Title: Comparative energy and exergy studies of combined CO₂ Brayton-organic Rankine cycle integrated with solar tower plant

Authors: Abdullah A. AlZahrani; Ibrahim Dincer

Addresses: Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, 2000 Simcoe Street North, Oshawa, Ontario, L1H 7K4, Canada; Department of Mechanical Engineering, College of Engineering and Islamic Architecture, Umm Al-Qura University, Al Abdeyah, Makkah, 5555, Saudi Arabia ' Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, 2000 Simcoe Street North, Oshawa, Ontario, L1H 7K4, Canada

Abstract: The present study investigates the performance of a combined power cycle used for solar tower (central receiver) plant. The combined cycle employs a supercritical carbon dioxide (S-CO₂) Brayton cycle as a topping cycle cascaded by an organic Rankine cycle (ORC). In order to evaluate the system performance, a thermodynamic analysis is conducted through energy and exergy approaches for each subsystem and hence evaluation of its overall energy and exergy efficiencies. Furthermore, the energy and exergy efficiencies of the integrated system are parametrically studied under different operating conditions. The benefits of using CO₂ as a working fluid in a Brayton cycle are elaborated in the context of high-temperature solar tower technologies. The opportunity of recovering the topping cycle low-grade heat is investigated, through the proposal of utilising an n-butane ORC as a bottoming cycle.

Keywords: solar energy; solar tower; carbon dioxide; Brayton cycle; ORC; organic Rankine cycle; energy; exergy efficiency.

DOI: 10.1504/IJEX.2018.092501

International Journal of Exergy, 2018 Vol.26 No.1/2, pp.21 - 40

Received: 28 Jul 2017
Accepted: 08 Nov 2017
Published online: 23 Jun 2018 *

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