Experimental And Theoretical Research On The Pressure Relief Of Thermal Runaway Reaction Systems

Reaction runaway which is also called reaction thermal runaway means that the exothermic reaction system due to broken heat balance causes the temperature to rise,with the process of "exothermic reaction-temperature rise-reaction acceleration-temperature increase-re-acceleration-re-rise...",the heat release rate exceeds the control limit of the reactor cooling capacity,which results in the decomposition of reactants and products,where pressure rises sharply due to a large amount of gas generation,finally,reaction runaway causes the spray and destroyment of the reactor,and even the phenomenon of burning and thermal explosion.The safety relief system is an important protective measure to prevent accidents for the loss of heat control process equipment,which works independently to reduce the severity of accidents and has important protection for people,property and environment.Therefore,the experimental and theoretical research on the pressure relief of thermal runaway reaction system is extremely important.The theoretical and experimental research of three kind relief reaction systems(also called relief system: vapor system,gassy system and hybrid system)is performed in this paper,where each system selects two typical materials.(1)In order to determine the worst scenario of the relief process,it is necessary to identify the hazardous scenarios and materials in the process,meanwhile whether the material has autocatalytic property and its autocatalytic strength is one of the important basis for judging the hazard degree of the material.So,the autocatalytic decomposition characteristics under adiabatic conditions are researched by Thermal Safety Software(TSS).By changing the kinetic and thermodynamic parameters in the Benito-Perez model,25 groups of autocatalytic decomposition curves are obtained,combined with statistical methods and dimensionless methods,two new methods for identifying material autocatalytic strength are proposed(i.e.energy ratio classification method and dimensionless standard curve classification method),the energy ratio of two-step reaction and autocatalytic factor in B-P model are used as determination parameters,which divides autocatalytic strength into five levels(i.e.weak or no,less weak,medium,less strong and strong autocatalysis).(2)In order to obtain the relevant data of the relief design,adiabatic correction is necessary to be applied in the experimental results,because the thermal inertia at the laboratory scale is often larger than that value in the plant scale.However,the material kinetics is an indispensable prerequisited condition for the adiabatic correction of experimental results.Therefore,according to the characteristics of six materials,several different equipments including Reaction Calorimetry(RC1),Accelerating Rate Calorimeter(ARC),Differential Scanning Calorimeter(DSC)and Vent Sizing Package2(VSP2),are selected for kinetics study.The model-based accurate kinetics calculation method and some common kinetics calculation methods are used to analyze and calculate the test results.Then,the kinetic expressions of the six materials are obtained,which includes activation energy,frequency factor,mechanism function.By combining the kinetics of six-group materials and their VSP2 test data,a kineticbased adiabatic correction method is proposed,which expands the applicable field on the basis of the traditional adiabatic correction methods.(3)Material 5#(20% DTBP in toluene solution)is selected for filling ratio effect test by ARC.According to the test results,the pressure composition of material 5# during decomposition is analyzed,combined with adiabatic correction method,a pressure correction method and application procedure is established,which provides a theoretical basis for the pressure correction of the remaining five materials.Based on this,the correction results including pressure rise rate,gas generation rate etc are obtained.(4)In order to obtain a reasonable relief design result,a systematic study of the singlephase flow and two-phase flow venting of the three systems is carried out.By setting different set pressures,the corrected relief design parameters corresponding to set pressures are obtained.The appropriate relief design method is selected to calculate and judge information such as the relief flow state and flow model,the required relief area etc.The results show that: 1)For the single-phase flow venting design of the three systems,the increasing of the set pressure will reduce the required relief area,the difference is that the vapor system will quickly reach a stable value after the reduction,the gassy system will continue to decrease,and the hybrid system will gradually reach a stable value;2)For the two-phase flow venting design,only vapor system occurs the venting area continuously increases with the set pressure.The area of gassy system and hybrid system(top relief)continue to decrease as the set pressure increases;3)the area required for the two-phase flow venting is always larger than the single-phase flow,therefore,the two-phase flow relief is much more dangerous than single-phase flow.(5)In order to further study the differences of processes and results of the relief design between different systems,it is found by comparson that the area required for one-phase or twophase flow venting of untemper system(gassy system and partial hybrid system)is often larger than temper system(vapor system and partical hybrid system),which illustrates that the existence of vapor can reduce the required relief mass flow.The bottom relief design of untemper system is much smaller than the top relief design result.So,under engineering achievable,the bottom relief design of untemper system can be greatly reduce the relief area,which helps engineers select suitable relief equipment.This paper provides important reference and guidance for the analysis and determination of the reaction system thermal runaway hazard,the acquisition and correction of the relief design parameters,and the design and application of the relief system.