Emission Characteristics of a Premixed Cyclic-Periodical-Mixing Combustor Operated With Hydrogen-Natural Gas Fuel Mixtures

2009 ◽  
Vol 132 (2) ◽  
Author(s):  
Jochen R. Brückner-Kalb ◽  
Michael Krösser ◽  
Christoph Hirsch ◽  
Thomas Sattelmayer
Keyword(s):  
Natural Gas ◽  
Gas Turbines ◽  
Combustion Process ◽  
Chemical Reactor ◽  
Combustion Products ◽  
Chemical Effect ◽  
Nox Emissions ◽  
Nox Formation ◽  
Lean Blowout ◽  
Asme Turbo Expo

The concept of the cyclic periodical mixing combustion process (Kalb, and Sattelmayer, 2004, “Lean Blowout Limit and NOx-Production of a Premixed Sub-ppm-NOx Burner With Periodic Flue Gas Recirculation,” Proceedings of the ASME Turbo Expo 2004, Paper No. GT2004-53410; Kalb, and Sattelmayer, 2006, “Lean Blowout Limit and NOx-Production of a Premixed Sub-ppm-NOx Burner With Periodic Recirculation of Combustion Products,” ASME J. Eng. Gas Turbines Power, 128(2), pp. 247–254) for the extension of the lean blowout limit had been implemented in an atmospheric experimental combustor for testing with both external perfect (Brückner-Kalb, Hirsch, and Sattelmayer, 2006, “Operation Characteristics of a Premixed Sub-ppm NOx Burner With Periodical Recirculation of Combustion Products,” Proceedings of the ASME Turbo Expo 2006, Paper No. GT2006-90072) and technical (Brückner-Kalb, Napravnik, Hirsch, and Sattelmayer, 2007, “Development of a Fuel-Air Premixer for a Sub-ppm NOx Burner,” Proceedings of the ASME Turbo Expo 2007, Paper No. GT2007-27779) premixing of reactants. It had been tested with natural gas and has now been tested with a mixture of 70%vol of hydrogen and 30%vol of natural gas (98% CH4) as fuel. With natural gas the NOx emissions are unaffected by the limited technical premixing quality, as long as the air preheat is in the design range of the premixers (Brückner-Kalb, Napravnik, Hirsch, and Sattelmayer, 2007, “Development of a Fuel-Air Premixer for a Sub-ppm NOx Burner,” Proceedings of the ASME Turbo Expo 2007, Paper No. GT2007-27779). Then, for adiabatic flame temperatures of up to 1630 K NOx emissions are below 1 ppm(v) with CO emissions below 8 ppm(v) in the whole operation range of the test combustor (15% O2, dry). With the “70%volH2−30%volCH4” mixture the NOx emissions increase by nearly one order of magnitude. Then, NOx emissions below 7 ppm(v) (15% O2, dry) are achieved for adiabatic flame temperatures of up to 1600 K. They approach the 1 ppm(v) level only for flame temperatures below 1450 K. CO emissions are below 4 ppm(v). The reason for the increase in the NOx emissions is the higher reactivity of the mixture, which leads to earlier ignition in zones of still elevated unmixedness of reactants near the premixer-injector exits. This effect was investigated by chemical reactor network simulations analyzing a pressure effect and an additional chemical effect of hydrogen combustion on NOx formation.

Emission Characteristics of a Premixed Cyclic-Periodical-Mixing Combustor Operated With Hydrogen-Natural Gas Fuel Mixtures

2008 ◽  
Author(s):  
Jochen R. Bru¨ckner-Kalb ◽  
Michael Kro¨sser ◽  
Christoph Hirsch ◽  
Thomas Sattelmayer
Keyword(s):  
Natural Gas ◽  
Combustion Process ◽  
Chemical Reactor ◽  
Chemical Effect ◽  
Nox Emissions ◽  
Nox Formation ◽  
Lean Blowout ◽  
Order Of Magnitude ◽  
Network Simulations ◽  
Fuel Mixtures

