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

NOx Behavior for Lean-Premixed Combustion of Alternative Gaseous Fuels

[+] Author and Article Information
K. Boyd Fackler

Department of Mechanical Engineering,
University of Washington,
Seattle, WA 98195
e-mail: boydfackler@gmail.com

Megan Karalus

Department of Mechanical Engineering,
University of Washington,
Seattle, WA 98195
e-mail: megan.karalus@gmail.com

Igor Novosselov

Department of Mechanical Engineering,
University of Washington,
Seattle, WA 98195
e-mail: ivn@u.washington.edu

John Kramlich

Department of Mechanical Engineering,
University of Washington,
Seattle, WA 98195
e-mail: kramlich@u.washington.edu

Philip Malte

Department of Mechanical Engineering,
University of Washington,
Seattle, WA 98195
e-mail: malte@u.washington.edu

Shazib Vijlee

Shiley School of Engineering,
University of Portland,
Portland, OR 97203
e-mail: vijlee@up.edu

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 23, 2015; final manuscript received August 27, 2015; published online October 21, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(4), 041504 (Oct 21, 2015) (11 pages) Paper No: GTP-15-1364; doi: 10.1115/1.4031478 History: Received July 23, 2015; Revised August 27, 2015

Gaseous fuels other than pipeline natural gas are of interest in high-intensity premixed combustors (e.g., lean-premixed gas turbine combustors) as a means of broadening the range of potential fuel resources and increasing the utilization of alternative fuel gases. An area of key interest is the change in emissions that accompanies the replacement of a fuel. The work reported here is an experimental and modeling effort aimed at determining the changes in NOx emission that accompany the use of alternative fuels. Controlling oxides of nitrogen (NOx) from combustion sources is essential in nonattainment areas. Lean-premixed combustion eliminates most of the thermal NOx emission but is still subject to small, although significant amounts of NOx formed by the complexities of free radical chemistry in the turbulent flames of most combustion systems. Understanding these small amounts of NOx, and how their formation is altered by fuel composition, is the objective of this paper. We explore how NOx is formed in high-intensity, lean-premixed flames of alternative gaseous fuels. This is based on laboratory experiments and interpretation by chemical reactor modeling. Methane is used as the reference fuel. Combustion temperature is maintained the same for all fuels so that the effect of fuel composition on NOx can be studied without the complicating influence of changing temperature. Also the combustion reactor residence time is maintained nearly constant. When methane containing nitrogen and carbon dioxide (e.g., landfill gas) is burned, NOx increases because the fuel/air ratio is enriched to maintain combustion temperature. When fuels of increasing C/H ratio are burned leading to higher levels of carbon monoxide (CO) in the flame, or when the fuel contains CO, the free radicals made as the CO oxidizes cause the NOx to increase. In these cases, the change from high-methane natural gas to alternative gaseous fuel causes the NOx to increase. However, when hydrogen is added to the methane, the NOx may increase or decrease, depending on the combustor wall heat loss. In our work, in which combustor wall heat loss is present, hydrogen addition deceases the NOx. This observation is compared to the literature. Additionally, minimum NOx emission is examined by comparing the present results to the findings of Leonard and Stegmaier.

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References

Figures

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Fig. 1

Schematic of 15.8 cc JSR with premixer-injector

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Fig. 2

Schematic of baseline three-zone CRN

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Fig. 3

3D CFD simulation of static temperature in JSR for lean-premixed combustion of methane with air [2]. Combustion temperature of 1800 K.

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Fig. 4

Comparison of NOx (ppm, dry, actual O2) for methane combustion predicted by the baseline three-zone CRN using five different chemical kinetic mechanisms

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Fig. 5

Arrhenius plots of measured NOx formation rate (ppm, wet, actual O2 / ms). The vertical axis is log10.

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Fig. 6

Breakdown on NOx formation rate (gmol/s) by mechanism pathway and reaction zone for lean-premixed combustion of methane in the JSR

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Fig. 7

Effect of N2 and CO2 dilution on NOx for a combustion temperature of 1800 K [1]

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Fig. 8

Measured and modeled NOx for CH4-H2 combustion in the JSR at 1800 K

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Fig. 9

Schematic of two-zone CRN used to model combustion of fuel blends containing H2

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Fig. 10

Breakdown on NOx formation rate (gmol/s) by mechanism pathway and reaction zone for methane-hydrogen blends at 1800 K. Modeled by the two-zone CRN.

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Fig. 11

Measured and modeled NOx for H2-CO combustion in the JSR at 1800 K

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Fig. 12

NOx breakdown by mechanism for H2-CO combustion at 1800 K (2-zone CRN)

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Fig. 13

NOx formed in CH4-CO combustion in the JSR at 1800 K

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Fig. 14

Breakdown in NOx formation rate (gmol/s) by pathway and reaction zone for CH4-CO combustion at 1800 K

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Fig. 15

NOx formed in CH4-C2H6 combustion in the JSR at 1800 K

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Fig. 16

NOx (dry, 15% O2) measured in this study compared to Leonard and Stegmaier curve. NOx shown on log10 scale.

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Fig. 17

NOx (dry, 15% O2) as a function of the H2 content of CH4/H2 blends burned in various lean-premixed combustors

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Fig. 18

NOx (dry, actual O2) behavior with heat loss for various fuel blends. Combustion temperature held at 1800 K.

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Fig. 19

NOx at outlet of Bragg cell reactor versus percentage of reactor volume that is a PSR. Methane-air and hydrogen-air combustion for adiabatic flame temperature of 1800 K.

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