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

Alternative Fuels Based on Biomass: An Experimental and Modeling Study of Ethanol Cofiring to Natural Gas

[+] Author and Article Information
Marina Braun-Unkhoff

Institute of Combustion Technology,
German Aerospace Center (DLR),
Pfaffenwaldring 38-40,
Stuttgart 70569, Germany
e-mail: Marina.Braun-Unkhoff@dlr.de

Jens Dembowski, Jürgen Herzler, Jürgen Karle, Clemens Naumann, Uwe Riedel

Institute of Combustion Technology,
German Aerospace Center (DLR),
Pfaffenwaldring 38-40,
Stuttgart 70569, Germany

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received November 27, 2014; final manuscript received January 18, 2015; published online February 18, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(9), 091503 (Sep 01, 2015) (9 pages) Paper No: GTP-14-1640; doi: 10.1115/1.4029625 History: Received November 27, 2014; Revised January 18, 2015; Online February 18, 2015

In response to the limited resources of fossil fuels as well as to their combustion contributing to global warming through CO2 emissions, it is currently discussed to which extent future energy demands can be satisfied by using biomass and biogenic by-products, e.g., by cofiring. However, new concepts and new unconventional fuels for electric power generation require a re-investigation of at least the gas turbine burner if not the gas turbine itself to ensure a safe operation and a maximum range in tolerating fuel variations and combustion conditions. Within this context, alcohols, in particular, ethanol, are of high interest as alternative fuel. Presently, the use of ethanol for power generation—in decentralized (microgas turbines) or centralized gas turbine units, neat, or cofired with gaseous fuels like natural gas (NG) and biogas—is discussed. Chemical kinetic modeling has become an important tool for interpreting and understanding the combustion phenomena observed, for example, focusing on heat release (burning velocities) and reactivity (ignition delay times). Furthermore, a chemical kinetic reaction model validated by relevant experiments performed within a large parameter range allows a more sophisticated computer assisted design of burners as well as of combustion chambers, when used within computational fluid dynamics (CFD) codes. Therefore, a detailed experimental and modeling study of ethanol cofiring to NG will be presented focusing on two major combustion properties within a relevant parameter range: (i) ignition delay times measured in a shock tube device, at ambient (p = 1 bar) and elevated (p = 4 bar) pressures, for lean (φ = 0.5) and stoichiometric fuel–air mixtures, and (ii) laminar flame speed data at several preheat temperatures, also for ambient and elevated pressure, gathered from literature. Chemical kinetic modeling will be used for an in-depth characterization of ignition delays and flame speeds at technical relevant conditions. An extensive database will be presented identifying the characteristic differences of the combustion properties of NG, ethanol, and ethanol cofired to NG.

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Figures

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Fig. 1

Pressure (right axis) and emission signals (left axis) of a C2H5OH/O2/Ar mixture (φ = 1.0), at p5 = 4.12 bar and T5 = 1050 K, dilution with Ar 1:5

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Fig. 8

Comparison between calculated (curve, small symbol, DLR-RG model, p.w.) and measured (large symbol, Beekmann et al. [18]) burning velocities of ethanol/air and 10% ethanol/NG/air mixtures at T0 = 373 K for p = 1 bar (open symbol) and p = 5 bar (full symbol)

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Fig. 9

Comparison between measured (symbols) and calculated (curves) ignition delay times of fuel/O2/Ar mixtures (φ = 1.0, dilution with Ar 1:5): triangles: ethanol; circles: NG + 10% ethanol; squares: NG. Calculations with reaction models of: DLR-RG, p.w., full, Marinov [23], dashed, Curran and coworkers [14], dotted, Left: p = 1 bar; right: p = 4 bar.

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Fig. 10

Predicted (curves) ignition delay times of fuel/O2/Ar mixtures (φ = 1.0, dilution with Ar 1:5): ethanol: full; NG + 10% ethanol: dashed, NG + 20% ethanol: dotted, NG + 50% ethanol: dashed–dotted; NG: dashed–dotted–dotted. Calculations with reaction model of DLR-RG, p.w. Left: p = 1 bar; right: p = 4 bar.

