煤自燃是影响煤矿安全生产的重大灾害之一。封闭火区作为控制火势及防止火灾蔓延的重要手段之一，通常情况下其内部为贫氧气氛，煤体能维持较长时间的阴燃状态，当煤壁间存在裂隙或封闭不严，存在漏风通道时，新鲜风流可渗入火区内部，引起煤体复燃。热辐射为高温传热的主要方式，其辐射过程不需要任何介质，辐射量与温度的四次方成正比，在封闭火区内部可加快煤自燃的燃烧速度，引燃相邻煤体，扩大封闭火区内部火势，因此对热辐射引燃煤体临界条件及其影响因素进行研究，有利于探明封闭火区内部热辐射引燃煤体的机理，达到控制火势，防止火灾蔓延的目的，进一步保障煤矿安全生产。

本文设计并搭建了煤体受热辐射实验台，利用该实验台对不同辐射温度（200 ℃、250 ℃、300 ℃）、不同煤样粒径（10目、18目、30目）条件下的热辐射引燃煤体临界参数进行测定。以温度变化特征、失重量及失重率、气体产生量、煤样燃烧形态为评价指标确定出热辐射引燃煤样的临界辐射温度及临界粒径，进一步通过低热导率的石英砂对煤样氧化放热进行分析，最后探究了辐射距离、空气流速、浸水率、煤样厚度、辐射倾角等五种环境变量对热辐射引燃煤体的影响。

研究表明，煤样引燃的难易程度随着辐射温度的升高、煤样粒径的减小而逐渐降低，当外部辐射温度为250 ℃，煤样粒径为30目时达到煤样引燃的临界条件；在煤样氧化放热研究中发现，当达到煤样临界引燃条件时（250 ℃，30目）煤样中层开始自发氧化并向外界持续散热，此时热传导与煤氧化放热之间存在明显的热叠加现象，煤样氧化进程加快；根据煤氧化过程中相关变量（温度、质量、气体、表层燃烧形态）的变化特征，初步判断当热辐射源温度为250 ℃，煤样粒径为30目时，热辐射引燃煤样的临界距离为6 cm~9 cm；空气流速为1.0 m/s~1.5 m/s时，既能增加热辐射穿透效率，又能为煤样氧化提供新鲜风流；浸水率对热辐射引燃煤样的效果呈现两面性，较低的浸水率可为煤样提供良好的润湿热及汽化热，加快煤体燃烧，较高的浸水率则隔绝煤氧接触界面，消耗煤氧化过程中积蓄的热量，初步确定临界浸水率为10.14%~14.84%；煤样厚度对煤样是否被引燃影响不大，其厚度为4 cm、6 cm、8 cm时均被引燃，但由于煤样罐的原因，氧气未能及时供应，导致煤样无法维持较长时间的燃烧状态；辐射倾角小于15°时煤样可被引燃，倾角越大煤样表层燃烧效果越差。本研究对封闭火区内部热辐射引燃相邻煤体及封闭火区内部火灾的防控具有重要的理论和现实意义。

Coal spontaneous combustion is one of the major disasters that affect the safety of coal mine production. As one of the important means to control the fire and prevent the spread of fire, the closed fire area is usually an oxygen-poor atmosphere inside, and the coal mass can maintain a smoldering state for a long time. When there are cracks or loosely closed coal walls, and there are air leakage channels, fresh air flow can penetrate into the fire area and cause the coal mass to reignite. Thermal radiation is the main way of heat transfer at high temperature. Its radiation process does not require any medium, and the amount of radiation is proportional to the fourth square of temperature. In the closed fire zone, the existence of high temperature thermal radiation will accelerate the combustion speed of coal spontaneous combustion, and then ignite the adjacent coal and expand the fire in the closed fire zone. Therefore, the research on the critical conditions and influencing factors of thermal radiation ignition of coal mass is conducive to finding out the mechanism of thermal radiation ignition of coal mass in the closed fire area, achieving the purpose of controlling fire and preventing fire spread, and further ensuring the safety of coal mine production.

In this paper, a thermal radiation test platform is designed and built to measure the critical parameters of coal ignited by thermal radiation under different radiation temperatures (200 ℃, 250 ℃, 300 ℃) and different coal sample sizes (10 mesh, 18 mesh, 30 mesh). The critical radiation temperature and critical particle size of the coal sample were determined based on the characteristics of temperature change, weight loss and weight loss rate, gas production and combustion form of the coal sample. The oxidation and heat release of the coal sample were further analyzed by quartz sand with low thermal conductivity. Finally, the effects of radiation distance, air velocity, water immersion rate, coal sample thickness and radiation inclination on thermal radiation ignition of coal are investigated.

The results show that the degree of difficulty of ignition of coal sample decreases with the increase of radiation temperature and the decrease of particle size of coal sample. The critical condition of ignition of coal sample is reached when the external radiation temperature is 250 ℃ and the particle size is 30 mesh. In the study of coal sample oxidation and heat release, it is found that when the critical ignition condition of coal sample is reached (250 ℃, 30 mesh), the middle layer of coal sample begins to spontaneously oxidize and continue to dissipate heat to the outside world. At this time, there is an obvious thermal superposition phenomenon between heat conduction and coal oxidation and heat release, and the coal sample oxidation process is accelerated. According to the change characteristics of relevant variables (temperature, weight, gas, surface combustion form) in the coal oxidation process, it is preliminarily determined that when the temperature of thermal radiation source is 250 ℃ and the particle size of coal sample is 30 mesh, the critical distance of thermal radiation transfer coal sample is 6 cm~9 cm. When the air flow rate is 1.0 m/s~1.5 m/s, it can not only increase the thermal radiation penetration efficiency, but also provide fresh air flow for coal sample oxidation. The immersion rate has two sides to the thermal radiation induced coal sample. The lower immersion rate can provide good wetting heat and vaporization heat for the coal sample and accelerate the coal combustion, while the higher immersion rate can isolate the coal-oxygen contact interface and consume the heat accumulated in the coal oxidation process. The critical immersion rate is initially determined to be 10.14%~14.84%. The thickness of the coal sample has little influence on whether the coal sample is ignited. When the thickness is 4 cm, 6 cm and 8 cm, the coal sample is ignited. However, due to the reason of the coal sample tank, the oxygen cannot be supplied in time, so the coal sample cannot maintain the combustion state for a long time. The coal sample can be ignited when the radiation inclination is less than 15°, and the higher the inclination is, the worse the surface combustion effect of the coal sample is. This study has important theoretical and practical significance for the ignition of adjacent coal and the prevention and control of fire in the closed fire area.

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