火风压驱动地裂缝气流作用下地下煤火蔓延规律与演变机制

Underground coal fire (UCF) is one of the most persistent fires on the Earth, which is attributed to the fact that thermal buoyance force induced by UCF drives air infiltration through cracks into underground coal seams, leading to fire propagation and dynamics of UCF. Current research that has been challenged by external wind, depth, and complex geological settings is limited to descriptive and statistical analyses. This proposal will develop an advanced experimental framework via pseudo-ground surface, hollow plug and key parameter measurement tools to break through the bottle neck of current research. All experimental studies will be compared and improved by theoretical and fieldwork investigations. A relationship between fresh air velocity and thermal buoyancy force induced by hot smoke will be established. Mechanism of air infiltration through crack driven by thermal buoyancy force will be elucidated. A relationship between fire propagation rate and thermal buoyancy force, air velocity as well as burning temperature will be formulated, which helps to understand the influences of thermal buoyancy force, depth and aperture of crack on the rate of fire propagation. The role of external factors in the transitions of low-temperature oxidation to smoldering as well as smoldering to flaming will be illustrated in detail. Chemical kinetics attributed to the transitions will be in-depth studied. Dynamic mechanism of UCF impacted by couplings of external factors and chemical kinetics will be revealed. This proposal will facilitate quantitative and kinetic investigations on fire spread and dynamics of UCFs, and give in-depth insights into understanding the true nature of UCF disaster.

地下煤火是全球最难扑灭的火灾之一，其主要根源在于无需外部风力，仅在自身产生的火风压作用下驱动外部空气通过地裂缝进入地下煤层，促使地下煤火蔓延和演变。由于外部风力干扰、深度和地裂缝复杂条件等问题，针对该关键科学问题的研究目前局限于定性、统计分析。本项目通过设计准地表面、空心塞子和测量系统等先进实验技术，解决制约研究的上述问题。采用该先进的实验手段，结合理论分析和野外调研，建立火风压与地裂缝气流速率定量关系，揭示火风压对地裂缝气流的驱动作用规律；构建火风压、地裂缝气流速率和煤层温度三者与火蔓延速率的相互关系，揭示火风压、地裂缝深度和宽度等对火蔓延速率的影响规律；厘清影响低温氧化—阴燃演变、阴燃—明火演变的外部主控因素，探究不同演变阶段的动力学反应内在机理，揭示内在反应与外部因素对地下煤火演变的耦合作用机制。本项目将推进基于模拟实验的地下煤火机制机理动力学研究，深化对地下煤火灾害本质的认识。

地下煤火是一种在火风压驱动地裂缝气流流动作用下地下煤层非控燃烧而形成的受限空间特殊火灾，它严重危害了我国煤炭资源和生态环境。由于深度、地质和气象等复杂条件给地下煤火基础研究带来的巨大挑战，导致目前研究局限于定性、统计分析。.本项目研究建立了热浮力驱动地裂缝气流作用下地下煤火渗流一维模型，通过对比实验数据，验证了理论模型的有效性。研究发现了一种特殊的“烟囱效应”：在热浮力驱动气流作用下，只要当气流运输通道渗透性满足一定条件时（>10-7 m2），随着地下煤火深度（h）的增加，地下煤火燃烧速率、火蔓延速率和峰值温度“不减反增”规律。该发现革新了关于地下煤火与深度关系的传统认识，在一定程度上较好地解释了地下煤火极端持久燃烧现象，对地下煤火防控具有一定的理论指导意义。.本项目通过大量实验研究发现，地裂缝供氧速率（Va）不仅受热浮力影响，而且与烟气成分（CO2、CO和O2）浓度（ΔM）有紧密关系，即地裂缝气流是在地下煤火产生的热浮力和浓度浮力（thermo-solutal buoyancy）共同驱动作用下供氧给地下煤火。提出了地下煤火烟气浮力驱动作用下地裂缝供氧速率预测模型（Va=f(Tg, ΔM, h)），该模型具有较好的普适性。阐明了热浮力和浓度浮力对供氧驱动作用的贡献程度。该研究弥补了烟气浓度浮力驱动地裂缝气流驱动作用的认知空白，揭示供氧与化学反应之间的潜在耦合作用，这有助于进一步完善地下煤火多场耦合模型。.本项目实验研究表明，当烟气温度较低（<400℃）时，地裂缝供氧速率、烟气温度和成分浓度等比较稳定、变化不大；当烟气温度超过450℃时，地裂缝入口气流速率、地下煤层阴燃、烟气温度和成分浓度出现明显变化。地下煤火此种演变机制主要是：在高温烟气对流传热作用下碳氧化前锋远端的煤层快速热解，煤层热解释放出大量的热解气体，煤层渗透性增强，进而改善了地裂缝供氧。该研究初步揭示了地下煤阴燃的热-流-固-化耦合关系，对地下煤火演变规律与多场耦合作用关系等研究奠定了基础。