The concept of the cyclic periodical mixing combustion process (CPMCP) [1, 2] for the extension of the lean blowout limit had been implemented in an atmospheric experimental combustor for testing with both external perfect [3] and technical [4] premixing of reactants. It had been tested with natural gas and has now been tested with a mixture of 70%Vol of hydrogen and 30%Vol of natural gas (98% CH4) as fuel. With natural gas the NOx emissions are unaffected by the limited technical premixing quality, as long as the air preheat is in the design range of the premixers [4]. Then, for adiabatic flame temperatures of up to 1630 K NOx emissions are below 1 ppm(v) with CO emissions below 8 ppm(v) in the whole operation range of the test combustor (15% O2, dry). With the “70%Vol H2 – 30%Vol CH4” mixture the NOx emissions increase by nearly one order of magnitude. Then, NOx emissions below 7 ppm(v) (15% O2, dry) are achieved for adiabatic flame temperatures of up to 1600 K. They approach the 1 ppm(v) level only for flame temperatures below 1450 K. CO emissions are below 4 ppm(v). The reason for the increase of the NOx emissions is the higher reactivity of the mixture, which leads to earlier ignition in zones of still elevated unmixedness of reactants near the premixer-injector exits. This effect was investigated by chemical reactor network simulations, analyzing a pressure effect and an additional chemical effect of hydrogen combustion on NOx formation.

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

2004 ◽  
Vol 128 (2) ◽  
pp. 247-254 ◽  
Author(s):  
Jochen R. Kalb ◽  
Thomas Sattelmayer
Keyword(s):  
Natural Gas ◽  
Flue Gas ◽  
Combustion Products ◽  
Gas Content ◽  
Stable Operation ◽  
Reacting Flow ◽  
Nox Emissions ◽  
Current Standard ◽  
Lean Blowout ◽  
Fresh Mixture

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.

Operation Characteristics of a Premixed Sub-ppm NOx Burner With Periodical Recirculation of Combustion Products

2006 ◽  
Author(s):  
Jochen R. Bru¨ckner-Kalb ◽  
Christoph Hirsch ◽  
Thomas Sattelmayer
Keyword(s):  
Pressure Drop ◽  
Thermodynamic Equilibrium ◽  
Atmospheric Pressure ◽  
Combustion Process ◽  
Combustion Products ◽  
Low Pressure ◽  
Nox Emissions ◽  
Lean Blowout ◽  
Stable Combustion ◽  
Operation Characteristics

The concept of the periodic mixing and combustion process, which has been presented earlier [1,2], has been implemented in a nearly adiabatic combustor for investigations at atmospheric pressure. The objective of this combustion process is to achieve stable combustion at adiabatic flame temperatures being considerably lower than the lean blowout temperature of aerodynamically stabilized flames with low pressure drop in the combustor in order to reduce NOx emissions and to achieve CO emissions near the thermodynamic equilibrium. For preheat temperatures between 390 K and 790 K, the periodic mixing combustor can be operated near the lean blowout limit with adiabatic flame temperatures down to 1510 K – 1600 K. The test combustor yields over the entire operation range of 1:4 (thermal powers from 47 kW up to 175 kW) very low emissions of NOx below 1 ppm(v) (15% O2, dry) and of CO below 8 ppm(v).

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

2013 ◽  
Author(s):  
Sebastian Göke ◽  
Sebastian Schimek ◽  
Steffen Terhaar ◽  
Thoralf Reichel ◽  
Katharina Göckeler ◽  
...  
Keyword(s):  
Natural Gas ◽  
Scaling Laws ◽  
Combustion Process ◽  
Operating Conditions ◽  
Nox Emissions ◽  
Nox Formation ◽  
Combustion Chemistry ◽  
Air Mass ◽  
Gas Flame ◽  
Reactor Network

In the current study, the influence of 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 premixed, swirl-stabilized combustor is developed that provides a stable flame up to very high steam contents. Combustion tests are conducted at different pressure levels for 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 for all operating conditions. The reactor network is used for a detailed investigation of the influence of steam and pressure on the NOx formation pathways. In the experiments, 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 of 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 of 20%, the NOx pressure exponent 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 of atomic oxygen at steam-diluted conditions, constraining the thermal pathway.

