(442f) Study On a Cryogenic Separation System Under Abnormal Situations Via Dynamic Simulation

A cryogenic separation system, especially the chilling train and de-methanizer facilities, plays an important role in olefin plants. This system can chill and refrigerate the cracked gas from cracking furnaces to -160 °C, so as to separate the light components such as hydrogen, methane, and C2+ at different temperatures. As it closely relates to heat exchange at low temperatures, previous studies mainly focused on the energy use efficiency of this system. Because the cryogenic separation system operates at low temperature and high pressure, it features inherently un-safety, this paper will address its design and operational safety issues at dynamic situations, i.e. identify the safe operation capability of the cryogenic separation system under abnormal situations. In addition to the safety concerns, this paper will also study air emission problems during these abnormal situations. A large-scale dynamic simulation system integrating rigorous models of chilling train and de-methanizer facilities is developed for these study purposes. The abnormal situations such as system start-up, upsets, and shutdown will be simulated. They may cause off-spec product generations or system over-pressure events, which eventually lead to the flaring emissions. Dynamic simulated emission source profiles will be provided when these induced emission events arise. Based on the safety and environmental impact analysis for the current cryogenic separation system, design and operational improvements will be proposed and tested in the virtual dynamic environment. A case study is employed to demonstrate the efficacy of this study.