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Assessment of different configurations of solar energy driven organic flash cycles (OFCs) via exergy and exergoeconomic methodologies

Nemati, Arash, Nami, Hossein, Yari, Mortaza
Renewable energy 2018 v.115 pp. 1231-1248
ethylbenzene, exergy, solar energy, temperature, toluene, xylene
Different configurations of organic flash cycles (OFCs), including simple OFC, dual flash OFC, improved OFC, expander-OFC and improved expander-OFC, analyzed from the viewpoints of exergy and exergoeconomic. Five appropriate working fluid including Toluene, p-Xylene, m-Xylene, Ethylbenzene and o-Xylene are considered as working fluid. The effect of flashing temperature is investigated on the exergy and exergoeconomic performance of the system. Also, an optimization procedure is carried out to find the most efficient configuration and optimum flashing temperature from the viewpoints of exergy and exergoeconomic. Results show that the minimum and maximum optimal exergy efficiency belongs to the simple OFC and improved expander-OFC, respectively. Also, the lowest and the highest minimum unit cost of produced power refers to the simple OFC and dual flash OFC. Moreover, the results indicate that Toluene as working fluid has the best performance from the viewpoints of both exergy and exergoeconomic. Based on the results, expander-OFC is chosen as the configuration that satisfies both exergy and economic criteria, simultaneously. Finally, an optimal design point for expander-OFC is obtained from Pareto frontier with the exergy efficiency of 49.1% and unit cost of produced power of 31.4 $/GJ which occurs at the flashing temperature of 427.6 K.