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煤炭是我国现阶段最重要的能源，并且我国陆上埋深1000～2000 m的深层煤炭资源量为 2.44万亿吨，是探明技术可采煤炭储量的12倍之多。但现阶段煤矿开采存在着开采深度浅、事故频发、回采率低、环境污染等问题。而煤炭地下气化技术是解决上述问题的有效采煤技术。该技术通过注气井往地下煤层中加入气化剂，使地层中的煤炭经过一系列的燃烧、气化反应，在煤层原位转化为氢气、甲烷等清洁合成气，并通过产气井导出合成气。以40%的能源转化率计算，煤炭地下气化技术可为中国提供足以使用数百年的清洁能源和丰富的化工原材料。为了加速我国煤炭地下气化商业化进程，需提高合成气的品质与产量。本文采用数值模拟的方法，通过构建涉及多孔介质渗流、质量传递、能量传递和化学反应多场耦合的多组分反应流气化腔模型，来预测煤炭地下气化的演化过程。本文对煤炭地下气化腔采取分步模拟的技术路线，获得了如下主要结果：

建立了恒温、无反应的多孔介质渗流、湍流与质量传递耦合气化腔模型，计算得到了气化腔内的流场特征和气体组分分布场特征，分析了气化腔内的流动与质量传递的演化过程。流场分布较为稳定，除出入口外，燃空区右下侧流动最为显著。初始时刻通入的气化剂在250 s时到达了焦炭区，700 s时到达了燃空区，2000 s时流经燃空区后回到了焦炭区，2300 s时到达了产气井。气化开始后的10000 s，注入的气化剂占据了整个煤炭地下气化腔。

建立了恒定热源功率密度、单组分、无反应的流动与能量传递耦合气化腔模型，分析了气化腔中热源功率密度、注气井通入气化剂的注入速度、多孔介质区域孔隙率等对气化腔内温度场的影响。得到了热源功率密度对气化腔内温度的影响最大，其次为气化剂的注入速度和焦炭区孔隙率。实际煤炭地下气化工程可通过精确控制有效气化剂的注入速度来改变气化腔内的化学反应速率，进而改变热源功率密度，对气化腔内的温度分布进行粗调；通过增减气化剂中的惰性成分的比例，对气化腔内的温度分布进行微调。煤灰区可以不考虑气体流动动量方程的重力项，大幅缩减运算成本，提高运算速度。

建立了多场耦合的多组分反应流气化腔模型，并计算和分析了气化剂氧含量和气化腔初始温度对合成气产量与品质的影响。产气井导出的合成气有效组分的产气速率，合成气热值和产气热功率均随气化腔初始温度、气化剂的氧含量呈正相关。高温和氧含量较高的条件可以得到更高的合成气热值与产气热功率，有利于加快煤炭能源的开采速度。氧气利用率与初始温度呈正相关，但与气化剂氧含量呈负相关。高温气化腔与氧含量较低的气化剂条件在煤炭地下气化项目中商业价值更高。

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Coal is the most important energy resource in China at the present stage, and the deep coal resources onshore in China with the depth of 1000-2000 m are 2.44 trillion tons, which is 12 times the proven technically recoverable coal reserves. But at this stage, coal mining has problems such as shallow mining depth, frequent accidents, low recovery rate, and environmental pollution. The underground coal gasification technology is an effective coal mining technology to solve the above problems. This technology involves adding gasifying agent to the underground coal seam through an injection well, which initiates a series of combustion and gasification reactions. As a result, the coal is converted in situ into clean syngas, such as hydrogen and methane, and is then exported through a production well. Calculated with an energy conversion rate of 40%, the underground coal gasification technology can provide China with enough clean energy for hundreds of years and abundant chemical raw materials. In order to accelerate the commercialization of underground coal gasification in my country, it is necessary to improve the quality and output of the syngas. In this paper, the numerical simulation method is used to predict the evolution process of underground coal gasification by constructing a multi-component reacting flow gasification cavity model involving multifield coupling of flow through porous media, mass transfer, energy transfer and chemical reaction. This paper adopts the technical route of step-by-step simulation of underground coal gasification cavity, and obtains the following main results:

Establish an isothermal, reaction-free, flow through porous media, turbulent flow and mass transfer coupling model for the gasification cavity, and calculate the characteristics of the flow field and the distribution of gas components within the cavity. Analyze the evolution process of flow and mass transfer within the gasification cavity. The flow field distribution is relatively stable, with the most significant flow observed at the lower right side of the void space, excluding the inlet and outlet areas. The gasifying agent initially introduced reached the char region at 250 seconds, reached the void space at 700 seconds, returned to the char region after passing through the void space at 2000 seconds, and reached the production well at 2300 seconds. Ten thousand seconds after the initiation of gasification, the gasifying agent introduced had filled the entire coal underground gasification cavity.

Establish a constant heat source power density, single-component, reaction-free flow and energy transfer coupling model for the gasification cavity, and analyze the effects of gasification cavity heat source power density, injection velocity of gasifying agent from the injection well into the cavity, and porosity of the porous medium region on the temperature field within the gasification cavity. It is found that the heat source power density has the most significant impact on the temperature within the gasification cavity, followed by the injection velocity of the gasifying agent and the porosity of the char region. Practical coal underground gasification projects can adjust the chemical reaction rate within the cavity by precisely controlling the injection velocity of the effective gasifying agent, thereby coarse-tuning the heat source power density and altering the temperature distribution within the cavity. Fine-tuning of the temperature distribution can be achieved by varying the proportion of inert components in the gasifying agent. The char region can neglect the gravity term in the flow momentum equation, significantly reducing computational costs and enhancing computation speed.

Establish a multi-component reacting flow coupling model for the gasification cavity. Calculate and analyze the impact of oxygen content in the gasifying agent and the initial temperature of the gasification cavity on the quality of syngas. The production rate of effective components in the syngas extracted from the production well, as well as the calorific value and thermal power of the syngas, are positively correlated with the initial temperature of the gasification cavity and the oxygen content of the gasifying agent. Conditions of high temperature and higher oxygen content can yield syngas with higher calorific value and thermal power, which is beneficial for accelerating the exploitation speed of coal energy. The utilization rate of oxygen is positively correlated with the initial temperature but negatively correlated with the oxygen content of the gasifying agent. A gasification cavity at high temperature and with a gasifying agent of lower oxygen content has higher commercial value in underground coal gasification projects.