(167b) Simulation of a Gas-Generating System Under Runaway Conditions: Studying the Behavior during Venting and Assessing Current Approaches for Evaluating the Gas Generation Rate

Emergency relief systems (ERS) serve as the last line of defense against the explosion of a vessel enclosing a reactive gas-generating mixture under runaway conditions. ERS design for gas-generating systems requires the evaluation of the gas generation rate under runaway conditions. Current methodologies, mainly developed through the work of the Design Institute for Emergency Relief Systems, are based on the experimental evaluation of the gas generation rate under runaway conditions using pseudo-adiabatic calorimetry at a laboratory scale. Such experiments involve the measurement of the temperature and pressure resulting from the runaway in a test cell in either a closed or open (to a containment vessel) cell configuration. The ideal gas law is used with the measured gas temperature and pressure to assess the gas generation rate. Although this methodology is relatively easy to implement, there is currently no consensus on the best experimental conditions, cell configuration, and their interpretation (correction for the effect of thermal inertia) to measure the gas generation rate.

In order to improve the methods used to evaluate the gas generation rate and, to a greater extent, the ERS design methodologies, it is crucial to gain a comprehensive understanding of the phenomena that occur in a vessel containing a gas-generating mixture under runaway conditions before and during the venting process. As a step in this direction, the paper will discuss the use of a dynamic simulator capable of rigorously calculating the temperature, pressure, and phase composition in a vessel containing a gas-generating reactive mixture under runaway conditions. A series of simulations of runaway reactions under venting conditions was performed. The results are analyzed to highlight the behavior of the gas-generating reactive system before and during venting, with a special emphasis on the temperature, pressure, and phase composition at each time step of the runaway and how they are affected by the ERS diameter and the ERS set pressure. The gas generation rate rigorously calculated by the model is then compared with the gas generation rate calculated using the above-mentioned methodologies based on pseudo-adiabatic calorimetry, with an emphasis on the closed-cell test approach.