Thermal Hazards Of Ammonium Nitrate And Effect Of Copper Oxide Under Different Heating Experiments

As a typical reactive chemical,ammonium nitrate is one of the main sources of fire and explosion accidents in chemical industry parks.Most of the existing studies on the thermal risk of ammonium nitrate were carried out from the perspective of micro calorimetric thermal analysis.However,the heating condition in a real fire scenario is different.Taking the 8·12 Tianjin Port fire and explosion accideints as an example,thermal decomposition of ammonium nitrat was due to the thermal radiation caused by external fire.At present,there is no analysis of the thermal risk of ammonium nitrate under thermal radiation conditions.Copper oxide has recently been added to ammonium nitrate to improve its crystalline stability,but as an effective catalyst,the addition of copper oxide is likely to significantly reduce the thermal hazard of ammonium nitrate.At present,there are few studies on the thermal stability of such mixture.Based on the industrial background,a series of experimental and theoretical studies were carried out in this paper to explore the thermal hazards of ammonium nitrate under different heating conditions and the effects of copper oxide.The two heating conditions included micro calorimeter experiment and thermal radiation experiment,respectively.And the effects of cupric oxide content,particle size and atmosphere on thermal stability were studied.Two micro calorimeter techniques,the Simultaneous Thermal Analyzer and C80 Calorimeter were applied to study the mass loss and heat release behavior during thermal decomposition.Results indicated that in the open system of Simultaneous Thermal Analyzer,thermal decomposition of ammonium nitrate was endothermic,while exothermic effect was observed in the closed system of C80.Different thermal effects were explained through the complicated thermal decomposition reactions.Besides,the effects of particle size and atmosphere could not be observed in Simultaneous Thermal Analyzer,and thus C80 is more suitable to study the thermal hazards of this mixture.Thermal radiation experiments were conducted to study the mass loss,sample temperature and thermal decomposition stages under different radiant fluxes.Results indicated that under thermal radiation,the mass loss rate of ammonium nitrate underwent four stages,including slowly increase,steady,rapid increase and decrease.The involvement of copper oxide contributed to the combination of the first two stages and reduced the time.On basis of evolved gas analysis and micro calorimeter experiments,it was found that the catalytic effects of copper oxide on thermal decomposition of ammonium nitrate was due to the formation of new components in liquid by reducing liquid acid and the absorption of ammonia,which both influenced the chemical equilibrium state and contributed to the rapid decomposition of ammonium nitrate.In terms of theoretical analysis,the kinetic parameters of thermal decomposition of ammonium nitrate were calculated by using different classical kinetic analysis methods,and the applicability of different methods was compared.The calculation indicated that whether the model-free kinetic models consider the reaction rate could significantly influence the kinetics.On the basis of kinetic parameters,a series of thermal safety parameters was selected to characterize the thermal hazards of pure ammonium nitrate and ammonium nitrate mixture with copper oxide.The critical thermal runaway conditions were predicted through different thermal explosion models.The suitable thermal risk index was found which could effectively distinguish the thermal hazards of pure ammonium nitrate and ammonium nitrate mixture with copper oxide.In order to realize the connection between micro-heating experiment and radiation heating,the thermal decomposition model of ammonium nitrate was established by means of condensed phase thermal decomposition gasification model and a simplified two-step thermal decomposition reaction mechanism.The establishment of the model included the verification of thermodynamic and kinetic parameters in the thermal decomposition process through the inverse calculation analysis of micro-heating experiment,and the verification of other thermophysical parameters that affect the mass loss and temperature distribution of thermal decomposition through the inverse calculation analysis of radiation heating experiment.The study in this paper is helpful to grasp the thermal hazards of both ammonium nitrate and its mixture with copper oxide from different dimensions and the various basic parameters obtained from the analysis can provide some references for controlling fire and explosion accidents of ammonium nitrate.In addition,the model and method established in this paper could also provide reference for the study of thermal hazards other reactive chemicals.