Influence of Steam Dilution on Nitrogen Oxide Formation in Premixed Methane/Hydrogen Flames

Göke, Sebastian; Paschereit, Christian Oliver

doi:10.2514/1.b34577

Cited by 23 publications

(12 citation statements)

References 22 publications

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“…It reduces the flame temperature and therewith restrains the thermal NOx formation pathway. This is in contrast to a recent study for pre mixed methane/hydrogen flames [8], which found that the prompt pathway can be slightly increased at wet conditions, whereas, the other pathways are significantly reduced due to lower oxygen atom concentrations, leading to reduced overall NOx emissions. It affects the reaction kinetics by changing the concen trations of the chain branching species O, OH, and H [6]; this is also involved in the NOx formation.…”

Section: Introductioncontrasting

confidence: 99%

“…The influence of steam on this pathway, however, is rela tively limited as was shown in a previous study [8]. This is the case also for the same flame temperature when the equivalence ratio is increased to compensate for the higher heat capacity of the added steam.…”

Section: Co Formationmentioning

confidence: 61%

“…The prompt pathway requires CHV The influence of steam on the radical pool and on the NOx for mation was recently investigated for a premixed flame and differ ent fuel mixtures of methane and hydrogen at atmospheric pressure [8], It was shown that steam directly affects the NOxchemistry. Four major pathways con tribute to the formation of NOx in combustion processes.…”

Section: Modeling Results the Measured And Calculated Co Andmentioning

confidence: 99%

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Influence of Pressure and Steam Dilution on NOx and CO Emissions in a Premixed Natural Gas Flame

Göke

Schimek

Steffen

et al. 2014

Journal of Engineering for Gas Turbines and Power

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C h ris tia n O liv e r P a s c h e r e it1In flu en ce of Pressure and S team D ilu tio n on NOx and CO Em issions in a P rem ixed N atu ral Gas F lam eIn the current study, the influence o f pressure and steam on the emission formation in a premixed natural gas flame is investigated at pressures between 1.5 bar and 9 bar. A pre mixed, swirl-stabilized combustor is developed that provides a stable flame up to very high steam contents. Combustion tests are conducted at different pressure levels fo r equivalence ratios from lean blowout to near-stoichiometric conditions and steam-to-air mass ratios from 0% to 25%. A reactor network is developed to model the combustion process. The simulation results match the measured NOx and CO concentrations very well fo r all operating conditions. The reactor network is used fo r a detailed investigation o f the influence o f steam and pressure on the NOx formation pathways. In the experi ments, adding 20% steam reduces NOx and CO emissions to below 10 ppm at all tested pressures up to near-stoichiometric conditions. Pressure scaling laws are derived: CO changes with a pressure exponent o f approximately -0.5 that is not noticeably affected by the steam. For the NOx emissions, the exponent increases with equivalence ratio from 0.1 to 0.65 at dry conditions. At a steam-to-air mass ratio o f 20%, the NOx pressure expo nent is reduced to -0.1 to +0.25. The numerical analysis reveals that steam has a strong effect on the combustion chemistry. The reduction in NOx emissions is mainly caused by lower concentrations o f atomic oxygen at steam-diluted conditions, constraining the ther mal pathway. plants [1,2] but with lower installation costs and emission levels [3]. In contrast to the complex combined-cycle plants, ultra wet gas turbines have a substantially smaller footprint. Depending on the cycle configuration, short start-up times and excellent load control capabilities can be achieved. Furthermore, the high steam content allows for low-NOx, near-stoichiometric combustor oper ation and, thus, enables postcombustion CO2 capture at low cost, since the concentration of CO2 reaches the highest possible value for air breathing gas turbines after condensation of the steam. It was recently shown for a lean premixed and for a rich-quenchlean combustor, that steam dilution significantly reduces NOx

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Section: Introductioncontrasting

confidence: 99%

Section: Co Formationmentioning

confidence: 61%

Section: Modeling Results the Measured And Calculated Co Andmentioning

confidence: 99%

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Influence of Pressure and Steam Dilution on NOx and CO Emissions in a Premixed Natural Gas Flame

Göke

Schimek

Steffen

et al. 2014

Journal of Engineering for Gas Turbines and Power

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“…Using the exhaust heat for steam generation in humidified gas turbines promises high cycle efficiencies at low NOx emissions Westermark, 2005a, 2005b;Bhargava et al, 2000;Göke and Paschereit, 2013). Compared to combined cycle power generation, steam-diluted gas turbines have the advantage that no steam turbine is required, which reduces plant complexity and installation costs.…”

