Research On The Effect Of Different Kinds Of Additives On The Thermal Decomposition Kinetics And Thermal Risk Of Ammonium Nitrate

As an important chemical product,ammonium nitrate has been widely used in the field of industry and agriculture.However,due to its thermal decomposition property,thermal decomposition or even explosion may occur during improper storage,transportation,or use.Especially when ammonium nitrate contains different additives or impurities,its danger tends to change in nature,leading to a large number of catastrophic accidents at home and abroad in history.These accidents have resulted in particularly significant casualties and property damage,as well as huge social impacts.This paper aims at the practical safety problems existing in the actual production,storage,and use of ammonium nitrate.The influence mechanism of different additives(or impurities)on the thermal decomposition kinetics and thermal hazard of ammonium nitrate has been systematically studied,and its thermal safety property has also been predicted.In this paper,the parameters of the thermal decomposition kinetics of ammonium nitrate are firstly analyzed and solved by high-precision non-isothermal linear heating thermogravimetric experiments.A composite algorithm combining the isoconversional method and the model-fitting approach is chosen to obtain the accurate reaction activation energy.Then,the accurate solution of Arrhenius parameters,the verification of parameter simulation,the solution of kinetic compensation effect,and the accurate reconstruction of the kinetic model of thermal decomposition reaction are carried out.The expression of the optimal kinetic mechanism model for the thermal decomposition of ammonium nitrate under the four heating rates is f(α)=α-0.0259(1-α)0.0617.The fit of this model to the experimental data is substantially improved over the empirical model.At the same time,an accurate method for solving the kinetic triplet of thermal decomposition of substances based on non-isothermal linear heating experiments is also proposed.Secondly,considering the actual situation of ammonium nitrate used in industry and agriculture,the law of the influence of additives such as sodium halide,ammonium phosphate,and urea on the thermal decomposition kinetics of ammonium nitrate has been experimentally studied.The thermal decomposition activation energy,pre-exponential factor,and reaction mechanism function models with different additives and contents of ammonium nitrate are obtained.Combining the obtained results,it is found that ammonium phosphate and urea significantly increase the activation energy of the thermal decomposition reaction of ammonium nitrate.Meanwhile,the addition of additives shifts the kinetic mechanism of the thermal decomposition of ammonium nitrate to different dominant reaction modes.In this process,according to the actual situation of the multi-component reaction system,the method for solving the kinetic parameters of thermal decomposition of substances proposed above is verified and optimized.Thirdly,by means of C80 microcalorimetry experiment,ARC adiabatic experiment,and evolved gas analysis methods,the effects of different additives on the energy release and evolved gas products during the thermal decomposition of ammonium nitrate are systematically studied.In addition,the effects of various additives on the chemical reaction energy,product types,and the risk of thermal decomposition of ammonium nitrate thermal decomposition are analyzed,and the action mechanism of the additives is proposed.The results show that the characteristic product of the thermal decomposition of all samples is nitrous oxide.At the same time,the additives represented by urea can delay the progress of the main reaction of thermal decomposition of ammonium nitrate,decrease the heat released by the reaction,and reduce the overall pressure rise rate under an adiabatic environment,which is beneficial to the improvement of its thermal safety performance.Further research shows that the substance that mainly inhibits thermal decomposition is the ammonia gas released during the chemical reaction of the additive itself.Eventually,according to the obtained basic kinetic and thermodynamic parameters,combined with the actual application of ammonium nitrate,on the basis of traditional single index evaluation,the thermal safety of the ammonium nitrate system under different ambient temperatures and stacking scales has been simulated and predicted.In the prediction process,the thermal hazard of ammonium nitrate under the action of additives is comprehensively evaluated in combination with the actual conditions such as ambient temperature and stacking scale.Relevant results show that a single basic kinetic or thermodynamic index and a simple combination of them may not be able to accurately assess the thermal hazard of a substance.For ammonium nitrate,the thermal hazard increases sharply as the ambient temperature or the stack size increases.Therefore,in the actual storage,transportation,and use,it is necessary to avoid a large number of centralized stacking and pay attention to timely ventilation and heat dissipation.