Suppression Mechanism Of Al Dust Explosion By Solid Suppressants

A large amount of waste aluminum dust can be fonned during the processing aud surface treatmeut of metal products,such as machining and polishing.When the concentration of suspended dust in the air reaches the explosion limit range,an explosion may likely occur once the ignition source is encountered.Solid suppressants,as effective chemical suppressants,are widely colceened in recent years.The effects of solid suppressants on the explosion severity of aluminum dust have been eanied out in the previous studies.However,the effects of solid suppressants on flame propagation behaviors are not adequately acknowledged.The study of the chemical kinetic mechanism of aluminum dust explosion suppression in particular remains to be improved.In this essay,5?m and 30?m aluminum particles are selected as experimental sample.NaHCO3(SBC),ABC powder,melamine cyanurate(MCA)and melamine polyphosphate(MPP)are selected as solid suppressants.The effects of solid suppressants on overpressure and flame propagation of aluminum dust explosion are studied.And the suppression mechanism of solid suppressants for aluminum dist explosion is investigated using numerical simulation.The main work and conclusions are as follows:(1)The effect of concentration species of solid suppressants on explosion pressure of aluminum dust was performed.When the concentration of ABC,MCA and MPP is low,the increase of gas-phase products and heat released from NH3 combustion could cause the pressure to rise.When ABC,MCA and MPP concentration was high,the pressure could be reduced by the explosion suppression.However,for the case of SBC addition,the increase caused by the increase of gas phase products was always less than the pressure drop caused by the explosion suppression.As a result,the maxumun pressure in explosion chamber first inereased and then decreased,as the concentration of ABC,MCA and MPP increased.However,the maximum pressure gradually decreased,as the concentration of SBC increased When aluminum combustion was dominated by gas-phase reaction,the order of concentration requiled to suppress alimimum dust explosion was:MCA<MPP<ABC<SBC.When aluminum combustion was dominated by both gas-phase and surface reaction,tlie order of concentration required to suppress aluminum dust explosion was:ABC<MCA<MPP<SBC.(2)The effect of solid suppressants on aluminum flame was studied.Solid suppressant coild suppress the diffusion flale of aluminum particles,so that the continuous flame front of aluminum dust cloud became to a discrete flame front.As the concentration of solid suppressants increased,flame propagation velocity and flame temperature of aluminum dust explosion significantly decreased,and the stable propagating flame began to oscillate.(3)Combined with thermal analysis and X-ray photoelectron spectroscopy(XPS)analysis,the decomposition products of solid suppressants and chemical composition of explosion products were determined.Based on the suppressants sub-mechanism and the kinetic mechanism of aluminum combustion considering both gas-phase reaction and surface reaction,the detailed kinetics model of four solid suppressants for aluminum dust explosion suppression was established.The gas-phase mechanism consisted of 93 gas-phase species and 489 gas-phase reactions.The surface mechanism consisted of 19 surface species and 49 surface reactions.(4)The suppression mechanism of aluminum dust explosion by suppressants was revealed.With respect to physical effect,the decomposition of solid suppressants could absorb the heat released from reaction zone,and ABC,MCA and MPP could coat on aluminum particles to prevent aluminum dust burning.With respect to chemical suppression,the suppressants could consume key flame radicals by free radical trapping and suppression cycles(such as NaO(?)Na and HPO3(?)PO2),thereby interuptiing the gas-phase reaction of aluminum combustion.The suppressants could reduce tle concentration of open site Al(L)of aluminum particles,thereby interrupting the surface reaction of aluminum combustion,and could decrease the surface reaction rate by reducing the diffusion rate of the oxidant near the aluminum particles surface.