scholarly journals Effects of Incomplete Premixing on NOx Formation at Temperature and Pressure Conditions of LP Combustion Turbines

1997 ◽  
Author(s):  
Teodora Rutar ◽  
Scott M. Martin ◽  
David G. Nicol ◽  
Philip C. Malte ◽  
David T. Pratt
Keyword(s):  
Air Temperature ◽  
Chemical Reactor ◽  
Nox Emissions ◽  
Reactor Model ◽  
Nox Formation ◽  
Air Temperatures ◽  
Primary Zone ◽  
Lean Premixed ◽  
Temperature And Pressure

A probability density function/chemical reactor model (PDF/CRM) is applied to study how NOx emissions vary with mean combustion temperature, inlet air temperature, and pressure for different degrees of premixing quality under lean-premixed (LP) gas turbine combustor conditions. Inlet air temperatures of 550, 650 and 750 K, and combustor pressures of 10, 14 and 30 atm are examined in different chemical reactor configurations. Primary results from this study are: incomplete premixing can either increase or decrease NOx emissions, depending on the primary zone stoichiometry; an Arrhenius-type plot of NOx emissions may have promise for assessing the premixer quality of lean-premixed combustors; and decreasing premixing quality enhances the influence of inlet air temperature and pressure on NOx emissions.

scholarly journals Characterization of NOx, N2O, and CO for Lean-Premixed Combustion in a High-Pressure Jet-Stirred Reactor

1996 ◽  
Author(s):  
Robert C. Steele ◽  
Jon H. Tonouchi ◽  
David G. Nicol ◽  
David C. Horning ◽  
Philip C. Malte ◽  
...  
Keyword(s):  
High Pressure ◽  
Computational Models ◽  
Chemical Reactor ◽  
Reactor Model ◽  
N2o Formation ◽  
Nox Formation ◽  
Lean Premixed Combustion ◽  
Stirred Reactor ◽  
Lean Premixed ◽  
In Series

A high-pressure jet-stirred reactor (HP-JSR) has been built and applied to the study of NOx and N2O formation and CO oxidation in lean-premixed (LPM) combustion. The measurements obtained with the HP-JSR provide information on how NOx forms in lean-premixed, high-intensity combustion, and provide comparison to NOx data published recently for practical LPM combustors. The HP-JSR results indicate that the NOx yield is significantly influenced by the rate of relaxation of super-equilibrium concentrations of the O-atom. Also indicated by the HP-JSR results are characteristic NOx formation rates. Two computational models are used to simulate the HP-JSR, and to provide comparison to the measurements. The first is a chemical reactor model (CRM) consisting of two perfectly-stirred reactors (PSRs) placed in series. The second is a stirred reactor model with finite rate macromixing (i.e., recirculation) and micromixing. The micromixing is treated by either coalescence-dispersion (CD) or interaction-by-exchange-with-the-mean (IEM) theory. Additionally, a model based on one-dimensional gas dynamics with chemical reaction is used to assess chemical conversions within the gas sample probe.

Characterization of NOx, N20, and CO for Lean-Premixed Combustion in a High-Pressure Jet-Stirred Reactor

1998 ◽  
Vol 120 (2) ◽  
pp. 303-310 ◽  
Author(s):  
R. C. Steele ◽  
J. H. Tonouchi ◽  
D. G. Nicol ◽  
D. C. Horning ◽  
P. C. Malte ◽  
...  
Keyword(s):  
High Pressure ◽  
Computational Models ◽  
Chemical Reactor ◽  
Reactor Model ◽  
N2o Formation ◽  
Nox Formation ◽  
Lean Premixed Combustion ◽  
Stirred Reactor ◽  
Lean Premixed ◽  
In Series

A high-pressure jet-stirred reactor (HP-JSR) has been built and applied to the study of NOx and N2o formation and CO oxidation in lean-Premixed (LPM) combustion. The measurements obtained with the HP-JSR Provide information on how NOx forms in lean-premixed, high-intensity combustion, and provide comparison to NOx data published recently for practical LPM combustors. The HP-JSR results indicate that the NOx yield is significantly influenced by the rate of relaxation of super-equilibrium concentrations of the O-atom. Also indicated by the HP-JSR results are characteristic NOx formation rates. Two computational models are used to simulate the HP-JSR and to provide comparison to the measurements. The first is a chemical reactor model (CRM) consisting of two perfectly stirred reactors (PSRs) placed in series. The second is a stirred reactor model with finite rate macromixing (i.e., recirculation) and micromixing. The micromixing is treated by either coalescence-dispersion (CD) or interaction by exchange with the mean (IEM) theory. Additionally, a model based on one-dimensional gas dynamics with chemical reaction is used to assess chemical conversions within the gas sample probe.

