Experimental Research Of Aluminum Powder Explosion And Explosion Venting Characteristics

In industrial explosion accidents,metal dust explosion accidents accounted for a significant proportion,especially the emergence of ultrafine aluminium powder increased the potential for aluminum powder explosion,so the study of aluminium dust explosions is extremely important.At present,there are many researches on the characteristics of dust explosion in airtight vessels at home and abroad,but the research on dust explosion venting and flame propagation characteristics in the process of dust explosion venting is not deep enough.In this paper,the explosion characteristic parameters?maximum explosion pressure and maximum explosion pressure rise rate?of aluminum powder were tested in the 20-liter explosion chamber.And on this basis,using of modified 20-liter explosion chamber,the dust explosion venting experiments of aluminum dust was carried out,and the experiment process was filmed using a high-speed camera.The pressure and flame propagation characteristics in this process are analyzed.Finally,based on the experimental results,the design basis of the explosion venting is calculated and analyzed.The research achievement show that:?1?The experiment of aluminium dust explosions in sealed 20 liter explosion chamber found that the effect of dust concentration on explosive parameters of aluminum powder is obvious,the maximum pressure and the increase rate of explosion pressure increase with the increase of dust concentration and then decrease and when the dust concentration c=500 g/cm³ reached the maximum value,namely the P_max=1.03 MPa,?dp/dt?_max=73.93MPa/s,explosion index K_st=20.1 MPa·m/s,the aluminium dust explosions level is?.?2?From the aluminum dust explosion venting experiment without venting duct,maximum reduced explosion overpressure under different vent diameters gradually increased with the increase of the static opening pressure,and gradually approaches to the equilibrium leakage line,and when the static opening pressure reaches 0.6 MPa,the increasing tendency gets slow.The larger vent diameters and the smaller static opening pressure can get the smaller maximum reduced explosion overpressure.The static opening pressure decreases with the increase of the vent diameter.When the static opening pressure is greater than the maximum explosion pressure in the sealed device,the explosion venting device fails.Two types of venting feature were founded in the experiment:a single flame and secondary flame,the secondary flame usually appeared in the larger vent diameter the larger concentration.Under the same vent diameter,the flame length increased with the increase of reduced explosion overpressure and dust concentration.Under the same concentration,the flame length increased with the decrease of the vent diameter and the increase of static opening pressure.?3?From the aluminum dust explosion venting experiment with venting duct,the explosion venting with venting duct contains three stages:the flame front facing forward rapid propagation stage,the flame front facing forward slow propagation stage,the flame front facing forward stable stage.Under the same venting duct length,lame propagation speed increases with the increase of concentration of dust cloud,when the explosion venting dust for1 meter,dust cloud concentration for respectively 250 g/m³,500 g/m³ and 750 g/m³,the initial flame propagation speed reached 460 m/s,510 m/s and the 550 m/s.Flame propagation speed and the distance from the flame front to the container wall increase with the increase of length of venting duct,when the length of venting duct were 0.3 m,0.5 m,1.0 m respectively,the distance from the flame front to the container wall increase were stable at 1.2 m,1.5 m and1.2 m.?4?The venting area of explosion venting without venting duct at static activation pressure of 0.1¹.04 MPa is predicted based on NFPA68 and EN14491 two standard,and the predicted values and experimental values are compared,the comparison results show that the predictive results of the standard NFPA68 is relatively stable,proper margin should be left when the venting dust diameter is too large.The predictive result of standard EN14491 is relatively unstable,the prediction result is too conservative,and the predicted value is more than 10 times larger than the actual value,the prediction accuracy is lower.There are significant differences between the two predictive results.