Example 6-2
One of the most efficient types of power plant in service
today is a Combined Cycle Power Plant, which includes
both a high temperature gas turbine and a low
temperature steam turbine. In one such plant, 480 MW of
net power is produced. The cooling water that removes
heat from the cycle enters at 45°F, leaves at 65°F, and
flows at a rate of 1.52 x10
4
lbm/s. The firing temperature
in the gas turbine is 2600°F. Compare the efficiency of
this cycle to the efficiency of a theoretical maximum power
cycle operating between these temperature limits. Also
compute the efficiency of the Carnot cycle for the same
temperature limits.
Solution:
Heat is rejected from the cycle in the cooling water at the
rate:
L
p
Q
mc
T
=
∆
±
±
Btu
cp(water,
55,
14.7)
1.00
lbm R
p
c
T
P
=
=
=
=
⋅
(
)
4
o
lbm
Btu
1.52
10
1.00
65
45
F
s
lbm R
L
Q
⎛
⎞⎛
⎞
=
×
−
⎜
⎟⎜
⎟
⋅
⎝
⎠⎝
⎠
±
5
Btu
3.04
10
s
L
Q
=
×
±
The first law for a cycle is
H
net
L
Q
W
Q
=
+
±
±
±
(
)
5
1000 kw
Btu
1.055 kw
480MW
3.04
10
Btu
1 MW
s
1
s
H

This
** preview**
has intentionally

**sections.**

*blurred***to view the full version.**

*Sign up*