(595d) Preventing Thermal Runaway Reaction of Ethylene Oxidation Via Plant-Wide Dynamic Simulation

Ethylene oxide (EO) is highly reactive, flammable and colorless gas at temperatures above 51.3 °F. EO is an important chemical intermediate for the production of various chemical products, such as solvents, antifreeze, textiles, detergents, adhesives, polyurethane foam, and pharmaceuticals.1 The manufacturing of EO involves critical exothermic reactions at high temperature and high pressure. When the EO plant experience process upsets and turnaround operations, the EO reactor may release much more heat than that in normal operation conditions and might be pushed into runaway conditions resulting in catastrophic personal injury, severe air pollution, and tremendous economic loss. EO reactor explosions have been reported several times in the nation.2-3

To prevent runaway reactions at an EO plant, the disturbances to EO reactors should be avoided, reduced, or mitigated to the maximum extent. The study of EO reactor subsystem itself is not adequate for this purpose. From the system point of view, this requires the operation of the entire EO plant be well-scheduled and controlled under various situations, including operations for normal process upsets and turnaround (start-up and shutdown) conditions. Currently, a systematic study in this area is still lacking. In this paper, an EO plant dynamic simulation model is developed and implemented to study various scenarios that might cause runaway conditions. The developed plant-wide dynamic model includes reaction, mixing, compression, recycling, and recovery sections. The integrated plant model is validated before application by both steady-state and dynamic historian data. Through the plant-wide dynamic simulation, the system dynamic behaviors under different upsets and turnaround scenarios are disclosed. It provides a comprehensive understanding of how the disturbance sources would affect the upper and/or down stream processes. Upset scenarios causing potential runaway reactions under the current design and control strategy are identified. Based on such quantitative analysis, the improved design and control strategy to for safety operations under normal and turnaround operation conditions will be proposed and examined. A virtual study with real industrial data is utilized to demonstrate the significance and benefits of this methodology.

Reference

1. Yang, X.; Xu, Q.; Li, K.; Sagar, C. D. Dynamic Simulation and Optimization for the Start-up Operation of an Ethylene Oxide Plant. Ind. Eng. Chem. Res., 2010, 49 (9), P4360

2. Investigation report- Sterigenics, Report No.: 2004-11-I-CA, U.S. Chemical Safety and Hazard Investigation Board, March 2006

3. Kletz, T. A. Fires and explosions of hydrocarbon oxidation plants, Plant/Operations Progress, 1988, 7(4), P226