Operations Improvement in LNG Re-Gasification Terminal through Corrected Storage Tank Model

The simulation of liquefied natural gas (LNG) storage tanks is often grounded on numerous problematic assumptions, for example, assessment of boil-off gas (BOG) generation using boil-off rate, static liquid-level, vapor liquid equilibrium in the tank, use of only lateral area for heat loss calculations, and etcetera. Few of these assumptions are built into frequently used commercial simulators, making further challenges in simulating the real behavior of LNG tanks. This study highlights these challenges in the background of a commonly used process simulator, Aspen HYSYS, and provides analytical and intuitive solutions to those problems. Then the corrected tank model is used for operations improving in LNG re-gasification terminal. Based on the study following rules of thumb for enhanced operations of LNG re-gasification terminal are deduced:

• The pressurization rate of the tank with the highest liquid level is the slowest
• Ambient heat leak dominates BOG generation at a low re-circulation rate
• In-tank pump work dominates BOG generation at a high re-circulation rate
• Minimum re-circulation that prevents 2-phase is the best operating policy

If implemented, the deduced rules could help enhance LNG terminals’ energy efficiency and reduce operational costs while increasing safety.