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

Assessment of a Gas Turbine NOx Reduction Potential Based on a Spatiotemporal Unmixedness Parameter

[+] Author and Article Information
Stefan Dederichs

e-mail: stefan.dederichs@partner.kit.edu

Nikolaos Zarzalis

e-mail: Nikolaos.Zarzalis@kit.edu

Peter Habisreuther

e-mail: peter.habisreuther@kit.edu
Karlsruhe Institute of Technology,
Engler-Bunte-Ring 1,
Karlsruhe 76131, Germany

Christian Beck

e-mail: beckchristian@siemens.com

Bernd Prade

e-mail: prade.bernd@siemens.com

Werner Krebs

e-mail: wernerkrebs@siemens.com
Siemens AG,
Mellinghofer Str. 55,
Muelheim an der Ruhr 45473, Germany

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 9, 2013; final manuscript received July 16, 2013; published online September 17, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 135(11), 111504 (Sep 17, 2013) (8 pages) Paper No: GTP-13-1248; doi: 10.1115/1.4025078 History: Received July 09, 2013; Revised July 16, 2013

The paper presents a one-dimensional approach to assess the reduction potential of NOx emissions for lean premixed gas turbine combustion systems. NOx emissions from these systems are known to be mainly caused by high temperatures, not only from an averaged perspective but especially related to poor mixing quality of fuel and air. The method separates the NOx chemistry in the flame front zone and the postflame zone (slow reaction). A one-dimensional treatment enables the use of detailed chemistry. A lookup table parameterized by reaction progress and equivalence ratio is used to improve the computational efficiency. The influence of mixing quality is taken into account by a probability density function of the fuel element–based equivalence ratio, which itself translates into a temperature distribution. Hence, the NOx source terms are a function of reaction progress and equivalence ratio. The reaction progress is considered by means of the two-zone approach. Based on unsteady computational fluid dynamics (CFD) data, the evolution of the probability density function with residence time has been analyzed. Two types of definitions of an unmixedness quantity are considered. One definition accounts for spatial as well as temporal fluctuations, and the other is based on the mean spatial distribution. They are determined at the location of the flame front. The paper presents a comparison of the modeled results with experimental data. A validation and application have shown very good quantitative and qualitative agreement with the measurements. The comparison of the unmixedness definitions has proven the necessity of unsteady simulations. A general emissions-unmixedness correlation can be derived for a given combustion system.

Copyright © 2013 by ASME
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Fig. 1

Exemplary sketch of a technical combustion system

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Fig. 2

NOx source term and temperature as a function of the laminar flame spread for two exemplary equivalence ratios; natural gas at a pressure of 8 bar

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Fig. 3

CFD-based probability (sampled over a generic flame front) compared to the modeled probability density function (Gaussian PDF)

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Fig. 4

Contour plot of mean isoresidence time; time starts at a reaction progress of 0.5; coordinates normalized with the premixing passage diameter

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Fig. 5

Normalized postflame standard deviation versus residence time; CFD marks obtained at instantaneous isotime surfaces; model is obtained by a regression

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Fig. 6

Calculated emissions versus experimental data from Biagioli and Güthe [9]

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Fig. 7

Measured NOx emissions related to different CFD-based unmixedness parameters and comparison against the modeled emissions

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Fig. 8

Distribution of spatial, spatiotemporal, and transient-spatial unmixedness over the time




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