3. Energy Flow in Combined Cycle
G
out
Q ,
G
in
Q ,
G
net
P ,
Fuel Power
Waste Heat
G
in
S
in Q
Q ,
,
Final Waste heat
S
net
P ,
S
out
Q ,
4. Thermal Analysis of Combined Cycle
G
in
G
G
net Q
P ,
,
G
in
G
G
out Q
Q ,
, 1
G
in
G
G
out
S
in Q
Q
Q ,
,
, 1
G
in
G
S
S
in
S
S
net Q
Q
P ,
,
, 1
Net Power Output of Gas Cycle:
Rate of Heat Rejection in Gas Cycle:
Rate of Heat input to steam Cycle:
Net Power Output of Steam Cycle:
5. G
in
G
S
G
in
G
tot Q
Q
P ,
, 1
G
in
tot
ov
Q
P
,
G
in
G
in
G
S
G
in
G
ov
Q
Q
Q
,
,
, 1
S
net
G
net
tot P
P
P ,
,
Overall Efficiency of Sandwich:
Net Power Output of Sandwich:
G
S
G
ov
1
6.
G
S
G
ov
1
Law of Combination
G
S
G
ov
1
1
1
G
S
G
ov
1
1
1
S
G
ov
1
1
1
7. CC
AIR
INLET
GAS INLET
G
HP IP LP
HRSG
STACK
CONDENSER
PUMP
TURBINE
G
T=5500C
T=8500C
T=1500C
T=500C
T=1000C
T=5000C
T=600C T=500C
T=500C
P=1bar
P=10bar
P=10bar
P=2bar
P=170bar
P=.1 bar P=1bar
COMBINED CYCLE POWER PLANT
9. Types of HRSG
• Basic types of standard design of heat recovery steam
generators are differentiated by the direction of the flue gases
flow.
• Vertical HRSG
• Small footprint
• Simple concept of service
• Hanging design of heating surfaces
• Horizontal HRSG
• Small construction height
• High cycling ability
• Operational flexibility
• Hanging design of heating surfaces
16. •This configuration is very popular
for HRSG units recovering heat
from small gas turbines and diesel
engines.
•It is a very compact design and
can be shipped totally assembled.
• Main Drawback: The bent tube
arrangement quickly causes the
module to exceed shipping
limitations for units having a large
gas flow
D-Frame evaporator layout
17. • This configuration has probably
been used for more years than
any of the others.
• It has the advantage of the
upper header being configured
as the steam separation drum.
• Alternately, The upper header
can be connected to the steam
drum by risers.
• This allows more than one O-
Frame evaporator to be
connected to the same steam
drum.
• Results in shipable modules
being able to handle very large
gas flows.
O-Frame evaporator layout
18. • This configuration is simply a
variation of the O-Frame
Evaporator.
• It was popular for services with a
large amount of ash, since the
center area between the lower
drums could be configured as a
hopper to collect and remove
solid particles.
A-Frame evaporator layout
19. • In the past twenty years, this
configuration has become the most
popular.
• This type module can be built in multiple
axial modules or in multiple lateral
modules, allowing it to be designed to
accept any gas flow.
• There are numerous variations of this
design where tube bundles may contain
one, two, or three rows of tubes per
header.
• It is also, normally, more economical to
manufacture, ship and field construct.
• The tube bundles may be shipped to field
installed in the modules, or as loose
bundles which are installed into a field
erected shell.
I-Frame evaporator layout
20. The horizontal tube evaporator is used,
not only for heat recovery from Gas
Turbine exhaust, but for recovery from
flue gases in Refinery and
Petrochemical furnaces also.
Horizontal tube evaporator layout
• It has similar size limitations due to shipping restrictions
similar to the O-frame modules.
• It is generally a less expensive unit to manufacture than the
other configurations.
27. VARIATION OF NUMBER OFTUBES IN HRSG WITH CAPACITY
1000
2000
3000
4000
5000
6000
7000
8000
100 150 200 250 300
CAPACITY (MW)
NO.
OF
TUBES
HP
IP
LP
28. Today’s Limits
• Limits are, in this case, meant to be state of the art
values of key performance factors of a HRSG application
• limits driven by economical and technical considerations.
• Triple Pressure Reheat Drum Type Boilers, natural
circulation: