NOx Reduction by Air-Side vs. Fuel-Side Dilution in Hydrogen Diffusion Flame Combustors

2009 ◽  
Author(s):  
Nathan T. Weiland ◽  
Peter A. Strakey
Keyword(s):  
Residence Time ◽  
Diffusion Flame ◽  
Nox Reduction ◽  
Flame Temperature ◽  
Air Entrainment ◽  
Combined Cycle ◽  
Nox Emissions ◽  
Residence Times ◽  
High Hydrogen ◽  
Separation Unit

Lean-Direct-Injection (LDI) combustion is being considered at NETL as a means to attain low NOx emissions in a high-hydrogen gas turbine combustor. Integrated Gasification Combined Cycle (IGCC) plant designs can create a high-hydrogen fuel using a water-gas shift reactor and subsequent CO2 separation. The IGCC’s air separation unit produces a volume of N2 roughly equivalent to the volume of H2 in the gasifier product stream, which can be used to help reduce peak flame temperatures and NOx in the diffusion flame combustor. Placement of this diluent in either the air or fuel streams is a matter of practical importance, and has not been studied to date for LDI combustion. The current work discusses how diluent placement affects diffusion flame temperatures, residence times, and stability limits, and their resulting effects on NOx emissions. From a peak flame temperature perspective, greater NOx reduction should be attainable with fuel dilution rather than air or independent dilution in any diffusion flame combustor with excess combustion air, due to the complete utilization of the diluent as a heat sink at the flame front, although the importance of this mechanism is shown to diminish as flow conditions approach stoichiometric proportions. For simple LDI combustor designs, residence time scaling relationships yield a lower NOx production potential for fuel-side dilution due to its smaller flame size, whereas air-dilution yields a larger air entrainment requirement and a subsequently larger flame, with longer residence times and higher thermal NOx generation. For more complex staged-air LDI combustor designs, dilution of the primary combustion air at fuel-rich conditions can result in full utilization of the diluent for reducing the peak flame temperature, while also controlling flame volume and residence time for NOx reduction purposes. However, differential diffusion of hydrogen out of a diluted hydrogen/nitrogen fuel jet can create regions of higher hydrogen content in the immediate vicinity of the fuel injection point than can be attained with dilution of the air stream, leading to increased flame stability. By this mechanism, fuel-side dilution extends the operating envelope to areas with higher velocities in the experimental configurations tested, where faster mixing rates further reduce flame residence times and NOx emissions. Strategies for accurate CFD modeling of LDI combustors’ stability characteristics are also discussed.

scholarly journals NO x Reduction by Air-Side Versus Fuel-Side Dilution in Hydrogen Diffusion Flame Combustors

2010 ◽  
Vol 132 (7) ◽  
Author(s):  
Nathan T. Weiland ◽  
Peter A. Strakey
Keyword(s):  
Residence Time ◽  
Diffusion Flame ◽  
Nox Reduction ◽  
Flame Temperature ◽  
Air Entrainment ◽  
Combined Cycle ◽  
Nox Emissions ◽  
Residence Times ◽  
High Hydrogen ◽  
Separation Unit

Lean-direct-injection (LDI) combustion is being considered at the National Energy Technology Laboratory as a means to attain low NOx emissions in a high-hydrogen gas turbine combustor. Integrated gasification combined cycle (IGCC) plant designs can create a high-hydrogen fuel using a water-gas shift reactor and subsequent CO2 separation. The IGCC’s air separation unit produces a volume of N2 roughly equivalent to the volume of H2 in the gasifier product stream, which can be used to help reduce peak flame temperatures and NOx in the diffusion flame combustor. Placement of this diluent in either the air or fuel streams is a matter of practical importance, and it has not been studied to date for LDI combustion. The current work discusses how diluent placement affects diffusion flame temperatures, residence times, and stability limits, and their resulting effects on NOx emissions. From a peak flame temperature perspective, greater NOx reduction should be attainable with fuel dilution rather than air or independent dilution in any diffusion flame combustor with excess combustion air, due to the complete utilization of the diluent as a heat sink at the flame front, although the importance of this mechanism is shown to diminish as flow conditions approach stoichiometric proportions. For simple LDI combustor designs, residence time scaling relationships yield a lower NOx production potential for fuel-side dilution due to its smaller flame size, whereas air dilution yields a larger air entrainment requirement and a subsequently larger flame, with longer residence times and higher thermal NOx generation. For more complex staged-air LDI combustor designs, the dilution of the primary combustion air at fuel-rich conditions can result in the full utilization of the diluent for reducing the peak flame temperature, while also controlling flame volume and residence time for NOx reduction purposes. However, differential diffusion of hydrogen out of a diluted hydrogen/nitrogen fuel jet can create regions of higher hydrogen content in the immediate vicinity of the fuel injection point than can be attained with the dilution of the air stream, leading to increased flame stability. By this mechanism, fuel-side dilution extends the operating envelope to areas with higher velocities in the experimental configurations tested, where faster mixing rates further reduce flame residence times and NOx emissions. Strategies for accurate computational modeling of LDI combustors’ stability characteristics are also discussed.

Combustion Optimization for the ALSTOM GT13E2 Gas Turbine

2006 ◽  
Author(s):  
Ch. Steinbach ◽  
N. Ulibarri ◽  
M. Garay ◽  
H. Lu¨bcke ◽  
Th. Meeuwissen ◽  
...  
Keyword(s):  
Temperature Distribution ◽  
Flame Temperature ◽  
Air Entrainment ◽  
Flame Stabilization ◽  
Flame Stability ◽  
Nox Emissions ◽  
Combustion Control ◽  
Control Logic ◽  
The Individual ◽  
Combustion Optimization

The NOx emissions of low NOx premix combustors are not only determined by the burner design, but also by the multi burner interaction and the related distribution of air and fuel flows to the individual burners. Often the factors that have a positive impact on NOx emission have a negative impact on the flame stability, so the main challenge is to find an optimum point with the lowest achievable NOx while maintaining good flame stability. The hottest flame zones are where most of the NOx is formed. Avoiding such zones in the combustor (by homogenization of the flame temperature) reduces NOx emissions significantly. Improving the flame stability and the combustion control allows the combustor to operate at a lower average flame temperature and NOx emissions. ALSTOM developed a combustion optimization package for the GT13E2. The optimization package development focused on three major issues: • Flame stability; • Homogenization of flame temperature distribution in the combustor; • Combustion control logic. The solution introduced consists of: • The reduction of cooling air entrainment in the primary flame zone for improved flame stability; • The optical measurement of the individual burner flame temperatures and their homogenization by burner tuning valves; • Closed loop control logic to control the combustion dependent on the pulsation signal. This paper shows how fundamental combustion research methods were applied to derive effective optimization measures. The flame temperature measurement technique will be presented along with results of the measurement and their application in homogenization of the combustor temperature distribution in an engine equipped with measures to improve flame stabilization. The main results achieved are: • Widening of the main burner group operation range; • Improved use of the low NOx operation range; • NOx reduction at the combustor pulsation limit and hence, large margins to the European emission limit (50 mg/m3 @ 15%O2).

Kinetics Modeling on NOx Emissions of a Syngas Turbine Combustor Using RQL Combustion Method

2019 ◽  
Author(s):  
Haoyang Liu ◽  
Wenkai Qian ◽  
Min Zhu ◽  
Suhui Li
Keyword(s):  
Gas Turbine ◽  
Residence Time ◽  
Air Flow ◽  
Nox Reduction ◽  
Outlet Temperature ◽  
Nox Emissions ◽  
Gas Turbine Combustor ◽  
Kinetics Modeling ◽  
The Rich ◽  
Nox Control

Abstract To avoid flashback issues of the high-H2 syngas fuel, current syngas turbines usually use non-premixed combustors, which have high NOx emissions. A promising solution to this dilemma is RQL (rich-burn, quick-mix, lean-burn) combustion, which not only reduces NOx emissions, but also mitigates flashback. This paper presents a kinetics modeling study on NOx emissions of a syngas-fueled gas turbine combustor using RQL architecture. The combustor was simulated with a chemical reactor network model in CHEMKIN-PRO software. The combustion and NOx formation reactions were modeled using a detailed kinetics mechanism that was developed for syngas. Impacts of combustor design/operating parameters on NOx emissions were systematically investigated, including combustor outlet temperature, rich/lean air flow split and residence time split. The mixing effects in both the rich-burn zone and the quick-mix zone were also investigated. Results show that for an RQL combustor, the NOx emissions initially decrease and then increase with combustor outlet temperature. The leading parameters for NOx control are temperature-dependent. At typical modern gas turbine combustor operating temperatures (e.g., < 1890 K), the air flow split is the most effective parameter for NOx control, followed by the mixing at the rich-burn zone. However, as the combustor outlet temperature increases, the impacts of air flow split and mixing in the rich-burn zone on NOx reduction become less pronounced, whereas both the residence time split and the mixing in the quick-mix zone become important.

