Operational gas turbine swirl combustors design map for pure methane and different outlet configurations

The effects of hydrogen substitution on methane/air combustion in a micro gas turbine were studied in this work. The combustion performance and emission characteristics of a can type combustor were investigated with model simulations using the commercial code STAR-CD, in which the three-dimension compressible k-ε turbulent flow mode and presumed probability density function for chemical reaction between methane/hydrogen/air mixtures were used. With hydrogen being the substituent, not a supplement to methane, the detailed flame structures, distributions of flame temperature and flow velocity, and gas emissions were presented and compared by using a fraction of hydrogen to substitute methane in the combustor. For the scenarios from pure methane to pure hydrogen, results show the flame temperature and exit gas temperature increase when only 10% methane is substituted. But as hydrogen substitution percentage increases, the flame temperature and exit gas temperature decrease because of a power shortage caused by lower mass flow rate and heating value of the resulting blended fuels, although the pattern factor drops drastically compared to that of pure methane. As the fuel inlet velocity decreases from 100 m/s to 20 m/s, the high temperature region shifts to the side of the combustor due to the high diffusivity of hydrogen. Increasing hydrogen substitution percentage at a fixed fuel injection velocity reduces NOx emission due to lower flame temperature, but CO emissions increase continually with increasing hydrogen substitution percentage because oxygen depletion for methane/air combustion. Before hydrogen blended fuels or pure hydrogen are used as an alternative fuel for the micro gas turbine, further experimental testing are needed as the CFD modeling results provide a guidance for the improved designs of the combustor.

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Fuel Variability Effects on Turbulent, Lean Premixed Flames at High Pressures

Volume 2: Turbo Expo 2007 ◽

10.1115/gt2007-27496 ◽

2007 ◽

Cited By ~ 5

Author(s):

E. Boschek ◽

P. Griebel ◽

P. Jansohn

Keyword(s):

Natural Gas ◽

Flame Front ◽

Gas Turbine ◽

Gas Turbines ◽

Turbulent Flame ◽

Premixed Flames ◽

Exhaust Gas ◽

Lean Blowout ◽

Lean Premixed Flames ◽

Pure Methane

Fuel flexibility will be a key issue for the operation of future stationary gas turbines because of the increasing amount of off-spec natural gas qualities from new resources and upcoming new fuels derived from biomass which will be more important in the near future. The performance of gas turbines in terms of flame stability and low emission combustion must be at least maintained also with these new fuels. Therefore, the impact of fuel variation on combustion characteristics must be known for the combustor design. This paper addresses the effect of hydrogen and propane addition on flame characteristics like lean blowout (LBO), emissions (NOx, CO), flame positions and turbulent flame speeds for flames at gas turbine relevant conditions. Hydrogen enriched fuels are typical constituents of gasification fuels such as those obtained from biomass, while propane is considered a typical higher hydrocarbon present in off-spec natural gas. Turbulent, lean premixed flames of different fuels (methane, methane/hydrogen and methane/propane) have been studied in a generic, axis-symmetric, high-pressure gas turbine combustor. Flame stabilization is achieved aerodynamically via a recirculation zone induced by the combustor geometry with sudden expansion. Turbulence at the combustor inlet is generated using a turbulence grid (perforated plate). LBO limits are detected using the global OH chemiluminescence flame signal collected with a photo-multiplier and a data acquisition system together with the exhaust gas temperature measured with a thermocouple. The species concentrations (CO2, O2, CO, NOx) are measured by exhaust gas analyzers. Flame front positions and turbulent flame speeds are determined with Laser Induced Fluorescence measurements of the OH radical (OH-PLIF). Flame characteristics will be presented for the following fuel/air mixtures at a mixture preheating temperature of 673 K: pure methane, H2-enriched flames containing up to 50% hydrogen by volume, methane/propane mixtures containing up to 50% propane by volume. LBO limits, NOx emissions will be presented for different pressures. Most probable flame front positions and turbulent flame speeds are presented at a pressure of 5 bars for fuel mixtures between pure methane and 50% of each additive (propane and hydrogen). Experiments have revealed that a premixed mixture of 50% hydrogen and 50% methane, by volume, can significantly extend the lean blowout limit by up to 22% compared to pure methane. Because of a 120 K lower flame temperature a drastic reduction of the NOx emission (about 57%) is observed. Addition of hydrogen also significantly decreases the flame position (50%), changes the shape of the flame front and because of a higher global reaction rate increases the turbulent flame speed. Experiments with different methane/propane mixtures showed an increase (approximately 25–30%) of the NOx concentration at a propane content of 50%. Additionally, the flame stabilizes closer to the combustor inlet for higher propane contents.

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Effect of Syngas Composition and CO2-Diluted Oxygen on Performance of a Premixed Swirl-Stabilized Combustor

Volume 2: Turbo Expo 2007 ◽

10.1115/gt2007-28286 ◽

2007 ◽

Cited By ~ 1

Author(s):

Christopher R. Shaddix ◽

Timothy C. Williams ◽

Robert W. Schefer

Keyword(s):

Gas Turbine ◽

Global Climate ◽

Nox Emissions ◽

Lean Blowout ◽

Pure Methane ◽

Gas Fuel ◽

End Use ◽

Fuel Mixtures ◽

Change Concerns ◽

Full Operation

Future energy systems based on solid fuel gasification for co-production of power and fuels may require gas turbine operation on unusual gas fuel mixtures. In addition, global climate change concerns may dictate the production of a CO2 product stream for end-use or sequestration, with potential impacts on the oxidizer used in the gas turbine. In this study the operation at atmospheric pressure of a small, optically accessible swirl-stabilized premixed combustor is investigated when burning fuels ranging from pure methane to shifted or filtered syngas mixtures. Both air and CO2-diluted oxygen are used as oxidizers. CO and NOx emissions for these flames have been determined over the full operation range from lean blowout to slightly rich conditions. In practice, CO2-diluted oxygen systems will likely be operated close to stoichiometric conditions to minimize oxygen consumption. The presence of hydrogen in the syngas fuel mixtures results in compact, high temperature flames, resulting in increased flame stability and higher NOx emissions. The lean blowout limit decreases with increasing H2 content in the syngas. Similarly, CO emissions for lean stoichiometries decrease with increasing H2 content. CO emissions near the stoichiometric combustion point do not become significant until φ > 0.95, at which point CO emissions rise more rapidly for combustion in O2-CO2 mixtures than for combustion in air.

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