贫氧火区自然对流条件下浮煤自维持阴燃的产热机理与主控机制

In the oxygen-depleted environment of the closed fire zone, coal pile is easy to sustain smoldering and it is difficult to be detected and controlled. When the fire zone is opened, it can rapidly develop, forcing the fire area to be closed again and even triggering a gas explosion. However, the smoldering characteristics and mechanism of coal is not clear at present, hindering the development of prevention and control technology. This project studies the competing mechanism of pyrolysis and oxidation reactions during smoldering of coal, and explores the kinetics and thermodynamic characteristics of smoldering reaction. The heat-fluid-chemical coupling numerical model for the occurrence and development of smoldering is constructed. Experiments were performed to test the variation of self-sustaining smoldering property (smoldering temperature, etc.) with the oxygen supplying conditions (oxygen concentration, natural convection) and coal pile characteristics (coal pile volume, etc.). Numerical simulation is used to study the chemical reaction, gas mass transfer and heat transfer process during self-sustaining smoldering of coal.It tries to reveal the heat production characteristics and mechanism of coal during self-sustaining smoldering in oxygen-lean environment, clarify the interaction mechanism between natural convection and smoldering intensity, and explore the influence mechanism of different factors such as coal rank. Entropy method was used to determine the weight of different influencing factors of self-sustaining smoldering of coal pile. The main control mechanism of self-sustaining smoldering of coal pile was revealed, and the calculation model of self-sustaining smoldering probability of coal pile was established. The results of the project can provide theoretical and scientific basis for scientifically determining the existence probability and existing zone of the smoldering fire in closed fire zone.

煤矿封闭火区的贫氧环境中，煤堆容易自维持阴燃，难以检测与治理，火区启封时能迅速发展，迫使火区再次封闭，甚至引发瓦斯爆炸。然而，煤的阴燃特性与机理尚不清楚，阻碍了防治技术的研发。本项目研究煤阴燃过程中热解与氧化反应的竞相发生机理，探究阴燃反应的动力学、热力学特性，构建煤堆阴燃发生、发展的热-流-化耦合数值模型，实验测试煤堆自维持阴燃特性（阴燃温度等）随供氧条件（氧浓度、自然对流）与煤堆特性（煤堆体积等）的变化规律，数值模拟煤堆自维持阴燃过程的化学反应、气体传质与热量传递过程，揭示贫氧环境中煤堆自维持阴燃的产热特性与机理，明确自然对流与阴燃强度之间的相互作用机制，探明煤阶等不同因素的影响机理；采用熵值法，确定煤堆自维持阴燃的不同影响因素的权重，揭示煤堆自维持阴燃的主控机制，建立煤堆自维持阴燃概率的计算模型。项目成果能为科学判定阴燃火源存在的概率、预测发生自维持阴燃的区域提供理论基础与科学依据。

本项目研究了煤阴燃过程中热解与氧化反应的竞相发生机理，发现不同氧气浓度条件下阴燃煤体包含煤氧化、半焦热解与半焦氧化三个反应序列，并且随着氧浓度的升高，各反应序列会逐渐叠加而共同在一个温度范围内发生。煤氧化序列在全氧尺度（1-21%）区间内是主体反应，半焦氧化与半焦热解序列的比重分别在氧浓度低于10%与5%后逐渐增加。建立了阴燃煤堆动态演变的热-流-化耦合一维瞬态数学模型，构建了阴燃煤堆特性参数可视化测试系统，研究了煤堆自维持阴燃特性随供氧条件与煤堆特性的变化规律，明确了煤堆自维持阴燃过程的化学反应、气体传质与热量传递过程，发现反向阴燃燃烧温度高于前向阴燃，竖直阴燃燃烧温度高于水平阴燃，在炉内热烟气与外界低温气体密度差的驱动下，阴燃煤堆内形成自然对流，且竖直阴燃过程中自然对流的质量流量远大于水平阴燃。研究了阴燃煤堆熄灭的临界来流速率及其氧浓度，并发现供氧条件的减弱主要是抑制半焦热解序列来影响煤堆的阴燃反应强度。