Energy and Exergy Analyses of Regenerative Gas Turbine Air-Bottoming Combined Cycle: Optimum Performance

Abstract

The current paper presents a thermodynamic analysis of an air-bottoming cycle (ABC) operated by the exhaust gasses of a regenerative gas turbine cycle. The partial exhaust heat of a topping gas turbine cycle is utilized to heat the compressed air of the ABC by passing it through a heat exchanger (H.E.2), whereas remaining heat is used to heat the compressed air of the topping cycle before entering a combustion chamber by passing it through a heat exchanger (H.E.1). The effects of the turbine inlet temperature of the topping cycle (1000 K ⩽ $${\text{TIT}}$$ ⩽ 1500 K) and fraction of mass flow rate of the exhaust gas (0 ⩽ $$x$$ ⩽ 1) on the net output, combined thermal efficiency, exergy destruction, exergy loss by exhaust gasses, and specific fuel consumption (SFC) are investigated parametrically for a particular value of the pressure ratio of the topping and bottoming cycles. At $$x = 0$$ , the net output and thermal efficiency of the combined cycle increase by 15.1% and 31.3%, respectively, whereas the SFC decreases by 13.1% and 15.5% at $${\text{TIT}} = 1000\;{\text{K}}$$ and $${\text{TIT}} = 1500\;{\text{K}}$$ , respectively. The exergy destruction of the heat exchanger of the topping cycle increases, whereas that of the bottoming cycle decreases with an increase in x. Overall, in terms of the net output and thermal efficiency, a simple gas turbine cycle with an air-bottoming combined cycle performs better than a simple regenerative gas turbine cycle; however, in view of the exergy loss by exhaust gasses, a simple regenerative gas turbine cycle is better than the combined cycle.