Advanced exergy analysis of a combined Brayton/Brayton power cycle

Abstract

A combined Brayton/Brayton power cycle has been investigated using the advanced exergy analysis. The combustion chamber was shown to be the component with the largest exergy destruction. However, the analysis revealed that most of the irreversibility generation at the combustion chamber was endogenous and unavoidable. In contrast, the irreversibility generation at both turbines and both compressors was largely endogenous and avoidable. The total exergy destruction, endogenous unavoidable and exogenous avoidable exergy destruction at the combustion chamber monotonically decreased, while the endogenous avoidable and exogenous unavoidable exergy destruction at the same component initially decreased, reached a minimum, and then increased when the topping cycle pressure ratio was increased. On the other hand, when the bottoming cycle pressure ratio was increased, the endogenous and exogenous unavoidable exergy destruction at the combustion chamber decreased, reached a minimum, and then increased. All four terms of the exergy destruction of the topping cycle turbine and compressor consistently increased with the topping cycle pressure ratio, while their sensitivity to the bottoming cycle pressure ratio was relatively small. Finally, varying the combustion temperature from 1000 K to 1600 K has resulted in a reduction of the total exergy destruction, as well as the endogenous unavoidable, endogenous avoidable, exogenous unavoidable and exogenous avoidable exergy destruction at the least efficient components of the power plant.