A benchmark comparative thermodynamic investigation of different organic Rankine cycle architectures

The Organic Rankine Cycle (ORC) is a promising thermodynamic cycle for exploiting low-grade energy sources such as solar and geothermal energy, as well as waste heat. Also, it is an important choice for decentralized electricity production, aiding the stability of the grid and enhancing the concept of smart grids. However, the thermodynamic efficiency of the ORC is not so competitive, and it can create restrictions on the energy and economic viability of this technology. In this direction, this examines 8 different ORC architectures aiming to determine the most efficient configuration energetically and exergetically, under different design conditions. Specifically, the basic ORC is compared with the recuperative, regenerative and reheating ORC, while also the combinations of regenerative-recuperative, regenerative-reheating, recuperative-reheating and regenerative-recuperative-reheating ORCs are investigated in detail. The isentropic efficiency of the expander is variable according to the operating conditions, something that leads to more realistic results and conclusions in this work. It was concluded that the regenerative ORC is a more effective choice compared to the recuperative and the reheating ORC, while the global best design is the regenerative-recuperative-reheating ORC. Also, it was concluded that regeneration and reheating do not present a highly synergetic effect. In the default comparative scenario with saturation temperature at 110 °C and condensation temperature at 40 °C, the thermal efficiency enhancement was found to be up to 32% and the exergy efficiency enhancement up to 17%. The conclusions of this analysis can be utilized for the design of the most efficient ORCs and, therefore, to make a step forward in the development of this technology.