Modeling the Behavior of a Vessel under Runaway Conditions

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runaway reactions, thermal explosions, modeling, process safety
thesis / dissertation description
Reactive chemicals may proceed into uncontrolled chemical reactions with significant evolutions in temperature and pressure due to vapor/gas production. This happens when there is loss of control of the temperature of the system, and self-heating occurs, thereby leading to a runaway reaction. The overpressurization of the vessel following the runaway may lead to an industrial accident, a thermal explosion, resulting in damages to people, property and the environment. Emergency relief systems (ERS) act as a last line of defense against vessel overpressure. It is therefore critical to the safe operation of chemical processes that they are adequately sized. Much effort is needed to overcome the limitations presented by the current ERS sizing method used. Also, reliance solely on experimental work can prove to be time consuming and provide difficulties during scale-up to industrial scale. Thus, there is a need to employ a comprehensive dynamic model that describes the vessel behavior throughout the reaction, during depressurization and relief action. This involves the understanding of the phenomenological links between thermodynamics, kinetic and fluid dynamics inside the vessel from the onset of the runaway until the end of the venting through an ERS. These outputs of this model could then to be used to enhance ERS sizing methods and consequence analysis. This work represents a step forward in this direction. It proposes a model that takes all these factors into account, with the exception of level swell. To achieve this, this work includes: (i) an experimental study of the reactive system using calorimetric techniques; (ii) determination of the kinetic rate expression for the reactive system; (iii) formulation of dynamic lumped model; (iv) dynamic simulations of a closed vessel and partial experimental validation; (v) a sensitivity analysis of the effects of ERS area and ERS set pressure on vessel behavior. This approach was carried out through the evaluation of the decomposition of di-tert-butyl peroxide in toluene, a potentially hazardous reactive system.

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