Deviation propagation along a propylene glycol process using dynamic simulation: An innovative contribution to the risk evaluation

Abstract

Nowadays, quantitative risk analysis is essential for safety process management. For this purpose, dynamic simulation is an efficient tool to predict the time evolution of process parameters during deviations from normal operating conditions. There is a real interest in knowing the system behavior during malfunctions for the design of safety barriers. As a matter of fact, the knowledge of the process dynamic behavior and the profiles of the operating parameters during a degraded mode permits to provide guidelines regarding the required safety barriers. Nevertheless, the description of the process dynamic behavior in case of failures remains a challenge. In this study, a methodology is proposed: it combines dynamic simulation with ASPEN PLUS DYNAMICS™ 9.0 software tool, lessons learnt from accidents and risk analysis. The primary focus of this paper is on risks occurring in distillation columns, unit operation involved in the case study. The case study concerns a continuous process of propylene glycol (C3H8O2) production. The synthesis unit involves three consecutive competitive reactions leading to the formation of by-products: di and tri glycols (C6H14O3 and C9H20O4 respectively). The process is composed of a CSTR reactor and two distillation columns in series (C1 and C2). Two deviation scenarios on C1 reboiler, chosen according lessons learnt from previous accidents, are simulated and the consequences on C1 and C2 operation analysed. Overpressure, flooding and weeping occurrence are put in evidence and quantified. This work provides a new perspective on risk quantification through the analysis of deviation propagation along a process involving several unit operations.