Thermodynamic Analysis and Comparison of Different Organic Rankine Cycle Configurations

The Organic Rankine Cycle (ORC) is an emerging technology for power generation through heat recovering from different thermal sources, based on the use of organic fluids as working medium. The arrangement of the components in the system leads to different layouts which affect the ORC performance. In particular, to improve the ORC recovery efficiency and net power output, different cycle modifications can be considered, such as superheated cycle, supercritical conditions and other cycle variants. This paper presents a numerical study to assess the relevance: i) of the thermodynamic cycle, ii) of the main design parameters and iii) of the working fluid, on the achievable performance. The investigation is carried out by means of an in-house developed calculation tool, based on a thermodynamic property database of the considered fluids, including aromatics, siloxanes, refrigerants and hydrocarbons. The ORC performance is calculated in terms of different indexes such as cycle efficiency, heat recovery efficiency, expander volumetric ratio and heat exchanger size. A parametric analysis of these cycles at different hot source temperature and different evaporation pressure values has been carried out. Results of the investigation provide useful guidelines to select the ORC configuration, the most appropriate fluid and to define the operating parameters, depending on the specific application.