Experimental Investigation On Venting Characteristics And Secondary Explosion Of Aluminum Dust Explosion

There is an important practical significance to research the venting of aluminum explosion with pipe for the venting and safety protection. Recently series of systematic study has been carried out on the characteristics of dust explosion, analyzing the influences of different parameters on the explosion and venting. There are seldom researches on the venting characteristics of explosion with pipe, especially on the secondary explosion phenomenon. Little literature could be found about the abnormal phenomenon, such as second peak in the vessel pressure curve, the abnormal pressure change in the different monitor on the pipe, etc. So the research on the secondary combustion and explosion is significant for the risk assessment and safety protection of the dust explosion.Based on the above situation, the present paper built up the explosion device on the basis of the1.3Hartmann experiment device, and designed the relief pipe of different length from900mm-1800mm. Through lots of experiments of the explosion venting and secondary injecting dust, the paper analyzed the pressure characteristics and abnormal phenomenon occurred in the different experiment conditions. The main work and conclusions are as follows:(1)1.3L Hartmann device was established and improved, adding the relief pipe device of different length. Dust explosion of2μm in the confined space, ductless and duct venting explosion dust were all carried out, obtaining the venting characteristics and the contrast of the pressure change with the condition ductless while LT≥900mm.(2) It is found in the experiment that the pressure in the vessel is higher than the condition without pipe. As the venting tube longer, the value of Pmax in the vessel and tube will increase. The diameter of tube also have a great influence on the pressure in the explosion, the value of Pmax will be greatly reduced with the diameter lagen. The concentration of dust and the pressure is not a monotone function in the present paper. The best optimum dust concentration is still at the value of500g/m-3while cp≤800g·m-3, and then as the cp increasing, the explosion pressure will be higher owing to the secondary combustion and explosion while cp>800g·m-3.(3)In the case of venting experiment without twice injecting, the secondary combustion and explosion more likely happens when the concentration is higher(cp>800g·m-3), the length of tube is longer(LT≥1500mm),and the diameter is smaller(φ<40mm). The second peak value turns up while venting the pressure after the first peak, and the second peak is lower than the first one.(4) As the abnormal phenomenon occurred in the venting experiment, the paper did the case of same pipe condition through injecting the aluminum dust twice. The experiment resulut shows that the secondary combustion and explosion happens with large possibility in this condition. With the ΦT being smaller, the LT being longer and the cp being higher, The characteristics of pressure and abnormal phenomenon occurred in the experiments will be higher, and the experimental phenomenon will also be more obvious.(5)The result shows that the abnormal phenomenon like two peak in the curve is caused by the secondary combustion and explosion in the pipe during venting. And the phenomenon occurred with probabilities. While the flame wave comes up with the dust unburned and ignited it in the pipe, the second combustion and explosion appeared. Through the experimental result the effective combustible dust is the main influencing factor of the secondary combustion and explosion. In the normal experiment, it can be concluded that the occurrence of secondary combustion while the pressure in the pipe is below0.2MPa and the second peak is lower than the first in the vessel. While the second peak has reached or exceeded the first peak, and the pressure in the pipe and vessel all increase, the secondary explosion has occurred. Through the value AP, the secondary explosion can be judged. The the secondary explosioncan must have occurred when△Pmin≤0.05MPa and the curve of△P appears a "V" shaped, but it only can be regard as Sufficient condition.