(180c) Operational and Safety Aspects of LNG Plants through Dynamic Simulations: Disturbance Scenarios, Storage and Flare Networks

LNG is an attractive technology for transporting natural gas across the globe. Due to the energy intensive nature of the LNG process, 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 and its importance to safe LNG design in three case studies. The first study will focus on dynamic simulation of a liquefaction process with parallel refrigerant compressor strings. Parallel configurations present unique operating challenges when a trip or scheduled maintenance event takes a string offline or when the same string needs to be returned to service without disrupting current operations. The presentation will provide examples as well as discuss other operational and safety aspects of an LNG plant that can be modeled to improve plant design and maximize performance. The second case study will demonstrate how dynamic modeling, based on first principles, is an essential requirement for the accurate assessment of LNG rollover in storage tanks; the rollover phenomenon occurs when rapid mixing of LNG of different conditions takes place within the storage tank, leading to the possible sudden release of large amounts of vapor and the potential over-pressurization of the tank resulting in potential damage or failure. This case study will demonstrate how dynamic simulation can be used to develop tools which can be applied to simulate the occurrence of rollover and to evaluate strategies to prevent it. The third case study considers the design of flare and blowdown systems for LNG facilities. A blowdown (depressurization of process equipment and piping) is a safety critical operation; required to ensure safe shut-down during a plant emergency. Although facility blowdown is a highly transient event, for large facilities it can take several hours when the operation is staggered, such that different parts of the plant are blown down sequentially. By contrast, conventional flare & blowdown systems are designed using static tools and methodologies. In this talk, we describe how a more rigorous dynamic assessment has been used to optimize the blowdown operation for a recently constructed LNG plant, reducing blowdown duration and delivering a safer facility.