甲烷-煤尘复合体系中煤尘爆炸下限的实验研究

On lower limit of explosive coal dust in coal dust mixture with methane

在3.2L的燃烧管道中,采用小能量的高压点火装置,通过改变甲烷体积分数、煤尘种类与粒径,研究了甲烷-煤尘复合体系中煤尘爆炸下限的变化规律。研究结果表明,在本文实验条件下,甲烷-煤尘混合物中甲烷体积分数的增加能明显降低煤尘的爆炸下限。对于煤尘粒径小于42μm煤样A,当甲烷体积分数从1.8%增加到2.2%时,煤尘的爆炸下限相应从30g/m3下降到6.25g/m3。煤尘的爆炸下限也随着煤尘中挥发分含量的增加而降低。煤尘粒径对其爆炸下限的影响较弱。实验结果与文献中高能量化学药头点火的测试结果进行比较表明,甲烷对煤尘爆炸下限的影响趋势并不随着点火源能量的改变而改变。

The present paper is aimed at disclosing the changing regularity of the coal dust explosion lower limit （LEL） under the effects of methane. For this purpose, we have chosen a small-size combustion chamber of 3.2 L and 500 mm height with square cross-section of 80 mm × 80 mm as research samples. At the same time, we have also chosen a high voltage ignition unit with nominal energy of 30 J as an ignition source. Then we have conducted experiments with different kinds of coal dust, dust size distribution and the methane concentration to study the effects of the methane concentration on the coal dust. To be exact, we have adopted two kinds of coal dust, five-size distribution （i.e. 77-90 μm, 61-77 μm, 54-61 tan, 42-54 tan and below 42 μm with methane concentration of 1.8 % and 2.2 % ）. All the experiments have been done at the atmospheric pressure with the higher end open and the lower end to supply the gas and dust. The results of our experiments show that, LEL of the eoal dust has been lowered with the inerease of methane eoneentration under the present experimental eondition. For eoal dust A with the dust diameter below 42 um, the coal dust LEL would be redueed from 30 g/m^3 to 6.25 g/m^3 while the methane concentration would rise from 1.8% to 2.2%. For eoal dust B with different-size distribution, the results also indicate the same tendency. The LEL of eoal dust proves also to drop with the rise of the eoal dust volatile eontent, whieh ean be eompared with eoal dust B with rather lower volatile content. It perhaps indieates that the effect of the dust size on its LEL would be minor even in its mixture with methane. However, the methane coneentration produees obvious effect on the eoal dust＇s LEL, particularly, when the coal dust size distribution is large. Thus, it can be concluded that the results of our experiments on the whole prove to be in conformity with those from the high-energy chemical igniters in large volume chambers.