Detailed Examination of Two-Staged Micro Gas Turbine Combustor

2016 ◽  
Author(s):  
A. Schwärzle ◽  
T. O. Monz ◽  
M. Aigner
Keyword(s):  
Gas Turbine ◽  
Flame Stabilization ◽  
Optimum Operating ◽  
Stable Operation ◽  
Main Stage ◽  
Nox Emissions ◽  
Residence Times ◽  
Original Design ◽  
Micro Gas Turbine ◽  
Operating Range

Jet-stabilized combustion is a promising technology for fuel flexible, reliable, highly efficient combustion systems. In this work, experiments have been carried out on a two-staged combustor, with a jet-stabilized main stage and a swirl-stabilized pilot stage. Both stages have been run separately to allow a more detailed understanding of the flame stabilization within the combustor and its range of stable operation. All experiments were conducted at atmospheric pressure and preheating temperatures of 650 °C. The air was fed to both stages of the combustor for all experiments. The flame was analyzed in terms of shape, length and lift-off height, using the OH* chemiluminescence signal detected by an ICCD-camera. Emission measurements for NOx, CO and UHC emissions were carried out. The pilot stage was examined at a local air number between 0.14 and 1.43, which corresponds to a global air number of 2.0 to 20.7. For lowest air numbers, the combustor works with the RQL principle with lowest emissions in pilot stage only operation. This is because the remaining fuel fed to the pilot stage mixes rapidly with the air from the main stage and reacts under lean conditions. The optimum operating range of the main stage is at global air numbers between 3 and 3.2 with a blow-off limit beyond λg = 4.0. At a global air number of λg = 2, a fuel split variation was carried out from 0 (only pilot stage) to 1 (only main stage). In combined operation and at higher fuel splits, the NOx emissions are reduced compared to the main stage only operation, while the opposing effect on NOx emissions was observed for lower fuel splits. CFD simulations of the combustor test rig showed higher residence times in the pilot stage compared to the main stage which facilitates higher NOx formation rates in the pilot stage. This could be improved by a geometry optimization. The operation of the pilot stage was beneficial at fuel splits above 90 %, especially concerning an extended operating range to higher global air numbers. In addition, the capability of the combustor to operate at higher thermal power inputs was investigated. Originally designed for the Turbec T100 micro gas turbine, the combustor was operated at 160% of the original design point. At a constant air number, this led to a decrease in NOx and to an increase in CO emissions, caused by shorter residence times in the combustion chamber at higher power input. An operation strategy of constant pilot air number increases the envelope of a stable operation regime further.

scholarly journals Detailed Examination of a Modified Two-Stage Micro Gas Turbine Combustor

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Andreas Schwärzle ◽  
Thomas O. Monz ◽  
Andreas Huber ◽  
Manfred Aigner
Keyword(s):  
Gas Turbine ◽  
Detailed Examination ◽  
Flame Stabilization ◽  
Nox Emissions ◽  
Gas Turbine Combustor ◽  
Two Stage ◽  
Micro Gas Turbine ◽  
Previous Design ◽  
Recirculation Zones ◽  
Asme Paper

Jet-stabilized combustion is a promising technology for fuel flexible, reliable, highly efficient combustion systems. The aim of this work is a reduction of NOx emissions of a previously published two-stage micro gas turbine (MGT) combustor (Zanger et al., 2015, “Experimental Investigation of the Combustion Characteristics of a Double-Staged FLOX-Based Combustor on an Atmospheric and a Micro Gas Turbine Test Rig,” ASME Paper No. GT2015-42313 and Schwärzle et al., 2016, “Detailed Examination of Two-Stage Micro Gas Turbine Combustor,” ASME Paper No. GT2016-57730), where the pilot stage (PS) of the combustor was identified as the main contributor to NOx emissions. The geometry optimization was carried out regarding the shape of the pilot dome and the interface between PS and main stage (MS) in order to prevent the formation of high-temperature recirculation zones. Both stages have been run separately to allow a detailed understanding of the flame stabilization within the combustor, its range of stable combustion, the interaction between both stages, and the influence of the modified geometry. All experiments were conducted at atmospheric pressure and an air preheat temperature of 650  °C. The flame was analyzed in terms of shape, length, and lift-off height, using OH* chemiluminescence (OH-CL) images. Emission measurements for NOx, CO, and unburned hydrocarbons (UHC) emissions were carried out. At a global air number of λ = 2, a fuel split variation was carried out from 0 (only PS) to 1 (only MS). The modification of the geometry leads to a decrease in NOx and CO emissions throughout the fuel split variation in comparison with the previous design. Regarding CO emissions, the PS operations are beneficial for a fuel split above 0.8. The local maximum in NOx emissions observed for the previous combustor design at a fuel split of 0.78 was not apparent for the modified design. NOx emissions were increasing, when the local air number of the PS was below the global air number. In order to evaluate the influence of the modified design on the flow field and identify the origin of the emission reduction compared to the previous design, unsteady Reynolds-averaged Navier–Stokes simulations were carried out for both geometries at fuel splits of 0.93 and 0.78, respectively, using the DLR (German Aerospace Center) in-house code turbulent heat release extension of the tau code (theta) with the k–ω shear stress transport turbulence model and the DRM22 (Kazakov and Frenklach, 1995, “DRM22,” University of California at Berkeley, Berkeley, CA, accessed Sept. 21, 2017, http://www.me.berkeley.edu/drm/) detailed reaction mechanism. The numerical results showed a strong influence of the recirculation zones on the PS reaction zone.

