Thermodynamic-based comparison of ORC, TFC and OFC systems for waste heat recovery from a marine diesel engine

Abstract

The aim of this research is to comparatively evaluate the thermodynamic performance of three different systems, namely the organic Rankine cycle (ORC), trilateral flash cycle (TFC), and organic flash cycle (OFC), for the purpose of recovering waste heat on ships. To analyze their performance, simulations were conducted using specific working fluids with favorable thermophysical properties, namely n-butane (R600), i-butane (R600a), n-pentane (R601), i-pentane (R601a), and toluene. The results indicate that, within the operating parameters considered in this study, the ORC system achieves higher thermal efficiency compared to the TFC and OFC systems. However, the TFC system exhibits the advantage of a lower specific volume of the working fluid at the end of the heat addition process (expander inlet) since it remains in a liquid state. This characteristic allows for the use of smaller-sized expanders, making the TFC system particularly appealing for marine applications. Furthermore, it was observed that all the selected working fluids outperform R245fa in terms of power generation within the ORC system. In the case of the TFC and OFC systems, only R601, R601a, and toluene surpass the performance of R245fa.