GAS TURBINE POWER PLANT 277

A.C.

Exhaust Fuel

Alternator

Tu r b i n eGas S.M.

Air in

1

(^263)
5
4
Starting motor
Regenerator
2a 2
36
5
5a
4
Te m p. R e d u c e d
due to Transfer
of Heat in H.E.
H
Regeneration cycle
Fig. 9.10 Fig. 9.11
For regeneration to take place T 5 should be greater than T 2.
In the heat exchanger, the temperature of air is increased from T 2 to T 3 , and the temperature of
the exhaust gases is reduced from T 5 to T 6. If the regeneration is perfect, the air would be heated to the
temperature of the exhaust gases entering the H.E. the effectiveness of the regeneration is defined as:
ε = effectiveness

Rise in air temperature
Max. possible rise
=^32
52
TT
TT
−
−
For ideal regeneration,
T 3 = T 5 and T 6 = T 2
The common values of effectiveness would be from
70 to 85%. The heating surface of the generator, as well
as the dimensions and price of the gas turbine increases
with the regeneration fraction. But to justify the regen-
eration economically, the effectiveness should atleast be
50%. The regenerative cycle has higher efficiency than
the simple cycle only at low-pressure ratios. If the pres-
sure ratio is raised above a certain limit, then the regen-
erator will cool the compressed air entering the combus-
tion chamber instead of heating it and the efficiency of
the regenerative cycle drops. This is clear from Fig. 9.12.
It is clear from Fig. 9.11, that the compressor turbine works are not affected by regeneration.
However, the heat to be supplied in the combustion chamber is reduced and also it is added at higher
temperature as compared to the cycle without regeneration. Thus, the thermal efficiency of the cycle
increases. It will be equal to,
ηt =
45 21
43
C(T T) C(T T)
C(T T)
pp
p
−− −
−
For ideal regeneration, T 3 = T 5
ηt = 1 –^21
45
(T T )
(T T )
−
−

(^00)
10
20
30
40
5101520
Pressure Ratio
Thermal Efficiency %
Regenerative
Simple
Fig. 9.12