Transient process simulation of a thermal explosion at a propylene purification unit using calorimetric techniques

Abstract

In Taiwan, on July 30, 2011, a huge explosion occurred at a propylene purification unit when eliminating impurities such as H2O, H2S, and COS. This incident severely eroded public faith in mechanisms for ensuring chemical process safety. Plant operators failed to identify the serious situation; this failure has been blamed on their use of insufficient detection equipment and inaccurate data. In this study, we demonstrated a relationship between propylene and the thermal characteristics of the sorbents used. To reconstruct the accident, reaction pathway analysis, pseudo-adiabatic adsorption conditions, and precise thermal parameters were modelled using vent sizing package 2, a pseudo-adiabatic calorimeter. For an in-depth analysis, computational fluid dynamics (CFD) modelling techniques were employed. The results indicated that propylene adsorption immediately raised the sorbent bed temperature. Severe oligomerisation was identified upon the temperature reaching 150 °C; this was suspected to be the main reason for the thermal chain reaction and its effects. Moreover, gaseous-phase propylene diminished the heat-removal capacity during the process. This led to considerable adsorption heat, causing a chain reaction that resulted in the explosion and fire. CFD results showed that shortening the liquefaction period was effective for operation safety. Finally, the unavoidable adsorption heat release acted as the initiator, triggering the advanced reaction in a nonrigorous system. In this study, practicable numerical methods were expanded to predict the runaway reaction of the adsorbent system, and the results revealed blind spots in the system data with respect to the accident scenario.