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.
Negli ultimi anni sono stati sviluppati sistemi a generazione diretta di vapore (DSG) con acqua come alternativa agli impianti parabolici con olio diatermico. Dopo accurati studi, sono stati realizzati i primi impianti DSG commerciali. Cicli Rankine a fluido organico (ORC), che sono ampiamente utilizzati per la produzione di energia elettrica da fonti termiche a bassa temperatura (energia geotermica), sono stati implementati anche in impianti solari termodinamici. Nessuna attività di ricerca è stata dedicata fino ad ora allo studio di generazione diretta di vapore di un composto organico tramite lo sfruttamento dell’energia solare. L’obiettivo principale di questa tesi è stato valutare i processi ORC che possono rivelarsi favorevoli a questo tipo di applicazione. Innanzitutto, è stata condotta una profonda analisi per identificare i fluidi più adatti ad essere utilizzati in un impianto DSG. Particolare interesse è stato rivolto verso applicazioni ad alta temperatura e processi supercritici, al fine di stabilire la migliore configurazione. Dopo aver definito due possibili processi con i silossani (un ciclo saturo con ottametilciclotetrasilossano D4 e un ciclo supercritico con esametildisilossano MM), è stata valutata una possibile integrazione con un accumulo termico, focalizzandosi sul sistema di accumulo indiretto a doppio serbatoio. La fattibilità dei processi di carica e scarica dell’accumulo termico è stata valutata, insieme alle prestazioni dell’impianto, per entrambe le configurazioni scelte.
Evaluation of ORC processes and their implementation in solar thermal DSG plants
DEGLI ESPOSTI, DALMA
2013/2014
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.| File | Dimensione | Formato | |
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2014_04_DegliEsposti.pdf
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https://hdl.handle.net/10589/91281