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Behavior of a Gas-Generating System Under Runaway Conditions: Dynamic Modeling of Open and Closed Vessels
Abstract
Exothermic chemical reactions can potentially cause runaway conditions, leading to an exponential rise in temperature and pressure within reactor vessels or storage tanks. This can overpressurize the vessel, potentially leading to catastrophic events such as vessel explosions. An emergency relief system (ERS) serves as the last line of defense against such hazards by relieving the overpressure. However, to serve its purpose effectively, it must be adequately sized. In the case of gas-generating reactive chemical systems (gassy or hybrid), the maximum specific gas generation rate (ng max) evaluated under runaway conditions is a critical parameter for ERS sizing.
In the 1980s, the Design Institute of Emergency Relief Systems (DIERS) developed an experimental method to determine ng max in runaway reactions. This method is based on adiabatic calorimetric data, particularly temperature, and pressure measured under adiabatic runaway conditions. However, there is currently no industry consensus on the appropriate adiabatic test configuration (closed or open) nor the interpretation of the experimental data for determining g max. Furthermore, existing methods tend to overestimate the size of the vents in some systems. Therefore, there was a need to develop a model that could effectively and precisely assess the behavior of a vessel undergoing a runaway reaction before and during the entire venting process to improve the methods used to evaluate ng max and, therefore, improve ERS sizing in gas generating systems.
The dynamic simulator under development at Texas A&M University in Qatar (TAMUQ), under the collaborative work of Dr. Luc Véchot and Dr. Marcelo Castier, is a step toward attaining this goal. This master’s thesis is the direct continuation of the previous master’s theses on this topic.
The study discusses the influence of varying the vessel fill level in a closed system, as well as varying the diameter and set pressure of an ERS venting device in an open system on the behavior of the vessel under runaway conditions. The closed vessel simulations will focus on evaluating the contribution of the generated gas to the overall vessel pressure and the attained g max during the runaway reaction. In addition to assessing the approach proposed by DIERS to estimate ng max using calorimetric data in a closed cell configuration. The open vessel simulations will be used to evaluate the contribution of the generated gas to the overall vessel pressure in venting conditions. In addition to validating the approach of predicting ng max in a vented cell through the closed-cell method.
This thesis aims to understand the complex behavior of untempered reactive mixtures under runaway conditions during venting through ERS and improve the current ERS design methodologies to protect pressurized reactor vessels. These goals will be achieved by utilizing the dynamic simulator to study the dynamic behavior of a gassy/hybrid chemical system in two vessel configurations: closed and open, using an ERS device.
Subject
Runaway reactionsgassy and hybrid systems
maximum gas generation rate
correcting for thermal inertia
dynamic simulation
emergency relief system sizing
Citation
Grati, Amani Tariq Wahid (2023). Behavior of a Gas-Generating System Under Runaway Conditions: Dynamic Modeling of Open and Closed Vessels. Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /199969.