Scaling of Stability Limits in Lean-Premixed Gas Turbine Combustors

2004 ◽  
Author(s):  
Martin Lohrmann ◽  
Horst Bu¨chner
Keyword(s):  
Gas Turbine ◽  
Scaling Laws ◽  
Transfer Functions ◽  
Burning Velocity ◽  
Phase Reaction ◽  
Combustion Instabilities ◽  
Burner Exit ◽  
Periodic Disturbances ◽  
Lean Premixed ◽  
Coherent Vortex

The prediction and the systematic suppression of self-sustained combustion instabilities in combustors for gas turbine applications still suffer from incomplete physical understanding of the feedback mechanisms and lack of experimental data of the dynamic flame characteristics of Lean-Premixed swirl flames. Hence, the experimental determination of the flame transfer functions of LP swirl flames was achieved using a mixing unit to generate a time-independent and spatial homogeneous mixture of natural gas and combustion air at the burner exit. The determined LP flame dynamics are strongly affected by the formation and in-phase reaction of coherent vortex structures, well known as drivers of combustion instabilities, that have been visualized with an phase-correlated imaging technique. The results discussed in this paper lead to a basic understanding of the frequency-dependent dynamics of LP swirl flames on periodic disturbances and especially, of the influence of the preheating temperature and the air equivalence ratio on the amplitude responses and phase angle functions. Based on the measurements and theoretical considerations concerning the burning velocity of steady-state premixed flames a physical model and — derived from it — scaling laws for the prediction of unstable operation modes in dependence of main operation parameters of the flame were formulated and validated by measurements.

Scaling Thermo-Acoustic Characteristics of LP and LPP Swirl Flames

2007 ◽  
Author(s):  
Michael Russ ◽  
Axel Meyer ◽  
Horst Bu¨chner
Keyword(s):  
Gas Turbine ◽  
Transfer Functions ◽  
Burning Velocity ◽  
Pollutant Emissions ◽  
Operating Pressure ◽  
Swirl Number ◽  
Frequency Dependent ◽  
Lean Premixed ◽  
Operation Parameters ◽  
Main Operation

One of the main objectives of combustion research in field of gas turbine application during the last decades was and still is the reduction of pollutant emissions. The most promising technology to reduce these pollutants turned out to be Lean Premixed (LP) and Lean Premixed Pre-Vaporized (LPP) combustion. However, serious problems concerning combustion-driven instabilities occurred with the implementation of the LP/LPP-concept. Today, prediction and systematic suppression of self-sustained combustion instabilities is an issue still unsolved, due to incomplete understanding of the physical feedback mechanism and the lack of models for dynamic flame response, i.e. frequency dependent characteristics of LP/LPP swirl flames. In that context, the purpose of the current paper is the establishment of a physical model to describe frequency dependent flame dynamics concerning burning velocity of steady-state premixed flames. Derived from that basic understanding, scaling laws for the prediction of unstable operation conditions will be established in dependence on main operation parameters such as thermal load, mixture temperature, air equivalence ratio and especially of fuel and operating pressure. Therefore, a new swirl-burner has been designed, offering the feasibility to choose the type of fuel, to adjust the swirl number for main and pilot burner and the burner exit geometry steplessly and to vary preheating temperatures, air equivalence ratios and thermal loads in a range of industrial relevance for gas turbine applications. To establish a periodical modulation of the mixture mass flow of the main L(P)P flame at the burner outlet sinusoidally in-time with well-defined frequencies and amplitudes, a pulsating unit was used. Using a mixing/ pre-vaporizing unit to create a time-independent and spatial homogeneous mixture of natural gas/ kerosene vapor and combustion air at the burner outlet, flame transfer functions of LP- and LPP swirl flames depending on main operating parameters were determined. The discussed results then lead to stability map for a given combustion system depending on the main operation parameters based on the knowledge of only one fully-described parameter combination leading to an instable condition. Based on this scaling procedure and confirmed by further experimental work the prediction of stability limits depending especially on the type of fuel, the swirl number and the operating pressure will be possible.

Application of a 1-D Predicting Tool to the Analysis of Pressure Oscillations in an Industrial Gas Turbine Combustor: GE10 Machine

2007 ◽  
Author(s):  
Antonio Asti ◽  
Luca Mangani ◽  
Antonio Andreini
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Operating Conditions ◽  
Equivalent Model ◽  
Design Phase ◽  
Trial And Error ◽  
Combustion Instabilities ◽  
Pressure Oscillations ◽  
Lean Premixed ◽  
Good Agreement

The development of current industrial gas turbines is strictly constrained by legislative requirements for low polluting emissions. Lean Premixed combustion technology has become through the years the necessary standard to meet such requirements. Premixed technology introduces a new range of problems: combustion instabilities in many operating conditions. Specifically, lean premixed flames pose the threat of pressure oscillations. This phenomenon is the effect of the strong interaction between combustion heat-release and fluid dynamics aspects. The prediction of acoustic oscillations and combustion instabilities is generally difficult because of the complexity of real combustor geometries. As a result, the design phase is usually performed as a trial-and-error task: a specific design is constructed, tested and modified, in a process that continues until acceptable results are found. A specific tool was developed by GE Energy to help predicting the acoustic behaviour of newly designed partially-premixed combustors, avoiding the traditional trial-and-error process: the tool allows the designer to analyze the problem of combustion instabilities since the early design phase, limiting subsequent testing efforts. A mono-dimensional tool based on the 1-D acoustic model was developed by GE Energy and was applied to the single-can combustor of the GE10 machine (a gas turbine in the 10MW class). All the main geometrical features of the GE10 machine, including fuel line geometry, were considered and modeled in a one-dimensional scheme, in order to build an equivalent model for the linear tool analysis. The main frequencies, measured during tests on the GE10 machine, were compared to the numerical results of the tool, showing good agreement between numerical and experimental results and confirming the predictive capability. This good agreement demonstrates that the model can be used for predicting the effects of design changes, with a reduced need of tests.

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.

Numerical Investigation of the Pressure Effect on the NOx Formation in a Lean-Premixed Gas Turbine Combustor

2021 ◽  
Vol 35 (8) ◽  
pp. 6776-6784
Author(s):  
Truc Huu Nguyen ◽  
Jungkyu Park ◽  
Changhun Sin ◽  
Seungchai Jung ◽  
Shaun Kim
Keyword(s):  
Numerical Investigation ◽  
Gas Turbine ◽  
Pressure Effect ◽  
Gas Turbine Combustor ◽  
Nox Formation ◽  
Lean Premixed

Fuel Flexibility Influences on Premixed Combustor Blowout, Flashback, Autoignition and Instability

2006 ◽  
Author(s):  
Tim Lieuwen ◽  
Vince McDonell ◽  
Eric Petersen ◽  
Domenic Santavicca
Keyword(s):  
Natural Gas ◽  
Gas Turbine ◽  
Dynamic Stability ◽  
Current Understanding ◽  
Fuel Composition ◽  
Fuel Flexibility ◽  
Lean Premixed ◽  
Gas Fuel ◽  
The Impact ◽  
Underlying Processes

This paper addresses the impact of fuel composition on the operability of lean premixed gas turbine combustors. This is an issue of current importance due to variability in the composition of natural gas fuel supplies and interest in the use of syngas fuels. Of particular concern is the effect of fuel composition on combustor blowout, flashback, dynamic stability, and autoignition. This paper reviews available results and current understanding of the effects of fuel composition on the operability of lean premixed combustors. It summarizes the underlying processes that must be considered when evaluating how a given combustor’s operability will be affected as fuel composition is varied.

Extension of the Combustion Stability Range in Dry Low NOx Lean Premixed Gas Turbine Combustor Using a Fuel Rich Annular Pilot Burner

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
L. Rosentsvit ◽  
Y. Levy ◽  
V. Erenburg ◽  
V. Sherbaum ◽  
V. Ovcharenko ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Combustion Zone ◽  
Combustion Instability ◽  
Experimental Results ◽  
Nox Emission ◽  
Combustion Stability ◽  
Stability Range ◽  
Numerical Effort ◽  
Lean Premixed ◽  
Pilot Burner

The present work is concerned with improving combustion stability in lean premixed (LP) gas turbine combustors by injecting free radicals into the combustion zone. The work is a joint experimental and numerical effort aimed at investigating the feasibility of incorporating a circumferential pilot combustor, which operates under rich conditions and directs its radicals enriched exhaust gases into the main combustion zone as the means for stabilization. The investigation includes the development of a chemical reactors network (CRN) model that is based on perfectly stirred reactors modules and on preliminary CFD analysis as well as on testing the method on an experimental model under laboratory conditions. The study is based on the hypothesis that under lean combustion conditions, combustion instability is linked to local extinctions of the flame and consequently, there is a direct correlation between the limiting conditions affecting combustion instability and the lean blowout (LBO) limit of the flame. The experimental results demonstrated the potential reduction of the combustion chamber's LBO limit while maintaining overall NOx emission concentration values within the typical range of low NOx burners and its delicate dependence on the equivalence ratio of the ring pilot flame. A similar result was revealed through the developed CHEMKIN-PRO CRN model that was applied to find the LBO limits of the combined pilot burner and main combustor system, while monitoring the associated emissions. Hence, both the CRN model, and the experimental results, indicate that the radicals enriched ring jet is effective at stabilizing the LP flame, while keeping the NOx emission level within the characteristic range of low NOx combustors.

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