scholarly journals Optical Measurements of a Lower Calorific Values-Combustor Operated in a Micro Gas Turbine With Various Fuel Compositions

2018 ◽  
Vol 141 (4) ◽  
Author(s):  
Timo Zornek ◽  
Thomas Mosbach ◽  
Manfred Aigner
Keyword(s):  
Gas Turbine ◽  
Recirculation Zone ◽  
Pollutant Emissions ◽  
Stable Operation ◽  
Oh Radicals ◽  
Main Stage ◽  
High Hydrogen ◽  
Micro Gas Turbine ◽  
Joint Research Project ◽  
Flame Behavior

In a recent joint research project, a new FLOX®-combustion system was developed to couple a fixed-bed gasifier with a micro gas turbine (MGT). Product gases from biomass gasification exhibit low calorific values and varying compositions of mainly H2, CO, CO2, N2, and CH4. Furthermore, combustion characteristics differ significantly compared to the commonly used natural gas. As the FLOX-technology is considered as efficient and fuel-flexible featuring low emissions of hazardous pollutants, the design of the lower calorific value (LCV) combustor is based on it. It contains a two-staged combustor consisting of a jet-stabilized main stage adapted from the FLOX-concept combined with a swirl stabilized pilot stage. The combustor was operated in a Turbec T100 test rig using an optically accessible combustion chamber, which allowed OH*-chemiluminescence and OH-PLIF measurements for various fuel compositions. In particular, the hydrogen content in the synthetically mixed fuel gas was varied from 0% to 30%. The exhaust gas composition was additionally analyzed regarding CO, NOx, and unburned hydrocarbons. The results provide a comprehensive insight into the flame behavior during turbine operation. Efficient combustion and stable operation of the MGT was observed for all fuel compositions, while the hydrogen showed a strong influence. It is remarkable that with hydrogen contents higher than 9%, no OH radicals were detected within the inner recirculation zone, while they were increasingly entrained below hydrogen contents of 9%. Without hydrogen, the inner recirculation zone was completely filled with OH radicals and the highest concentrations were detected there. Therefore, the results indicate a different flame behavior with low and high hydrogen contents. Although the flame shape and position were affected, pollutant emissions remained consistently below 10 ppm based on 15% O2. Only in the case of 0% hydrogen, CO-emissions increased to 43 ppm, which are still meeting the emission limits. Thus, the combustor allows operation with syngases having hydrogen contents from 0% to 30%.

scholarly journals Optical Measurements of a LCV-Combustor Operated in a Micro Gas Turbine With Various Fuel Compositions

2018 ◽  
Author(s):  
Timo Zornek ◽  
Thomas Mosbach ◽  
Manfred Aigner
Keyword(s):  
Gas Turbine ◽  
Recirculation Zone ◽  
Pollutant Emissions ◽  
Stable Operation ◽  
Oh Radicals ◽  
Main Stage ◽  
High Hydrogen ◽  
Micro Gas Turbine ◽  
Joint Research Project ◽  
Flame Behaviour