Kinetics Study of a Staged Combustor Concept for Oxy-Fuel Combustion Gas Turbine Cycles

2019 ◽  
Author(s):  
Wenkai Qian ◽  
Haoyang Liu ◽  
Min Zhu ◽  
Suhui Li
Keyword(s):  
Gas Turbine ◽  
Residence Time ◽  
Nox Reduction ◽  
Flame Temperature ◽  
Chemical Reactor ◽  
Fuel Combustion ◽  
Combustion Gas ◽  
Part Load ◽  
Primary Zone ◽  
Reactor Network

Abstract Oxy-fuel combustion has been identified as a promising technology for CO2 capture and NOx reduction. It has great potential to be applied in gas turbine cycles. Previous studies, however, reveal that simple oxy-fuel combustors suffer from issues like flame blowoff and CO emissions especially at part load, due to the high CO2 content in the combustion atmosphere. In this paper, a staged combustor concept is proposed to mitigate flame blowoff and CO emissions issues for load operations. The conceptual combustor consists of three zones axially: primary zone, CO burnout zone, and dilution zone. All fuel is fed to the primary zone, while O2 is distributed to the primary zone and CO burnout zone. CO2 is distributed to the primary zone and dilution zone. By adjusting the distribution of the O2 and CO2, the primary zone operates at a relatively higher flame temperature at part load, which helps improve the flame blowoff performance. A chemical reactor network model is developed to study the effects of key design/operating parameters on flame blowoff and CO emissions. Results show that the distribution ratios of O2, CO2 and residence time between different zones are the key factors that influence flame blowoff and CO emissions. To mitigate flame blowoff and CO emissions at part load, the distribution of O2 needs to be carefully chosen so that the primary zone operates under near-stoichiometric or slightly lean condition, while the distribution of CO2 to the primary zone also needs to be reduced. The residence time split has stronger influence on CO emissions than CO2 and O2 distribution.

Some Studies on NOX Reduction From a Diesel Engine Using Stabilized Emulsion

2018 ◽  
Author(s):  
Naveen Kumar ◽  
Harveer Singh Pali ◽  
Sidharth Bansal
Keyword(s):  
Diesel Engine ◽  
Water Content ◽  
Volume Fraction ◽  
Nox Reduction ◽  
Flame Temperature ◽  
Water Volume ◽  
Nox Emissions ◽  
Oxides Of Nitrogen ◽  
Engine Operation ◽  
Water Emulsion

The twentieth century has seen a rapid twenty-fold increase in the use of fossil fuels. Personal and commercial transportation consumes 2% of the total world energy. The main products of combustion of fossil fuel are carbon mono oxide (CO), unburned hydrocarbons (HC), Carbon dioxide (CO2), oxides of sulfur (SOx), oxides of nitrogen (NOx) and particulate matter. Oxides of nitrogen (NOx) are the major diesel engine pollutants and referred to as mixtures of nitric oxide (NO) and nitrogen dioxide (NO2). NOx emissions are required to be controlled because NO and NO2 contribute to the formation of smog, an environmental and human health hazard. NO2 is also directly of concern as a human lung aggravation. To reduce NOx emissions from a diesel engine, the introduction of water in the combustion chamber of a diesel engine is a promising option as vaporization of water reduces adiabatic flame temperature and micro-explosion phenomena lead to improved mixing. In the present study, stable D/W emulsion, with varying water content, up to 3% were prepared using span 80 as a surfactant. The results indicated a reduction in NOx and smoke with increasing water volume fraction in the emulsion compared to diesel baseline. However, beyond 2% water content led to increased ignition delay and higher diffusion phase heat release resulting in noisy engine operation. Therefore, it can be concluded that diesel-water emulsion with 2% water could be used for significant reduction of NOx emissions from diesel and biodiesel operation of a CI Engine.

