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

Low NOx Lean Premix Reheat Combustion in Alstom GT24 Gas Turbines

[+] Author and Article Information
Daniel Guyot

Alstom (Switzerland) Ltd.,
Brown Boveri Strasse 7,
Baden 5401, Switzerland
e-mail: daniel.guyot@power.alstom.com

Gabrielle Tea

Alstom (Switzerland) Ltd.,
Brown Boveri Strasse 7,
Baden 5401, Switzerland
e-mail: dazenon-gabrielle-regine.tea@power.alstom.com

Christoph Appel

Alstom (Switzerland) Ltd.,
Brown Boveri Strasse 7,
Baden 5401, Switzerland
e-mail: christoph.appel@power.alstom.com

1Corresponding author.

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 24, 2015; final manuscript received August 31, 2015; published online October 27, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(5), 051503 (Oct 27, 2015) (9 pages) Paper No: GTP-15-1366; doi: 10.1115/1.4031543 History: Received July 24, 2015; Revised August 31, 2015

Reducing gas turbine emissions and increasing their operational flexibility are key targets in today's gas turbine market. In order to further reduce emissions and increase the operational flexibility of its GT24 (60 Hz) and GT26 (50 Hz), Alstom has introduced an improved sequential environmental (SEV) burner and fuel lance into its GT24 and GT26 upgrades 2011 sequential reheat combustion system. Sequential combustion is a key differentiator of Alstom GT24/GT26 engines in the F-class gas turbine market. The inlet temperature for the SEV combustor is around 1000 °C and reaction of the fuel/oxidant mixture is initiated through auto-ignition. The recent development of the Alstom sequential combustion system is a perfect example of evolutionary design optimizations and technology transfer between Alstom GT24 and GT26 engines. Better overall performance is achieved through improved SEV burner aerodynamics and fuel injection, while keeping the main features of the sequential burner technology. The improved SEV burner/lance concept has been optimized toward rapid fuel/oxidant mixing for low emissions, improved fuel flexibility with regard to highly reactive fuels (higher C2+ and hydrogen content), and to sustain a wide operation window. The burner front panel features an improved cooling concept based on near-wall cooling as well as integrated acoustics damping devices designed to reduce combustion pulsations, thus extending the SEV combustor's operation window even further. After having been validated extensively in Alstom's high pressure (HP) sector rig test facility, the improved GT24 SEV burner has been retrofitted into a commercial GT24 field engine for full engine validation during long-term operation. This paper presents the obtained HP sector rig and engine validation results for the GT24 (2011) SEV burner/lance hardware with a focus on reduced NOx and CO emissions and improved operational behavior of the SEV combustor. The HP tests demonstrated robust SEV burner/lance operation with up to 50% lower NOx formation and a more than 70 K higher SEV burner inlet temperature compared to the GT24 (2006) hardware. For the GT24 engine with retrofitted upgrade 2011 SEV burner/lance, all validation targets were achieved including an extremely robust operation behavior, up to 40% lower GT NOx emissions, significantly lower CO emissions at partload and baseload, a very broad operation window (up to 100 K width in SEV combustor inlet temperature), and all measured SEV burner/lance temperatures in the expected range. Sector rig and engine validation results have confirmed the expected SEV burner fuel flexibility (up to 18 vol. % C2+ and up to 5 vol. % hydrogen as standard).

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Fig. 1

Engine cross section and operation concept of GT24 and GT26. The black box shows the region of interest in this report.

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Fig. 2

The SEV combustion system of the GT24 and GT26

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Fig. 3

General working principles of the SEV combustor (schematic sketch). Main flow direction is from left to right.

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Fig. 4

Simplified development strategy for SEV combustor hot gas geometry [11]

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Fig. 5

Geometry of the GT24 and GT26 sequential burners for the upgrades 2006 and 2011

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Fig. 6

GT24 (2011) SEV lance (left) and SEV burner front panel section (right) with integrated near-wall cooling channels and acoustic damping features

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Fig. 7

Calculated fuel mixture fraction at the SEV burner exit and isosurface of the fuel mixture fraction downstream of the SEV lance (hot gas flow from right to left). Comparable scales and views had been used within the two rows of the table [10].

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Fig. 8

The HP sector rig for the GT24 and GT26 SEV combustor tests

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Fig. 9

HP sector rig NOx formation in GT24 SEV combustor for upgrades 2011 and 2006

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Fig. 10

HP sector rig NOx formation in GT24 and GT26 (2011) SEV combustor

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Fig. 11

HP sector rig CO emissions in GT24 SEV combustor for upgrade 2011

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Fig. 12

HP sector rig CO emissions in GT24 (2011) SEV combustor, C2+ sensitivity

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Fig. 13

HP sector rig SEV off-design pre-ignition tests for upgrades 2011 and 2006

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Fig. 15

GT24 (2006) SEV burner (after removal from commercial engine) and GT24 (2011) SEV burner (prior retrofit into commercial engine)

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Fig. 16

SEV pulsation amplitude at baseload with GT24 (2011) SEV burner hardware. Due to the damping front panels pulsations amplitudes remain well below the limit [11].

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Fig. 17

The GT24 engine validation revealed a broad SEV operation window with retrofitted upgrade 2011 SEV burner/lance hardware (dots represent measurement points)

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Fig. 18

GT NOx emissions for variation in GT24 engine load

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Fig. 19

GT24 (2006) and GT24 (2011) CO emissions for variation in GT load

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Fig. 20

Borescope inspections of GT24 (2011) SEV burners after hot commissioning and during the first standard inspection in the GT24 commercial engine. SEV burners were found in excellent conditions.

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Fig. 21

GT24/GT26 field experience with different fuel gases. Different symbols represent different power plants.




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