In a recent joint research project, a new FLOX®-combustion system was developed to couple a fixed-bed gasifier with a micro gas turbine. Product gases from biomass gasification exhibit low calorific values and varying compositions of mainly H2, CO, CO2, N2 and CH4. Furthermore, combustion characteristics differ significantly compared to the commonly used natural gas. As the FLOX®-technology is considered as efficient and fuel-flexible featuring low emissions of hazardous pollutants, the design of the LCV-combustor is based on it. It contains a two-staged combustor consisting of a jet-stabilized main stage adapted from the FLOX®-concept combined with a swirl stabilized pilot stage. The combustor was operated in a Turbec T100 test rig using an optically accessible combustion chamber, which allowed OH*-chemiluminescence and OH-PLIF measurements for various fuel compositions. In particular, the hydrogen content in the synthetically mixed fuel gas was varied from 0 % to 30 %. The exhaust gas composition was additionally analysed regarding CO, NOx and unburned hydrocarbons. The results provide a comprehensive insight into the flame behaviour during turbine operation. Efficient combustion and stable operation of the micro gas turbine was observed for all fuel compositions, while the hydrogen showed a strong influence. It is remarkable, that with hydrogen contents higher than 9 % no OH radicals were detected within the inner recirculation zone, while they were increasingly entrained below hydrogen contents of 9 %. Without hydrogen, the inner recirculation zone was completely filled with OH radicals and the highest concentrations were detected there. Therefore, the results indicate a different flame behaviour with low and high hydrogen contents. Although the flame shape and position was affected, pollutant emissions remained consistent below 10 ppm based on 15% O2. Only in case of 0% hydrogen, CO-emissions increased to 43 ppm, which is still meeting the emission limits. Thus, the combustor allows operation with syngases having hydrogen contents from 0% to 30%.

Model Analysis of Syngas Combustion and Emissions for a Micro Gas Turbine

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Chi-Rong Liu ◽  
Hsin-Yi Shih
Keyword(s):  
Gas Turbine ◽  
Flow Rate ◽  
Heat Input ◽  
Emission Characteristics ◽  
Nox Emissions ◽  
Fuel Flow Rate ◽  
Micro Gas Turbine ◽  
Fuel Flow ◽  
Temperature Distributions ◽  
Flame Structures

The purpose of this study is to investigate the combustion and emission characteristics of syngas fuels applied in a micro gas turbine, which is originally designed for a natural gas fired engine. The computation results were conducted by a numerical model, which consists of the three-dimension compressible k–ε model for turbulent flow and PPDF (presumed probability density function) model for combustion process. As the syngas is substituted for methane, the fuel flow rate and the total heat input to the combustor from the methane/syngas blended fuels are varied with syngas compositions and syngas substitution percentages. The computed results presented the syngas substitution effects on the combustion and emission characteristics at different syngas percentages (up to 90%) for three typical syngas compositions and the conditions where syngas applied at fixed fuel flow rate and at fixed heat input were examined. Results showed the flame structures varied with different syngas substitution percentages. The high temperature regions were dense and concentrated on the core of the primary zone for H2-rich syngas, and then shifted to the sides of the combustor when syngas percentages were high. The NOx emissions decreased with increasing syngas percentages, but NOx emissions are higher at higher hydrogen content at the same syngas percentage. The CO2 emissions decreased for 10% syngas substitution, but then increased as syngas percentage increased. Only using H2-rich syngas could produce less carbon dioxide. The detailed flame structures, temperature distributions, and gas emissions of the combustor were presented and compared. The exit temperature distributions and pattern factor (PF) were also discussed. Before syngas fuels are utilized as an alternative fuel for the micro gas turbine, further experimental testing is needed as the modeling results provide a guidance for the improved designs of the combustor.

Combustion Characteristics of Small Size Gas Turbine Combustor Fueled by Biomass Gas Employing Flameless Combustion

2007 ◽  
Author(s):  
Masato Hiramatsu ◽  
Yoshifumi Nakashima ◽  
Sadamasa Adachi ◽  
Yudai Yamasaki ◽  
Shigehiko Kaneko
Keyword(s):  
Gas Turbine ◽  
Combustion Efficiency ◽  
Combustion Characteristics ◽  
Operating Conditions ◽  
Nox Emissions ◽  
Gas Turbine Combustor ◽  
Flameless Combustion ◽  
Engine Exhaust ◽  
Micro Gas Turbine

One approach to achieving 99% combustion efficiency (C.E.) and 10 ppmV or lower NOx (at 15%O2) in a micro gas turbine (MGT) combustor fueled by biomass gas at a variety of operating conditions is with the use of flameless combustion (FLC). This paper compares experimentally obtained results and CHEMKIN analysis conducted for the developed combustor. As a result, increase the number of stage of FLC combustion enlarges the MGT operation range with low-NOx emissions and high-C.E. The composition of fuel has a small effect on the characteristics of ignition in FLC. In addition, NOx in the engine exhaust is reduced by higher levels of CO2 in the fuel.

