导管泄放粉尘爆炸过程中二次爆炸现象研究

Secondary explosion during aluminum dust explosion venting with a relief duct

以2μm铝粉为介质,通过在1.3 L柱形容器顶端连接泄放导管,研究了导管泄放粉尘爆炸过程中容器及导管内的压力特性,探讨了粉尘爆炸泄放过程中二次爆炸的发生条件及规律。结果表明,采用导管泄放粉尘爆炸时,由于火焰较压力波有滞后,火焰进入导管会点燃已经随压力波进入导管的未燃粉尘,产生二次爆炸现象。当容器内铝粉质量浓度超过500 g/m3,且导管长度超过1 500mm时,导管内会出现二次爆炸现象。当容器内粉尘质量浓度为500～1 000 g/m3时,二次爆炸引起的容器内二次压力峰值不超过一次压力峰值。通过开展泄爆膜上二次放粉试验时发现,若爆炸开始前导管内存在可燃粉尘,则二次爆炸强度显著增大,容器内二次压力峰值接近甚至超过一次压力峰值。泄放导管越长,粉尘质量浓度越大,二次爆炸强度越大。

Explosion venting experiments were carried out by using aluminum powders with effective diameter of 2 μm and a 1.3 L cylindrical vessel connected to a relief duct. The length of relief duct and the dust concentration vary in experiments. Explosion pressure characteristics both in vessel and in relief duct during aluminum dust explosion venting were studied. The occurrence conditions and influence principles of secondary explosion phenomenon were discussed by varying dust concentrations from 300 g/m3 to 1 000 g/m3 and duct length from 900 mm to 1 800 mm. The results indicate that the cause of secondary explosion occurrence is that the flame ignites the unburned aluminum dust entering into the relief duct with explosion pressure waves before the flame arrives at the duct entrance. Secondary explosion occurs only when dust concentration achieves or surpasses 500 g/m3 and the duct length is up to 1 500 mm in the experiments. When dust concentration ranges from 500 g/m3 to 1 000 g/m3, the secondary explosion pressure peak resulting from secondary explosion is smaller than the first pressure peak, which usually equals to the acting pressure of relief membrane in our experimental conditions. The enhancement experiments were also designed through adding 0.1 g extra aluminum powders on the relief membrane aiming to increase the strength of secondary explosion and the effect on the original explosion venting process. It is found from experimental results that the secondary peak pressure closes to or even surpassed the first peak pressure. That is, the strength of secondary explosion will be greatly enhanced if there is unburned combustible dust in the relief duct. The precise occurrence conditions and the strength principle of secondary explosion have not been established. However, it has been seen that strength of secondary explosion is relative bigger in situation with bigger duct length and larger dust concentration.