TO STUDY THE PERFORMANCE ANALYSIS OF SOLAR THERMAL BASED COMBINED CYCLE FOR POWER GENERATION AND WASTE HEAT RECOVERY

Abstract

One of the most mature concentrating technology, i.e. solar parabolic trough collector (SPTC) system is really a promising option to harness the solar energy between the low to medium temperature range with the purpose of solar thermal electricity generation via power cycles. These days, combined cycles especially based on supercritical carbon dioxide (SCO2) cycle are very much popular whose performance have been further investigated in this thesis work. Apart from this, organic Rankine cycle (ORC) and vapour absorption refrigeration (VAR) cycle have been employed as bottoming cycles. Then, the effect of replacing simple configuration by recompression SCO2 (R-SCO2) cycle on the cycle performance has been examined. Finally, a short analysis of supercritical ORC (SORC) has been studied. Firstly, for the analysis of SPTC integrated combined SCO2-ORC system, five organic fluids such as R134a, R245fa, R1234yf, R1234ze, and R407c have been chosen for the ORC. Results concluded that R407c based SCO2-ORC system has the highest exergy and thermal efficiency, and minimum exergy destruction rate were 78.07% and 43.49%, and 4093 kW, respectively at direct normal irradiance (DNI) of 950 W/m2 followed by the R1234ze, R1234yf, R245fa, and R134a. Also, the maximum exergy and thermal efficiency for the R407c fluid was 75.21% and 41.9% at maximum turbine inlet pressure (P5) of 23 MPa; 81.79% and 45.57% at maximum turbine inlet temperature (T5) of 850 K; and 69.75% and 38.86% at minimum compressor inlet temperature (T9) of 300 K, respectively. Noted that SPTC field is a primary source of exergy destruction, i.e. more than 25% of solar inlet exergy and almost 54% of total exergy destruction rate has been destructed. Furthermore, the SPTC field’s improvement potential, fuel depletion ratio, and irreversibility ratio were 5282 kW, 0.2583, and 0.5388, respectively. Secondly, for the analysis of SPTC integrated combined R-SCO2-ORC system, eight fluids like R123, R1234ze, R1234yf, toluene, cyclohexane, isopentane, isobutene, and R290 have been selected. In general, exergy and thermal efficiency of system increases with the increase in DNI, ‘P5’, and ‘T5’ in contrast to the ‘T9’ as it shows inverse effect on efficiency. As a result, R123 based R-SCO2-ORC system shows maximum exergy and thermal efficiency of 86.75% and 48.33% at DNI of 950 W/m2; 79.04% and 44.03% at P5 of 23 MPa; 86.59% and 48.24% at T5 of 920 K; 84.64% and 47.15% at T9 of 327 K, respectively. Furthermore, it possesses highest net work output of 6231 kJ at T5 of 920 K and 6090 kJ at T9 of 327 K. Moreover, comparative study with and without recompression concludes that R123 based R vi SCO2-ORC system shows exergy and thermal efficiency of 85.09% and 47.4% as compared to 83.63% and 46.59%, respectively in case of simple SCO2-ORC system. Thirdly, the performance results of SPTC integrated combined SCO2-VAR system found that maximum exergy and thermal efficiency of SPTC for the April 15 on Mumbai was 32.58% and 63.46% at local apparent time (LAT(h)) = 1230, and 31.72% and 61.78%, respectively at LAT(h) = 1130 & 1230 for the December 15. Then, at maximum T5 of 920 K, the highest exergy and thermal efficiency, and net work output of the SCO2-VAR cycle were 80.13% and 44.64%, and 1668 kW, respectively. While, the highest coefficient of performance for cooling (COP$%%&’()) and heating (COP*+,-’()) were 0.4675 and 1.435, respectively found to be at lower T5 of 650 K. Furthermore, at maximum compressor pressure ratio of 2.67, the highest exergy and thermal efficiency, net work output, COP$%%&’() and COP*+,-’() were 81.51%, 45.41%, 1813 kW, 0.4722, and 1.207, respectively. Moreover, at lower T9 of 300 K, the maximum exergy and thermal efficiency, and net work output were 81.29% and 45.29%, and 1788 kW, respectively. Lastly, the performance of SPTC integrated SORC (SPTC-SORC system) has been examined by six fluids such as cyclohexane, isopentane, propane, R600a, n-Hexane, and n-Pentane. Findings reveal that at higher DNI of 950 W/m2 and turbine inlet pressure of 86 bar, the highest exergy efficiency was 83.15% and 81.19%; and thermal efficiency was 39.9% and 38.96%, respectively in case of propane. Additionally, more than 80% of total exergy destruction rate was found to be only in SPTC