Section: Introductionmentioning

confidence: 99%

Impact of Steam-Dilution on the Flame Shape and Coherent Structures in Swirl-Stabilized Combustors

Steffen

Oberleithner

Paschereit

2014

Combustion Science and Technology

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Humidified gas turbines and steam-injected gas turbines are promising technologies to lower the emissions and increase the efficiency and fuel flexibility of gas turbines. In the current study, the influence of steam-dilution on swirl-stabilized methane and hydrogenfired flames is experimentally investigated at Reynolds numbers in the range of 22,000 to 32,000. Velocity fields and flame positions were measured using high-speed particle image velocimetry and OH * chemiluminescence. An extension of the quantitative light sheet technique was employed to estimate the temperature fields. The combined results reveal strong changes in the flame position, the velocity field, and the temperature field with increasing rates of steam dilution. In particular, three different flow and flame patterns are encountered: At dry conditions, a V-shaped flame stabilizes in a broad inner recirculation zone with low local turbulent kinetic energy; at moderate steam content, the flame changes into a trumpet-like shape; and at very high rates of steam-dilution, the flame detaches and shows an annular shape. The associated coherent flow structures are extracted from the particle image velocimetry data employing proper orthogonal decomposition. The isothermal flow is dominated by a helical instability arising near the combustor inlet. This structure is completely suppressed for the dry flame and reappears for the heavily steam-diluted detached flame with a similar shape and frequency as for the isothermal case. The flow field of the trumpet-like flame at intermediate to high steam dilution rates features a helical instability of lower frequency that is located further downstream than in the isothermal and very wet case. A conceptional explanation is presented that relates the suppression of the helical instability to the specific encountered temperature fields and flame shapes.

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“…Re-injecting the steam into the turbine cycle upstream of the combustor results in a higher cycle efficiency at significantly reduced NOx emissions, meeting modem demands of power generation [1], For the influence of steam on the combus tion process, three mechanisms have been identified: (1) a dilution effect reducing the mole fraction of total reactive species, (2) a thermal effect due to an increased heat capacity and reduced thermal diffusivity, and (3) a chemical effect on kinetic reactions often related to an influence on active species concentrations and the high efficiency of steam in third-body reactions [2][3][4][5][6]. Re-injecting the steam into the turbine cycle upstream of the combustor results in a higher cycle efficiency at significantly reduced NOx emissions, meeting modem demands of power generation [1], For the influence of steam on the combus tion process, three mechanisms have been identified: (1) a dilution effect reducing the mole fraction of total reactive species, (2) a thermal effect due to an increased heat capacity and reduced thermal diffusivity, and (3) a chemical effect on kinetic reactions often related to an influence on active species concentrations and the high efficiency of steam in third-body reactions [2][3][4][5][6].…”

Section: Introductionmentioning

confidence: 99%

Laminar Burning Velocities and Emissions of Hydrogen–Methane–Air–Steam Mixtures

Göckeler

Krüger

Paschereit

2014

Journal of Engineering for Gas Turbines and Power

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Humidified gas turbines using steam generated from excess heat feature increased cycle efficiencies. Injecting the steam into the combustor reduces NOx emissions, flame temperatures, and burning velocities, promising a clean and stable combustion of highly reactive fuels such as hydrogen or hydrogen-methane blends. This study presents laminar burning velocities for methane and hydrogen-enriched methane (10 mol. % and 50 mol. %) at steam contents up to 30% of the air mass flow. Experiments were conducted on prismatic Bunsen flames stabilized on a slot-burner, employing OH planar laserinduced fluorescence (OH-PLIF) as an indicator for flame front areas. The experimental burning velocities agree well with results from one-dimensional simulations using the GRl 3.0 mechanism. Burning velocities reduce nonlinearly with ascending steam mole fractions and more rapid compared to simulations using "virtual H2O" stemming from a chemical influence on reactions. Hydrogen enrichment increases burning velocities, extending the flammability range toward leaner and more humid mixtures. Additionally, measured NOx and CO emissions reveal a strong reduction in NOx emissions for increas ing steam dilution rates, whereas CO curves are shifted toward higher equivalence ratios.

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Influence of Steam Dilution on Nitrogen Oxide Formation in Premixed Methane/Hydrogen Flames

Cited by 23 publications

References 22 publications

Influence of Pressure and Steam Dilution on NOx and CO Emissions in a Premixed Natural Gas Flame

Influence of Pressure and Steam Dilution on NOx and CO Emissions in a Premixed Natural Gas Flame

Impact of Steam-Dilution on the Flame Shape and Coherent Structures in Swirl-Stabilized Combustors

Laminar Burning Velocities and Emissions of Hydrogen–Methane–Air–Steam Mixtures

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