Study On Explosion Characteristics Of Polyethylene Dust

Polyethylene is one of the most productive and widely used synthetic materials in the world.Because of its excellent properties,the demand for polyethylene is increasing.Due to friction and collision of polyethylene dust in pipeline transportation,which is likely to cause dust explosion accidents,resulting in serious casualties and economic losses.Therefore,this paper selected polyethylene as the research object,and the minimum ignition energy and the minimum ignition temperature of polyethylene are studied by combining theory with experiment.The pyrolysis characteristics of polyethylene with different particle sizes in air were studied by differential scanning calorimeter.The results showed that 25-75um polyethylene can reach a higher peak temperature in a shorter time,and the decomposition rate increased at the same heating rate.The decomposition process was accompanied by the secondary combustion exothermic reaction of the decomposition products,which speeds up the reaction.It may even cause the combustion of small particles of dust when the heat released was enough.The influence of dust concentration,particle size and carbonate inert medium（Ca CO₃and Na HCO₃）on the minimum ignition energy was studied by 1.2L Hartman tube.The results predicted that the minimum ignition energy of polyethylene dust decreased first and then increased with the escalation of dust concentration,the ignition energy and dust sensitive concentration reduced with the decrease of particle size in the range of particle size 25-180 um and concentration 300 g/m³-1500g/m³.The minimum ignition energy was56.80 m J at the injection pressure of 0.25 MPa,the ignition delay time of 80 ms and the ambient humidity of 60±5%,demonstrating that the ignition energy level was M1,which belongs to the general ignition sensitivity.In addition,The minimum ignition energy model was established.The effect of external conditions on the minimum ignition temperature of polyethylene was studied by using a dust cloud minimum ignition temperature device.The results displayed that the minimum ignition temperature decreased first and then increased with the increment of dust concentration,and reduced with the decline of dust particle size in the range of 25-180 um and 222 g/m³-1556g/m³.The minimum ignition temperature was300℃.In addition,The optimum minimum ignition temperature model was established,and the model of minimum ignition energy and minimum ignition temperature was further established on the basis.The research on the explosion suppression of inert powder showed that the effect of 100-200 mesh Ca CO₃and Na HCO₃was insignificant at the same dust concentration,but inert powders of 200-300 mesh and 300-400 mesh had significant suppression effect,which indicates the explosion suppression effect is better with the reduction of particle size of inert powders,and 70%of 300-400 mesh Na HCO₃/HDPE was unburned within 1000 m J,indicating that the ignition threshold is reached.The explosion suppression effect of Na HCO₃was better than that of Ca CO₃,and the explosion suppression mechanism was described in detail.