1. Combined Cycle Power Plants
P M V Subbarao
Professor
Mechanical Engineering Department
Better Use of Energy resources….

2. More Entropy Vehicles for Better Success

3. Energy Flow in Combined Cycle
Final Waste heat
Fuel Power
Waste Heat

4. Thermal Analysis of Combined Cycle
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. Net Power Output of Sandwich:
Overall Efficiency of Sandwich:

6. Law of Combination

7. COMBINED CYCLE POWER PLANT
GAS INLET
P=10bar CC
T=1500C
T=8500C
P=10bar
TURBINE G
COMP
T=1000C
T=500C
P=2bar
STACK
P=1bar
T=5500C HP IP LP
AIR
INLET
HRSG
T=5000C
P=170bar
TURBINE
T=500C G
PUMP
P=1bar
P=.1 bar
T=500C
T=600C
CONDENSER

8. Cogeneration Plants

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

10. Vertical HRSG

11. Horizontal HRSG
Vertical HRSG

12. Heat Exchanging Curve
~5500C
~1000C
~400C

13. HRSG COMPONENTS

15. Types of Evaporator Sections
D-Frame evaporator layout
O-Frame evaporator layout
A-Frame evaporator layout
I-Frame evaporator layout
Horizontal tube evaporator layout

16. D-Frame evaporator layout
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

17. O-Frame evaporator layout
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.

18. A-Frame evaporator layout
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.

19. I-Frame evaporator layout
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.

20. Horizontal tube evaporator layout
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.
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.

21. Schematic Diagram of a Simple HRSG

22. Single Pressure Rankine Cycle

23. Dual Pressure Rankine Cycle

24. Triple Pressure Rankine Cycle

25. Layout of Triple Pressure Rankine Cycle

26. Calculated Values of HRSG Modules In A 101MW CCPP

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: