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Research Papers: Gas Turbines: Electric Power

A Simple Parametric Model for the Analysis of Cooled Gas Turbines

[+] Author and Article Information
S. Can Gülen

 GE Energy, 1 River Road, Building 40-412, Schenectady, NY 12345can.gulen@ge.com

J. Eng. Gas Turbines Power 133(1), 011801 (Sep 27, 2010) (13 pages) doi:10.1115/1.4001829 History: Received April 09, 2010; Revised April 19, 2010; Published September 27, 2010; Online September 27, 2010

A natural gas fired gas turbine combined cycle power plant is the most efficient option for fossil fuel based electric power generation that is commercially available. Trade publications report that currently available technology is rated near 60% thermal efficiency. Research and development efforts are in place targeting even higher efficiencies in the next two decades. In the face of diminishing natural resources and increasing carbon dioxide emissions, leading to greenhouse gas effect and global warming, these efforts are even more critical today than in the last century. The main performance driver in a combined cycle power plant is the gas turbine. The basic thermodynamics of the gas turbine, described by the well-known Brayton cycle, dictates that the key design parameters that determine the gas turbine performance are the cycle pressure ratio and maximum cycle temperature at the turbine inlet. While performance calculations for an ideal gas turbine are straightforward with compact mathematical formulations, detailed engineering analysis of real machines with turbine hot gas path cooling requires complex models. Such models, requisite for detailed engineering design work, involve highly empirical heat transfer formulations embedded in a complex system of equations that are amenable only to numerical solutions. A cooled turbine modeling system incorporating all pertinent physical phenomena into compact formulations is developed and presented in this paper. The model is fully physics-based and amenable to simple spreadsheet calculations while illustrating the basic principles with sufficient accuracy and extreme qualitative rigor. This model is valuable not only as a teaching and training tool, it is also suitable to preliminary gas turbine combined cycle design calculations in narrowing down the field of feasible design options.

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Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Air-cooled GT as a “combined” Brayton–Brayton cycle

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Figure 2

Control volumes for setting T3 to TIT or RIT (firing temperature)

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Figure 3

Total turbine cooling flow as a % of airflow including chargeable and nonchargeable flows (μc=0.113, β=0.83, φ∞=0.9)

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Figure 4

Schematic description of turbine expansion model

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Figure 5

GT efficiency (at the generator terminals) as a function of compressor PR; RIT=2462°F(1350°C). CAC from T2 to 600°F(315°C). Cycle improvements are cumulative.

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Figure 6

GT specific power output (at the generator terminals) as a function of compressor PR; RIT=2462°F(1350°C). CAC from T2 to 600°F(315°C). Cycle improvements are cumulative.

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Figure 7

CC net efficiency (at the generator terminals) as a function of compressor PR; RIT=2462°F(1350°C). CAC from T2 to 600°F(315°C). Cycle improvements are cumulative.

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Figure 8

Relative CC net efficiency as a function of GT Brayton cycle PR and RIT. The published CC rating data is from Ref. 24. The origin is for the “average” state-of-the-art F-Class air-cooled GT.

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Figure 9

Relative CC net efficiency and specific net power as a function of GT Brayton cycle PR and RIT. GT PR increases from 10 to 32 (from right to left) by increments of 2. The origin (0, 0) is the “average” state-of-the-art F-Class air-cooled GT.

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Figure 10

Impact of cooling flow reduction on CC performance. External (steam) cooling is assumed to replace 30–60% of total cooling duty with εSC=80%. The origin (0, 0) is the average state-of-the-art F-Class air-cooled GT.

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Figure 11

Air-cooled (AC-NRHT), air-cooled with reheat (AC-RHT), steam-cooled (SC-NRHT), and steam-cooled with reheat (SC-RHT) gas turbine based CC performance

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