Exergetic and power augmentation analyses of gas turbine with air-bottoming combined cycle

Abstract

Concept of exergy based analysis for the thermodynamic evaluation of energy conversion systems is steadily growing. Exergy analysis efficiently acts as a supplement with energy analysis to identify the origin of losses and the options for loss reductions to boost the power output of any thermal energy conversion system. To pander the immense energy demand especially in the hot summer days, the application of power augmentation technique on the existing thermodynamic power generating model is an emerging research field. In the present work, the exergetic and power augmentation analyses of a simple gas turbine cycle and a gas turbine with air bottoming cycle (ABC) is performed. To identify the effect of important parameters on the performance characteristics of the conventional gas turbine cycle and ABC is presented with the presence and absence of inlet fogging power augmenting technology, based on the first and second law of thermodynamics. In this study, work output, specific fuel consumption (SFC) and the quantitative exergy balance for each component and for the whole system are investigated using thermodynamic modeling software Cycle-Tempo. Power output and exergetic variations of simple gas turbine cycle due to the inlet fogging system are comprehensively discussed and compared with those of the ABC cycle. The results indicate that, in the air bottoming combined cycle (ABC), exergy recovery is greater than the exergy loss due to additional components, approximately 8.5% of fuel exergy is recovered; 3.4% accounts for the exergy destruction of the additional components in the ABC, while 5.1% results in the increase of the work output. And this gives a boon of 9% less SFC in ABC than that of the simple gas turbine cycle. Due to the installation of the inlet fogging system in the cycle, compressor mass flow increases averagely 21.6% and GT fuel flow rate experiences approximately 22.6% increment and the net result is increment of cycle power output. Average Power augmentation of simple gas turbine cycle is around 21.9%, and of ABC approximately 25.2 %, due to inlet fogging. First law and second law efficiency of the combined cycle (ABC) is higher than that of simple GT cycle, irrespective of presence and absence of inlet fogging system, due to the substantial exergy recovery in the air bottoming combined cycle over the simple gas turbine cycle. The rate of power augmentation by the inlet fogging still cause an extra energy input to the gas turbine, this makes a small change in efficiency of the power plant. So, cycle power augmentation with the inlet fogging is at the expense of marginal improvement of efficiency in order to boost power output.