Carbon Dioxide Mixtures as Working Fluid for High-Temperature Heat Recovery: A Thermodynamic Comparison with Transcritical Organic Rankine Cycles

Abubakr Ayub, Costante M. Invernizzi, Gioele Di Marcoberardino, Paolo Iora and Giampaolo Manzolini
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Abubakr Ayub: Department of Mechanical and Industrial Engineering, University of Brescia, via Branze, 38, 25123 Brescia, Italy
Costante M. Invernizzi: Department of Mechanical and Industrial Engineering, University of Brescia, via Branze, 38, 25123 Brescia, Italy
Gioele Di Marcoberardino: Department of Mechanical and Industrial Engineering, University of Brescia, via Branze, 38, 25123 Brescia, Italy
Paolo Iora: Department of Mechanical and Industrial Engineering, University of Brescia, via Branze, 38, 25123 Brescia, Italy
Giampaolo Manzolini: Energy Department, Politecnico di Milano, 20156 Milan, Italy

Energies, 2020, vol. 13, issue 15, 1-18

Abstract: This study aims to provide a thermodynamic comparison between supercritical CO 2 cycles and ORC cycles utilizing flue gases as waste heat source. Moreover, the possibility of using CO 2 mixtures as working fluids in transcritical cycles to enhance the performance of the thermodynamic cycle is explored. ORCs operating with pure working fluids show higher cyclic thermal and total efficiencies compared to supercritical CO 2 cycles; thus, they represent a better option for high-temperature waste heat recovery provided that the thermal stability at a higher temperature has been assessed. Based on the improved global thermodynamic performance and good thermal stability of R134a, CO 2 -R134a is investigated as an illustrative, promising working fluid mixture for transcritical power cycles. The results show that a total efficiency of 0.1476 is obtained for the CO 2 -R134a mixture (0.3 mole fraction of R134a) at a maximum cycle pressure of 200 bars, which is 15.86% higher than the supercritical carbon dioxide cycle efficiency of 0.1274, obtained at the comparatively high maximum pressure of 300 bars. Steam cycles, owing to their larger number of required turbine stages and lower power output, did not prove to be a suitable option in this application.

Keywords: transcritical cycles; waste heat recovery; fluid mixtures; carbon dioxide; Organic Rankine Cycles (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2020
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (8)

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