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TECHNICAL PAPERS: Gas Turbines: Combustion and Fuels

Lean Blowout Limit and NOx Production of a Premixed Sub-ppm NOx Burner With Periodic Recirculation of Combustion Products

[+] Author and Article Information
Jochen R. Kalb1

Lehrstuhl für Thermodynamik, Technische Universität München, D-85748 Garching, Germanykalb@td.mw.tum.de

Thomas Sattelmayer

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

1

To whom correspondence should be addressed.

J. Eng. Gas Turbines Power 128(2), 247-254 (Mar 01, 2004) (8 pages) doi:10.1115/1.2061267 History: Received October 01, 2003; Revised March 01, 2004

The technological objective of this work is the development of a lean-premixed burner for natural gas. Sub-ppm NOx emissions can be accomplished by shifting the lean blowout limit (LBO) to slightly lower adiabatic flame temperatures than the LBO of current standard burners. This can be achieved with a novel burner concept utilizing spatially periodic recirculation of combustion products: Hot combustion products are admixed to the injected premixed fresh mixture with a mass flow rate of comparable magnitude, in order to achieve self-ignition. The subsequent combustion of the diluted mixture again delivers products. A fraction of these combustion products is then admixed to the next stream of fresh mixture. This process pattern is to be continued in a cyclically closed topology, in order to achieve stable combustion of, for example, natural gas in a temperature regime of very low NOx production. The principal ignition behavior and NOx production characteristics of one sequence of the periodic process was modeled by an idealized adiabatic system with instantaneous admixture of partially or completely burnt combustion products to one stream of fresh reactants. With the CHEMKIN-II package, a reactor network consisting of one perfectly stirred reactor (PSR, providing ignition in the first place) and two plug flow reactors (PFR) has been used. The effect of varying burnout and the influence of the fraction of admixed flue gas has been evaluated. The simulations have been conducted with the reaction mechanism of Miller and Bowman and the GRI-Mech 3.0 mechanism. The results show that the high radical content of partially combusted products leads to a massive decrease of the time required for the formation of the radical pool. As a consequence, self-ignition times of 1 ms are achieved even at adiabatic flame temperatures of 1600 K and less, if the flue gas content is about 50–60% of the reacting flow after mixing is complete. Interestingly, the effect of radicals on ignition is strong, outweighs the temperature deficiency and thus allows stable operation at very low NOx emissions.

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Figures

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Figure 1

Sub-ppm process with spatially periodic admixing of combustion products

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Figure 2

Geometry of the sub-ppm NOx Burner and the burnout combustion chamber

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Figure 3

(a) Total temperature (in Kelvin) and (b) CO mass fraction

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Figure 4

Schematic diagram of the reactor network

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Figure 5

Flue gas fractions required for tIgn<1ms (GRI-Mech 3.0)

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Figure 6

Flue gas fractions required for tIgn<1ms (Miller and Bowman mechanism)

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Figure 7

tIgn for various fractions of flue gas of different burnout for TAd=1600K: (a) p=0.1MPa and (b) p=2MPa (GRI-Mech 3.0)

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Figure 8

tIgn for various fractions of flue gas of different burnout for TAd=1600K: (a) p=0.1MPa and (b) p=2MPa (Miller and Bowman mechanism)

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Figure 9

NO Formation in the first stage: (a) GRI-Mech 3.0 and (b) Miller and Bowman mechanism

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Figure 10

NO Formation in the second stage: TAd=1600K and p=2MPa: (a) GRI-Mech 3.0 and (b) Miller and Bowman mechanism

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Figure 11

Cutaway view of the precombustor

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Figure 12

Drawing of the precombustor test rig

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