Numerical study of pulverized coal ignition under different oxygen conditions based on solid-gas coupling
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摘要: 平面热板实验是评价煤粉自热和着火危害最常用的方法，特别适用于煤粉在热表面积聚的情况。针对目前基于热板实验的煤粉着火特性的研究缺乏对煤粉与空气相耦合的煤粉着火特性的数值研究问题，在文献[
9 ]的基础上，建立了固−气耦合的煤自燃多物理场数值模型。模拟结果表明：烟煤煤粉的厚度分别为5，12.5，20，30 mm，直径为100 mm，煤粉发生热失控情况时，烟煤煤粉在30 min之前缓慢升温到170 ℃，在煤粉层中心处出现高温区域，在37 min时突然发生热失控。烟煤煤粉未发生热失控情况时，煤样在30 min后温度变得稳定，温度低于150 ℃，不存在明显高温点。模拟结果与文献[9 ]的实验结果有较好的一致性。在更厚烟煤煤粉条件下，对该数值模型最小点火温度与文献[9 ]结果进行对比，两者差异较小，验证该数值模型的可靠性。基于该数值模型，分析了不同氧气体积分数条件下烟煤煤粉自燃特性，结果表明：① 随着烟煤煤粉厚度增加，最小点火温度呈减小趋势。② 热失控阶段，高温区域位于煤粉中心上部位置。③ 煤粉前期温升是由于热板热传递导致，随煤粉温度增加，煤氧化反应主导因素由热量转变为氧气。④ 煤粉温度峰值随氧气体积分数线性增加，点火延迟时间随氧气体积分数呈指数减小。Abstract: The plane hot plate test is the most commonly used method to evaluate the self-heating and ignition hazards of pulverized coal, especially for the accumulation of pulverized coal on the hot surface. In order to solve the problem of lacking of numerical study on the ignition characteristics of pulverized coal coupled with air based on hot plate experiment, a multi-physical field numerical model of coal spontaneous combustion with solid gas coupling is established on the basis of literature [9 ]. The simulation results show that the thickness of bituminous pulverized coal is 5 mm, 12.5 mm, 20 mm and 30 mm, and the diameter is 100 mm. When the thermal runaway of pulverized coal occurs, the bituminous pulverized coal slowly heats up to 170 ℃ before 30 min, and a high temperature region appears in the center of the coal layer, and the thermal runaway occurs suddenly at 37 min. When the thermal runaway of bituminous pulverized coal does not occur, the temperature of coal sample becomes stable after 30 min, and the temperature is lower than 150 ℃, without obvious high temperature point. The simulation results are in good agreement with the experimental results in literature 9. Under the condition of thicker bituminous pulverized coal, the minimum ignition temperature of the numerical model is compared with the results of literature 9, and the difference between the two is small, which verifies the reliability of the numerical model. Based on the numerical model, the spontaneous combustion characteristics of bituminous pulverized coal under different oxygen mass fractions are analyzed. ① As the thickness of bituminous pulverized coal increases, the minimum ignition temperature tends to decrease. ② In the thermal runaway stage, the high temperature area is located at the upper part of the pulverized coal center. ③ The temperature rise of pulverized coal in the early stage is caused by the heat transfer of hot plate. With the increase of pulverized coal temperature, the dominant factor of coal oxidation reaction changes from heat to oxygen. ④ The peak value of pulverized coal temperature increases linearly with the oxygen mass fraction, and the ignition delay time decreases exponentially with the oxygen mass fraction. -
图 1 煤粉最大温度随时间变化曲线
Figure 1. Varitation cure of maximum temperature of pulverized coal with time
图 2 不同求解步长得到的温度失控时间
Figure 2. Temperature runaway time obtained by different solving steps
图 3 实验温度结果与数值模型结果对比
Figure 3. Comparison of experimental temperature and numerical model results
图 5 不同氧气体积分数条件下煤粉温度变化
Figure 5. Temperature changes of pulverized coal under different oxygen volume fraction
图 6 点火延迟时间和温度峰值与氧气体积分数的关系
Figure 6. The relationship between ignition delay time and temperature peak and oxygen volume fraction
表 1 煤样工业分析与元素分析
Table 1. The industrial and elemental analyses of coal sample
% 煤样 工业分析 元素分析 水份 灰份 挥发份 固定碳 碳 氢 氧 氮 烟煤 2.7 14.1 26.9 56.3 67.5 4.26 11.58 1.76 
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