(48a) Safer and Improved Process Design of LNG Plants Using Dynamic Simulation

Due to its clean fuel credentials, the demand for LNG is set to continue to increase in the near future with more remote stranded gas being exploited. Due to the energy intensive nature of the LNG processes, significant effort is being invested in improving the efficiency of the operation in a safe way. High-fidelity dynamic models coupled with accurate thermodynamics are a necessary tool to analyze, understand and predict the transient behavior of LNG plants under various operational and safety events. This presentation will demonstrate high-value applications of advanced process modeling technology through dynamic simulations in two case studies.

The first case study will focus on a liquefaction process with parallel refrigerant compressor strings; a configuration presenting unique design and operating challenges. Dynamic simulation is used to address these challenges prior to startup.

The second case study is about the protection of process equipment exposed to fire. LNG plants typically have a significant inventory of light hydrocarbon gas under high pressure, and so a depressurization system is an essential safety component for the plant; this aims to prevent escalation of a local fire into a larger uncontrollable fire. The depressurization system should ensure that flammable hydrocarbon gas can be safely disposed of via the flare system in the event of a detection of a fire or a gas leak. API 521 (6^th edition, Appendix A) introduces the rigorous analytical methodology for depressurization system design. Dynamic modelling is a key component for this methodology that assesses the rupture time for piping and vessels under fire attack. For this case study, we will demonstrate how dynamic analysis ensured a safer design for a recently constructed LNG plant and we discuss the key modeling requirements for such an assessment; specifically the need for rate-based thermodynamics and for a geometric representation for all pipes and vessels in the fire zone.