Minimizing Power Consumption Related to BOG Reliquefaction in an LNG Regasification Terminal.

The generation of boil-off gas (BOG) is inevitable in liquefied-natural-gas (LNG) regasification terminals. It can be a safety concern and, in most cases, demands BOG reliquefaction before regasification. This study presents a fundamental thermodynamic analysis of the BOG reliquefaction-LNG regasification process, which consumes significant power. We propose an evolving series of schemes that exploit the cryogenic energy of the send-out LNG to reduce the total power consumption. We synergistically integrate options such as BOG precooling, recompression, interstage cooling, and recondensation in our proposed schemes. We develop a nonlinear programming (NLP) formulation to minimize the power required for each scheme for a given amount of BOG. Under some idealistic assumptions, the optimal solutions to these NLPs give lower bounds on the total power consumption, which can be used to evaluate the cost-effectiveness of terminal operations. A novel scheme consisting of BOG precooling before compression and two-stage recondensation by direct mixing has the least power consumption. For a case-study terminal, it offers 11.9% lower power consumption than the best-reported design in the literature for 15% BOG. [ABSTRACT FROM AUTHOR]