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

# Emission Characteristics of a Premixed Cyclic-Periodical-Mixing Combustor Operated With Hydrogen-Natural Gas Fuel Mixtures

[+] Author and Article Information
Jochen R. Brückner-Kalb1

Lehrstuhl für Thermodynamik, Technische Unversität München, Garching D-85748, Germanybrueckner-kalb@mytum.de

Michael Krösser, Christoph Hirsch, Thomas Sattelmayer

Lehrstuhl für Thermodynamik, Technische Unversität München, Garching D-85748, Germany

This behavior could be used for the replacement of the pilot burner by additional annular fuel passages around the optimized VPMI fuel orifices, which would allow low-emissions operation in low part load.

Furthermore, some tests have been conducted with higher hydrogen content: With a $90%volH2−10%volCH4$ fuel mixture and $dO=2.5 mm$, the $NOx$ emissions keep below 6 ppm(v) (15% $O2$, dry) for $Tad≤1520 K$.

In case the early ignition in regions of too high unmixedness at high pressures turns out to be problematic, the ignition delay could be increased by the addition of water vapor to the reactants, because $H2O$ as collision partner enhances in particular at high pressure a three-body chain break reaction reducing the radical concentration (34).

1

Corresponding author.

J. Eng. Gas Turbines Power 132(2), 021505 (Oct 30, 2009) (8 pages) doi:10.1115/1.3124789 History: Received April 09, 2008; Revised April 23, 2008; Published October 30, 2009

## Abstract

The concept of the cyclic periodical mixing combustion process (Kalb, and Sattelmayer, 2004, “Lean Blowout Limit and $NOx$-Production of a Premixed Sub-ppm-$NOx$ Burner With Periodic Flue Gas Recirculation,” Proceedings of the ASME Turbo Expo 2004, Paper No. GT2004-53410; Kalb, and Sattelmayer, 2006, “Lean Blowout Limit and $NOx$-Production of a Premixed Sub-ppm-$NOx$ Burner With Periodic Recirculation of Combustion Products,” ASME J. Eng. Gas Turbines Power, 128(2), pp. 247–254) for the extension of the lean blowout limit had been implemented in an atmospheric experimental combustor for testing with both external perfect (Brückner-Kalb, Hirsch, and Sattelmayer, 2006, “Operation Characteristics of a Premixed Sub-ppm $NOx$ Burner With Periodical Recirculation of Combustion Products,” Proceedings of the ASME Turbo Expo 2006, Paper No. GT2006-90072) and technical (Brückner-Kalb, Napravnik, Hirsch, and Sattelmayer, 2007, “Development of a Fuel-Air Premixer for a Sub-ppm $NOx$ Burner,” Proceedings of the ASME Turbo Expo 2007, Paper No. GT2007-27779) premixing of reactants. It had been tested with natural gas and has now been tested with a mixture of $70%vol$ of hydrogen and $30%vol$ of natural gas (98% $CH4$) as fuel. With natural gas the $NOx$ emissions are unaffected by the limited technical premixing quality, as long as the air preheat is in the design range of the premixers (Brückner-Kalb, Napravnik, Hirsch, and Sattelmayer, 2007, “Development of a Fuel-Air Premixer for a Sub-ppm $NOx$ Burner,” Proceedings of the ASME Turbo Expo 2007, Paper No. GT2007-27779). Then, for adiabatic flame temperatures of up to 1630 K $NOx$ emissions are below 1 ppm(v) with CO emissions below 8 ppm(v) in the whole operation range of the test combustor (15% $O2$, dry). With the “$70%volH2−30%volCH4$” mixture the $NOx$ emissions increase by nearly one order of magnitude. Then, $NOx$ emissions below 7 ppm(v) (15% $O2$, dry) are achieved for adiabatic flame temperatures of up to 1600 K. They approach the 1 ppm(v) level only for flame temperatures below 1450 K. CO emissions are below 4 ppm(v). The reason for the increase in the $NOx$ emissions is the higher reactivity of the mixture, which leads to earlier ignition in zones of still elevated unmixedness of reactants near the premixer-injector exits. This effect was investigated by chemical reactor network simulations analyzing a pressure effect and an additional chemical effect of hydrogen combustion on $NOx$ formation.

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## Figures

Figure 1

The cyclic periodical mixing combustion process: (a) block diagram of the subprocesses and (b) schematic of the flow field in the precombustor

Figure 2

Cut-away view of the precombustor test rig: (1) fresh mixture or air supply tube, (2) injector tubes, (3) precombustor liner, (4) duct to burnout combustor, (5) optical access, (6) burnout combustor, (7) suction probe, (8) air-cooled liner support, (9) void space filled with insulating material, and (10) fresh mixture injection direction

Figure 3

Schematic drawing of the vortex-premixer injector (10)

Figure 4

NOx emissions with natural gas as fuel for (a) dO=2.5 mm(dO/dI=0.125) and (b) dO=3.2 mm(dO/dI=0.160)

Figure 5

NOx emissions with the “70%volH2−30%volCH4” fuel mixture for dO=2.5 mm

Figure 6

NOx emissions with the 70%volH2−30%volCH4 fuel mixture for dO=2.5 mm, plotted against the VPMI momentum flux ratio

Figure 7

NOx emissions with the 70%volH2−30%volCH4 fuel mixture at Tad≈1500 K for dO=2.5 mm and dO=3.2 mm, plotted against the VPMI momentum flux ratio

Figure 8

Schematic of the chemical reactor network used for the analysis of fuel-dependent self-ignition kinetics and chemical effects on NOx formation

Figure 9

Self-ignition time of mixtures of reactants with certain amounts of hot combustion products of various burnout for different fuels and pressures (Tad=1600 K, GRI-MECH 3.0 (15))

Figure 10

Relative changes of (a) O, (b) OH, and (c) NOx mole fractions with the hydrogen content in the fuel mixture and the pressure (Tad=1600 K, GRI-MECH 3.0 (15))

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