RECOVERING BOIL-OFF GAS DURING LNG SHIP LOADING

摘要

Boil-off gas (BOG) is generated during the ship-loading process. Many factors contribute to the BOG generation and not all can be eliminated. There are many examples where ship loading BOG is flared at ship berth areas. However, as environmental regulations become more stringent, flaring of BOG during ship loading is not a viable option.When jetties are short, ship BOG is relatively minor. The onboard compressors can return the gas to onshore facilities where it can be recovered through process flows. Certain degrees of disturbances to the normal LNG production may be incurred, but would be tolerated.In scenarios where long jetties are required, the BOG handling faces new challenges. Long jetties imply long LNG loading lines which, in turn, result in higher pumping energy and heat leakage. Consequently, the BOG generation rate during ship loading can be much higher. Furthermore, transferring large volumes of low-pressure BOG across long jetties is fairly costly. The combined effects make it economically challenging to recover BOG from long jetties.This paper presents a systematic investigation into various BOG recovery options, with an emphasis on the suitability for long jetties. The paper includes a discussion on final destination of the recovered BOG, generation and storage of refrigerant, and operating parameters of BOG pipelines on long jetties. The final selection of the BOG recovery system is project-specific and is strongly influenced by the marine considerations. The findings of this work will serve as useful guidelines for BOG recovery evaluation on future LNG projects.