Combustion of Natural Gas, Hydrogen and Bio-Fuels at Ultra-Wet Conditions

2011 ◽  
Author(s):  
Sebastian Go¨ke ◽  
Steffen Terhaar ◽  
Sebastian Schimek ◽  
Katharina Go¨ckeler ◽  
Christian O. Paschereit
Keyword(s):  
Natural Gas ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Combustion Process ◽  
Pure Hydrogen ◽  
Nox Emissions ◽  
Steam Content ◽  
Wide Range ◽  
Air Mixing ◽  
Flame Flashback

Humidified Gas Turbines promise a significant increase in efficiency compared to the dry gas turbine cycle. In single cycle applications, efficiencies up to 60% seem possible with humidified turbines. Additionally, the steam effectively inhibits the formation of NOx emissions and also allows for operating the gas turbine on hydrogen-rich fuels. The current study is conducted within the European Advanced Grant Research Project GREENEST. The premixed combustion at ultra wet conditions is investigated for natural gas, hydrogen, and mixtures of both fuels, covering lower heating values between 27 MJ/kg and 120 MJ/kg. In addition to the experiments, the combustion process is also examined numerically. The flow field and the fuel-air mixing of the burner were investigated in a water tunnel using Particle Image Velocimetry and Laser Induced Fluorescence. Gas-fired tests were conducted at atmospheric pressure, inlet temperatures between 200°C and 370°C, and degrees of humidity from 0% to 50%. Steam efficiently inhibits the formation of NOx emissions. For all tested fuels, both NOx and CO emissions of below 10 ppm were measured up to near-stoichiometric gas composition at wet conditions. Operation on pure hydrogen is possible up to very high degrees of humidity, but even a relatively low steam content prevents flame flashback. Increasing hydrogen content leads to a more compact flame, which is anchored closer to the burner outlet, while increasing steam content moves the flame downstream and increases the flame volume. In addition to the experiments, the combustion process was modeled using a reactor network. The predicted NOx and CO emission levels agree well with the experimental results over a wide range of temperatures, steam content, and fuel composition.

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

2014 ◽  
Vol 136 (9) ◽  
Author(s):  
Sebastian Göke ◽  
Sebastian Schimek ◽  
Steffen Terhaar ◽  
Thoralf Reichel ◽  
Katharina Göckeler ◽  
...  
Keyword(s):  
Natural Gas ◽  
Scaling Laws ◽  
Combustion Process ◽  
Operating Conditions ◽  
Nox Emissions ◽  
Nox Formation ◽  
Combustion Chemistry ◽  
Air Mass ◽  
Gas Flame ◽  
Reactor Network

In the current study, the influence of 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 premixed, swirl-stabilized combustor is developed that provides a stable flame up to very high steam contents. Combustion tests are conducted at different pressure levels for 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 for all operating conditions. The reactor network is used for a detailed investigation of the influence of steam and pressure on the NOx formation pathways. In the experiments, 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 of 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 of 20%, the NOx pressure exponent 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 of atomic oxygen at steam-diluted conditions, constraining the thermal pathway.

Comparison of Numerical Combustion Models for Hydrogen and Hydrogen-Rich Syngas Applied for Dry-Low-NOx-Micromix-Combustion

2016 ◽  
Author(s):  
H. H.-W. Funke ◽  
N. Beckmann ◽  
J. Keinz ◽  
S. Abanteriba
Keyword(s):  
Reaction Mechanism ◽  
Gas Turbines ◽  
Combustion Process ◽  
Computational Effort ◽  
Hydrogen Combustion ◽  
Combustion Stability ◽  
Research Approach ◽  
Pure Hydrogen ◽  
Nox Emissions ◽  
Combustion Models

The Dry-Low-NOx (DLN) Micromix combustion technology has been developed as low emission combustion principle for industrial gas turbines fueled with hydrogen or syngas. The combustion process is based on the phenomenon of jet-in-crossflow-mixing. Fuel is injected perpendicular into the air-cross-flow and burned in a multitude of miniaturized, diffusion-like flames. The miniaturization of the flames leads to a significant reduction of NOx emissions due to the very short residence time of reactants in the flame. In the Micromix research approach, CFD analyses are validated towards experimental results. The combination of numerical and experimental methods allows an efficient design and optimization of DLN Micromix combustors concerning combustion stability and low NOx emissions. The paper presents a comparison of several numerical combustion models for hydrogen and hydrogen-rich syngas. They differ in the complexity of the underlying reaction mechanism and the associated computational effort. For pure hydrogen combustion a one-step global reaction is applied using a hybrid Eddy-Break-up model that incorporates finite rate kinetics. The model is evaluated and compared to a detailed hydrogen combustion mechanism derived by Li et al. including 9 species and 19 reversible elementary reactions. Based on this mechanism, reduction of the computational effort is achieved by applying the Flamelet Generated Manifolds (FGM) method while the accuracy of the detailed reaction scheme is maintained. For hydrogen-rich syngas combustion (H2-CO) numerical analyses based on a skeletal H2/CO reaction mechanism derived by Hawkes et al. and a detailed reaction mechanism provided by Ranzi et al. are performed. The comparison between combustion models and the validation of numerical results is based on exhaust gas compositions available from experimental investigation on DLN Micromix combustors. The conducted evaluation confirms that the applied detailed combustion mechanisms are able to predict the general physics of the DLN-Micromix combustion process accurately. The Flamelet Generated Manifolds method proved to be generally suitable to reduce the computational effort while maintaining the accuracy of detailed chemistry. Especially for reaction mechanisms with a high number of species accuracy and computational effort can be balanced using the FGM model.

