Thermal runaway reaction, hazard evaluation

L. Van Roeicel. Thermal Runaway Reactions Hazard Evaluation. In Chemical Process Hazard Review (1. M. Hoffmann and D. C. Maser, eds.), ACS Symposium Series 274, American Chemical Society, Washington, DC, 1985, Chapter 8. 

An investigation of potential thermal runaway reactions is a significant part of a thorough hazard evaluation. Important parameters of the exothermic reaction as well as of the large-scale system are discussed. Their relationship is explained through the Semenov Theory. 

The first aim of a thermal stability screening test (e.g., DSC/DTA) is to obtain data on the potential for exothermic decomposition and on the enthalpy of decomposition (AHd). These data, together with the initial theoretical hazard evaluation, are used in reviewing the energetic properties of the substance (Box 4) and the detonation and deflagration hazards of the substance (Boxes 7 and 8). The screening tests also provide data on the thermal stability of the substance or mixture, on the runaway potential, on the oxidation properties, and to a lesser extent, on the kinetics of the reaction (Box 10). 

Mix, K. K., "The Use of Advanced DTA Methods for the Evaluation of Thermal Instability, Hazard Evaluation, and Process Design," in Proceedings Runaway Chemical Reaction Hazards Symposium, IBC, London, England (1987). 

For the thermal runaway hazard evaluation, the "chemistry" of the exothermic reaction can be defined in terms of three sets of parameters the thermodynamic, kinetic, and physical parameters. (1) A list of some of the parameters of interest is given in Table I. 

The results of the hazardous chemical evaluation are used to determine to what extent detailed thermal stability, runaway reaction, and gas evolution testing is needed. The evaluation may include reaction calorimetry, adiabatic calorimetry, and temperature ramp screening using accelerating rate calorimetry, a reactive system screening tool, isoperibolic calorimetry, isothermal storage tests, and adiabatic storage tests. 

The discussions in Sections 3.1 and 3.2 show that the interaction among enthalpies of reaction, reaction kinetics, and surrounding conditions is of paramount importance relative to the existence of potential thermal hazards such as runaways. Whereas valuable information on parameter sensitivity can be estimated by a theoretical approach, it remains of vital importance to evaluate hazards by appropriate and adequate laboratory tests to obtain information on the rates of heat and gas generation, and the maximum quantities of heat and gas involved. Materials which are real to the process should be used in tests to assure that the effects of any contaminants are recognized. 

In 55% of the cases, the accidents could have been foreseen by use of risk analysis, and in 35% of the cases by thermal stability testing. Different methods of stability testing were evaluated comparatively during the investigation of a runaway exothermic reaction which occurred during the preparation of a component mixture for a sealing composition in a 1200 1 reactor only DSC was effective in identifying the cause of the hazard. 

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