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

Methane Oxycombustion for Low CO2 Cycles: Blowoff Measurements and Analysis

[+] Author and Article Information
A. Amato1

Ben T. Zinn Combustion Laboratory, Georgia Institute of Technology, Atlanta, GA 30318aamato3@mail.gatech.edu

B. Hudak, P. D’Carlo, D. Noble, D. Scarborough, J. Seitzman, T. Lieuwen

Ben T. Zinn Combustion Laboratory, Georgia Institute of Technology, Atlanta, GA 30318

Used, for example, in systems that burn high H2 fuels; these systems currently operate nonpremixed to avoid flashback, so N2 is used to suppress flame temperatures and, therefore, NOx emissions.

1

Corresponding author. Present address: Ben T. Zinn Combustion Lab, 635 Strong Street, Atlanta, GA 30318.

J. Eng. Gas Turbines Power 133(6), 061503 (Feb 16, 2011) (9 pages) doi:10.1115/1.4002296 History: Received May 18, 2010; Revised June 16, 2010; Published February 16, 2011; Online February 16, 2011

Increasing concerns about climate change have encouraged interest in zero-CO2 emission hydrocarbon combustion techniques. In one approach, nitrogen is removed from the combustion air and replaced with another diluent, typically carbon dioxide or steam. In this way, formation of nitrogen oxides is prevented and the exhaust stream can be separated into concentrated CO2 and water by a simple condensation process. The concentrated CO2 stream can then be sequestered or used for enhanced oil recovery. Burning fuels in an O2/CO2 diluent raises new combustion opportunities and challenges for both emissions and operability: this study focuses on the latter aspect. CH4/O2/CO2 flames have slower chemical kinetics than methane-air flames and as such, flame stability is more problematic as they are easier to blow off. This issue was investigated experimentally by characterizing the stability boundaries of a swirl stabilized combustor. Near stoichiometric CO2 and N2 diluted methane/oxygen flames were considered and compared with lean methane/air flames. Numerical modeling of chemical kinetics was also performed to analyze the dependence of laminar flame speeds and extinction strain rates upon dilution by different species and to develop correlations for blowoff boundaries. Finally, blowoff trends at high pressure were extrapolated from atmospheric pressure data to simulate conditions closer to those of gas turbines.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Dependence of adiabatic flame temperature upon mole fraction of oxygen in the reactants for near stoichiometric CH4/O2/CO2 flames (Tin=533 K, p=1 atm)

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Figure 2

Notional description of operational space in the equivalence ratio—flame temperature coordinates

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Figure 3

Dependence of τpf upon adiabatic flame temperature for different reacting blends, baseline CH4/air, and oxyfuel flames diluted with N2 or CO2. Reactant conditions are p=1 atm and Tin=533 K(0.35<ϕair<0.8).

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Figure 4

Dependence of (a) chemical time and (b) molar concentration of O2 in reactants normalized by the maximum chemical time value (τpf,max) and minimum O2 concentration (% O2,min) upon equivalence ratios at fixed adiabatic flame temperature

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Figure 5

Dependence of τESR upon adiabatic flame temperature for different reacting blends. Reactant conditions are p=1 atm and Tin=533 K(0.365<ϕair<0.65).

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Figure 6

Comparison between chemical time τpf and τESR for CH4/O2/CO2 and CH4/air. Chemical times are calculated at the same adiabatic flame temperature (p=1 atm, Tin=533 K).

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Figure 7

Illustration of the procedure for extrapolating blowoff conditions of CO2/O2 flames from air flames

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Figure 8

Calculated difference ΔTad between adiabatic flame temperatures of oxyflames and CH4/air flames at the same chemical τpf (Fig. 3). Reactant conditions are p=1 atm and Tin=533 K.

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Figure 9

Comparison between calculated ΔTad of CO2/O2 oxyflames obtained from τpf and τESR chemical time scaling. Reactant conditions are p=1 atm and Tin=533 K.

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Figure 10

Difference between temperature differentials calculated with unstretched (ΔTad,pf) and stretched flame (ΔTad,ESR) for CO2/O2 oxyflames

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Figure 11

Combustor facility schematic (dimensions in mm): L=304.8 mm (short quartz tube) and L=508 mm (long quartz tube)

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Figure 12

Baseline CH4/air experimental blowoff points for two different quartz tube lengths L=304.8 mm (short quartz tube) and L=508 mm (long quartz tube)

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Figure 13

Comparison between blowoff points for N2 and CO2 diluted systems at ϕ=1.0 and CH4/air system blowoff boundaries (both long and short quartz tube)

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Figure 14

Blowoff points for N2/O2 oxyfuel flames at different equivalence ratios

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Figure 15

Blowoff points for CO2/O2 oxyfuel flames at different equivalence ratios

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Figure 16

Comparison between experimental blowoff points and predictions based on CH4/air data and different chemical time scaling (τpf,τESR) for CH4/O2/CO2 flames at ϕ=1.0

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Figure 17

Comparison between experimental blowoff points and predictions based on CH4/air data and τpf scaling for CH4/O2/N2 flames at ϕ=1.0

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Figure 18

Comparison between experimental blowoff points (large empty symbols) and predictions (lines with small full symbols) based on τpf chemical time scaling and CH4/air data for CH4/O2/CO2 flames at different equivalence ratios. Only means without error bars are reported for clarity.

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Figure 19

Dependence of τpf upon adiabatic flame temperature for CH4/O2/CO2 oxyflames (ϕ=0.9,1.0,1.1) and CH4/air flames at 15 atm. Values of τpf at p=1 atm of CH4/air and CH4/O2/CO2 at ϕ=1.0 (Fig. 3) are also shown for comparison. Reactant initial temperature is fixed to Tin=533 K.

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Figure 20

Difference ΔTad between adiabatic flame temperatures of CH4/O2/CO2 and CH4/air flames at the same chemical time. Reactant conditions are p=1 atm/15 atm and Tin=533 K.

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