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

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

CFD Simulation of Microchannel Reactor Block for Fischer–Tropsch Synthesis: Effect of Coolant Type and Wall Boiling Condition on Reactor Temperature

Computational fluid dynamic (CFD) simulation of heat transfer in a microchannel reactor block for low temperature Fischer–Tropsch (FT) synthesis was considered. Heat generation profiles for different operating conditions (GHSV 5000 h^–1; catalyst loading 60%–120%, where 100% loading equals 1060 kg/m³ of cobalt based catalyst from Oxford Catalyst Ltd.) were obtained from a single channel model. Simulations on a reactor block quantified the effects of three coolant types: cooling oil (Merlotherm SH), subcooled water and saturated water, on reactor temperature, and also evaluated the effect of wall boiling conditions. At process conditions of GHSV 5000 h^–1 and catalyst loading of 120%, predicted temperature gradients along channel length were 32, 17 and 12 K for cooling oil, subcooled water and saturated water, respectively. A modified reactor block showed improved thermal performance as well as heat transfer enhancement due to wall boiling conditions

Computational Fluid Dynamics Based Optimal Design of Guiding Channel Geometry in U‑Type Coolant Layer Manifold of Large-Scale Microchannel Fischer–Tropsch Reactor

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 ≤ <i>Re</i>_GF ≤ 10800)