Chemical Kinetic Modeling of Ignition and Emissions From Natural Gas and LNG Fueled Gas Turbines

2012 ◽  
Author(s):  
P. Gokulakrishnan ◽  
C. C. Fuller ◽  
R. G. Joklik ◽  
M. S. Klassen
Keyword(s):  
Natural Gas ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Chemical Kinetic ◽  
Higher Order ◽  
Premixed Combustion ◽  
Nox Emissions ◽  
Lean Premixed Combustion ◽  
Lean Premixed ◽  
Combustion Systems

Single digit NOx emission targets as part of gas turbine design criteria require highly accurate modeling of the various NOx formation pathways. The concept of lean, premixed combustion is adopted in various gas turbine combustor designs, which achieves lower NOx levels by primarily lowering the flame temperature. At these conditions, the post-flame thermal-NOx pathway contribution to the total NOx can be relatively small compared to that from the prompt-NOx and the N2O-route, which are enhanced by the super-equilibrium radical pathway at the flame front. In addition, new sources of natural gas fuel (e.g., imported LNG) with widely varying chemical compositions including higher order hydrocarbon components, impact flame stability, lean blow-out limits and emissions in existing lean premixed combustion systems. Also, the presence of higher order hydrocarbons can increase the risk of flashback induced by autoignition in the premixing section of the combustor. In this work a detailed chemical kinetic model was developed for natural gas fuels that consist of CH4, C2H6, C3H8, nC4H10, iC4H10, and small amounts of nC5H12, iC5H12 and nC6H14 in order to predict ignition behavior at typical gas turbine premixing conditions and to predict CO and NOx emissions at lean premixed combustion conditions. The model was validated for different NOx-pathways using low and high pressure laminar premixed flame data. The model was also extended to include a vitiated kinetic scheme to account for the influence of exhaust gas recirculation on fuel oxidation. The model was employed in a chemical reactor network to simulate a laboratory scale lean premixed combustion system to predict CO and NOx. The current kinetic mechanism demonstrates good predictive capability for NOx emissions at lower temperatures typical of practical lean premixed combustion systems.

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.

Experimental and Numerical Characterization of Lean Hydrogen Combustion in a Premix Burner Prototype

2011 ◽  
Author(s):  
Iarno Brunetti ◽  
Giovanni Riccio ◽  
Nicola Rossi ◽  
Alessandro Cappelletti ◽  
Lucia Bonelli ◽  
...  
Keyword(s):  
Natural Gas ◽  
Gas Turbine ◽  
Hydrogen Content ◽  
Premixed Combustion ◽  
Nox Emissions ◽  
Cfd Model ◽  
Air Velocity ◽  
Lean Premixed Combustion ◽  
Lean Premixed

The use of hydrogen as derived fuel for low emission gas turbine is a crucial issue of clean coal technology power plant based on IGCC (Integrated Gasification Combined Cycle) technology. Control of NOx emissions in gas turbines supplied by natural gas is effectively achieved by lean premixed combustion technology; conversely, its application to NOx emission reduction in high hydrogen content fuels is not a reliable practice yet. Since the hydrogen premixed flame is featured by considerably higher flame speed than natural gas, very high air velocity values are required to prevent flash-back phenomena, with obvious negative repercussions on combustor pressure drop. In this context, the characterization of hydrogen lean premixed combustion via experimental and modeling analysis has a special interest for the development of hydrogen low NOx combustors. This paper describes the experimental and numerical investigations carried-out on a lean premixed burner prototype supplied by methane-hydrogen mixture with an hydrogen content up to 100%. The experimental activities were performed with the aim to collect practical data about the effect of the hydrogen content in the fuel on combustion parameters as: air velocity flash-back limit, heat release distribution, NOx emissions. This preliminary data set represents the starting point for a more ambitious project which foresees the upgrading of the hydrogen gas turbine combustor installed by ENEL in Fusina (Italy). The same data will be used also for building a computational fluid dynamic (CFD) model usable for assisting the design of the upgraded combustor. Starting from an existing heavy-duty gas turbine burner, a burner prototype was designed by means of CFD modeling and hot-wire measurements. The geometry of the new premixer was defined in order to control turbulent phenomena that could promote the flame moving-back into the duct, to increase the premixer outlet velocity and to produce a stable central recirculation zone in front of the burner. The burner prototype was then investigated during a test campaign performed at the ENEL’s TAO test facility in Livorno (Italy) which allows combustion test at atmospheric pressure with application of optical diagnostic techniques. In-flame temperature profiles, pollutant emissions and OH* chemiluminescence were measured over a wide range of the main operating parameters for three fuels with different hydrogen content (0, 75% and 100% by vol.). Flame control on burner prototype fired by pure hydrogen was achieved by managing both the premixing degree and the air discharge velocity, affecting the NOx emissions and combustor pressure losses respectively. A CFD model of the above-mentioned combustion test rig was developed with the aim to validate the model prediction capabilities and to help the experimental data analysis. Detailed simulations, performed by a CFD 3-D RANS commercial code, were focused on air/fuel mixing process, temperature field, flame position and NOx emission estimation.

