Suppression Mechanism Of Nano PMMA Dust Explosions

Due to the special surface properties and intermolecular forces of nano particles,they have high explosion risks and the explosion suppression which is the most cost-effective way to reduce the explosion accident can prevent the dust explosion from propagating in the early stage of flame propagation.However,there was a lack of research on the suppression mechanisms,flame microscopic morphology and flame evolution mechanism of nano dust explosions in the process of explosion suppression.The experimental system of dust explosion suppression in open space was used to study the suppression effects of ABC（mainly composed of NH₄H₂PO₄）and KHCO₃ which had the synergistic explosive suppression ability of physics and chemistry.Meanwhile,KHCO₃ particle size on the flame propagation behavior of nano dust explosion was also investigated.And it was combined thermal analysis and chemical reaction kinetic analysis to reveal the suppression mechanisms of nano dust explosions.The main details and conclusions of this paper were presented as follows:（1）It was investigated the effects of ABC and KHCO₃ particles on the nano polymethyl methacrylate（PMMA）dust explosions flame propagation behaviors（flame propagation process,flame microstructure,flame propagation velocity,flame temperature）.With the increase of the proportion of suppressors in the dust cloud,the flame propagation processes slowed down.The rate of gasification and decomposition in the preheating zone and the rate of chemical reaction in the combustion reaction zone decreased.It was also found that the two suppressors had different critical suppression ratios for micron and nano PMMA dust explosions.The critical suppression ratios of micro/nano PMMA at different concentrations were determined.For 30μm PMMA dust cloud flame,the suppression effect of ABC particles was better than KHCO₃ particles.For 100 nm PMMA dust cloud flame,the suppression effect of KHCO₃ particles was better than that of ABC particles.（2）The effects of KHCO₃ particle size on the nano PMMA flame propagation processes,flame velocities and flame temperatures were investigated.For 100 nm PMMA dust cloud flame,the maximum temperature of 10%59μm KHCO₃ suppression flame was almost equal to that of 100%83μm KHCO₃.With increasing of particle size of suppressor,the specific surface area of the particle decreased and the decomposition rate decreased.The suppression effect was gradually weakened.（3）Thermogravimetric analysis（TGA）and differential scanning calorimetry（DSC）were used to reveal the physical endothermic mechanism from both decomposition initial temperature values and endothermic heat.The decomposition temperatures of 30μm PMMA,100 nm PMMA,56μm ABC particles and 59μm KHCO₃ particles were 240℃>238℃>158℃>120℃,respectively.After mixing PMMA with 10%suppressor particles,for 30μm PMMA,the heat absorption of ABC particles was 35 J/g and the heat absorption of KHCO₃particles was 20 J/g.For 100 nm PMMA,the heat absorption of ABC particles was 14 J/g and the heat absorption of KHCO₃ particles was 28 J/g.After mixing 59μm,83μm and 204μm KHCO₃ with 100 nm PMMA,the heat absorption of KHCO₃ of three particle sizes were 28J/g>26 J/g>21 J/g.（4）Chemical reaction kinetics models were established.It was presented that the maximum mole fractions and the mole fractions at equilibrium of H and OH free radicals were reduced in the chain reaction processes with the addition of suppressors.For ABC particles,OH+HOPO=H₂O+PO₂ and H+PO₂+m=HOPO+m formedHOPO?PO₂ suppression cycle.For KHCO₃ particles,KOH+H=K+H₂O and K+OH+m=KOH+m formed K?KOH suppression cycle.The above two suppression cycles promoted the combination of H and OH radicals to produce more stable H₂O.Finally,the model of nano PMMA dust explosion suppression mechanism was established based on physical endothermic suppression and chemical suppression.