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Fig. 11

Predicted (curves) ignition delay times of fuel/O2/Ar mixtures (φ = 0.5, dilution with Ar 1:5): ethanol: full; NG + 10% ethanol: dashed, NG + 20% ethanol: dotted, NG + 50% ethanol: dashed–dotted; NG: dashed–dotted–dotted. Calculations with reaction model of DLR-RG, p.w. Left: p = 1 bar; right: p = 4 bar.

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Fig. 12

Comparison between calculated (curves) and measured (large symbols, Beekmann et al. [18]) burning velocities of fuel/air mixtures at T0 = 373 K: triangles: ethanol; circles: 90% NG + 10% ethanol; 80% NG + 20% ethanol; 50% NG + 50% ethanol; squares: NG. Calculations with reaction model DLR-RG, p.w. Left: p = 1 bar; right: p = 5 bar.

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Fig. 13

Comparison between calculated (curves) and measured (large symbols, Beekmann et al. [18]) burning velocities of fuel/air mixtures at T0 = 373 K: NG: (squares); ethanol: (stars, circles, triangles, rhombs); NG + 10% ethanol: (curves, with circles). Calculations with reaction model DLR-RG, p.w. Left: p = 1 bar; right: p = 5 bar.

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Fig. 14

Characteristic combustion properties. Left: laminar flame speeds of different fuel–air mixtures, p = 1 bar, T0 = 373 K. Experiments −50%H2/50% methane mixture [8]; calculations (curves) with a detailed reaction model, GRI 3.0 [22]. Right: ignition delay times of different fuel–air mixtures diluted in argon 1:5. Comparison between experiment (symbols) and calculations (curves, with DLR-RG reaction model, p.w.) for: φ = 1.0, p = 4 bar, oxidizer: 79% Ar, 21% O2. Circles: H2 [24]; squares: 50% H2/50% CO [17]; stars: biogenic mixture [6,35]; rhombs: NG [24]; triangles: CH4.

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Fig. 2

Comparison between measured (symbols) and calculated (curves) ignition delay times of ethanol/O2/Ar mixtures (φ = 1.0, dilution with Ar 1:5). Calculations with reaction models of: DLR-RG, p.w., full, Marinov [23], dashed, Curran and coworkers [14], dotted, Left: p = 1 bar; right: p = 4 bar.

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Fig. 5

Comparison between measured (symbols) and calculated (curves) ignition delay times of 10% ethanol/NG/O2/Ar mixtures (φ = 0.5, dilution with Ar 1:5). Calculations with reaction models of: DLR-RG, p.w., full, Marinov [23], dashed, Curran and coworkers [14], dotted, Left: p = 1 bar; right: p = 4 bar.

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Fig. 6

Comparison between measured (symbols) and calculated (curves) ignition delay times of 10% ethanol/NG/O2/Ar mixtures (φ = 1.0, dilution with Ar 1:5). Calculations with reaction models of: DLR-RG, p.w., full, Marinov [23], dashed, Curran and coworkers [14], dotted, Left: p = 1 bar; right: p = 4 bar.

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Fig. 7

Comparison between measured (symbols) and calculated (curves) ignition delay times of 10%-ethanol/NG/O2/Ar mixtures (dilution with Ar 1:5) for p = 1 bar and p = 4 bar. Calculations with reaction models of: DLR-RG, p.w., full, Marinov [23], dashed, Curran and coworkers [14], dotted, Left: φ = 0.5; right: φ = 1.0.

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Fig. 3

Burning velocities of ethanol/air mixtures at p = 1 bar and four preheat temperatures: T0 = 298 K, T0 = 343 K, T0 = 363 K, and T0 = 453 K. Measurements (symbols): triangles: Egolfopoulos et al. [19]. Calculations (curves, small symbols) with DLR-RG.

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Fig. 4

Burning velocities of ethanol/air mixtures at T0 = 373 K for p = 1bar (open symbols) and p = 5 bar (full symbols). Measurements: Beeckmann et al. [18]; calculations (curves, small symbols) with DLR-RG.

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