TECHNICAL PAPERS: Gas Turbines: Combustion and Fuel

A Novel Approach to Predicting NOx Emissions From Dry Low Emissions Gas Turbines

[+] Author and Article Information
Khawar J Syed, Peter Martin

 Siemens Industrial Turbomachinery Ltd., P. O. Box 1, Lincoln LN5 7FD, UK

Kirsten Roden

 Siemens AG Guenther-Scharowsky-Str. 1, D-91058 Erlangen, Germany

J. Eng. Gas Turbines Power 129(3), 672-679 (Dec 22, 2006) (8 pages) doi:10.1115/1.2718564 History: Received June 10, 2006; Revised December 22, 2006

An empirical modeling concept for the prediction of NOx emissions from dry low emissions (DLE) gas turbines is presented. The approach is more suited to low emissions operation than are traditional approaches (Lefebrre, A. H., 1998, Taylor and Francis, New York). The latter, though addressing key operating parameters, such as temperature and pressure drop, do not address issues such as variation in fuel/air distribution through the use of multifuel stream systems, which are commonly applied in DLE combustors to enable flame stability over the full operating range. Additionally, the pressure drop dependence of NOx in such systems is complex, and the exponent of a simple pressure drop term can vary substantially. The present approach derives the NOx model from the equations that govern the NOx chemistry, the fuel/air distribution and the dependence of the main reaction zone on its controlling parameters. The approach is evaluated through comparing its characteristics to data obtained from high-pressure testing of a DLE combustor fueled with natural gas. The data were acquired at a constant pressure and preheat temperature (14 Bara and 400°C) and a range of flame temperatures and flow rates. Though the model is configured to address both relatively fast and slow NOx formation routes, the present validation is conducted under conditions where the latter is negligible. The model is seen to reproduce key features apparent in the data, in particular, the variable pressure drop dependence without any ad hoc manipulation of a pressure drop exponent.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

PSR NOx and adiabatic flame temperature against mixture fraction in the lean and stoichiometric regions: 14 Bara and 400°C inlet temperature. The fuel is natural gas.

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Figure 2

PSR NOx against tRes at different mixture fractions in the lean region: 14 Bara and 400°C inlet temperature. The fuel is natural gas.

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Figure 3

PSR results: ln (NOx) against 1∕Tflame at different tres including the theoretical activation temperatures: 14 Bara and 400°C inlet temperature. The fuel is natural gas.

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Figure 4

Different states of mixing within the combustor

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Figure 5

Impact of unmixedness on NOx-Zeldovich mechanism (2)

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Figure 6

NOx emissions from high-pressure test results (2). The data points are for the nonideally premixed configuration, and the shaded region indicates the results for the well-premixed case: P=14 Bara, inlet temperature=400°C. The fuel is natural gas.

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Figure 7

Decline of the unmixedness through the combustor

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Figure 9

Comparison between NOx from rig tests (2) and model (Eqs. 34,35)



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