Lean Blowout Limits and NOx Emissions of Turbulent, Lean Premixed, Hydrogen-Enriched Methane/Air Flames at High Pressure

2006 ◽  
Author(s):  
P. Griebel ◽  
E. Boschek ◽  
P. Jansohn
Keyword(s):  
High Pressure ◽  
Nox Reduction ◽  
Flame Temperature ◽  
Operating Conditions ◽  
Flame Stability ◽  
Nox Emissions ◽  
Lean Blowout ◽  
Wide Range ◽  
Pure Methane ◽  
Lean Premixed

Flame stability is a crucial issue in low NOx combustion systems operating at extremely lean conditions. Hydrogen enrichment seems to be a promising option to extend lean blowout limits of natural gas combustion. This experimental study addresses flame stability enhancement and NOx reduction in turbulent, high-pressure, lean premixed methane/air flames in a generic combustor, capable of a wide range of operating conditions. Lean blowout limits (LBO) and NOx emissions are presented for pressures up to 14 bars, bulk velocities in the range of 32–80 m/s, two different preheating temperatures (673 K, 773 K), and a range of fuel mixtures from pure methane to 20% H2/80% CH4 by volume. The influence of turbulence on LBO limits is discussed, too. In addition to the investigation of perfectly premixed H2-enriched flames, LBO and NOx are also discussed for hydrogen piloting. Experiments have revealed that a mixture of 20% hydrogen and 80% methane, by volume, can typically extend the lean blowout limit by roughly 10% compared to pure methane. The flame temperature at LBO is approximately 60 K lower resulting in the reduction of NOx concentration by ≈ 35% (0.5 → 0.3 ppm/15% O2).

Lean Blowout Limits and NOx Emissions of Turbulent, Lean Premixed, Hydrogen-Enriched Methane/Air Flames at High Pressure

2006 ◽  
Vol 129 (2) ◽  
pp. 404-410 ◽  
Author(s):  
P. Griebel ◽  
E. Boschek ◽  
P. Jansohn
Keyword(s):  
High Pressure ◽  
Nox Reduction ◽  
Flame Temperature ◽  
Operating Conditions ◽  
Flame Stability ◽  
Nox Emissions ◽  
Lean Blowout ◽  
Wide Range ◽  
Pure Methane ◽  
Lean Premixed

Flame stability is a crucial issue in low NOx combustion systems operating at extremely lean conditions. Hydrogen enrichment seems to be a promising option to extend lean blowout limits (LBO) of natural gas combustion. This experimental study addresses flame stability enhancement and NOx reduction in turbulent, high-pressure, lean premixed methane/air flames in a generic combustor capable of a wide range of operating conditions. Lean blowout limits and NOx emissions are presented for pressures up to 14bar, bulk velocities in the range of 32–80m∕s, two different preheating temperatures (673K, 773K), and a range of fuel mixtures from pure methane to 20% H2∕80%CH4 by volume. The influence of turbulence on LBO limits is also discussed. In addition to the investigation of perfectly premixed H2-enriched flames, LBO and NOx are also discussed for hydrogen piloting. Experiments have revealed that a mixture of 20% hydrogen and 80% methane, by volume, can typically extend the lean blowout limit by ∼10% compared to pure methane. The flame temperature at LBO is ∼60K lower resulting in the reduction of NOx concentration by ≈35%(0.5→0.3ppm∕15%O2).

Testing of a Hydrogen Dilute Diffusion Array Injector at Gas Turbine Conditions

2011 ◽  
Author(s):  
Nathan T. Weiland ◽  
Todd G. Sidwell ◽  
Peter A. Strakey
Keyword(s):  
Pressure Drop ◽  
Gas Turbine ◽  
Residence Time ◽  
Firing Temperature ◽  
Gas Turbines ◽  
Advanced Technology ◽  
Nox Emissions ◽  
High Hydrogen ◽  
Air Jet ◽  
Nitrogen Dilution

