Energy, exergy, and economic (3E) analysis of an organic Rankine cycle using zeotropic mixtures based on marine engine waste heat and LNG cold energy

In this paper, thermo-economic performance comparisons between zeotropic mixtures and pure fluids are conducted via simulation for a parallel two-stage organic Rankine cycle (PTORC) driven by waste heat from LNG-fueled ship. The exhaust gas and jacket water of the marine engine work as heat sources, and the LNG fuel is considered as heat sink. R1150/R170 and R170/R1270 are employed as the working fluids in the first stage while R600a/R601 a and R600/R601 are used in the second stage. The effects of working fluids and pinch point temperature difference (PPTD) on the PTORC performances are studied from the viewpoint of the first and the second law of thermodynamics. It concludes that the zeotropic mixtures do not always exhibit an advantage over the pure fluids. The highest net power of the PTORC is 146.9 kW obtained with R1150-R600a. The results of PPTD indicate that LNG regasification should occur in the first-stage condenser. The maximum energy efficiency and exergy efficiency of the PTORC are 22.09% and 23.28%, respectively. The best economic performances of the PTORC are achieved with R170/R1270 (0.9/0.1, mass fraction)-R600. The total cost, payback period, and levelized energy cost vary in the range of 5.98-8.08 x 105 $, 4.58-5.18 years, and 0.065-0.074 $/kWh, respectively.

Automated summary

This paper conducts a simulation to compare the thermo-economic performances of zeotropic mixtures and pure fluids in a parallel two-stage organic Rankine cycle (PTORC) driven by waste heat from LNG-fueled ships. The results indicate that zeotropic mixtures do not always have an advantage over pure fluids, with the optimal working fluid combination being R170/R1270-R600. The study also shows that the highest net power output is achieved with R1150-R600a, and LNG regasification should occur in the first-stage condenser for optimal performance.