为揭示制粉系统中沉积煤粉自燃引发爆炸临界条件和动力学特征, 该文建立了煤粉燃烧爆炸实验系统, 结合数值模拟对热环境下的沉积煤粉自燃、喷射和爆炸过程及行为特征进行研究。首先, 研究了煤粉在不同温度热板上的温度演化特征和自燃临界条件; 然后, 对不同自燃程度的煤粉层进行卷扬, 分析了煤粉云的形成、点火、爆炸过程; 最后, 基于Fluent软件的离散项(DPM)、气固燃烧及P-1辐射等模型仿真了煤粉卷扬引发爆炸的过程, 分析了颗粒轨迹、速度和爆炸温度等特征, 确定了诱发爆炸的氧气和煤粉云质量浓度的临界值。实验结果表明：沉积煤粉层厚度越大, 可引发自燃热板温度越低, 厚度为10 mm时, 热板温度最低为225℃; 当煤粉层内部温度处于275~395℃时, 卷扬后可诱发煤粉云爆炸; 当环境温度从120℃升高至200℃时, 煤粉燃爆的临界煤粉云质量浓度从380 g/m³降低至95 g/m³, 氧气体积分数从21%降低至13%。煤粉云爆炸主要发生在减速扩散和自由扩散阶段, 自燃阶段积累的CO等可燃气体被高温颗粒点燃, 气相燃烧点燃煤粉颗粒及其固相燃烧是自燃引发爆炸的重要过程。

Objective: In pulverizing systems, elevated ambient temperatures make coal dust deposited on hot surfaces prone to spontaneous ignition; once entrained by airflow into the surrounding space, such deposits may further evolve into coal dust cloud explosions, posing major risks to safe operations. The objective of this study is to reveal the critical conditions and kinetic characteristics under which self-ignition of deposited coal dust initiates explosions in such systems. Methods: In this study, a coal dust combustion—explosion experimental platform was combined with Fluent numerical simulations to conduct a systematic investigation of the self-ignition, ejection, and explosion processes of deposited coal dust under heated environments, as well as behavioral characteristics of these processes. First, a coal dust combustion—explosion experimental system capable of precise control of ambient temperature and hot-plate temperature was established; on this basis, the internal temperature distribution of coal dust layers at different hot-surface temperatures and the critical conditions for self-ignition were examined. Second, ejection tests were conducted with dust-layer center temperatures of 260-380 ℃ to analyze the formation, ignition, and explosion of deposited coal dust clouds. Finally, based on the experimental results, a Fluent-based numerical model was developed for the post-lofting processes, including moisture evaporation, devolatilization, gasphase combustion, and char combustion. The particle trajectories, velocities, and temperature evolution during lofting were analyzed, and the critical oxygen concentration and dust concentration required to induce an explosion were determined. Results: Experimental results show that the hotplate temperature required for thermal runaway decreases with increasing dust-layer thickness. For a 4 mm coal dust layer, the critical hotplate temperature for self-ignition is 255 ℃; when the thickness increases to 10 mm, this temperature drops to 225 ℃. When the internal temperature of a self-ignited dust layer lies within 275-395 ℃ (corresponding to a center temperature of 300-340 ℃), the resulting coal dust cloud can trigger an explosion. The lofting process can be divided into three stages—rapid ejection, decelerating diffusion, and free diffusion—with explosions occurring mainly in the latter two; the maximum particle velocity is approximately 60 m/s, and the peak temperature is approximately 2 400 ℃. Mechanistically, volatiles released from coal particles undergo homogeneous combustion outside the particles, whereas char undergoes heterogeneous combustion within the particle interior; these simultaneous phenomena significantly elevate the flame-core temperature. As the ambient temperature increases, both the critical coal dust mass concentration and the critical oxygen concentration for explosion decrease: when the ambient temperature rises from 120 ℃ to 200 ℃, the critical dust cloud concentration decreases from 380 to 95 g/m³, and the critical oxygen concentration decreases from 21% to 13%. Conclusions: Combustible gases (e.g., CO) generated during the self-ignition stage accumulate and are subsequently ignited by high-temperature particles, initiating gas-phase combustion. The resulting heat release then ignites suspended coal dust particles, triggering solid-phase combustion. This sequence constitutes a critical pathway by which self-ignition escalates into an explosion. These findings provide a theoretical basis for explosion prevention and control in pulverizing systems and offer practical guidance for risk mitigation measures, including hot-surface temperature control, dust-layer thickness management, ventilation and oxygen concentration limits, and operational strategies that minimize the lofting of preheated deposits.