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.
A microchannel Fischer−Tropsch reactor retaining high heat and mass transfer performance requires uniform flow distribution on the coolant side to induce isothermal condition for controllable and sustainable operation. The present work improved the flow performance of a large-scale layer of over 100 channels by introducing an extremely simple guiding fin in the inlet and outlet rectangular manifolds. Case studies with three-dimensional computational fluid dynamics (CFD) were carried out where the upper and bottom lengths of the guiding fin were the main geometric variables. Then the optimization work was conducted to estimate the performance of the optimal design. The robustness for the proposed geometry was tested with varying the flow rate, fluid type, and temperature. The result showed that the proposed design can retain uniform distribution over a wide operation range (500 ≤ Re GF ≤ 10800).
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