LNG AGEING DURING SHIP TRANSPORTATION

摘要

International LNG trade has undergone a considerable increase in recent years, with a growth rate of 120% since 2000. This increment of LNG demand has generated a fast augmentation of LNG transport by sea. The knowledge of LNG composition acquires special importance in long-duration trips and is essential for importers, exporters, shipments, etc., to know the 'quality' of the LNG that is to be unloaded in the Regasification Terminal, so that LNG meets quality specifications of each country. In order to solve the existing lack of knowledge on the behaviour of LNG during ship transportation, a group of European gas companies led by Enagas has developed a useful tool called MOLAS for predicting changes in LNG composition at any time during the voyage and just at the end. MOLAS application contains two different approaches. A Physical Model based on mass balances and equilibrium state between liquid and vapour phases, and an 'intelligent' Model, based on Artificial Neural Networks that takes into account nonlinear relationship among the variables involved. MOLAS has been tried out comprehensively and an average error in Wobbe Index and Gross Calorific Value less than 0.20% and 0.30% has been obtained respectively. The results provided by MOLAS, can help Terminal Operators to manage Regasification Plants in a more safe and efficient manner and can help Engineers and Technicians to take, in advance, necessary actions on natural gas so that it can comply with required Quality Specifications.