LNG Cold Energy Utilization for Power Generation: A Case Study on Coupling with the Thermal Discharge from the Power Plant

Thermodynamic analysis reveals that each kilogram of LNG liberates 830 kJ of exergy during vaporization, representing an energy recovery gap in conventional regasification systems. LNG cold energy power generation based on the Organic Rankine Cycle (ORC) is considered an effective method for utilizing this cold energy. In this study, a cold energy project at an LNG station in Tangshan is used as a research object to propose a model for LNG cold energy power generation combined with thermal discharge from a power plant. An ORC model is established in Aspen HYSYS to determine the optimal process parameters of the system using a ternary mixture of propane and a ternary mixture of methane, ethane, and propane with a molar fraction of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$5: 3: 2$</tex>, with the goal of maximizing net power. The results show that net power increases with evaporation temperature. For the propane system, net power increases with inlet pressure. For the mixed working fluid system, net power first increases and then decreases with inlet pressure. Under optimal process parameters, the net power of the LNG cold power generation system using mixed working fluid combined with thermal discharge from the power plant is 4387.28 kW, which is 30.19 % higher than that of the LNG cold power generation system using propane and seawater. Additionally, the cold energy utilization efficiency is <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{3 0. 1 8 \%}$</tex> higher, the thermal efficiency is <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{2 5. 0 6 \%}$</tex> higher, and the exergy efficiency is 37 % higher.