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.
