1.1. GENERAL OVERVIEW

Advanced numercial techniques combined with decomposition kinetics can be used for predicting the reaction progress of exothermic reactions under heat accumulation conditions (-2). As discussed in the International ICTAC Kinetics Project (3-6), advanced kinetic description is required to correctly describe the progress of decomposition reactions because these reactions generally have a multi-step nature. The use of simplified kinetic models for the assessment of runaway reactions can, on the one hand, lead to economic drawbacks, since they result in exaggerated safety margins. On the other hand, it can cause dangerous situations when the heat accumulation is underestimated. For self-heating reactions, incorrect kinetic description of the process is usually the main source of prediction errors.

To be able to assess the probability of occurrence of a runaway reaction, it is necessary to replace the commonly used methods applying simplified assumptions by advanced numerical methods able to determine the trustworthy kinetic parameters. The concept of Time to explosion or TMRad (Time to Maximum Rate under adiabatic conditions), the performing of cook-off experiments and their comparison with the simulation are of great utility for the assessment of the modelling capability.

Applications of Finite Element Analysis (FEA) and accurate kinetic description enable the analysis of influence of the effects of scale, geometry, thermal conductivity, heat transfer (e.g. from the sample towards the environment or towards the sample container from an external source of heat such as fire) and ambient temperature on the heat accumulation. Due to limited thermal conductivity, a progressive temperature increase in the sample can easily take place resulting in an explosion. This analysis can then be used to determine critical design parameters such as the critical radius for a container, the necessary thickness of insulation, and the influence of the surrounding temperature on storage and transport safety. Verification of the computations can be achieved by comparison of the experimental and calculated ignition time of cook-off (kilo scale), where the scale-up is achieved by combining FEA and the kinetics obtained from the DSC experiments (mg scale). Once the corroboration of the computations is achieved, simulation can be used to examine the safety and the properties of the systems containing a larger amount of energetic materials for any surrounding temperature profiles such as isothermal, non-isothermal, stepwise, modulated, shock and additionally for temperature profiles reflecting the real atmospheric temperature changes (yearly temperature profiles of different climates with daily minimal and maximal fluctuations). This analysis can then be used to determine critical design parameters such as the critical radius for a container, the necessary thickness of insulation, and the influence of the surrounding temperature on storage and transport safety.


AKTS AG -Switzerland

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AKTS AG
Advanced Kinetics And Technology Solutions
TECHNO-Pole
3960 Siders - Switzerland
Phone: +41-848-800221 Fax: +41-848-800222


(1) Advanced Kinetics and Technology Solutions: http://www.akts.com (AKTS-Thermokinetics software and AKTS-Thermal Safety software)
(2) B. Roduit, C. Borgeat, U. Ticmanis, M. Kaiser, P. Guillaume, B. Berger, P. Folly, Thermal stability and safety analysis of explosives under different temperature modes, 35th International Annual Conference of ICT July, 2004, 37-1.
(3) M.E. Brown et al. Computational aspects of kinetic analysis. The ICTAC Kinetics project data, methods and results. Thermochim. Acta, 355 (2000) 125.
(4) M. Maciejewski, Computational aspects of kinetic analysis. The ICTAC Kinetics Project - The decomposition kinetics of calcium carbonate revisited, or some tips on survival in the kinetic minefield. Thermochim. Acta, 355 (2000) 145.
(5) A. Burnham, Computational aspects of kinetic analysis. The ICTAC Kinetics Project - multi-thermal-history model-fitting methods and their relation to isoconversional methods. Thermochim. Acta, 355 (2000) 165.
(6) B. Roduit, Computational aspects of kinetic analysis. The ICTAC Kinetics Project - numerical techniques and kinetics of solid state processes. Thermochim. Acta, 355 (2000) 171.