Dynamic optimization of the Boil-Off Gas (BOG) fluctuations at an LNG receiving terminal

Abstract

Heat leakage and mechanical energy input by equipment evaporate Liquefied Nature Gas (LNG) in LNG receiving terminals into Boil-Off Gas (BOG), which must be compressed and liquefied by sub-cooled LNG in a recondenser. During ship unloading, there are sharp fluctuations in BOG waste resources, causing economic loss. Meanwhile, the liquid levels of the recondenser are unstable, and the consequent pump cavitation and equipment vibration introduce risks to the operation. This study focuses on the above problems in an actual LNG receiving terminal. The factors affecting the BOG generation in the LNG receiving terminal and the generation rules are analyzed. To find effective improvements for these problems, an optimization model is built and solved using a dynamic simulation tool, which provides a reference for further dynamic research. After optimization, 0.19 million m3 of natural gas avoid being flared, and the energy consumption of the BOG compressors is reduced by 4.2%, i.e., 0.19 million kWh. As a result, annually 0.14 million USD are saved in total. In addition, pump cavitation and recondenser vibration are also reduced, and the recondensing system is easier to control, which contributes to the safe operation of the terminal.