Fuel Flexibility Test Campaign on a GE10 Gas Turbine: Experimental and Numerical Results

2006 ◽  
Author(s):  
Antonio Andreini ◽  
Bruno Facchini ◽  
Luca Mangani ◽  
Stefano Cocchi ◽  
Roberto Modi
Keyword(s):  
Natural Gas ◽  
Gas Turbine ◽  
Load Condition ◽  
Co2 Concentration ◽  
Flame Stabilization ◽  
Pollutant Emissions ◽  
Nox Emissions ◽  
Predictive Tool ◽  
Fuel Flexibility ◽  
Base Load

Medium- and low-LHV fuels are receiving a continuously growing interest in stationary power applications. Besides that, since in many applications the fuels available at a site can be time by time of significantly different composition, fuel flexibility has become one of the most important requirements to be taken into account in developing power systems. A test campaign, aimed to provide a preliminary assessment of a small power gas turbine’s fuel flexibility, was carried over a full-scale GE10 prototypical unit, located at the Nuovo-Pignone manufacturing site, in Florence. The engine is a single shaft, simple cycle gas turbine designed for power generation applications, rated at 11 MW electrical power and equipped with a silos-type combustor. A variable composition gas fuel was obtained by mixing natural gas with CO2 to about 40% by vol. at engine base-load condition. Tests involved two different diffusive combustion systems: the standard version, designed for operation with natural gas, and a specific system designed for low-LHV fuels. Tests performed aimed to investigate both ignition limits and combustors’ performances, focusing on hot parts’ temperatures and pollutant emissions. Regarding NOx emissions, data collected during standard combustor’s tests were matched a simple scaling law (as a function of cycle parameters and CO2 concentration in the fuel mixture), which can be used in similar applications as a NOx predictive tool. In a following step, a CFD study was performed in order to verify in detail the effects of LHV reduction on flame structure and to compare measured and calculated NOx. STAR-CD™ code was employed as main CFD solver while turbulent combustion and NOx models were specifically developed and implemented using STAR’s user-subroutine features. Both models are based on classical laminar-flamelet approach. Three different operating points were considered at base-load conditions, varying CO2 concentration (0%, 20% and 30% vol. simulated). Numerical simulations point out the flexibility of the GE10 standard combustor to assure flame stabilization even against large variation of fuel characteristics. Calculated NOx emissions are in fairly good agreement with measured data confirming the validity of the adopted models.

Detailed Examination of a Modified Two-Staged Micro Gas Turbine Combustor

2017 ◽  
Author(s):  
A. Schwärzle ◽  
T. O. Monz ◽  
A. Huber ◽  
M. Aigner
Keyword(s):  
Geometry Optimization ◽  
Local Maximum ◽  
Detailed Examination ◽  
Flame Stabilization ◽  
Main Stage ◽  
Nox Emissions ◽  
Sst Turbulence Model ◽  
Previous Design ◽  
Recirculation Zones ◽  
Lift Off

Jet-stabilized combustion is a promising technology for fuel flexible, reliable, highly efficient combustion systems. The aim of this work is a reduction of NOx emissions of a previously published two-staged MGT combustor [1, 2], where the pilot stage of the combustor was identified as the main contributor to NOx emissions. The geometry optimization was carried out regarding the shape of the pilot dome and the interface between pilot and main stage in order to prevent the formation of high temperature recirculation zones. Both stages have been run separately to allow a detailed understanding of the flame stabilization within the combustor, its range of stable combustion, the interaction between both stages and the influence of the modified geometry. All experiments were conducted at atmospheric pressure and an air preheat temperature of 650 °C. The flame was analyzed in terms of shape, length and lift-off height, using OH* chemiluminescence images. Emission measurements for NOx, CO and UHC emissions were carried out. At a global air number of λ = 2, a fuel split variation was carried out from 0 (only pilot-stage) to 1 (only main stage). The modification of the geometry lead to a decrease in NOx and CO emissions throughout the fuel split variation in comparison with the previous design. Regarding CO emissions, the pilot stage operations is beneficial for a fuel split above 0.8. The local maximum in NOx emissions observed for the previous combustor design at a fuel split of 0.78 was not apparent for the modified design. NOx emissions were increasing, when the local air number of the pilot stage was below the global air number. In order to evaluate the influence of the modified design on the flow field and identify the origin of the emission reduction compared to the previous design, unsteady RANS simulations were carried out for both geometries at fuel splits of 0.93 and 0.78, respectively, using the DLR in-house code THETA with the k-w SST turbulence model and the DRM22 [3] detailed reaction mechanism. The numerical results showed a strong influence of the recirculation zones on the pilot stage reaction zone.

