Thermodynamic analysis of a cryogenic power generation system recovering both sensible heat and latent heat of flue gas

Abstract

This paper proposed a cryogenic power generation system composed of Rankine cycles and direct expansion cycle, aiming at the efficient utilization of flue gas waste heat and liquefied natural gas (LNG) cold energy. Both the sensible heat and latent heat of the humid flue gas are recovered to meet the heat demand of a typical LNG terminal. Performance analysis was conducted to reveal the potential improvement direction and determine the key parameters. Then, parametric study was carried out to evaluate the effects of key design parameters on system performance. Four combinations of working fluids were compared, and the system performance was analyzed at different flow rates of natural gas. Results indicate that the net power output decreases as the condensing temperature of the bottoming Rankine cycle increases, and there exists a volcano-type relationship between the net power output and natural gas expansion pressure. R290/R1150 is the preferred combination of working fluids under the design conditions, and the maximum thermal efficiency, exergy efficiency, and specific power can reach 27.07%, 48.42%, and 74.15 kWh/ton-LNG, respectively. Moreover, the specific power decreases with the increase of LNG flow rate. R1270/R1150 becomes the best combination of working fluids, when the LNG flow rate exceeds 120.28 kg/s.