (3) Numerical calculation method:

[0133] Figure 2 A flowchart illustrating the numerical implementation process is provided. First, simulation parameters are initialized, and the gasification cavity grid in the geological model is predefined. At each time step, porosity is updated according to formula (14), and the gasification cavity grid (cells with porosity equal to 1 or exceeding a predetermined threshold) is marked. Subsequently, cells adjacent to the gasification cavity are identified, and the temperature of the non-gasification cavity grid is calculated according to formula (15), thereby identifying the gasification cavity wall grid. The component concentration within the gasification cavity is updated with the newly injected gasifying agent, and the total pore volume of the gasification cavity is determined. Assuming uniform component distribution within and on the gasification cavity wall, the chemical reaction rates in the cavity and cavity wall grid are determined according to the kinetic model described in the previous section, and the solid phase density is updated according to formula (13). Finally, the syngas productivity and composition are determined.

[0134] The details of production rate calculation are summarized below:

[0135] (16)

[0136] The total amount of the i-th gas is determined based on the reaction results; V tot C0 represents the total pore volume of the vaporization chamber; C0 represents the gas phase concentration at a predetermined chamber pressure and temperature. The composition of the syngas is calculated as follows:

[0137] (17)

[0138] After producing syngas, the concentration of the i-th gas needs to be updated:

[0139] (18)

[0140] (4) Numerical simulation process:

[0141] This invention further proposes a numerical simulation workflow for UCG processes. Specifically, it relates to a numerical simulation method and system based on multi-module collaborative processing, including a data preparation unit, a numerical calculation unit, a result analysis unit, and a visualization generation unit. This method can accurately predict the evolution of the gasification chamber and gas composition, dynamically characterize the characteristic semi-teardrop-shaped gasification chamber of UCG, and analyze the effects of gasification chamber temperature, pressure, water-oxygen ratio, injection rate, temperature gradient, and their anisotropy on UCG efficiency.

[0142] ① Data preparation unit:

[0143] The data preparation unit receives raw data from experimental tests, field monitoring, or user input; performs data cleaning and normalization; sets initial conditions, boundary conditions, physical property parameters, and numerical format parameters according to the needs of numerical simulation; and generates a standardized input dataset that meets the computational requirements. The main parameter sets and units prepared are shown in the table below:

[0144] Table 2 UCG Numerical Simulation Parameters

[0145]

[0146] ② Numerical calculation unit:

[0147] Based on the established mathematical model and numerical solution method of the UCG process, the numerical simulation calculation of the UCG process is performed according to the parameters in the data preparation unit.

[0148] ③ Results Analysis Unit:

[0149] Post-processing and statistical analysis of the numerical calculation data; extraction of key physical quantities (such as gas composition and vaporization chamber shape); parameter sensitivity analysis (such as vaporization chamber temperature, pressure, water-oxygen ratio, injection rate, and temperature gradient); generation of analysis reports or auxiliary decision-making data.

[0150] ④ Visualization generation unit:

[0151] Visualize the evolution of the vaporization chamber.

[0152] Example 2:

[0153] See Figure 3 This embodiment aims to describe in detail a numerical simulation method for a UCG process.

[0154] Start process 100, which includes step 101.

[0155] In step 101, the calculated data is summarized according to the given numerical simulation parameter table, unit conversion is completed, and process 100 ends. The calculated data includes parameters such as particle size, coke molar mass, coke density, coal seam size, initial porosity, coal seam temperature, gasification chamber pressure, gasification chamber temperature, initial gasification chamber grid ID (2D), initial chamber grid ID (3D), oxygen injection rate, steam injection rate, simulation time, time step, temperature gradient (2D), temperature gradient (3D), grid size (2D), grid size (3D), grid resolution (2D), and grid resolution (3D).

[0156] Start process 200, which includes steps 201, 202, and 203.

[0157] In step 201, the simulation parameters are initialized and the calculation step size is set.

[0158] In step 202, numerical simulation iterative calculations are completed according to the numerical calculation method in the invention, including porosity update, cavity grid marking, calculation of gasification cavity component concentration and solid density, etc.

[0159] In step 203, the simulation is performed up to the set reaction time to obtain the simulation calculation results.

[0160] Process 300 includes step 301, which can visualize the calculation results in process 200, including curve visualization, two-dimensional and three-dimensional visualization.

[0161] Start process 400, process 400 includes steps 401 and 402.

[0162] In step 401, the two-dimensional and three-dimensional evolution processes of the gasification cavity, porosity, and formation temperature during the UCG process can be obtained. Taking the three-dimensional evolution process of the gasification cavity as an example, such as... Figure 4 As shown, Figure 4 In the diagram, (a) represents the visualization results for 1 day, (b) represents the visualization results for 5 days, (c) represents the visualization results for 10 days, and (d) represents the visualization results for 15 days. Combined with process 300, the three-dimensional evolution process of the semi-teardrop-shaped vaporization chamber during UCG can be visualized.

