Exergetic efficiency potential of double-stage ORCs with zeotropic mixtures of natural hydrocarbons and CO2

Konstantinos Braimakis, Victoras Grispos and Sotirios Karellas

Energy, 2021, vol. 218, issue C

Abstract: The present study investigates the exergetic efficiency potential of zeotropic mixtures of five natural hydrocarbons and CO2 as working fluids in double-stage Organic Rankine Cycles (DS-ZORCs) driven by waste heat at temperatures from 100 °C to 160 °C. The DS-ZORCs are optimized and their performance is compared to standard (SORCs), single-stage zeotropic (ZORCs) and double-stage pure fluid cycles (DSORCs). From a thermodynamic perspective, DS-ZORCs reach the highest exergetic efficiencies, especially at heat source temperatures of 100 °C (31.7%), 120 °C (35.5%) and 140 °C (38%). At 160 °C, the highest exergetic efficiency (42.4%) is achieved by a ZORC, followed by a DS-ZORC (39.8%). The maximum relative efficiency improvement of DS-ZORCs, ZORCs and DSORCs compared to SORCs at temperatures of 100 °C and 160 °C ranges from 50.5% to 22.5%, 44.5%–37.0% and 21.2%–6.7%, respectively. Because of their increased capital costs, DS-ZORCs are more appealing at heat source temperatures of 120 °C and 140 °C, at which their thermodynamic superiority over ZORCs is more significant. Due to their complexity, DS-ZORCs are subject to multiple thermodynamic constraints, which make them feasible under a limited set of boundary conditions. Furthermore, the selection of optimal mixture compositions and evaporator pressures greatly influences their feasibility and performance.

Keywords: ORC; Exergetic; Double-stage ORC; Zeotropic mixtures; Optimization (search for similar items in EconPapers)
Date: 2021
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Citations: View citations in EconPapers (6)

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Persistent link: https://EconPapers.repec.org/RePEc:eee:energy:v:218:y:2021:i:c:s0360544220326840

DOI: 10.1016/j.energy.2020.119577

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