The Study Of Pyrolysis Kinetics And Smoldering Propagation Model Of Combustible Powders

Combustible dust fire or explosion accidents often cause serious casualties and loss of property, and even lead to disastrous consequences, the dust fire or explosion accidents caused by smoldering is becoming more and more frequent. At the moment the research of dust smoldering process and smoldering mechanism is not enough because of the complexity of smoldering process. Research on thermal decomposition kinetics and smoldering process of dust has import theoretical significance and application value for preventing and controlling of fire and explosion accidents triggered by dust smoldering. This paper studied pyrolysis characteristic of lycopodium powder, maize starch and pulverized coal under inter gas atmosphere, oxidation characteristic of pyrolysis residue (coke) under air atmosphere, as well as the calculation of the oxidation kinetics parameters of lycopodium powder. Dust smoldering process on a hot surface and the influences of dust thickness and temperature of hot surface to smoldering process were also studied. Three-step kinetic reaction mechanism was used to establish smoldering process model and a numerical simulation of lycopodium powder smoldering process on a hot surface was carried out.Three topic aspects as fllowing were carried out in this paper:(1) Experiment research on dust thermal analysis kineticsFirstly, TG analysis was used to observe the pyrolysis process of lycopodium powder, maize starch and pulverized coal in pure argon atmosphere. Three stages of dust pyrolysis process were obtained from the results of TG profiles, and pyrolysis properties in different stages of3kinds of dusts were analysed.Then oxidation kinetics experiment study of dust pyrolysis residue (coke) was carried out. The oxidation kinetics equations of3kinds of dust pyrolysis residues were obtained by analyzing the DSC profiles using single scan rate method. The equations are as follows: Lycopodium powder: Maize starch: Pulverized coal:Lycopodium powder’s oxidation kinetic parameters were calculated by Friedman-Reich- Levi method and Flynn-Wall-Ozawa method respectively. Results showed that the activation energy under the conversion rate range from0.1to0.9was not fixed, the activation energy of lycopodium powder was in the range of70-115kJ/mol. The activation energy decreased with the increase of temperature and conversion process. It implied that the reactivity of lycopodium powder increased with the reaction rate.(2) Experimental study on smoldering process of dustsA temperature acquisition system was added to the minimum ignition temperature test apparatus of dust layer and dust smoldering process experimental study was carried out. Influence of dusts thickness and hot surface temperature to dust smoldering process was mainly considered.Experiment results indicated that there were two stages in the smoldering process of dust on a hot surface:smoldering initialization stage and smoldering propagation stage. Smoldering process experiments on different thickness of dust indicated that dust thickness had no effect on the rate of smoldering propagation. Experiments under different hot surface temperatures showed that dust smoldering process needed certain external temperature. The ignition delay was lower at higher temperature of hot surface, but hot surface temperature did not affect the smoldering propagation velocity from top surface downwards.(3) Numerical simulation of dust smoldering processDust smoldering model was established based on three-step reaction kinetics mechanism, the basic principles of fluid dynamics. A generalized pyrolysis model for combustible solids (Gpyro) software was used to simulate the process of dust smoldering. Two-dimensional temperature field change and dynamic reaction rate were also obtained through the simulation results. The temperature correlation of each sampling point of simulation and experiment results was good.