Optimal design of dual-stage combined cycles to recover LNG cold energy and low-temperature waste thermal energy for sustainable power generation

Abstract

To overcome the shortcomings of the low net power output of a single power generation cycle for LNG cold energy recovery, investigating dual-stage combined cycles with different cycle configurations under the same heat and cold source conditions is mandatory. Hence, this study proposes 12 dual-stage combined power generation cycles to utilize LNG cold energy and low-temperature (below 200 °C ) waste thermal energy. The developed method adopts an organic Rankine cycle and Brayton cycle as the bottoming cycle and the organic Rankine cycle, Brayton cycle, and supercritical carbon dioxide power cycle as the topping cycle with parallel and serial configurations. The optimization results show that the thermodynamic and economic performance are compared quantitatively. The optimally combined cycle is a dual-stage serial organic Rankine cycle with the highest specific net power output of 202.15 kJ/kg and lowest levelized cost of electricity of 0.11 $/kWh. Regarding the parallel configuration, it can enhance thermal and exergy efficiency via its internal heat integration. Moreover, the evaporation and condensation pressure of the bottoming cycle has a more significant influence on the optimally combined cycle than the topping cycle. Overall, this study paves the way to design economics-efficient dual-stage combined cycles for sustainable power generation by utilizing LNG cold energy and low-temperature waste thermal energy.