Development of a Natural Gas-Fired, Ultra-Low NOx Can Combustor for an 800 KW Gas Turbine

1991 ◽  
Author(s):  
K. O. Smith ◽  
A. C. Holsapple ◽  
H. K. Mak ◽  
L. Watkins
Keyword(s):  
Natural Gas ◽  
Gas Turbine ◽  
Premixed Combustion ◽  
Experimental Results ◽  
Nox Emissions ◽  
Variable Geometry ◽  
Lean Premixed Combustion ◽  
Full Load ◽  
Primary Zone ◽  
Lean Premixed

The experimental results from the rig testing of an ultra-low NOx, natural gas-fired combustor for an 800 to 1000 kw gas turbine are presented. The combustor employed lean-premixed combustion to reduce NOx emissions and variable geometry to extend the range over which low emissions were obtained. Testing was conducted using natural gas and methanol. Testing at combustor pressures up to 6 atmospheres showed that ultra-low NOx emissions could be achieved from full load down to approximately 70% load through the combination of lean-premixed combustion and variable primary zone airflow.

scholarly journals The Importance of the Nitrous Oxide Pathway to NOx in Lean-Premixed Combustion

1993 ◽  
Author(s):  
David G. Nicol ◽  
Robert C. Steele ◽  
Nick M. Marinov ◽  
Philip C. Malte
Keyword(s):  
Nitrous Oxide ◽  
Pressure Dependence ◽  
Porous Plate ◽  
Premixed Combustion ◽  
Nox Formation ◽  
Lean Premixed Combustion ◽  
Turbine Engine ◽  
Stirred Reactor ◽  
Primary Zone ◽  
Lean Premixed

This study addresses the importance of the different chemical pathways responsible for NOx formation in lean-premixed combustion, and especially the role of the nitrous oxide pathway relative to the traditional Zeldovich pathway. NOx formation is modeled and computed over a range of operating conditions for the lean-premixed primary zone of gas turbine engine combustors. The primary zone, of uniform fuel-air ratio, is modeled as a micro-mixed well-stirred reactor, representing the flame zone, followed by a series of plug flow reactors, representing the post-flame zone. The fuel is methane. The fuel-air equivalence ratio is varied from 0.5 to 0.7. The chemical reactor model permits study of the three pathways by which NOx forms, which are the Zeldovich, nitrous oxide, and prompt pathways. Modeling is also performed for the well-stirred reactor alone. Three recently published, complete chemical kinetic mechanisms for the C1-C2 hydrocarbon oxidation and the NOx formation are applied and compared. Verification of the model is based on the comparison of its NOx output to experimental results published for atmospheric pressure jet-stirred reactors and for a ten atmosphere porous-plate burner. Good agreement between the modeled results and the measurements is obtained for most of the jet-stirred reactor operating range. For the porous-plate burner, the model shows agreement to the NOx measurements within a factor of two, with close agreement occurring at the leanest and coolest cases examined. For lean-premixed combustion at gas turbine engine conditions, the nitrous oxide pathway is found to be important, though the Zeldovich pathway cannot be neglected. The prompt pathway, however, contributes small-to-negligible NOx. Whenever the NOx emission is in the 15 to 30ppmv (15% O2, dry) range, the nitrous oxide pathway is predicted to contribute 40 to 45% of the NOx for high pressure engines (30atm), and 20 to 35% of the NOx for intermediate pressure engines (10atm). For conditions producing NOx of less than 10ppmv (15% O2, dry), the nitrous oxide contribution increases steeply and approaches 100%. For lean-premixed combustion in the atmospheric pressure jet-stirred reactors, different behavior is found. All three pathways contribute; none can be dismissed. No universal behavior is found for the pressure dependence of the NOx. It does appear, however, that lean-premixed combustors operated in the vicinity of 10atm have a relatively weak pressure dependence, whereas combustors operated in the vicinity of 30atm have an approximately square root pressure dependence of the NOx.

