Study On Preparation Technology Of Superfine Sodium Bicarbonate Dry Powder Fire Extinguishing Agent

Due to the strong ozone destruction capability of halon extinguishing agents,Halon was banned by UN EPA.However,the more frequency the fire accident occurres,the more economy development and it is causing serious economic losses and personal injuries.Therefore,it has attached great importance to the development of Halon Substitutes.and it has becoming one of the research hotspots of fire science and technology.Among the developed halon substitutes,the superfine dry powder fire extinguishing agent has obtained fast development and popular applied in the fire yield,because of its advantages of high fire extinguishing efficiency,zero ODP and no greenhouse effect.However,in current national standard,the D₉₀ particle size of superfine dry powder fire extinguishing agent is below 20?m,but this particles with20?m are still a large number of molecular aggregates,brownian motion ability is weak,flow diffusion ability is obviously weaker than gas fire extinguishing agent,so it is relatively reluctant to apply in the full flooding fire extinguishing system.In order to greatly improve the flow diffusion ability and expanding the application scope,it is a effective technical measures to reducing the particle size of superfine dry powder.In this paper,the particle size reduction of superfine dry powder fire extinguishing agent is studied.In view of the convenience and industrialization of mechanical comminution method,we chooses the mechanical comminution method as the technical way to reduce superfine dry powder particles.Also,a typical formula of sodium bicarbonate dry powder extinguishing agent was chosen.The essence of mechanical method to reduce the superfine dry powder size was attributed to mechanical problems.Therefore,based on analyzing the influence of crystal lattice point defect,line defect and surface defect on the mechanical properties of the crystal from the microstructure of sodium bicarbonate particles,we think that the breaking of sodium bicarbonate is actually the separation and splitting of crystal slip surface.According to the mechanical principle,the advantages and disadvantages of various mechanical comminution methods and their comminution capacity were analyzed.Through comprehensive comparison,we drown the conclusion that the ball milling method and air flow comminution method were suitable methods for preparing sodium bicarbonate superfine fire extinguishing agent.In order to preparing sodium bicarbonate ultrafine dry powder by ball milling,the technical route was designed that raw material mixing,ball milling,surface treatment,drying and cooling.According to the comminution effect,it has great influence on reducing particle size that ball mill speed,ball milling time,the amount of material filling and the proportion of ball milling.A systematic experimental study was carried out.The results show that under the conditions of ball mill rotation speed400r·min^-1,ball milling time 30min,single grinding tank material filling volume 180g,3mm ceramic grinding ball 540g,the mixed material comminuted from D₉₀ 175?m to25.4?m,which didn't meet the particle size requirements.the agglomeration of fine particles is the main reason that the particle size can't be further reduced.Therefore,the material comminuted were added surface modifier X for surface treatment by the high-speed mixer,then the particle size was reduced to D₉₀7.61?m by ball mill grinding.In order to preparing sodium bicarbonate ultrafine powder by air flow comminution,the technical route was put forward including raw material mixing,air flow comminution,surface treatment,drying and cooling.TQG-20 air flow comminutor was selected for comminution.After many experiments,the best technical parameters were got:air flow comminution pressure 0.8MPa,feeding speed10kg·h^-1,air flow speed 3m³·min^-1,classification wheel frequency 50Hz.the material was reduced from 175?m to 13.4?m by air flow in that technical parameters,while the size wasn't meet the standard.the agglomeration also existed.In order to solving the problem,surfactant X was added to the mixed material by high-speed mixer,and the superfine dry powder was prepared by the above process after surface modification.The particle size was reduced to 6.18?m.The results show that the ultrafine powder produced by ball milling was spherical and hemispherical,while the ultrafine powder produced by air milling was long strip.In view of the fact that the fluidity of spherical and hemispherical particles is better than that of long strip particles,the joint method was studied that combined the ball milling method and air flow comminution.The results show that the ultrafine dry powder prepared by joint methods were spherical and hemispherical.Finally,the physical and chemistry performance of sodium bicarbonate superfine dry powder prepared by ball milling and air flow comminution was tested by SEM,TGA,powder X-ray diffraction and fire extinguishing efficiency was got by analyzing essays.The tests results showed that the initial decomposition temperature decreased from 100?to 62?while the particle size decreased from D₉₀ 175?m to 6.18?m,and the fire extinguishing concentration was 90.5g·m^-3 to extinguish heptane fire by superfine dry powder that we made.