Effects Of Oxygen Reduction On The Flame Propagation Of Coating Powder/air Mixtures

The main component of coating powder is a combustible polymer material.In the process of electrostatic spraying,the coating powder/air mixture in local space is in the range of explosion concentration.In recent years,it has attracted more attention that includes the risk of dust explosion in the factories,the targeted explosion prevention and control measures.Because of this,this paper selects five representatives of coating powder,e.g.flash silver III,flash silver,black sand grain,black sand grain II and black water grain.Firstly,the explosion sensitivity and intensity indexes are measured.The influencing factors of the above parameters are analyzed,which aim to provide a reference for the risk assessment of dust explosion in the factories.Further,the study on the flame propagation of coating powder/air mixture explosion is proceed.It focuses on the attenuation of explosion propagation process and the change of flame shape that is caused by the reduction of oxygen concentration.This study could provide a preliminary basis for the feasibility of inserting for the prevention of explosion.Through the above research,the following conclusions can be drawn:The maximum explosion pressure of the five selected coating powder is higher than 0.55MPa,the lower explosion limit is lower than 75g/m³,and the minimum ignition energy is lower than 100m J.The decrease of powder particle size has a limited effect on the increase of explosion intensity.The reason of the phenomenon is that the agglomeration of small particle size coating powder is more obvious,while the organic pigments have a more significant effect on the increase of explosion intensity of coating powder.The explosion index K_st also shows a similar pattern.In general,the above coating powder is in the category of ST1.Compared to other coating powder,the black water grain powder coatings have lower explosion limit and lower minimum ignition energy.It indicates that the addition of organic pigments further improves the explosion sensitivity index of coating powder.The peak value of flame propagation velocity of various coating powder is quite different.In the case of the same main components of coating powder,the decrease of particle size is more conducive to flame propagation.With the decrease of oxygen concentration,the flame shape of coating powder changes correspondingly.As the radiation intensity of flame weakens,the heterogeneous reaction of dust explosion turns to homogeneous reaction gradually.The decrease of oxygen content can attenuate the propagation of explosion flame.The different coating powder would be differently influenced by the concentration of oxygen in the process of explosion.In general,for coating powder with weak explosiveness,as the decrease of oxygen concentration,it would be more effectively to weaken the spread of explosion flame.It is reasonable to use an inert medium,such as combustion flue gas,to prevent explosion in the electrostatic spraying place of coating powder.