This Thesis investigates the production of electric energy from the exploitation in binary ORC plants of medium-enthalpy liquid-dominated resources characterized by high concentration of non-condensable gases in the geothermal fluid. The modelling and simulation of the plants was performed using the commercial software Aspen Plus V10. After an initial overview of geothermal energy, the attention is turned to ORC binary conversion systems, focusing on working fluids: the main thermophysical properties and their effects on the thermodynamic cycle discussed. The emphasis is then placed on the impact these fluids have on health and environment (ODP and GWP indices), examining the international regulations in force. Afterwards the case of Turkey is presented as the example of a country in which geothermal resources contains high concentration of carbon dioxide. Two Turkish binary power plants were simulated in Aspen Plus to verify the validity of the simulation strategies and methods. Subsequently, different ORC layouts, sub- and supercritical, single and double pressure levels, are simulated with the threefold aim of: observe the effect of the CO2 concentration on the plants performance and layout; compare different plant layouts; study next generation eco-fluids, whose future adoption is becoming more and more probable given the increasing severity of EU regulations, and compare them to conventional commercial fluids. These plants were coupled with a fictional CO2 rich two-phase geothermal resource at 170°C. From the carried-out analysis, there is reason to believe that next-generation eco-fluids can replace their equivalents achieving the same or even higher performance. Finally, due to the high CO2 content in the reservoir which makes impossible the adoption of submersible pumps to limit emissions, two alternative systems for CO2 capture and re-injection are proposed: compression & re-injection and water-absorption. These systems are evaluated through Aspen Plus modelling.
La Tesi indaga la produzione di energia elettrica dalla conversione, mediante impianti binari ORC, di risorse a media entalpia a liquido dominante caratterizzate da un'alta concentrazione di gas non condensabili nel fluido geotermico. La simulazione degli impianti si serve del software commerciale Aspen Plus V10. Dopo una panoramica iniziale riguardante l’energia geotermica, l'attenzione è rivolta ai sistemi di conversione binari ORC, concentrandosi sui fluidi di lavoro: sono discusse le proprietà termofisiche principali e i loro effetti sul ciclo termodinamico. L'accento è poi posto sull'impatto che questi fluidi hanno sulla salute e sull'ambiente (indici ODP e GWP), approfondendo le normative internazionali in vigore. Successivamente la Turchia viene presentata come esempio di Paese in cui le risorse geotermiche contengono un'alta concentrazione di anidride carbonica. Due impianti binari turchi sono simulati, utilizzando Aspen Plus, per verificare la validità delle strategie e dei metodi di simulazione. In seguito, diverse configurazioni d'impianto ORC, sotto- e supercritiche, a singolo e doppio livello di pressione, vengono simulate con il triplice obiettivo di: osservare l'effetto della concentrazione di CO2 sulle prestazioni e sul layout degli impianti; confrontare i diversi layout; studiare gli eco-fluidi di prossima generazione, la cui futura adozione è sempre più probabile considerando le normative UE sempre più stringenti, e confrontarli con i fluidi commerciali più convenzionali. Tali impianti sono stati associati ad una risorsa geotermica fittizia, bifase, a 170°C. Dall’analisi effettuata c’è ragione di credere che i fluidi di nuova generazione possano sostituire i loro equivalenti ottenendo prestazioni di pari livello o persino superiori. Infine, a causa dell'elevato contenuto di CO2 nel serbatoio, che rende impossibile l'adozione di pompe sommerse per limitare le emissioni, sono stati proposti due sistemi alternativi per la cattura della CO2 e la sua reiniezione: compressione & reiniezione e water-absorption. Di questi sistemi sono state valutate le prestazioni mediante modellazione in Aspen Plus.
Two-phase binary ORC plants for electricity production from CO2-rich geothermal resources
Marcandelli, Laura;Marchiori, Gabriele
2019/2020
Abstract
This Thesis investigates the production of electric energy from the exploitation in binary ORC plants of medium-enthalpy liquid-dominated resources characterized by high concentration of non-condensable gases in the geothermal fluid. The modelling and simulation of the plants was performed using the commercial software Aspen Plus V10. After an initial overview of geothermal energy, the attention is turned to ORC binary conversion systems, focusing on working fluids: the main thermophysical properties and their effects on the thermodynamic cycle discussed. The emphasis is then placed on the impact these fluids have on health and environment (ODP and GWP indices), examining the international regulations in force. Afterwards the case of Turkey is presented as the example of a country in which geothermal resources contains high concentration of carbon dioxide. Two Turkish binary power plants were simulated in Aspen Plus to verify the validity of the simulation strategies and methods. Subsequently, different ORC layouts, sub- and supercritical, single and double pressure levels, are simulated with the threefold aim of: observe the effect of the CO2 concentration on the plants performance and layout; compare different plant layouts; study next generation eco-fluids, whose future adoption is becoming more and more probable given the increasing severity of EU regulations, and compare them to conventional commercial fluids. These plants were coupled with a fictional CO2 rich two-phase geothermal resource at 170°C. From the carried-out analysis, there is reason to believe that next-generation eco-fluids can replace their equivalents achieving the same or even higher performance. Finally, due to the high CO2 content in the reservoir which makes impossible the adoption of submersible pumps to limit emissions, two alternative systems for CO2 capture and re-injection are proposed: compression & re-injection and water-absorption. These systems are evaluated through Aspen Plus modelling.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/170600