A significant portion of the new electrical generating capacity installed in the past decade has employed heavy-duty gas turbines operating in a combined cycle configuration with a steam turbine bottoming cycle. In these power plants approximately one-third of the power is generated by the bottoming cycle. To ensure that the highest possible combined cycle efficiency is realized it is important to develop the combined cycle power plant as a system. Doing so requires a solid understanding of the efficiency entitlement of both, topping and bottoming, cycles separately and as a whole. This paper describes a simple but accurate method to estimate the Rankine bottoming cycle power output directly from the gas turbine exhaust exergy, utilizing the second law of thermodynamics. The classical first law approach, i.e., the heat and mass balance method, requires lengthy calculations and complex computer-based modeling tools to evaluate Rankine bottoming cycle performance. In this paper, a rigorous application of the fundamental thermodynamic principles embodied by the second law to the major cycle components clearly demonstrates that the Rankine cycle performance can be accurately represented by several key parameters. The power of the second law approach lies in its ability to highlight the theoretical entitlement and state-of-the-art design performances simultaneously via simple fundamental relationships. By considering economically and technologically feasible upper limits for the key parameters, the maximum achievable bottoming cycle power output is readily calculable for any given gas turbine from its exhaust exergy.

1.
Cohen
,
H.
,
Rogers
,
G. F. C.
, and
Saravanamuttoo
,
H. I. H.
, 1991,
Gas Turbine Theory
,
3rd ed.
,
Longman Scientific & Technical
,
Essex, England
.
2.
Young
,
J. B.
, and
Wilcock
,
R. C.
, 2002, “
Modeling the Air-Cooled Gas Turbine: Parts 1 and 2
,”
ASME J. Turbomach.
0889-504X,
124
, pp.
207
222
.
3.
El-Masri
,
M. A.
, 1986, “
On Thermodynamics of Gas Turbine Cycles: Part 1—Second Law Analysis of Combined Cycles
,”
ASME J. Eng. Gas Turbines Power
0742-4795,
108
, pp.
151
159
.
4.
Chin
,
W. W.
, and
El-Masri
,
M. A.
, 1987, “
Exergy Analysis of Combined Cycles: Part 2—Analysis and Optimization of Two-Pressure Steam Bottoming Cycles
,”
ASME J. Eng. Gas Turbines Power
0742-4795,
109
, pp.
237
243
.
5.
Horlock
,
J. H.
,
Young
,
J. B.
, and
Manfrida
,
G.
, 2000, “
Exergy Analysis of Modern Fossil-Fuel Power Plants
,”
ASME J. Eng. Gas Turbines Power
0742-4795,
122
, pp.
1
7
.
6.
Hofer
,
D. C.
, and
Gülen
,
S. C.
, 2006, “
Efficiency Entitlement for Bottoming Cycles
,” ASME Paper No. GT2006-91213.
7.
Moran
,
M. J.
, and
Shapiro
,
H. N.
, 1988,
Fundamentals of Engineering Thermodynamics
,
Wiley
,
New York
, p.
292
.
8.
Walter
,
J.
, and
Searles
,
D. E.
, 1997, “
Process Optimization of an Integrated Combined Cycle—The Impact & Benefit of Sequential Combustion
,” ASME Paper No. 97-GT-490.
9.
Kehlhofer
,
R. H.
,
Warner
,
J.
,
Nielsen
,
H.
, and
Bachmann
,
R.
, 1999,
Combined Cycle Gas & Steam Turbine Power Plants
,
2nd ed.
,
PennWell
,
Tulsa, OK
.
10.
Dechamps
,
P. J.
, 1998, “
Advanced Combined Cycle Alternatives With the Latest Gas Turbines
,”
ASME J. Eng. Gas Turbines Power
0742-4795,
120
, pp.
350
357
.
11.
Pasha
,
A.
,
Ragland
,
A. S.
, and
Sun
,
S.
, 2002, “
Thermal and Economic Considerations for Optimizing HRSG Design
,” ASME Paper No. GT2002–30250.
12.
1995,
Heat Exchange Institute Standards for Steam Surface Condensers
,
9th ed.
,
HEI
,
Cleveland, OH
.
13.
Hensley
,
J. C.
, 1989, “
Cooling Towers
,”
Standard Handbook of Powerplant Engineering
,
McGraw-Hill
,
New York
, Chap. 1.9.
14.
Pritchard
,
J. E.
, 2003, “
H-System™ Technology Update
,” ASME Paper No. GT2003-38711.
15.
Nakhamkin
,
M.
,
Swensen
,
E. C.
,
Wilson
,
J. M.
,
Gaul
,
G.
, and
Alba
,
J.
, 1995, “
The Cascaded Humidified Air Turbine (CHAT)
,”
ASME Cogen Turbo Power 1995
, Vienna, Austria.
16.
El-Masri
,
M. A.
, 1988, “
A Modified, High-Efficiency Recuperated Gas Turbine Cycle
,”
ASME J. Eng. Gas Turbines Power
0742-4795,
110
, pp.
233
242
.
17.
Jonsson
,
M.
, and
Yan
,
J.
, 2002, “
Exergy Analysis of Part Flow Evaporative Gas Turbine Cycles, Parts I and II
,” ASME Paper Nos. GT2002-30125 and GT2002-30126.
18.
Gas Turbine World
, 2006,
2006 Gas Turbine World Handbook
,
Pequot
,
Fairfield, CT
.
19.
Chiesa
,
P.
, and
Macchi
,
E.
, 2004, “
A Thermodynamic Analysis of Different Options to Break 60% Electric Efficiency in CC Power Plants
,”
ASME J. Eng. Gas Turbines Power
0742-4795,
126
, pp.
770
785
.
20.
Narula
,
R.
,
Zachary
,
J.
, and
Olson
,
J.
, 2004, “
Matching Steam Turbines With the New Generation of Gas Turbines
,”
PowerGen Europe
, Barcelona, Spain.
21.
Cotton
,
K. C.
, 1998,
Evaluating and Improving ST Performance
,
2nd ed.
,
Cotton Fact
,
Rexford, NY
, pp.
88
94
.
22.
2006, GT PRO Version 16.0.0, Thermoflow, Inc., Sudbury, MA.
23.
2007, “
GT24 and GT26 Gas Turbines
,” www.power.alstom.comwww.power.alstom.com.
24.
Kalina
,
A. I.
, 1984, “
Combined-Cycle System With Novel Bottoming Cycle
,”
ASME J. Eng. Gas Turbines Power
0742-4795,
106
, pp.
737
742
.
25.
Smith
,
R. W.
,
Johansen
,
A. D.
, and
Ranasinghe
,
J.
, 2005, “
Fuel Moisturization for Natural Gas Fired Combined Cycles
,” ASME Paper No. GT2005-69012.
26.
Bohn
,
D.
, 2006, “
SFB 561: Aiming For 65% CC Efficiency With an Air-Cooled GT
,” Modern Power Systems, pp.
26
29
.
27.
Boss
,
M. J.
,
Gradoia
,
M.
, and
Hofer
,
D.
, 2005, “
Steam Turbine Technology Advancements for High Efficiency, Reliability and Cost of Electricity
,”
POWER-GEN International
, Dec. 6–8.
28.
2004, GateCycle for Windows, Version 5.61.2.i, General Electric Company, www.gepower.com/enterwww.gepower.com/enter.
29.
Stull
,
D. R.
, and
Prophet
,
H.
, 1971,
JANAF Thermodynamic Tables
,
2nd ed.
, NSRDS-NBS 37,
National Bureau of Standards
.
You do not currently have access to this content.