Systematic comparison of ORC configurations by means of comprehensive performance indexes

The Organic Rankine Cycle (ORC) is considered as an emerging technology for power generation through heat recovering from different thermal sources, based on the use of organic fluids as working medium. 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 ORC performance is here calculated in terms of six different thermodynamic indexes, offering comprehensive information, namely: cycle efficiency, specific work, recovery efficiency, turbine volumetric expansion ratio, ORC fluid-to-hot source mass flow ratio and heat exchangers size parameter. In the framework of a systematic investigation approach, various possible modifications to the simple ORC plant layout are here analyzed and compared, in order to improve the ORC recovery performance; arrangements such as recuperation, superheated cycle, supercritical conditions, regenerative cycle and their combinations are taken into account. 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. A comprehensive parametric analysis of these cycles at different hot source temperature and different evaporation pressure values is carried out. The objectives of this investigation are to provide useful guidelines to select the ORC configuration, the most appropriate fluid and to define the operating parameters, depending on the specific application. Thermodynamic results are also related with sizing of ORC components and thus can be used for economic assessment of the different ORC design alternatives.