Compression ratio energy and exergy analysis of a developed Brayton-based power cycle employing CAES and ORC

Energy consumption growth in the world is one of the primary concerns of researchers in the energy fields. Providing demanded power, especially in peak consumption times besides less emission production, is always been the goal of power plants designers. Utilizing auxiliary devices or cycles such as compressed air energy system or organic Rankine cycle can help them to achieve their goal. However, the performance of these auxiliary instruments should be evaluated having the best design achieving the target. In this research, employing compressed air energy besides utilizing an organic Rankine cycle is proposed for improving the performance of a Brayton power cycle; moreover, optimum operating condition for compression ratio of each cycle is found with energy-exergy analysis. Various working fluids for organic Rankine cycle are explored, and the best conditions are introduced based on energy and exergy parameters, namely the first- and second-law efficiencies, power and exergy destruction. Results show that the optimum compression ratio of Brayton cycle is 7.5 for all considered organic fluids, and optimum pressure ratio of organic Rankine cycle is 5.5 for isopentane and n-pentane. Isopentane has the least exergy destruction, while the maximum first- and second-law efficiencies are achieved by R123.