Energy, exergy, economic, and environmental assessment and performance optimization of dual-stage discharge Carnot battery systems for floating liquefied natural gas

Floating liquefied natural gas platforms offer a flexible solution for offshore natural gas production, storage, and transfer, but their energy-intensive operations require reliable power supply. This study investigates the use of Carnot batteries to enhance power reliability and energy efficiency on floating liquefied natural gas platforms by effectively utilizing the inherent cold energy of liquefied natural gas. A dual-stage discharge strategy is proposed, where the cold energy of liquefied natural gas is first stored and later reheated using low-temperature oceanic waste heat for a second discharge phase. A thermodynamic model of the floating liquefied natural gas-Carnot battery system is developed, and a comprehensive energy, exergy, economic, and environmental analysis is conducted to assess the impact of key parameters on system performance. Multi-objective optimization using genetic algorithms is employed to optimize system efficiency and operational requirements. The dual-stage discharge system increased round-trip efficiency from 82.4% to 86.2%, while discharge power was enhanced from 1008.8 kW over 4 h in the first stage to an additional 94.4 kW over 17.6 h in the second. The results demonstrate significant improvements in both exergy and round-trip efficiency through strategic adjustments. The proposed system offers substantial potential for enhancing energy utilization on floating liquefied natural gas platforms and provides a scalable solution with promising applications for offshore natural gas operations.