Energy integration of light hydrocarbon separation, LNG cold energy power generation, and BOG combustion: Thermo-economic optimization and analysis

To recover boil-off gas (BOG) and liquefied natural gas (LNG) cold energy, this paper proposes three systems integrating light hydrocarbon separation (LHS), BOG combustion, organic Rankine cycle (ORC) with different structures and natural gas (NG) direct expansion. Both single and multi-objective optimizations are implemented to find the best system performance. Meanwhile, two multi-objective decision methods are also used to refine this work. Single objective optimization depicts that the system with parallel ORC has the highest net electric power (NEP), exergy efficiency, and net present value (NPV) of 6.85 MW, 29.07%, and 31.08 x 107 $ respectively. Multi-objective optimization results indicate the NEP, exergy efficiency, and NPV of the system with parallel ORC still outperform the other two systems. From the energy analysis, it is found that the system with parallel ORC achieves 81.07% utilization of LNG cold energy, which is the highest among the three systems. The exergy analysis indicates that the combustion chamber and heat exchanger (HX) with the highest exergy destruction in any system. Moreover, economic analysis demonstrates that the three systems are more sensitive to fluctuations in interest rates than in electricity prices.