Thermodynamic analysis of a Rankine dual loop waste thermal energy recovery system

This paper presents the comparison between a single loop and a dual loop waste energy recovery system specifically designed as a bottomer to marine engines of different power range. The particular application considered shows several advantages for the installation of a waste energy recovery system; in particular, the basically infinite availability of the cooling medium represented by the seawater substantially facilitates the condenser design. R 245fa and R600 have been implemented in the second recovery loop and their performance has been addressed. The paper shows how adding a second recovery loop based on organic Rankine cycle to the steam Rankine cycle loop improves the system performance both in terms of recovered electric power (up to 8.11% and 2.67% respectively in small and large application size) and heat source utilization rate, since the heat source temperature could reach values as low as 343.15 K when considering a sulfur free fuel. In addition, R 245fa is to be preferred over the R 600 since it allows for the production of the same power considering lower values for the cycle top pressures.