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

2004 ◽  
Author(s):  
Jochen R. Kalb ◽  
Thomas Sattelmayer
Keyword(s):  
Natural Gas ◽  
Flue Gas ◽  
Gas Content ◽  
Stable Operation ◽  
Reacting Flow ◽  
Nox Emissions ◽  
Lean Blowout ◽  
Fresh Mixture ◽  
Flue Gas Recirculation ◽  
Gas Recirculation

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 periodic flue gas recirculation: Hot flue gas is 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 flue gas. A fraction of the 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 e.g. 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 flue gas 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 have 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.

scholarly journals The Effect of Discrete Pilot Hydrogen Dopant Injection on the Lean Blowout Performance of a Model Gas Turbine Combustor

1999 ◽  
Author(s):  
Oanh Nguyen ◽  
Scott Samuelsen
Keyword(s):  
Gas Turbine ◽  
Atmospheric Pressure ◽  
Gas Turbines ◽  
Nox Emissions ◽  
Gas Turbine Combustor ◽  
Lean Blowout ◽  
Lean Combustion ◽  
Attractive Option ◽  
Overall Performance ◽  
Model Gas Turbine Combustor

In view of increasingly stringent NOx emissions regulations on stationary gas turbines, lean combustion offers an attractive option to reduce reaction temperatures and thereby decrease NOx production. Under lean operation, however, the reaction is vulnerable to blowout. It is herein postulated that pilot hydrogen dopant injection, discretely located, can enhance the lean blowout performance without sacrificing overall performance. The present study addresses this hypothesis in a research combustor assembly, operated at atmospheric pressure, and fired on natural gas using rapid mixing injection, typical of commercial units. Five hydrogen injector scenarios are investigated. The results show that (1) pilot hydrogen dopant injection, discretely located, leads to improved lean blowout performance and (2) the location of discrete injection has a significant impact on the effectiveness of the doping strategy.

The Effect of Water Injection for Emissions Control on Industrial Gas Turbine Combustors

1984 ◽  
Author(s):  
R. J. Antos ◽  
W. C. Emmerling
Keyword(s):  
Gas Turbines ◽  
Mechanical Design ◽  
Water Injection ◽  
Combustion Process ◽  
Liquid Fuels ◽  
Nox Emissions ◽  
Design Features ◽  
Industrial Gas Turbines ◽  
Comprehensive Test ◽  
Industrial Gas Turbine

One common method of reducing the NOx emissions from industrial gas turbines is to inject water into the combustion process. The amount of water injected depends on the emissions rules that apply to a particular unit. Westinghouse W501B industrial gas turbines have been operated at water injection levels required to meet EPA NOx emissions regulations. They also have been operated at higher injection levels required to meet stricter California regulations. Operation at the lower rates of water did not affect combustor inspection and/or repair intervals. Operation on liquid fuels with high rates of water also did not result in premature distress. However, operation on gas fuel at high rates of water did cause premature distress in the combustors. To evaluate this phenomenon, a comprehensive test program was conducted; it demonstrated that the distress is the result of the temperature patterns in the combustor caused by the high rates of water. The test also indicated that there is no significant change in dynamic response levels in the combustor. This paper presents the test results, and the design features selected to substantially improve combustor wall temperature when operating on gas fuels, with the high rates of water injection required to meet California applications. Mechanical design features that improve combustor resistance to water injection-induced thermal gradients also are presented.

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