Energy, Exergy, and Parametric Analysis of Simple and Recuperative Organic Rankine Cycles Using a Gas Turbine–Based Combined Cycle

Abstract

In this study, simple and recuperative organic Rankine cycles (ORCs) were designed as the bottoming cycle to a simple gas turbine. After the design, the performance of the ORC engines was analyzed for varying turbine inlet temperature and pressure. During the study, eight different working fluids were selected for the design of the ORCs to identify the best-performing working candidate, namely, benzene, cyclohexane, ethanol, methanol, R21, R152a, toluene, and trans-2-butane. For all turbine inlet pressure values, the maximum performance was obtained from methanol for simple ORC (sORC) and from trans-2-butane for recuperative ORC (rORC). The maximum net power production, thermal efficiency, and exergy efficiency of the sORC were obtained with methanol at 45 bar 350°C, achieving 1967 kW, 24.5%, and 48.9%, respectively. For rORC, the maximum net power production, thermal efficiency, and exergy efficiency were obtained with trans-2-butane at 40 bar 240°C as 2,523 kW, 31.1%, and 62.4%, respectively. The highest net power production, thermal efficiency, and exergy efficiency of the gas turbine (GT)-ORC combined cycle are found at 40 bar and 240°C for rORC, reaching 8,723 kW, 47.63%, and 67.33%, respectively. This means that almost 1,605 kg-CO2/h reduction in CO2 emission is possible with the use of rORC as a bottoming cycle in the GT. When the total heat input from the fuel in the burner of the GT is considered, it is observed that the power production of the GT-rORC combined cycle can be increased up to 40.7%. In order to identify optimum performance under real operating conditions, the designed system can be used by ORC engine designers, manufacturers, and in facilities where simple gas turbines are available.