Environmental and exergoeconomic assessment of a geothermal-LNG hybrid S-CO 2 system toward sustainable power generation

Abstract

This study presents a hybrid recompression supercritical CO₂ (S-CO₂) power cycle that simultaneously utilizes geothermal heat and the cryogenic exergy of liquefied natural gas (LNG) to enhance sustainable electricity generation. A comprehensive modeling framework combining thermodynamic, exergoeconomic, and exergoenvironmental analyses, together with advanced exergy-based methods, is developed to identify the dominant sources of inefficiencies and cost/environmental burdens. The system performance is further evaluated through sensitivity analyses and multi-objective optimization using the Non-dominated Sorting Genetic Algorithm II (NSGA-II), considering exergy efficiency, unit product cost, and environmental impact as competing objectives. The results indicate that the natural gas turbine (NT), LNG pump (LP), and heat exchangers HE-2 and HE-3 exhibit the highest potential for improvement based on avoidable exergy destruction and cost contribution. Compared to the baseline design, the optimized configuration improves the overall exergy efficiency from 54.96% to 55.94% (1.78% improvement), reduces the average unit product cost from 5.33 to 5.10 $/GJ (4.32% decrease), and decreases the average unit environmental impact from 9.11 to 8.70 (4.50% decrease). These results demonstrate that the integration of geothermal energy with LNG cryogenic exergy provides a promising pathway for improving resource utilization and reducing the environmental footprint of hybrid power systems.