Energy- and exergy-based performance evaluation of solar powered combined cycle (recompression supercritical carbon dioxide cycle/organic Rankine cycle)

Abstract

Nowadays, the recompression supercritical carbon dioxide (R-SCO2) cycle has emerged as a promising option for power conversion systems because of its boundless potential to tackle energy and environmental issues. In this study, we examined the performance of the solar parabolic trough collector (SPTC) integrated combined cogeneration system for the purpose of power generation as well as recovery of waste exhaust heat from the R-SCO2 cycle with the help of the organic Rankine cycle (ORC). An exergy and energy analysis was performed for a combined recompression cycle (R-SCO2-ORC) by varying the input variables such as intensity of solar irradiation (Gb), pressure at the inlet of SCO2 turbine (P5), mass flow rate of SCO2 (mSCO2 ) inlet temperature of SCO2 turbine (T5), inlet temperature of main compressor (T9) and effectiveness of the high- and low-temperature recuperator (εHTR and εLTR ). Eight organic working fluids were considered for the ORC: R123, R290, isobutane, R1234yf, R1234ze, toluene, isopentane and cyclohexane. The study revealed that R123-based R-SCO2-ORC demonstrates the highest thermal and exergy efficiency: ~73.4 and 40.89% at Gb = 0.5 kW/m2; 78.8 and 43.9% at P5 = 14 MPa; 63.86 and 35.57% at T5 = 650 K; 74.84 and 41.69% at mSCO2 = 7 kg / s; 85.83 and 47.82% at T9 = 300 K; 84.57 and 47.11% at εHTR = 0.65; 85.06 and 47.38% at εLTR = 0.65, respectively. Alternatively, R290 showed the minimum value of exergy and thermal efficiency. As can be seen, the maximum amount of exergy destruction or exergy loss occurs in a solar collector field, ~58.25% of the total exergy destruction rate (i.e. 6703 kW) and 18.99% of the solar inlet exergy (i.e. 20 562 kJ). Moreover, R123 has the highest net work output, ~4594 kJ at T5 = 650 K and 6176 kJ at T9 = 300 K.