(584r) Optimal Aspect Ratio and Recirculation Rate for LNG Storage Tanks in a Regasification Terminal

Authors: 
Khan, M. S., National University of Singapore
Effendy, S., National University of Singapore
Farooq, S., National University of Singapore
Karimi, I. A., National University of Singapore
In the present work, a rigorous process model of an LNG regasification terminal is developed on Aspen HYSYS. The model is then used to study the design and operation of regasification terminals. It is observed that a near-unity H/D ratio results in a minimum average boil-off gas generation for a wide range of tank volumes and operating parameters. The typical H/D ratio of 0.5 used in the industry results in 1 to 5% increased average boil-off gas generation. It is also observed that the average boil-off gas generation decreases monotonically with recirculation rate. This is understood to be the composite effect of decreasing heat ingress from the recirculation line and a decrease in in-tank pump duty. However, excessively low recirculation rate results in two-phase flow in the recirculation line. Based on these observations, an equation for selecting an optimal recirculation rate is developed. The equation is general, and only requires as input the heat transfer characteristics of the recirculation line. A separate figure predicts average compressor power as a function of tank volume, heat transfer characteristics of the recirculation line and send-out rate. The present study further concludes that the average boil-off gas generation arises from five effects (1) heat ingress into the tank, (2) decreasing liquid level, (3) vapor expansion, (4) heat ingress into the recirculation line and (5) pump duty. The concepts and results presented in this study should prove useful in the design and operation of regasification terminals.