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

Large Eddy Simulations of Hydrogen Oxidation at Ultra-Wet Conditions in a Model Gas Turbine Combustor Applying Detailed Chemistry

[+] Author and Article Information
Oliver Krüger

e-mail: o.krueger@tu-berlin.de

Christian Oliver Paschereit

Chair of Fluid Dynamics,
Hermann-Föttinger-Institut,
Technische Universität Berlin,
Müller-Breslau-Str. 8,
D-10623 Berlin, Germany

Christophe Duwig

Division of Fluid Mechanics,
Department of Energy Sciences,
Lund University,
Box 118,
SE-22100 Lund, Sweden

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Engineering for Gas Turbines and Power. Manuscript received June 18, 2012; final manuscript received August 9, 2012; published online January 8, 2013. Editor: Dilip R. Ballal.

J. Eng. Gas Turbines Power 135(2), 021501 (Jan 08, 2013) (10 pages) Paper No: GTP-12-1162; doi: 10.1115/1.4007718 History: Received June 18, 2012; Revised August 09, 2012

Humidified gas turbines (HGT) offer the attractive possibility of increasing plant efficiency without the cost of an additional steam turbine as is the case for a combined gas-steam cycle. In addition to efficiency gains, adding steam into the combustion process reduces NOx emissions. It increases the specific heat capacity (hence, lowering possible temperature peaks) and reduces the oxygen concentration. Despite the thermophysical effects, steam alters the kinetics and, thus, reduces NOx formation significantly. In addition, it allows operation using a variety of fuels, including hydrogen and hydrogen-rich fuels. Therefore, ultra-wet gas turbine operation is an attractive solution for industrial applications. The major modification compared to current gas turbines lies in the design of the combustion chamber, which should accommodate a large amount of steam without losing in stability. In the current study, the premixed combustion of pure hydrogen diluted with different steam levels is investigated. The effect of steam on the combustion process is addressed using detailed chemistry. In order to identify an adequate oxidation mechanism, several candidates are identified and compared. The respective performances are assessed based on laminar premixed flame calculations under dry and wet conditions, for which experimentally determined flame speeds are available. Further insight is gained by observing the effect of steam on the flame structure, in particular HO2 and OH* profiles. Moreover, the mechanism is used for the simulation of a turbulent flame in a generic swirl burner fed with hydrogen and humidified air. Large eddy simulations (LES) are employed. It is shown that by adding steam, the heat release peak spreads. At high steam content, the flame front is thicker and the flame extends further downstream. The dynamics of the oxidation layer under dry and wet conditions is captured; thus, an accurate prediction of the velocity field, flame shape, and position is achieved. The latter is compared with experimental data (PIV and OH* chemiluminescence). The reacting simulations were conducted under atmospheric conditions. The steam-air ratio was varied from 0% to 50%.

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Figures

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Fig. 1

Schematic drawing of the computational domain

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Fig. 2

Laminar burning velocity of hydrogen at 1 atm and Tu = 373 K for different steam levels and reaction mechanisms. Comparison between experimental data (symbols) and model predictions (lines). Experimental data according to Koroll and Mulpuru [14].

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Fig. 3

Thermal thickness δL0 of a hydrogen/air/steam flame at 1 atm and Tu = 373 K for different steam contents and reaction mechanisms

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Fig. 4

Steam content dependence of the laminar burning velocity (top), the thermal thickness (middle), and the flame thickening factor (bottom) at constant outlet temperatures Tb. The inlet temperature was 600 K. Model predictions were assessed with the mechanism of Burke et al. [18]. For comparison purposes calculations with methane (denoted as CH4) are depicted (GRI 3.0-Mech, Tb = 1773 K).

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Fig. 5

Burning velocities of 2:1 H2/O2 mixtures at 373 K and ambient pressure with the diluents He, Ar, N2, and H2O. Experimental data (symbols) according to Koroll and Mulpuru [14]. Lines indicate model predictions employing the mechanism of Burke et al. [18].

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Fig. 6

Molar fraction of OH and OH* as a function of the inverse temperature for three different steam contents Ω. The temperature of the burned gases was kept constant (Tb = 1773 K). Preheating zones for wet and dry cases are also provided.

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Fig. 7

Molar fraction of HO2 and H2O2 as a function of the inverse temperature for three different steam contents Ω. The temperature of the burned gases was kept constant Tb = 1773 K. Preheating zones for wet and dry cases are also provided.

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Fig. 8

Molar fraction of NO and NO2 as a function of the inverse temperature for three different steam contents Ω. The temperature of the burned gases was kept constant Tb = 1773 K. Preheating zones for wet and dry cases are also provided.

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Fig. 9

Mean axial velocity profiles at different streamwise positions (x/Dh = 0.5;1.0;2.0) at dry and wet conditions. Profiles are normalized by the contraction exit velocity references u0. (a) Dry case (Ω = 0.0, Φ = 0.45, Tu = 293 K). (b) Wet case (Ω = 0.5, Φ = 0.9, Tu = 600 K).

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Fig. 10

Slices in streamwise direction showing the instantaneous temperature fields for the dry (Ω = 0.0, Φ = 0.45, Tu = 293 K) and the wet case (Ω = 0.5, Φ = 0.9, Tu = 600 K)

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Fig. 11

Comparison of the LES (top) with experimental OH* chemiluminescence measurements (bottom) for the dry case (Ω = 0.0, Φ = 0.45, Tu = 293 K). Top: Slice of the normalized OH* mass fraction, Bottom: Processed Abel inversion of OH* recordings. For better comparison, contour lines of the OH* concentration (mass fraction) of the LES are superimposed.

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Fig. 12

Comparison of the LES (top) with experimental OH* chemiluminescence measurements (bottom) for the wet case (Ω = 0.5, Φ = 0.9, Tu = 600 K). Top: slice of the normalized OH* mass fraction, Bottom: processed Abel inversion of OH* recordings. For better comparison, contour lines of the OH* concentration (mass fraction) of the LES are superimposed.

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