Performance Comparison of Organic Rankine Cycle (ORC) and CO₂ Cycle for Simultaneous Utilization of Liquefied Natural Gas (LNG) Cold Energy and Solar Energy

LNG is a good way to transport natural gas from suppliers to consumers. However, the LNG cold energy is generally lost during the regasification process at the receiving terminals. LNG cold energy can be a great heat sink for power cycles. Meanwhile, solar energy is abundant on the earth and it is a great heat source for the power cycles. If solar energy and the LNG cold energy can be utilized in an integrated power system, the efficiency of energy utilization and economical profitability would be increased substantially. Organic Rankine Cycle (ORC) and CO₂ cycle can utilize LNG cold energy and solar energy. ORC performs better than the CO₂ cycle for LNG cold energy utilization since organic working fluid can condensate at a much lower temperature, while the transcritical CO₂ cycle may perform better since the supercritical CO2 can match well with the transfer fluid from the solar collector. One-cycle and dual-cycle power generation systems are proposed and modeled in this study. A single unified model is developed in the Python language and presents the capacity to model different cycle configurations (subcritical, transcritical, supercritical). The rigorous thermodynamic model and system configuration model are established based on the CoolProp platform. The transcritical power generation system has the maximum power output, while the transcritical CO₂ cycle has a much lower volume flowrate at the outlet of the turbine, which may be a better option from the techno-economic point of view.