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Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

Off-Design Performance Investigation of a Low Calorific Value Gas Fired Generic-Type Single-Shaft Gas Turbine

[+] Author and Article Information
Raik C. Orbay

Department of Energy Sciences, Lund University, Lund 22100, Swedenraik.orbay@vok.lth.se

Magnus Genrup

 Siemens Industrial Turbomachinery AB, Finspong, Sweden

Pontus Eriksson, Jens Klingmann

Department of Energy Sciences, Lund University, Lund 22100, Sweden

At the lowest heating values, the increased mass flow through the swirlers will change the air split toward less air and thus higher equivalence ratio in the primary zone. This is not taken into account here.

J. Eng. Gas Turbines Power 130(3), 031504 (Apr 02, 2008) (7 pages) doi:10.1115/1.2836482 History: Received May 10, 2007; Revised September 24, 2007; Published April 02, 2008

When low calorific value gases are fired, the performance and stability of gas turbines may deteriorate due to a large amount of inertballast and changes in working fluid properties. Since it is rather rare to have custom-built gas turbines for low lower heating value (LHV) operation, the engine will be forced to operate outside its design envelope. This, in turn, poses limitations to usable fuel choices. Typical restraints are decrease in Wobbe index and surge and flutter margins for turbomachinery. In this study, an advanced performance deck has been used to quantify the impact of firing low-LHV gases in a generic-type recuperated as well as unrecuperated gas turbine. A single-shaft gas turbine characterized by a compressor and an expander map is considered. Emphasis has been put on predicting the off-design behavior. The combustor is discussed and related to previous experiments that include investigation of flammability limits, Wobbe index, flame position, etc. The computations show that at constant turbine inlet temperature, the shaft power and the pressure ratio will increase; however, the surge margin will decrease. Possible design changes in the component level are also discussed. Aerodynamic issues (and necessary modifications) that can pose severe limitations on the gas turbine compressor and turbine sections are discussed. Typical methods for axial turbine capacity adjustment are presented and discussed.

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Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 7

Combustor loading versus LHV for different EGTs. Legend as in Fig. 4.

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Figure 10

Net power versus LHV for different EGTs. Legend as in Fig. 4.

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Figure 8

TIT versus turbine outlet temperature. Legend as in Fig. 4.

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Figure 9

Net efficiency versus LHV for different EGTs. Legend as in Fig. 4.

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Figure 1

Off-design deck schematics

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Figure 2

Heating value and Wobbe index versus ωCO2

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Figure 3

Centrifugal compressor map for π≅5.5

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Figure 4

Surge margin versus LHV for different EGTs

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Figure 5

Pressure ratio versus LHV for different EGTs. Legend as in Fig. 4.

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Figure 6

LBO limits for the CO2∕CH4 mixture

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