Thermodynamic analysis of a novel organic Rankine cycle operating with various thermal energy sources

The goal of this work lies in the investigation of a highly efficient organic Rankine cycle (ORC) under operation with various heat sources. The suggested cycle includes recuperation, regeneration and reheating, called RRR-ORC, and it is studied for operation with biomass, solar thermal collectors (evacuated flat plate units) and waste heat recovery. The analysis is parametric by investigating different design scenarios, as well as there is optimization aiming at the maximization of energy efficiency. Moreover, the reported results are directly compared with the respective with the recuperative ORC (benchmark scenario). The results prove that the RRR-ORC is a more efficient choice than the Recuperative-ORC thermodynamically and for operation with biomass and solar thermal collectors in all the studied scenarios. However, the use of the waste heat source for feeding the cycle is beneficial in most of the studied cases and not in all the examined scenarios; there are some reported reductions in the performance in the scenarios with low waste heat source temperatures. In the typical scenario of T_sat=110 °C and T_cond=40 °C, the energy efficiency enhancement compared to the recuperative cycle for the biomass-based system is 20.89 %, for the solar-based system is 20.22 %, while for the waste heat recovery system is only 2.72 %. However, it is useful to add that the reported exergy efficiency values with the waste heat recovery systems are significantly higher compared to the biomass and solar-based configurations.