Evaluation of ORC processes and their implementation in solar thermal DSG plants

Kurzfassung

Abstract In recent years Direct Steam Generation (DSG) systems using water have been developed as an alternative to state-of-the-art parabolic trough plants with thermal oil. After a comprehensive research, first commercial DSG plants have already been realized. Organic Rankine Cycles (ORC) that have been widely used for electricity production with low-temperature heat (e.g. geothermal energy) are also suited for the implementation in solar thermal power plants. To the knowledge of the author, no previous research has been dedicated to the investigation of direct steam generation of an organic compound. The aim of this work is the evaluation of ORC processes that are promising for this application. Firstly, a deep analysis for finding the most suitable fluids for DSG was conducted. Particular interest was set on high-temperature applications and supercritical processes in order to value the best configuration. After defining two possible process layouts with siloxanes (a saturated cycle with octamethylcyclotetrasiloxane D4 and a supercritical cycle with hexamethyldisiloxane MM), a possible integration with a thermal storage system was investigated, focusing on the state-of-the-art indirect two-tank system. The feasibility of the charging and discharging processes of the storage system together with the performances of the whole plant system was assessed for both chosen configurations.