Application of Thermal Oxidation to a Recuperated Gas Turbine: The Path to PPB NOx Emissions

2013 ◽  
Author(s):  
Jeffrey Armstrong ◽  
Douglas Hamrin ◽  
Steve Lampe
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Fuel Injection ◽  
Landfill Gas ◽  
Premixed Combustion ◽  
Nox Emissions ◽  
Single Digit ◽  
Lean Premixed Combustion ◽  
Lean Premixed ◽  
Order Of Magnitude

Dry, low NOx emissions developments in the industrial gas turbine industry have focused on lean-premixed combustion to reduce NOx to single digit parts-per-million (ppmV) emissions. The reduction of thermal NOx is limited by the lowest lean-premix combustion temperatures. To overcome this limit, a thermal oxidizer is applied which can oxidize hydrocarbon fuels at temperatures below those of lean-premixed combustion in a Brayton cycle. This oxidation technique is explained in a combustion taxonomy model. This paper presents the historical development and demonstration of technology with two different recuperated gas turbines operating on landfill gas. A unique fuel-injection strategy was used to introduce the fuel into the inlet of the gas turbine’s air compressor. The technology demonstrated an order-of-magnitude reduction in the emissions of NOx to the parts-per-billion range.

Development of a Dual-Fuel Injection System for Lean Premixed Industrial Gas Turbines

1996 ◽  
Author(s):  
Luke H. Cowell ◽  
Amjad Rajput ◽  
Douglas C. Rawlins
Keyword(s):  
Natural Gas ◽  
Gas Turbines ◽  
Liquid Fuel ◽  
Fuel Injection ◽  
Premixed Combustion ◽  
Injection System ◽  
Fuel Injection System ◽  
Load Range ◽  
Lean Premixed Combustion ◽  
Lean Premixed

A fuel injection system for industrial gas turbine engines capable of using natural gas and liquid fuel in dry, lean premixed combustion is under development to significantly reduce NOx and CO emissions. The program has resulted in a design capable of operating on DF#2 over the 80 to 100% engine load range meeting the current TA LUFT regulations of 96 ppm (dry, @ 15% O2) NOx and 78 ppm CO. When operating on natural gas the design meets the guaranteed levels of 25 ppm NOx and 50 ppm CO. The design approach is to apply lean premixed combustion technology to liquid fuel. Both injector designs introduce the majority of the diesel fuel via airblast alomization into a premixing passage where fuel vaporization and air-fuel premixing occur. Secondary fuel injection occurs through a pilot fuel passage which operates in a partially premixed mode. Development is completed through injector modeling, flow visualization, combustion rig testing, and engine testing. The prototype design tested in development engine environments has operated with NOx emissions below 65 ppm and 20 ppm CO at full load. This paper includes a detailed discussion of the injector design and qualification testing completed on this development hardware.

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.

Suppression of Dynamic Combustion Instabilities by Passive and Active Means

2000 ◽  
Author(s):  
Peter Berenbrink ◽  
Stefan Hoffmann
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Premixed Combustion ◽  
Combustion Instabilities ◽  
Active System ◽  
Lean Premixed Combustion ◽  
Exit Nozzle ◽  
Lean Premixed ◽  
Dynamic Combustion ◽  
Suppression Of Combustion

In the gas turbine industry, lean premixed combustion is a state-of-the-art technology for the reduction of NOx emissions. Due to the ever increasing reaction densities and turbine inlet temperatures in modern gas turbines, the combustors reveal an increased tendency to form dynamic combustion instabilities. This paper reports on the use of passive and active methods for the suppression of combustion oscillations in heavy-duty gas turbines featuring lean premixed combustion: Modifications of the burner exit nozzle are implemented in order to avoid fluiddynamic feedback and to change the acoustic behavior of the flame. An asymmetric circumferential distribution of flames with different thermoacoustic responses serves to avoid or at least attenuate the self-excitation within the combustor in multiburner systems. In some applications, these methods are successfully coupled with an active system for the suppression of combustion instabilities (AIC) to further extend the operation envelope. Field demonstrations in different Siemens gas turbines serve to demonstrate the benefit and flexibility of these measures for practical gas turbine combustion systems.

