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

Extension of the Combustion Stability Range in Dry Low NOx Lean Premixed Gas Turbine Combustor Using a Fuel Rich Annular Pilot Burner

[+] Author and Article Information
L. Rosentsvit, Y. Levy, V. Erenburg, V. Sherbaum, V. Ovcharenko

Faculty of Aerospace Engineering,
Technion, Israel Institute of Technology,
Technion, Naifa 320000, Israel

B. Chudnovsky, A. Herszage, A. Talanker

Israel Electric Corporation,
P.O. BOX 10,
Haifa 3100001, Israel

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received November 18, 2013; final manuscript received December 5, 2013; published online January 9, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(5), 051509 (Jan 09, 2014) (10 pages) Paper No: GTP-13-1419; doi: 10.1115/1.4026186 History: Received November 18, 2013; Revised December 05, 2013

The present work is concerned with improving combustion stability in lean premixed (LP) gas turbine combustors by injecting free radicals into the combustion zone. The work is a joint experimental and numerical effort aimed at investigating the feasibility of incorporating a circumferential pilot combustor, which operates under rich conditions and directs its radicals enriched exhaust gases into the main combustion zone as the means for stabilization. The investigation includes the development of a chemical reactors network (CRN) model that is based on perfectly stirred reactors modules and on preliminary CFD analysis as well as on testing the method on an experimental model under laboratory conditions. The study is based on the hypothesis that under lean combustion conditions, combustion instability is linked to local extinctions of the flame and consequently, there is a direct correlation between the limiting conditions affecting combustion instability and the lean blowout (LBO) limit of the flame. The experimental results demonstrated the potential reduction of the combustion chamber's LBO limit while maintaining overall NOx emission concentration values within the typical range of low NOx burners and its delicate dependence on the equivalence ratio of the ring pilot flame. A similar result was revealed through the developed CHEMKIN-PRO CRN model that was applied to find the LBO limits of the combined pilot burner and main combustor system, while monitoring the associated emissions. Hence, both the CRN model, and the experimental results, indicate that the radicals enriched ring jet is effective at stabilizing the LP flame, while keeping the NOx emission level within the characteristic range of low NOx combustors.

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Fig. 1

Flame stability and lean blowout limit of swirl stabilized methane combustion chamber [5]

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Fig. 2

Longitudinal section of a step combustor axisymmetric geometry for CFD model [14]

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Fig. 3

Sudden expansion recirculation zone boundary as calculated from CFD simulation (velocity vectors)

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Fig. 4

CFD simulations of the temperature distribution (K); C3H8; ϕ = 0.45; vinlet = 13 (m/s)

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Fig. 5

Division of the flame using RPV and velocity magnitude contours

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Fig. 6

The final CRN model: residence times (msec) and mass flow rates (%) (of each reactor) are indicated

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Fig. 7

General view of the test rig and general scheme of the test rig

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Fig. 8

Combustion chamber cross section (including pilot burner) [14]

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Fig. 9

Pilot burner cross section, including igniter (see also Fig. 8)

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Fig. 10

Variation of LBO limit with the pilot's equivalence ratio (constant d)

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Fig. 11

Global NOx emissions at LBO limit as a function of ϕpilot

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Fig. 12

Total CO emissions (at MIX 7 outlet) at LBO limit

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Fig. 13

CO concentration throughout PFR 8 in the case without pilot burner

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Fig. 14

(a) Main combustor combined with pilot burner global LBO limit study (varying d value); (b) main combustor combined with pilot burner global LBO limit study (constant d value)

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Fig. 15

Main combustor combined with pilot burner NOx emissions at LBO limit

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Fig. 16

Main combustor combined with pilot burner CO emissions at LBO limit

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Fig. 17

Main combustor combined with pilot burner temperatures along the axis at LBO limit and different ϕpilot




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