Investigation On The Explosibility And Explosion Venting Characteristics Of Hybrid Mixtures

Hybrid mixtures of flammable gas and dust are commonly encountered in the industrial production process.Explosion accidents initiated by them have made great threat to industrial production safety.Understanding in depth of the explosibility and explosion venting characteristics of hybrid mixture can provide guidance for perfecting explosion theory and establishing scientific explosion venting technology.Existing researches have shown that the explosion characteristics of hybrid mixture are special,but they are not enough.Especially,the quantitative relationships of the explosion and explosion venting characteristics between hybrid mixtures and single-phase medium have not been understood.Therefore,in this paper,the way combined with theory and experiment was used to study the change law of the lower explosion limit,the maximum explosion pressure and the maximum rate of pressure rise of hybrid mixture.On this basis,the explosion venting characteristics of hybrid mixture were investigated.The main content and conclusions are as follows:(1)A 20 L shperical vessel was modified.The dust was dispersed by premixed mixture to obtain the hybrid mixture.The explosion and explosion venting parameters of methane,ethylene,lycopodium,polyethylene and hybrid mixtures of methane-lycopodium,methane-polyethylene,ethylene-lycopodium and ethylene-polyethylene were measured under the same turbulent condition.(2)The change law of the lower explosion limit of hybrid mixtures was measured.According to the influences of the chamical reactivity of flammable gas and the decomposition characteristics of dust on the lower explosion limit of hybrid mixture,a parameter of limit factor was defined to evaluate the explosion risk of hybrid mixture.A model to calculate the limit factor was established,which related to the maximum explosion pressure(gas:PmaxG,dust:PmaxSt)and explosion index(gas:KG,dust:KSt)of the flammable gas and dust,as follows:?= 5.12×10-7×e(?)(3)The applicability of Le Chatelier,Bartknecht,Jiang models to the four kinds of hybrid mixture investigated in this paper was evalulated.The results showed that all of the three methods couldn't give accurate predictions.Based on the limit factor,a new predicting model was established,as follows:c/MEC =(1-y/LEL)?(4)The influences of methane and ethylene on the maximum explosion pressure Pmax and explosion index Kst of lycopodium and polyethylene dust were studied.The results showed that adding flammable gas to a dust cloud increase its maximum explosion pressure Pmax and explosion index Kst obviously.The increase ratio of explosion index was clearly higher than that of the maximum explosion pressure Pmax,indicating that the influence of flammable gas on dust explosion index was more significant.According to the experimental results,a prediction model was established to predictive the explosion parameters(PmaxH,KH)of hybrid mixtures,using the explosion parameters(PmaxG,PmaxSt,KG,KSt)of the single-phase medium.(5)The reduced pressure Pred and explosion venting flame of hybrid mixture of methane and lycopodium dust under different venting diameters and static activation pressures were measured.The applicability of NFPA 68 and EN 14491 to hybrid mixture was evaluated.The results showed that,NFPA 68 was more suitable to the hybrid mixture explosion venting design.(6)The computational formula used to calculate the explosion venting area of hybrid mixtures in NFPA 68 was optimized.The optimized formula associated with the maximum explosion pressure(PmaxG,PmaxSt)and the explosion index(KG,KSt)of the single-phase medium.In the practical application process,the design workload will be greatly reduced and the design accuracy will be imporved.