Numerical Modelling of NOx Emissions and Flame Stabilization Mechanisms in Gas Turbine Burners Operating With Hydrogen and Hydrogen-Methane Blends

2020 ◽  
Author(s):  
Roberto Meloni ◽  
Matteo Cerutti ◽  
Alessandro Zucca ◽  
Maurizio Mazzoni
Keyword(s):  
Gas Turbine ◽  
Fuel Injection ◽  
Laminar Flame ◽  
Numerical Models ◽  
Flame Stabilization ◽  
Combustion Model ◽  
Pure Hydrogen ◽  
Nox Emissions ◽  
Paper Test ◽  
Annular Combustor

Abstract Main objective of this paper is to assess the capability of numerical models in predicting NOx emissions and flame stabilization mechanisms of a heavy-duty gas turbine burner when operated with hydrogen and hydrogen-methane blends. Effort focused on the selection of the proper input to pre-tabulated Flamelet Generation Manifold combustion model. A dedicated sensitivity to laminar flame speed formulation has been performed as well, since it primarily affects flame stabilization through the closure term of the progress variable transport equation. Available NOx emissions data from full scale annular combustor rig test with hydrogen-air mixtures are presented first in this paper: test results have been used to validate the numerical setup for the reference geometry. Then, the model has been used to predict NOx emissions of alternative geometries in case of pure hydrogen, allowing screening of viable options to reduce the scope of a dedicated test campaign. Concerning flame stabilization mechanisms, simulations have been carried out for a reference geometry first: data from dedicated tests have been used to specialize the tool. Results of modified geometries are shown, to explore the effect of different fuel injection patterns or internal channel modifications. Based on the analysis outcomes, a discussion is provided regarding advantages and drawbacks of each proposed solution, as well as the ability of modelling setup in catching varied flame stabilization mechanisms.

NOx-Formation and CO-Burnout in Water Injected, Premixed Natural Gas Flames at Typical Gas Turbine Combustor Residence Times

2017 ◽  
Author(s):  
Stephan Lellek ◽  
Thomas Sattelmayer
Keyword(s):  
Gas Turbine ◽  
Water Droplet ◽  
Equivalence Ratio ◽  
Water Injection ◽  
Power Production ◽  
Nox Emissions ◽  
Residence Times ◽  
Gas Turbine Combustor ◽  
Reaction Progress ◽  
Progress Variable

With the transition of the power production markets towards renewable energy sources an increased demand for flexible, fossil based power production systems arises. Steep load gradients and a high range of flexibility make gas turbines a core technology in this ongoing change. In order to further increase this flexibility research on power augmentation of premixed gas turbine combustors is conducted at the Lehrstuhl für Thermodynamik, TU München. Water injection in gas turbine combustors allows for the simultaneous control of NOx emissions as well as the increase of the power output of the engine and has therefore been transferred to a premixed combustor at lab scale. So far stable operation of the system has been obtained for water-to-fuel ratios up to 2.25 at constant adiabatic flame temperatures. This paper focuses on the effects of water injection on pollutant formation in premixed gas turbine flames. In order to guarantee for high practical relevance experimental measurements are conducted at typical preheating temperatures and common gas turbine combustor residence times of about 20 ms. Spatially resolved and global species measurements are performed in an atmospheric single burner test rig for typical adiabatic flame temperatures between 1740 and 2086 K. Global measurements of NOx and CO emissions are shown for a wide range of equivalence ratios and variable water-to-fuel ratios. Cantera calculations are used to identify non-equilibrium processes in the measured data. To get a close insight into the emission formation processes in water injected flames local concentration measurements are used to calculate distributions of the reaction progress variable. Finally, to clarify the influence of spray quality on the composition of the exhaust gas a variation of the water droplet diameters is done. For rising water content at constant adiabatic flame temperature the NOx emissions can be held constant, whereas CO concentrations increase. On the contrary, both values decrease for measurements at constant equivalence ratio and reduced flame temperatures. Further analysis of the data shows the close dependency of CO concentration on the equivalence ratio, however, due to the water addition a shift of the CO curves can be detected. In the local measurements changes in the distribution of the reaction progress variable and an increase of the flame length were detected for water injected flames along with changes of the maximum as well as the averaged CO values. Finally, a strong influence of water droplet size on NOx and CO formation is shown for constant operating conditions.

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