NOx Formation in High-Pressure Jet-Stirred Reactors With Significance to Lean-Premixed Combustion Turbines

2001 ◽  
Author(s):  
Teodora Rutar ◽  
Philip C. Malte
Keyword(s):  
High Pressure ◽  
Nitrous Oxide ◽  
Chemical Reactor ◽  
Sampling Point ◽  
Damkohler Number ◽  
Flame Zone ◽  
Nox Formation ◽  
Damköhler Number ◽  
Lean Premixed ◽  
Stirred Reactors

Measurements of NOx and CO in methane-fired, lean-premixed, high-pressure jet-stirred reactors (HP-JSRs) independently obtained by Rutar [1] and Rutar et al. [2] and by Bengtsson [3] and Bengtsson et al. [4] are well predicted assuming simple chemical reactor models and the GRI 3.0 chemical kinetic mechanism. The single-jet HP-JSR of Rutar [1] and Rutar et al. [2] is well modeled for NOx and CO assuming a single PSR for Damköhler number below 0.15. Under these conditions, the estimates of flame thickness indicate the flame zone, that is, the region of rapid oxidation and large concentrations of free radicals, fully fills the HP-JSR. For Damköhler number above 0.15, that is, for longer residence times, the NOx and CO are well modeled assuming two PSRs in series, representing a small flame zone followed by a large post-flame zone. The multi-jet reactor of Bengtsson [3] and Bengtsson et al. [4] is well modeled assuming a large PSR (over 88% of the reactor volume) followed by a short PFR, which accounts for the exit region of the HP-JSR and the short section of exhaust prior to the sampling point. The Damköhler number is estimated between 0.01 and 0.03. Our modeling shows the NOx formation pathway contributions. Although all pathways, including Zeldovich (under the influence of super-equilibrium O-atom), nitrous oxide, Fenimore prompt, and NNH, contribute to the total NOx predicted, of special note are the following findings: 1) NOx formed by the nitrous oxide pathway is significant throughout the conditions studied; and 2) NOx formed by the Fenimore prompt pathway is significant when the fuel-air equivalence ratio is greater than about 0.7 (as might occur in a piloted lean-premixed combustor) or when the residence time of the flame zone is very short. The latter effect is a consequence of the short lifetime of the CH radical in flames.

The Importance of the Nitrous Oxide Pathway to NOx in Lean-Premixed Combustion

1995 ◽  
Vol 117 (1) ◽  
pp. 100-111 ◽  
Author(s):  
D. G. Nicol ◽  
R. C. Steele ◽  
N. M. Marinov ◽  
P. C. Malte
Keyword(s):  
Nitrous Oxide ◽  
Pressure Dependence ◽  
Porous Plate ◽  
Premixed Combustion ◽  
Nox Formation ◽  
Lean Premixed Combustion ◽  
Turbine Engine ◽  
Stirred Reactor ◽  
Primary Zone ◽  
Lean Premixed

This study addresses the importance of the different chemical pathways responsible for NOx formation in lean-premixed combustion, and especially the role of the nitrous oxide pathway relative to the traditional Zeldovich pathway. NOx formation is modeled and computed over a range of operating conditions for the lean-premixed primary zone of gas turbine engine combustors. The primary zone, of uniform fuel-air ratio, is modeled as a micromixed well-stirred reactor, representing the flame zone, followed by a series of plug flow reactors, representing the postflame zone. The fuel is methane. The fuel–air equivalence ratio is varied from 0.5 to 0.7.The chemical reactor model permits study of the three pathways by which NOx forms, which are the Zeldovich, nitrous oxide, and prompt pathways. Modeling is also performed for the well-stirred reactor alone. Three recently published, complete chemical kinetic mechanisms for the C1–C2 hydrocarbon oxidation and the NOx formation are applied and compared. Verification of the model is based on the comparison of its NOx output to experimental results published for atmospheric pressure jet-stirred reactors and for a 10 atm. porous-plate burner. Good agreement between the modeled results and the measurements is obtained for most of the jet-stirred reactor operating range. For the porous-plate burner, the model shows agreement to the NOx measurements within a factor of two, with close agreement occurring at the leanest and coolest cases examined. For lean-premixed combustion at gas turbine engine conditions, the nitrous oxide pathway is found to be important, though the Zeldovich pathway cannot be neglected. The prompt pathway, however, contributes small-to-negligible NOx. Whenever the NOx emission is in the 15 to 30 ppmυ (15 percent O2, dry) range, the nitrous oxide pathway is predicted to contribute 40 to 45 percent of the NOx for high-pressure engines (30 atm), and 20 to 35 percent of the NOx for intermediate pressure engines (10 atm). For conditions producing NOx of less than 10 ppmυ (15 percent O2, dry), the nitrous oxide contribution increases steeply and approaches 100 percent. For lean-premixed combustion in the atmospheric pressure jet-stirred reactors, different behavior is found. All three pathways contribute; none can be dismissed. No universal behavior is found for the pressure dependence of the NOx. It does appear, however, that lean-premixed combustors operated in the vicinity of 10 atm have a relatively weak pressure dependence, whereas combustors operated in the vicinity of 30 atm have an approximately square root pressure dependence of the NOx.

