In conventional power plants, gas turbine is the major source of
power generation in many countries. The gas turbine works on the
principle of Brayton cycle in which compressed air from the
compressor enters the combustion chamber. The high pressure and
high temperature combustion products from the combustion
chamber enter the gas turbine where they expand to low pressure
and produce the work [1]. Due to incomplete combustion in the
combustion chamber as well as short expansion of high pressure
and high temperature combustion products in the gas turbine, a lot
of energy gets lost to the environment which not only pollutes the
environment but also plays the vital role in global warming.
Sometimes this lost energy is abundant that is capable to run
another thermal power plant. The turbine exhaust temperature of a
simple gas turbine is in the range of 370e540 C but usually above
500 C [2]. Accordingly, the hot exhaust gases have significant
thermodynamic utility (exergy) that would otherwise be lost when
the exhaust gas discarded directly to the surroundings.
One way of utilizing this potential is by means of internal heat
recovery in which exhaust gas is utilized as the source of heat. The
various methods being employed include a regenerative heat
exchanger and steam injection. The regenerative heat exchanger
allows the air exiting the compressor to be preheated before
entering the combustor, thereby reducing the amount of fuel that
must be burned in the combustor. With the steam injection
method, the thermal energy of the exhaust gas is transferred to an
auxiliary fluid (water) in HRSG (heat recovery steam generator)
unit which is then injected into the combustor. In the HRSG unit,
water passes in a counter flow with the exhaust gas into three
separate heat exchangers: economizer, vaporizer and superheater.
Steam injection increases the turbine work by increasing the mass
flow rate of the working fluid and its specific heat [3]. In addition to
an increase in turbine output, steam injection method has the
advantage of controlling NOx emissions from the gas turbine
combustor