Safety and Environmental Challenges in Developing a Closed-Circuit LNG Regasification System for Offshore Natural Gas Export

This study examined the safety and environmental issues encountered in the course of development of a closed-circuit LNG regasification system to be installed on offshore LNG terminals or regasification shuttles. Restriction on sea water usage as the heating medium intrinsically determined that the developed system should be based on a closed circuit assisted by steam-generating boilers. Care were taken in establishing the operation and control philosophy, not to generate any residual steam that needed inevitably to be condensed with sea water or to be vented to the atmosphere. One of the most critical hazards was the huge amount of blowdown gas in case of emergency shutdown. It was found that the discharge through a vent mast still left a considerable risk due to the gas dispersion around the facility. Instead, a restricted blowdown to the LNG containment system or a combustion unit resulted in a less risk with a prolonged duration. Rigorous studies were performed to quantify the risks and to anticipate the system behavior. The leak and fire risk analysis indicated that the system had significantly low frequency of fire and explosion compared with usual offshore facilities. However, any guidelines were not available to assess the risk quantitatively. The process dynamic simulation suggested how the system should be shut down. This study showed that several critical challenges were solved successfully and the risk level of the closed-circuit regasification system was acceptable.Copyright © 2007 by ASME