(200f) Modeling, Simulation, and Optimization of Boil-off Losses in LNG

Natural gas (NG) is the cleanest fossil fuel, which is most popular and economical after crude oil. Liquefied Natural Gas (LNG) is the most economical way of transporting NG over long distances. Because of LNG transportation and storage at ?163 °C, boil-off losses are unavoidable reality. While these are significant, few systematic studies on boil-off exist in the literature. In this work, we first perform realistic, detailed, and extensive dynamic simulation and study the effects of various factors such as nitrogen content, tank pressure, ambient temperature, voyage length, etc., on boil-off during various steps of LNG transportation. Our analysis shows that heel can be reduced by up to 40% for a typical long voyage of 20 days, compared to the usual industrial practice of 5% of the cargo, and the reduction is significantly more for the shorter voyages.

Since such simulation-based approach is computationally demanding and it is difficult to explore the effects of all parameters fully, we also present a semi-analytical methodology to expedite the simulation experiments and expand the scope of our study. This allows us to determine the optimal heels for many more transport scenarios for both lean and rich LNG. Finally, we compare the simulation study with the semi-analytical methodology and present results that could be of use to the LNG industry. Our computations suggest savings of millions of dollars from heel optimization alone in LNG transportation.