Suppression Effect Of Carbon Dioxide On The Explosibility And Explosion Venting Characteristics Of Lycopodium Dust

With the rapid development of industry,combustible dust has been used more and more in engineering,and it is easy to explode in the process of dust transportation and storage.A deep understanding of the influence of the addition of inert gas on the explosion and venting characteristics of combustible dust can provide guidance for the improvement of explosion theory and the construction of scientific explosion venting technology.However,most of the existing studies on the inhibition of dust explosion by inert gas are concentrated in confined space,and there are few studies on how inert gas suppresses dust explosion under the condition of explosion venting.Based on this,this paper carried out a study on the explosion characteristics of lycopodium dust by adding different concentrations of carbon dioxide in an improved 20 L spherical vessel.The main work and conclusions are as follows:(1)The effect of carbon dioxide on the explosion characteristics of lycopodium dust under confined conditions was studied.The addition of carbon oxide led to the increase of the minimum explosion concentration of lycopodium dust,and the rate of pressure rise was greatly increased when the concentration of carbon dioxide was 9%.The addition of carbon dioxide also led to the delay of the lycopodium dust explosion.Compared with pure lycopodium dust,the explosion curves moved backward.There was a sensitive point in each measured lycopodium dust concentration.When the sensitive point was reached,the explosion pressure decreased rapidly.The sensitive point of suppression appeared before the minimum concentration of complete suppression,which was about 5% lower than that concentration.(2)The static operating pressure was measured with square,circular and eccentric vent of the same area.It was found that the static operating pressure of the circular vent was larger than that of the square vent,and the gap narrowed gradually with the increase of the area.The eccentric vent led to the uneven rupture of the film and the fluctuation of the static operating pressure measurement.(3)The maximum explosion pressure was measured under different venting diameters and static operating pressures.The results showed that the critical venting diameter was 40 mm and the corresponding critical static operating pressure was 0.15 MPa.With this venting diameter and static operating pressure,carbon dioxide had the best effect on explosion venting of lycopodium dust.(4)The applicability of NFPA 68 and EN 14491 to hybrid mixture was evaluated.NFPA 68 was approximately accurate when the venting diameters ware 20 mm,40 mm,and 60 mm.But only when the venting diameter was 60 mm,EN 14491 was applicable.When the venting diameters were 20 mm and 40 mm,prediction by EN 14491 was too high to be acceptable.NFPA 68 was more suitable for the venting design of dust explosion suppressed by inert gas,and under the same venting diameter and static operating pressure,the venting area calculated based on NFPA 68 was less than EN 14491.(5)The variation of flame structure with the venting diameter,static operation pressure and carbon dioxide concentration was studied.The results showed that the small venting diameters can reduce the flame intensity better when the same carbon dioxide concentration was added.The addition of carbon dioxide had a better inhibitory effect on the later stage of flame development under the condition of higher static operating pressure.The addition of carbon dioxide in the system helped to slow down the formation of the internal turbulence and delay the time of flame emission before reaching the vent.The existence of a certain concentration of carbon dioxide can reduce the maximum venting pressure of the system,thus reduce the pressure accumulation in the vessel before the flame reached the vent,and further reduce the flame velocity and intensity.