OCTOBER 19-20, 2012 - YMCA University of Science & Technology

Proceedings of the National Conference on
Trends and Advances in Mechanical Engineering,
YMCA University of Science & Technology, Faridabad, Haryana, Oct 19-20, 2012
Figure: 1 Schematic flow diagram of Co-Generation Cycle
In the present system ambient air is coming to air compressor and after compression its temperature and pressure
is increased. This compressed air is passed through regenerator. In regenerator compressed air is entering from
one side and combustion gases coming out of gas turbine from the other. High temperature combustion gases
transfer their heat to the compressed air. After gaining heat this compressed air comes to combustion chamber
and fuel is added in it. After burning in air chemical energy of fuel is converted into thermal energy.
Temperature of combustion products coming out of combustion chamber depends upon turbine inlet temperature.
Combustion product temperature is controlled by making A/F mixture a lean mixture. Gasses coming out from
gas turbine are having a large amount of thermal energy. Some part of this thermal energy is transferred to
compressed air in regenerator and remaining part is absorbed by high pressure water in steam generator. Flue gas
temperature coming out of steam generator is dependent upon the dew point temperature of flue gases. This dew
point temperature decides the temperature at which flue gases must enter the stack. Each component is modeled
by mass and energy balances. If the system operates in a steady-state, steady flow condition and all the
nonreacting gases are arbitrarily assigned as zero thermo mechanical enthalpy, entropy, and exergy at the
condition of ambient pressure and temperature regardless of their chemical composition, then the entropy of
mixing different gaseous components can be neglected, and the general exergy-balance equation is given by
For single stream flow
Specific exergy is given by
. n . . . .
∑ ∑ ∑
E = ( E ) i + me − me − E
W Q D
i=
1
in out
. . . . .
E = ( E ) + me − me − me
W Q in out D
⎛ T T ⎞
P ⎡
⎛1+
wa
⎞
( ) 1 ln (1 ) ln (1 )ln
⎛ w ⎞⎤
e = C
pa
+ wC
pv
Ta ⎜ − − ⎟ + + w RaTa + RaTa
⎢ + w ⎜ wln
T 1 ⎟ + ⎜ ⎟⎥
⎝ a
Ta ⎠ Pa
⎢⎣
⎝ + w ⎠ ⎝ wa
⎠⎥⎦
Where w = 1.608w
The mass, energy, and exergy balances of the component of the plant are given below.
2.1. Air Compressors
The inlet and outlet humidity ratios will be the same. The energy balance yields the compressor work
compressor outlet temperature.
w
ai
= w
ao
Wc
and
T
T
a o
a i
=
[ r ]
c
γ c − 1
γ cη
c
W
c
= h
a o
− h
a i
The exergy balance for the compressor gives the exergy destruction e DC as following
e = W + ( e − e )
DC C ai ao
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