Exergo-Economic Assessment of Power Generation Cycles in LNG Regasification Terminals

Energy efficiency is a critical avenue for reducing carbonaceous emissions across fossil fuel value chains. Specifically, utilization of liquefied natural gas (LNG) exergy for power generation upon regasification in an import terminal offers the opportunity to partially retrieve the energy invested during liquefaction. Power generation arises as a promising avenue to accomplish this by using ambient air or seawater to supply heat to a working fluid, while the regasified LNG stream behaves as the heat sink of the thermal machine. However, a trade-off between cycle complexity (capital investment) and process efficiency exists. To identify it, in this work, three Rankine cycle configurations, which operate through indirect heat exchange without the need of fuel combustion, are analyzed with a consistent methodology from an exergo-economic perspective. Using a 2.13 mtpa LNG regasification terminal without LNG exergy utilization as the baseline for the techno-economic assessment, the simplest configuration consisting of a two-pressure level propane cycle (C3) achieved an exergy efficiency of 34.0% and a levelized cost of electricity (LCOE) of 89.4 €/MWh. A cycle carrying out an expansion of a portion of the regasified LNG and employing a CO2 loop for the high temperature range (C1CO2) achieved an exergy efficiency of 42.5% but with a higher LCOE of 99.7 €/MWh. Finally, the most capital-intensive design, comprising two stages with a hydrocarbon mixed refrigerant and propane as working fluids (MRC3), reached an efficiency of 55.2% and a cost of electricity of 118.5 €/MWh. The exergy analysis revealed that minimizing the MITA of cryogenic exchangers should be prioritized to improve cycle performance. However, even when large LNG regasification capacities (>6 mtpa) are considered, the most cost-effective solution (C3) generates profits during less than 45% of the time in the electricity market from 2024 of an LNG importing region such as Spain, indicating a relatively low economic potential for power generation without complementary heat sources.