煤炭是我国的基础能源和重要工业原料，为国民经济和社会可持续发展提供了可靠能源保障。目前我国约有56%的煤矿存在煤自燃可能性，对煤矿安全生产带来巨大影响，因此开展煤矿自燃灾害的有效治理研究具有重要意义。传统灭火技术广泛应用于煤矿安全生产，但降温降氧能力有限。基于此，本文提出利用LN₂/CO₂制备干冰，并加入成核剂提升干冰成核效率，组成气液固三相混合物输入火区，并通过理论分析、实验测试和数值模拟的方法，对该技术开展研究，具体内容如下：

（1）基于干冰升华、凝华在平衡状态下的可逆特征，利用阿伦尼乌斯公式推导了平衡状态下的CO₂成核动力学模型；通过自主搭建的干冰升华实验系统，测定不同干冰质量在不同温度下的升华时间，计算了动力学模型中的干冰升华系数K为15.49，升华潜热E为97.45KJ/Kg。

（2）应用自主搭建的LN₂/CO₂干冰制备实验系统，分析LN₂/CO₂注输比、成核剂种类（氯化钙、尿素、氯化钠）、成核剂质量对混合管道内温度、压力及干冰生成的影响。结果表明：当CO₂注输量不变，增大LN₂/CO₂注输比时，管道内温度降低、压力升高，干冰生成量增多，CO₂更易发生凝华；LN₂/CO₂注输比不变，氯化钙成核剂提高CO₂转化效率能力最强，CO₂凝华需要的过冷度降低致使干冰颗粒增加，管道内温度最低，达157K；LN₂/CO₂注输比不变，加入氯化钙成核剂发现，质量为640g时管路内温度最低，为153K，压力最高，为789KPa，此时CO₂成核效率最高，并且干冰转化效率与成核剂质量成正相关。

（3）自主搭建松散煤体降温实验台，分析LN₂/CO₂注输比、成核剂种类对自燃煤体温度的影响。结果表明：在注输阶段，当提高LN₂/CO₂注输比，箱体内自燃煤体各测点温度持续下降，并且煤温降低速率随LN₂/CO₂注输比升高而增大，煤体低温区域呈锥形扩大；在停注阶段，随着LN₂/CO₂注输比增大，煤体回温速率减慢，平衡时箱体内温度更低；加入成核剂后，煤体在注输阶段温度仍有下降，温降速率更快，在停注阶段，回温速率进一步减慢，其中氯化钙成核剂对煤温抑制效果最佳。

（4）通过Ansys Fluent对注输LN₂/CO₂的采空区温度场和氧气浓度场进行模拟，通过改变注输流量、注入位置，探讨LN₂/CO₂对采空区的降温降氧效果。结果表明：注入位置不变，LN₂/CO₂注输比越大，对采空区惰化效果越强，三带宽度越窄，采空区降温区域越大；注输比不变，当注入口距离进风巷40m时，采空区内惰化效果最佳，低温区域面积最大。

Coal is the basic energy and important industrial material, and provides reliable energy guarantee for sustainable development of the national economy and society. At present, about 56% of coal mines have the possibility of spontaneous coal combustion, which has a huge impact on coal mine safety production. Therefore, it is of great significance to carry out effective control research on spontaneous coal disaster. Traditional fire extinguishing technology is widely used in coal mine safety production, but its cooling and oxygen reduction ability is limited. Based on this, this paper proposes to use LN₂/CO₂ to prepare dry ice, add nucleating agent to improve the nucleation efficiency of dry ice, compose gas-liquid-solid three-phase mixture and input it into the fire area, and carry out research on this technology through theoretical analysis, experimental testing and numerical simulation. Specific contents are as follows:

(1) Based on the reversible characteristics of sublimation and condensation of dry ice under equilibrium state, the dynamic model of CO₂ nucleation under equilibrium state was deduced by Arrhenius formula; The sublimation time of different masses of dry ice at different temperatures was measured by the independently built dry ice sublimation experiment system. The sublimation coefficient K of dry ice was calculated to be 15.49, and the latent heat of sublimation E was calculated to be 97.45KJ/Kg.

(2) The self-established LN₂/CO₂ dry ice preparation experimental system was used to analyze the effects of LN₂/CO₂ injection/delivery ratio, type of nucleating agent (calcium chloride, urea, sodium chloride) and quality of nucleating agent on temperature, pressure and dry ice generation in the mixing pipeline. The results showed that when the CO₂ injection and delivery rate remained unchanged and the LN₂/CO₂ injection and delivery ratio increased, the temperature in the pipeline decreased, the pressure increased, the dry ice production increased, and CO₂ was more likely to condense. LN₂/CO₂ injection and delivery ratio remained unchanged, calcium chloride nucleating agent had the strongest ability to improve CO₂ conversion efficiency, and the decrease of the undercooling required for CO₂ condensation resulted in the increase of dry ice particles, and the lowest temperature in the pipeline was 157K. LN₂/CO₂ injection and delivery ratio remained unchanged, and calcium chloride nucleating agent was added. It was found that when the mass was 640g, the temperature inside the pipeline was the lowest, 153K, and the pressure was the highest, 789KPa. At this time, CO₂ nucleation efficiency was the highest, and the dry ice conversion efficiency was positively correlated with the mass of nucleating agent.

(3) Independently build an experimental platform for cooling loose coal mass, and analyze the effects of LN₂/CO₂ injection/delivery ratio and types of nucleating agents on the temperature of spontaneous combustion coal mass. The results show that with the increase of LN₂/CO₂ injection/transport ratio, the temperature of spontaneous combustion coal at each measuring point in the box continues to decrease, and the coal temperature decreasing rate increases with the increase of LN₂/CO₂ injection/transport ratio, and the low temperature area of coal body expands conically. At the stop injection stage, with the increase of LN₂/CO₂ injection and delivery ratio, the coal body temperature recovery rate slows down, and the temperature inside the box is lower at equilibrium.

(4) The temperature field and oxygen concentration field of goaf during injection and transport of LN₂/CO₂ were simulated by Ansys Fluent, and the cooling and oxygen reduction effect of LN₂/CO₂ on goaf was discussed by changing the injection and transport flow rate and injection position. The results show that the higher LN₂/CO₂ injection/delivery ratio is, the stronger the effect on goaf inerting is, the narrower the width of the three zones is, and the larger the goaf cooling area is. When the injection and delivery ratio is unchanged, the idling effect in the goaf is the best and the area of low temperature area is the largest when the distance between the injection port and the air inlet is 40m.

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