Effect of temperature and gas flow on the efficiency of an air bottoming cycle

Abstract

The objective of this research is to analyze the performance of an Air Bottoming Cycle (ABC) by considering the effect of temperature and gas flow. Based on the energetic analysis, a thermodynamic calculation has been performed to investigate improving the thermal efficiency of the ABC. In this research, we consider the full cycle should consist of two sub-cycles: Braysson and Joule. The flue gas from the top cycle is used in Braysson cycle turbine to generate power and the rest of the energy of this flow is exchanged to the pressurized Joule cycle air flow. The results indicate that the higher inlet temperatures of the Braysson turbine and lower Braysson turbine outlet temperatures lead to higher thermal efficiencies. Moreover, the lower overall pressure ratios in Joule cycle are required to achieve the higher overall thermal efficiencies. The maximum thermal efficiency and also the optimal design point of this ABC have been found. The results of this ABC analysis show an increase in net output work and the thermal efficiency up to more than 55%, which in turn leads to have less specific fuel consumption. The proposed cycle has been found to have more energy recovery potential compared to some other gas turbine based ABCs. Besides, in contrast to common steam bottom cycles, some water can be generated using the flue gas stream which is important because the lack of water resources is going to be a major problem in many regions worldwide.