A Novel Low NOx Lean, Premixed, and Prevaporized Combustion System for Liquid Fuels

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
P. Gokulakrishnan ◽  
M. J. Ramotowski ◽  
G. Gaines ◽  
C. Fuller ◽  
R. Joklik ◽  
...  
Keyword(s):  
Natural Gas ◽  
Ignition Delay ◽  
Pilot Scale ◽  
Combustion Characteristics ◽  
Premixed Combustion ◽  
Liquid Fuels ◽  
Combustion System ◽  
Lean Premixed Combustion ◽  
Lean Premixed ◽  
Combustion Systems

Dry low emission (DLE) systems employing lean, premixed combustion have been successfully used with natural gas in combustion turbines to meet stringent emission standards. However, the burning of liquid fuels in DLE systems is still a challenging task due to the complexities of fuel vaporization and air premixing. Lean, premixed, and prevaporized (LPP) combustion has always provided the promise of obtaining low pollutant emissions while burning liquid fuels, such as kerosene and fuel oil. Because of the short ignition delay times of these fuels at elevated temperatures, the autoignition of vaporized higher hydrocarbons typical of most practical liquid fuels has been proven difficult to overcome when burning in a lean, premixed mode. To avoid this autoignition problem, developers of LPP combustion systems have focused mainly on designing premixers and combustors that permit rapid mixing and combustion of fuels before spontaneous ignition of the fuel can occur. However, none of the reported works in the literature has looked at altering fuel combustion characteristics in order to delay the onset of ignition in lean, premixed combustion systems. The work presented in this paper describes the development of a patented low NOx LPP system for combustion of liquid fuels, which modifies the fuel rather than the combustion hardware in order to achieve LPP combustion. In the initial phase of the development, laboratory-scale experiments were performed to study the combustion characteristics, such as ignition delay time and NOx formation, of the liquid fuels that were vaporized into gaseous form in the presence of nitrogen diluent. In the second phase, a LPP combustion system was commissioned to perform pilot-scale tests on commercial turbine combustor hardware. These pilot-scale tests were conducted at typical compressor discharge temperatures and at both atmospheric and high pressures. In this study, vaporization of the liquid fuel in an inert environment has been shown to be a viable method for delaying autoignition and for generating a gaseous fuel stream with characteristics similar to natural gas. Tests conducted in both atmospheric and high pressure combustor rigs utilizing swirl-stabilized burners designed for natural gas demonstrated an operation similar to that obtained when burning natural gas. Emission levels were similar for both the LPP fuels (fuel oils 1 and 2) and natural gas, with any differences ascribed to the fuel-bound nitrogen present in the liquid fuels. An extended lean operation was observed for the liquid fuels as a result of the wider lean flammability range for these fuels compared to natural gas.

scholarly journals Measurement of Air-Fuel Ratio Fluctuations Caused by Combustor Driven Oscillations

1998 ◽  
Author(s):  
Rajiv Mongia ◽  
Robert Dibble ◽  
Jeff Lovett
Keyword(s):  
Power Spectrum ◽  
Mole Fraction ◽  
Gas Turbines ◽  
Operating Conditions ◽  
Premixed Combustion ◽  
Pollutant Emissions ◽  
Combustion Instabilities ◽  
Pressure Oscillations ◽  
Lean Premixed Combustion ◽  
Lean Premixed

Lean premixed combustion has emerged as a method of achieving low pollutant emissions from gas turbines. A common problem of lean premixed combustion is combustion instability. As conditions inside lean premixed combustors approach the lean flammability limit, large pressure variations are encountered. As a consequence, certain desirable gas turbine operating regimes are not approachable. In minimizing these regimes, combustor designers must rely upon trial and error because combustion instabilities are not well understood (and thus difficult to model). When they occur, pressure oscillations in the combustor can induce fluctuations in fuel mole fraction that can augment the pressure oscillations (undesirable) or dampen the pressure oscillations (desirable). In this paper, we demonstrate a method for measuring the fuel mole fraction oscillations which occur in the premixing section during combustion instabilities produced in the combustor that is downstream of the premixer. The fuel mole fraction in the premixer is measured with kHz resolution by the absorption of light from a 3.39 μm He-Ne laser. A sudden expansion combustor is constructed to demonstrate this fuel mole fraction measurement technique. Under several operating conditions, we measure significant fuel mole fraction fluctuations that are caused by pressure oscillations in the combustion chamber. Since the fuel mole fraction is sampled continuously, a power spectrum is easily generated. The fuel mole fraction power spectrum clearly indicates fuel mole fraction fluctuation frequencies are the same as the pressure fluctuation frequencies under some operating conditions.

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