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

Influence of Pressure and Steam Dilution on NOx and CO Emissions in a Premixed Natural Gas Flame

[+] Author and Article Information
Sebastian Göke, Thoralf Reichel, Katharina Göckeler

Chair of Fluid Dynamics,
Hermann-Föttinger-Institute,
Technische Universität,
Berlin 10623, Germany

Sebastian Schimek

Chair of Fluid Dynamics,
Hermann-Föttinger-Institute,
Technische Universität,
Berlin 10623, Germany
e-mail: sebastian.goeke@tu-berlin.de

Steffen Terhaar

Chair of Fluid Dynamics,
Hermann-Föttinger-Institute,
Technische Universität,
Berlin 10623, Germany

Oliver Krüger

Chair of Fluid Dynamics,
Hermann-Föttinger-Institute,
Technische Universität
Berlin 10623, Germany

Julia Fleck, Peter Griebel

German Aerospace Center (DLR),
Institute of Combustion Technology,
Stuttgart 70569, Germany

Christian Oliver Paschereit

Chair of Fluid Dynamics,
Hermann-Föttinger-Institute,
Technische Universität,
Berlin 10623, Germany
e-mail: oliver.paschereit@tu-berlin.de

1Corresponding author.

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received January 26, 2014; final manuscript received February 9, 2014; published online April 18, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(9), 091508 (Apr 18, 2014) (8 pages) Paper No: GTP-14-1050; doi: 10.1115/1.4026942 History: Received January 26, 2014; Revised February 09, 2014

In the current study, the influence of pressure and steam on the emission formation in a premixed natural gas flame is investigated at pressures between 1.5 bar and 9 bar. A premixed, swirl-stabilized combustor is developed that provides a stable flame up to very high steam contents. Combustion tests are conducted at different pressure levels for equivalence ratios from lean blowout to near-stoichiometric conditions and steam-to-air mass ratios from 0% to 25%. A reactor network is developed to model the combustion process. The simulation results match the measured NOx and CO concentrations very well for all operating conditions. The reactor network is used for a detailed investigation of the influence of steam and pressure on the NOx formation pathways. In the experiments, adding 20% steam reduces NOx and CO emissions to below 10 ppm at all tested pressures up to near-stoichiometric conditions. Pressure scaling laws are derived: CO changes with a pressure exponent of approximately −0.5 that is not noticeably affected by the steam. For the NOx emissions, the exponent increases with equivalence ratio from 0.1 to 0.65 at dry conditions. At a steam-to-air mass ratio of 20%, the NOx pressure exponent is reduced to −0.1 to +0.25. The numerical analysis reveals that steam has a strong effect on the combustion chemistry. The reduction in NOx emissions is mainly caused by lower concentrations of atomic oxygen at steam-diluted conditions, constraining the thermal pathway.

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Figures

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Fig. 2

Setup for the gas-fired tests

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Fig. 1

Sketch of the injector. The circular combustion chamber for the water tunnel experiments is shown.

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Fig. 4

Line-of-sight integrated OH* chemiluminescence images of the flame (window size is 140 mm × 140 mm)

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Fig. 3

Schematic of the reactor network

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Fig. 6

Measured CO concentrations. For each curve, the equivalence ratio is decreased from φ = 0.95 in steps of Δφ = 0.05 until blowout occurs.

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Fig. 8

Measured NOx concentrations for different pressures at Ω = 0 and Ω = 0.2

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Fig. 9

Measured and simulated emissions for Ω = 0 and Ω = 0.2 at various pressures: (a) CO emissions, and (b) NOx emissions

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Fig. 7

Measured NOx concentration for 1.5 bar

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Fig. 10

Contribution of the NOx formation pathways: (a) p = 1.5 bars, ω = 0; (b) p = 9 bars, ω = 0; (c) p =  6.5 bars, ω = 0.2; and (d) p = 9 bars, ω  = 0.2

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