Flame Propagation Behaviors Of Lysine Sulfate Dust And Its Green Suppression Technology

With the wide application of mechanized production and powder technology,dust explosion accidents are increasingly frequent,66% of which occur in the grain and feed processing industry.At present,there are a lot of researches on grain dust explosion at home and abroad,but little attention has been paid to feed dust explosion.In addition,considering the edible value of food and feed dust,the explosion inhibitors selected should have good inhibition effect and be green and safe.A feed addition of lysine sulfate(LS)dust is taken as the research object to study its kinetic behaviors of pyrolysis and the deflagration flame propagation under different parameters(atmosphere,particle size,concentration,moisture content,etc.),and to reveals the control mechanism of the three sub processes of combustion,pyrolysis,and heat transfer in the dust flame propagation by using the hot flame model and time scale analysis method.The flame propagation behaviors of LS deflagration and the product characterization test under the action of two green safety inhibitors,sodium phytate(SP)and deoxyribonucleic acid(DNA)were studied,and compared with those under traditional inhibitor,ammonium polyphosphate(APP),to reveal their inhibition effects and mechanism on the flame propagation of dust deflagration.This study is of theoretical significance to predict and evaluate the deflagration behavior and risk of food and feed dust such as LS,and to realize the intrinsic safety of food and feed dust.Based on TG-DSC,the pyrolysis kinetics of LS was studied,which mainly went through three stages: Stage I was mainly endothermic process,corresponding to decarboxylation and sulfuric acid removal process;stage II was exothermic reaction,mainly deamination and oxidation of pyrolysis products in stage I;Stage III was the further pyrolysis and oxidation of the pyrolysis products in the first two stages.The influence of atmosphere on the pyrolysis behavior of LS was mainly reflected in stage II and stage III,mainly because the oxidation reaction of pyrolysis products was inhibited in the atmosphere of nitrogen.The water content pairs would slightly change the initial reaction temperature and activation energy of LS.Then,the influence of different parameters(moisture content,particle size distribution and concentration)on the flame propagation behavior of LS dust was studied.The flame propagation of LS deflagration included three stages: free propagation,acceleration and attenuation,in which the flame acceleration is controlled by combustion,expansion,turbulence and thermal feedback.The effect of moisture content on the flame propagation behavior of LS dust was similar to SEEP effect,that was to say,when the moisture content was insufficient,it would promote the flame propagation,which is mainly due to the joint effect of work done by water evaporation expansion and heat transfer promotion;when the moisture content was too large,it would produce obvious inhibitory effect.The flame propagation speed of LS dust decreased with the increase of particle size,and increased first and then decreased with the increase of concentration,in which the most violent deflagration concentration was around 350 g/m3,which was very close to the theoretical equivalent concentration.FThen,by comparing the propagation speed and temperature of dust deflagration flame with different inhibitors(APP,SP and DNA),it was found that APP and SP had better inhibition effect,and the effect of DNA is not obvious,which proved that SP could be used as a green and safe inhibitor.Through SEM and XPS analysis,the inhibition mechanisms of APP and SP on LS dust deflagration were deduced,which was the combined action of physical and chemical factors,including thermal desorption,diluting oxygen and inerting effect of pyrolysis products,heat insulation,oxygen isolation of phosphorus group covering generated and capturing free radical.Finally,based on the thermal flame model and time scale,the internal control mechanisms of the three sub processes of gas combustion,solid-phase pyrolysis and heating in the flame propagation process of LS dust were analyzed.It was found that the pyrolysis and volatilization process of particles were mainly controlled by the external heat transfer rate(Bi<1 and Th>1),while the premixed combustion process of combustible pyrolytic volatile was mainly controlled by the pyrolysis resolution rate of volatile of dust particles(Da>1).The increase of particle size and moisture content could significantly reduce the value of Th,weaken heat transfer control and enhance pyrolysis process.However,the addition of inhibitors could significantly reduce the external heat transfer rate and prevent the heat transfer from the combustion reaction zone to the dust particles,which resulted in the significant increase of Th and flame thickness.The particles with smaller particle size had higher pyrolysis rate and reaction rate,so the flame microstructure parameters(preheating zone thickness,reaction zone thickness and flame zone thickness)decreased with the decrease of particle size.Appropriate moisture content could promote the pyrolysis and gasification process in flame propagation,intensified combustion reaction and reduced flame thickness.