scholarly journals Experimental Evaluation of a Low Emissions, Variable Geometry, Small Gas Turbine Combustor

1990 ◽  
Author(s):  
K. O. Smith ◽  
M. H. Samii ◽  
H. K. Mak
Keyword(s):  
Gas Turbine ◽  
Experimental Evaluation ◽  
Premixed Combustion ◽  
Nox Emissions ◽  
Variable Geometry ◽  
Test Results ◽  
Gas Turbine Combustor ◽  
Lean Premixed Combustion ◽  
Primary Zone ◽  
Lean Premixed

The results of an on-engine evaluation of an ultra-low NOx, natural gas-fired combustor for a 200 kW gas turbine are presented. The combustor evaluated used lean-premixed combustion to reduce NOx emissions and variable geometry to extend the range over which low emissions were obtained. Test results showed that ultra-low NOx emissions could be achieved from full load down to approximately 50% load through the combination of lean-premixed combustion and variable primary zone airflow.

Numerical Investigation of NOx Emissions Characteristics of a Natural Gas Premixed Burner Based on Chemical Reactor Network Model

2019 ◽  
Author(s):  
Bin Mu ◽  
Fulin Lei ◽  
Weiwei Shao ◽  
Xunwei Liu ◽  
Zhedian Zhang ◽  
...  
Keyword(s):  
Experimental Data ◽  
High Pressure ◽  
Chemical Reactor ◽  
Nox Emission ◽  
Recirculation Region ◽  
Nox Emissions ◽  
Nox Formation ◽  
Chemical Reactor Network ◽  
Thermal Nox ◽  
Reactor Network

Abstract Numerical optimization of nitrogen oxides (NOx) formation is an essential factor during developing low pollution combustor of gas turbine. The Computational Fluid Dynamics-Chemical Reactor Network (CFD-CRN) hybrid method has a great advantage in fast and accurate prediction of combustor NOx emissions. In this work, a hybrid CFD-CRN approach is established to predict pollutant emissions of a lean premixed model burner for gas turbine applications. Several criteria are compared for separating the combustor into chemically and physically homogeneous zones, and the crucial parameters such as residence time and flue gas recirculation ratio are calculated. The CRN model is preliminarily verified with experimental data. The effects of pressure and fuel-air unmixedness on NOx formation are subsequently investigated. In addition, the effects of changes in fuel/air flow distribution and crucial parameters of CRN model on NOx emissions are also estimated under different pressures and fuel-air unmixedness. The combustor is divided into several zones including reaction preheating region, flame front region, flame transition region, post flame region, main recirculation region and corner recirculation region based on CFD results of fuel-air mixing characteristics, velocity field, temperature field, distribution of OH mass fraction and Damkohler number. The complex CRN model has the advantage of predicting NOx emission characteristics under higher Tad conditions compared with the simple model, and its prediction of NOx emission shows good agreement with experimental data under various equivalence ratio conditions. The structure and distribution of several regions of CRN model are analogous but not significant when Reynolds number exceeds 105 under high pressure. The pathway analysis shows that the NOx emission gradually decreases through N2O and NNH mechanisms, resulted from the decreasing concentration of O radical under low Tad and high pressure. However, the pressure could significantly promote thermal NOx formation resulting form increase of temperature. The fuel-air unmixedness results in the increase of maximum flame temperature, which has significant effect on change of the CRN regions-separating. The fuel-air unmixedness causes the significant increasing of thermal NOx formation.

