Comparative Study of Process Integration and Retrofit Design of a Liquefied Natural Gas (LNG) Regasification Process Based on Exergy Analyses: A Case Study of an LNG Regasification Process in South Korea

Abstract

Exergy analysis of the retrofit design scheme of a conventional liquefied natural gas (LNG) regasification process in South Korea was considered in this study. A new exergy evaluation method called exergy decomposition is introduced, in which the exergy is decomposed into thermal and chemical exergies. In studying the conventional LNG regasification process, we found that a large portion of chemical exergy is lost by boil-off gas flaring. Of 17 MW of thermal exergy transferred from cold LNG to seawater in the regasification unit, a fraction as large as 16 MW (close to 95%) is wasted because of heat-transfer irreversibility, limiting the rational exergetic efficiency of the overall process to merely 0.847. Previously reported design schemes, namely, the dual Brayton cycle and the organic Rankine cycle, with low-grade heat sources were also evaluated using the new method and were found to limit the overall rational exergetic efficiencies to 0.890 and 0.849, respectively. A new integrated, retrofitted scheme for LNG regasification with a gas-to-liquid (GTL) process is proposed as an alternative to minimize thermal and chemical exergy losses. The integrated LNG regasification–GTL process improves the overall rational exergetic efficiency to 0.868.