The thesis focuses on the study of concentrating solar plants coupled with organic Rankine cycles equipped with thermal energy storage system. In particular, the aim of the work is to perform a complete and exhaustive comparison between direct and indirect cycles for small-scale applications. To do this, a Matlab model able to optimize various cycle configurations, from the global efficiency point of view, has been developed. The optimization of each cycle has been applied to various fluids with different solar field outlet temperatures. Two models were also developed and introduced in the form of options for the calculation of the turbine efficiency and the pressure losses of the solar field in order to obtain a specific value for each case considered. Each model also presents different options to allow the user to optimize the individual configuration at his discretion. Finally, the model examines two values for the lower limit of the condensation pressure and a sensibility analysis is performed to show the differences introduced by the various possible choices. The final analysis was based on the global efficiency and on the energy accumulated specific to the storage volume. The results obtained showed that the direct cycles do not stand comparison with the indirect ones, presenting in any case analysed lower values of both global efficiency and equivalent electric energy density.
La Tesi si focalizza sullo studio di impianti solari a concentrazione accoppiati a cicli Rankine organici dotati di sistema di accumulo termico. In particolare, si propone di effettuare un confronto completo ed esaustivo tra cicli diretti e indiretti per applicazioni di piccola taglia. Per fare questo è stato sviluppato un codice in Matlab in grado di ottimizzare, dal punto di vista del rendimento globale, varie configurazioni di ciclo. L'ottimizzazione di ogni ciclo è stata applicata a vari fluidi con diverse temperature all'uscita del campo solare. Sono stati inoltre sviluppati e introdotti nel codice sotto forma di opzioni due modelli per il calcolo del rendimento di turbina e delle perdite di pressione del campo solare in modo da ottenere un valore più preciso per ogni caso considerato. Ogni modello presenta anche diverse opzioni per permettere all'utente di ottimizzare la singola configurazione a propria discrezione. Infine, il modello prende in esame due valori per il limite inferiore della pressione di condensazione e presenta un'analisi di sensibilità per mostrare le differenze introdotte dalle varie scelte possibili. L'analisi finale è stata basata sul rendimento globale e sull’energia accumulabile specifica al volume. I risultati ottenuti mostrano come i cicli diretti non reggano il confronto con quelli indiretti presentando in ogni caso analizzato valori inferiori sia per quanto riguarda l'efficienza globale che per quando riguarda la densità di energia elettrica equivalente.
Comparison between direct and indirect ORCs for CSP applications provided with sensible heat storage
PERUSI, DAMIANO
2017/2018
Abstract
The thesis focuses on the study of concentrating solar plants coupled with organic Rankine cycles equipped with thermal energy storage system. In particular, the aim of the work is to perform a complete and exhaustive comparison between direct and indirect cycles for small-scale applications. To do this, a Matlab model able to optimize various cycle configurations, from the global efficiency point of view, has been developed. The optimization of each cycle has been applied to various fluids with different solar field outlet temperatures. Two models were also developed and introduced in the form of options for the calculation of the turbine efficiency and the pressure losses of the solar field in order to obtain a specific value for each case considered. Each model also presents different options to allow the user to optimize the individual configuration at his discretion. Finally, the model examines two values for the lower limit of the condensation pressure and a sensibility analysis is performed to show the differences introduced by the various possible choices. The final analysis was based on the global efficiency and on the energy accumulated specific to the storage volume. The results obtained showed that the direct cycles do not stand comparison with the indirect ones, presenting in any case analysed lower values of both global efficiency and equivalent electric energy density.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/141502