The U.S. Department of Energy’s Turbines Program is developing advanced technology for high-hydrogen gas turbines to enable integration of carbon sequestration technology into coal-gasifying power plants. Program goals include aggressive reductions in gas turbine NOx emissions: less than 2 ppmv NOx at 15% oxygen and 1750 K firing temperature. The approach explored in this work involves nitrogen dilution of hydrogen diffusion flames, which avoids problems with premixing hydrogen at gas turbine pressures and temperatures. Thermal NOx emissions are partially reduced through peak flame temperature control provided by nitrogen dilution, while further reductions are attained by minimizing flame size and residence time. The injector design includes high-velocity coaxial air injection from lobes surrounding the central fuel tube in each of the 48 array units. This configuration strikes a balance between stability and ignition performance, combustor pressure drop, and flame residence time. Array injector test conditions in the optically accessible Low Emissions Combustor Test & Research (LECTR) facility include air preheat temperatures of 500 K, combustor pressures of 4, 8 and 16 atm, equivalence ratios of 0.3 to 0.7, and three hydrogen/nitrogen fuel blend ratios. Test results show that NOx emissions increase with pressure and decrease with increasing fuel and air jet velocities, as expected. The magnitude of these emissions changes deviate from expected NOx scaling relationships, however, due to active combustor cooling and array spacing effects. At 16 atm and 1750 K firing temperature, the lowest NOx emissions obtained is 4.4 ppmv at 15% O2 equivalent (3.0 ppmv if diluent nitrogen is not considered), with a corresponding pressure drop of 7.7%. While these results demonstrate that nitrogen dilution in combination with high strain rates provides a reliable solution to low NOx hydrogen combustion at gas turbine conditions, the injector’s performance can still be improved significantly through suggested design changes.

The FMT Criterion to Optimize the Quench Zone in RQL Combustors

2013 ◽  
Author(s):  
Yong Huang ◽  
Lei Liu ◽  
Fang Wang ◽  
Shaolin Wang
Keyword(s):  
Environmental Protection ◽  
Residence Time ◽  
Mixing Time ◽  
The Other ◽  
Nox Emissions ◽  
First Principle ◽  
Residence Times ◽  
Pollution Emission ◽  
Thermal Nox ◽  
Good Agreement

As environmental protection is more and more important, pollution emission in aircraft combustors should be low. The RQL (rich-quench-lean) technique is one of the promising ways to control NOx emissions from combustors. In RQL combustors, NOx is mostly produced in quench zone. So the optimization of quench zone is very important to control NOx emissions. According to thermal NOx mechanism, NOx emissions are determined by residence times. For a RQL combustor all the mainflow fuel should be burned out in quench zone. Then the maximum residence time is the time for the flame to transport the longest distance. Based on the first-principle analysis of the flow and combustion in the quench zone, the FMT (flame mixing time) criterion for the optimization of quench jets has been proposed. There are two typical quench ducts. One is the annular shape and the other is the can shape. The two types of ducts are similar but there are some differences between them. In this paper both of them were analyzed in terms of the FMT criterion. The maximum residence times calculated by FMT criterion were compared with the experiments by Chiappetta et. al. [3] and Holdeman & Chang[13] for annular and can combustors, respectively. The comparison shows the very good agreement between the maximum residence times calculated by FMT criterion and the experiments. That means the FMT criterion can be validated by both annular and can shape combustors. And the FMT criterion could be used to optimize the configuration of quench zones.

The Effect of Impurities in Fuel Grade Dimethyl-Ether on Combustion Characteristics

2004 ◽  
Author(s):  
Kimihito Narukawa ◽  
Hiromi Koizumi ◽  
Hiroshi Inoue ◽  
Nariyoshi Kobayashi
Keyword(s):  
Dimethyl Ether ◽  
Diffusion Flame ◽  
High Purity ◽  
Burning Velocity ◽  
Flame Temperature ◽  
Combustion Characteristics ◽  
Nox Emissions ◽  
Laminar Burning Velocity ◽  
Gas Turbine Combustor ◽  
Effect Of Impurities

In order to investigate the effect of impurities contained in fuel grade dimethyl-ether on combustion characteristics, laminar burning velocity tests and diffusion flame combustor tests were carried out with various contents of impurities in fuel grade dimethyl-ether (with about 0–9wt% methanol and 0–10wt% moisture). From the laminar burning velocity tests, it was found that the burning velocity of fuel grade dimethyl-ether was slightly slower than that of high purity dimethyl-ether and it was faster than that of methane. This indicates that fuel grade dimethyl-ether has a high potential of flash back, like high purity dimethyl-ether. Moreover, the diffusion flame combustor tests showed that NOx emission decreased when the impurities contained in fuel grade dimethyl-ether were increased, however CO emissions were almost constant, irrespective of the content of impurities. Further, by comparing NOx emissions with various contents of impurities in fuel grade dimethyl-ether, it was clear that NOx emissions could be estimated from the adiabatic flame temperature. From these results, a lot of valuable data regarding impurities content has been obtained, which will assist in the development of a gas turbine combustor for fuel grade dimethyl-ether.

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