Predictions of NOx Formation Under Combined Droplet and Partially Premixed Reaction of Diffusion Flame Combustors

1999 ◽  
Vol 124 (1) ◽  
pp. 31-38 ◽  
Author(s):  
N. K. Rizk ◽  
J. S. Chin ◽  
A. W. Marshall ◽  
M. K. Razdan
Keyword(s):  
Diffusion Flame ◽  
Liquid Droplet ◽  
Mixture Distribution ◽  
Fuel Vapor ◽  
Nox Emissions ◽  
Gas Temperature ◽  
Nox Formation ◽  
Primary Zone ◽  
Wide Range ◽  
Partially Premixed

A methodology is presented in this paper on the modeling of NOx formation in diffusion flame combustors where both droplet burning and partially premixed reaction proceed simultaneously. The model simulates various combustion zones with an arrangement of reactors that are coupled with a detailed chemical reaction scheme. In this model, the primary zone of the combustor comprises a reactor representing contribution from droplet burning under stoichiometric conditions and a mixing reactor that provides additional air or fuel to the primary zone. The additional flow allows forming a fuel vapor/air mixture distribution that reflects the unmixedness nature of the fuel injection process. Expressions to estimate the extent of deviation in fuel/air ratios from the mean value, and the duration of droplet burning under stoichiometric conditions were derived. The derivation of the expressions utilized a data base obtained in a parametric study performed using a conventional gas turbine combustor where the primary zone equivalence ratio varied over a wide range of operation. The application of the developed model to a production combustor indicated that most of the NOx produced under the engine takeoff mode occurred in the primary as well as the intermediate regions. The delay in NOx formation is attributed to the operation of the primary zone under fuel rich conditions resulting in a less favorable condition for NOx formation. The residence time for droplet burning increased with a decrease in engine power. The lower primary zone gas temperature that limits the spray evaporation process coupled with the leaner primary zone mixtures under idle and low power modes increases the NOx contribution from liquid droplet combustion in diffusion flames. Good agreement was achieved between the measured and calculated NOx emissions for the production combustor. This indicates that the simulation of the diffusion flame by a combined droplet burning and fuel vapor/air mixture distribution offers a promising approach for estimating NOx emissions in combustors, in particular for those with significant deviation from traditional stoichiometry in the primary combustion zone.

scholarly journals Variables Affecting NOx Formation in Lean-Premixed Combustion

1997 ◽  
Vol 119 (1) ◽  
pp. 102-107 ◽  
Author(s):  
R. C. Steele ◽  
A. C. Jarrett ◽  
P. C. Malte ◽  
J. H. Tonouchi ◽  
D. G. Nicol
Keyword(s):  
Residence Time ◽  
Combustion Temperature ◽  
Flow Reactor ◽  
Plug Flow ◽  
Volume Ratio ◽  
Chemical Reactor ◽  
Inlet Temperature ◽  
Reactor Model ◽  
Reactor Modeling ◽  
Lean Premixed

The formation of NOx in lean-premixed, high-intensity combustion is examined as a function of several of the relevant variables. The variables are the combustion temperature and pressure, fuel type, combustion zone residence time, mixture inlet temperature, reactor surface-to-volume ratio, and inlet jet size. The effects of these variables are examined by using jet-stirred reactors and chemical reactor modeling. The atmospheric pressure experiments have been completed and are fully reported. The results cover the combustion temperature range (measured) of 1500 to 1850 K, and include the following four fuels: methane, ethylene, propane, and carbon monoxide/hydrogen mixtures. The reactor residence time is varied from 1.7 to 7.4 ms, with most of the work done at 3.5 ms. The mixture inlet temperature is taken as 300 and 600 K, and two inlet jet sizes are used. Elevated pressure experiments are reported for pressures up to 7.1 atm for methane combustion at 4.0 ms with a mixture inlet temperature of 300 K. Experimental results are compared to chemical reactor modeling. This is accomplished by using a detailed chemical kinetic mechanism in a chemical reactor model, consisting of a perfectly stirred reactor (PSR) followed by a plug flow reactor (PFR). The methane results are also compared to several laboratory-scale and industrial-scale burners operated at simulated gas turbine engine conditions.

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