[0163] In step 402, the transient behavior of the syngas and dried syngas during the UCG process, as well as the molar flow rate and mass flow rate of the syngas, can be obtained. Taking the transient behavior of the syngas as an example, such as... Figure 5 As shown, the evolution of syngas components can be observed by combining process 300.

[0164] Step 403 analyzes the effect of chamber temperature on the UCG process. In step 403, different chamber temperatures are set to perform the numerical calculations in process 200. Based on the dynamic composition of syngas (H2, CH4, CO2, H2O) and the mass flow rate of syngas in the UCG process at different chamber temperatures, the effect of chamber temperature on the UCG process is analyzed.

[0165] Step 404 analyzes the effect of the water-oxygen ratio on the UCG process. In step 404, different water-oxygen ratios are set to perform numerical calculations in process 200. Based on the dynamic composition of syngas (H2, CH4, CO2, H2O) and the mass flow rate of syngas in the UCG under different water-oxygen ratio conditions, the effect of the water-oxygen ratio on the UCG process is analyzed.

[0166] Step 405 analyzes the impact of the injection rate on the UCG process. In step 405, different injection rates are set to perform the numerical calculations in process 200. Based on the dynamic composition of syngas (H2, CH4, CO2, H2O) and the mass flow rate of syngas in the UCG under different injection rate conditions, the impact of the injection rate on the UCG process is analyzed.

[0167] Step 406 analyzes the effect of temperature gradient on the UCG process. In step 406, different temperature gradients are set to perform numerical calculations in process 200. Based on the dynamic composition of syngas (H2, CH4, CO2, H2O) and the mass flow rate of syngas in the UCG process under different temperature gradients, the effect of temperature gradient on the UCG process is analyzed.

[0168] Embodiments of the present invention may be implemented using software, hardware, firmware, or any combination thereof. In one embodiment, at least a portion of the invention may be implemented in the form of a computer-readable medium.

[0169] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A numerical simulation method for a coal underground gasification process, characterized in that, The method comprises: Step one, constructing a UCG conceptual model, dividing the underground space into three regions of gasification cavity, gasification cavity wall and raw coal; Step two, establishing a UCG mathematical model, coupling five chemical reaction kinetics equations, including: complete oxidation reaction, water vapor conversion reaction, Boudouard reaction, hydrogen gasification reaction, water gas shift reaction; Step three, performing a numerical solution method; (1) the change in solid density is quantified using solid mass balance, wherein, Mco is the molar mass of the coke; K is the reaction rate constant for the coke, ρs is the solid density, t is time, k is the chemical reaction rate for the reaction The relationship between porosity and solid density during the UCG process is wherein subscript 0 denotes initial conditions, φ is the porosity, ρs is the solid density; (2) the thermal field is described by predefining the uniform distribution of the temperature in the cavity and the non-uniform distribution of the temperature on the cavity wall, wherein, denotes the temperature of the cavity, denotes the shortest distance from the point of interest to the interface of the cavity and the cavity wall; (3) The numerical solution method is as follows: Initialize simulation parameters; Step size setting; Update porosity, mark cavity grid; Identify the cells adjacent to the cavity; Calculate the temperature of the non-cavity grid and identify the cavity wall grid; Update the gasification cavity component concentration and total pore volume, determine the chemical reaction rate in the cavity and cavity wall grid, and update the solid phase density; Determine the production rate and components of syngas; Step four, execute the UCG process numerical simulation process, based on a multi-module system to realize data preparation, numerical calculation, result analysis and visualization.

2. A numerical simulation method for underground coal gasification process according to claim 1, characterized in that, Assuming that the components in the gasification cavity and on the gasification cavity wall are uniformly distributed, the chemical reaction rate in the cavity and cavity wall grid is determined according to the kinetic model, the solid phase density is updated, and the production rate and components of syngas are determined, including: Calculation of production rate, wherein: ； wherein the first total amount of the gas is determined from the reaction results, represents the total pore volume of the gasification cavity, represents the gas phase concentration at a predetermined cavity pressure and temperature, represents the total amount of the first gas, represents the time step; Composition calculation of syngas, wherein: ； After the production of synthesis gas, the concentration of the first kind of gas is calculated, wherein: 。 3. A numerical simulation method for underground coal gasification process according to claim 1, wherein, The multi-module system comprises a data preparation unit, a numerical calculation unit, a result analysis unit and a visualization generation unit, which can accurately predict the evolution of the gasification cavity and the gas component, dynamically depict the characteristic semi-teardrop-shaped gasification cavity of UCG, and realize the analysis of the gasification cavity temperature, pressure, water-oxygen ratio, injection rate, temperature gradient and its anisotropy on the UCG efficiency.

4. The method for numerical simulation of underground coal gasification process according to claim 1, characterized in that, The method analyzes the effects of cavity temperature, water-oxygen ratio, injection rate, temperature gradient on the UCG process.

5. A numerical simulation system for a coal underground gasification process, characterized by, Apply the numerical simulation method of any one of claims 1-4 to dynamically control the injection parameters of the gasification agent to improve the syngas yield.

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