Combustion Instabilities in Industrial Gas Turbines—Measurements on Operating Plant and Thermoacoustic Modeling

2000 ◽  
Vol 122 (3) ◽  
pp. 420-428 ◽  
Author(s):  
David E. Hobson ◽  
John E. Fackrell ◽  
Gary Hewitt
Keyword(s):  
Time Delay ◽  
Gas Turbines ◽  
Acoustic Resonance ◽  
Resonant Mode ◽  
Combustion Stability ◽  
Combustion Instabilities ◽  
Strong Function ◽  
Fuel Supply ◽  
Industrial Gas Turbines ◽  
Stability Limits

Measurements of vibration and combustion chamber dynamic pressures have been taken on a number of 150 MW industrial gas turbines operating on pre-mixed natural gas, both during long periods of base-load operation and during short duration load-swings. The data has been analyzed in terms of the frequency and bandwidth of the principle peak in the vibration and pressure spectra as a function of load and other operating parameters. It is observed that bandwidth, which is a measure of the damping of the resonant mode of the combustion chamber’s acoustic resonance, decreases towards zero as the machines approach their combustion stability limits. A theoretical model of the thermoacoustic behavior of the combustion system has been developed to see to what extent the observed behavior on the operational machines can be explained in terms of an acoustic model of the ductwork and a flame characterized simply by a time-delay. This time delay is obtained from the frequency response function of the flame in response to unsteady perturbations in inlet velocity and is calculated using computational fluid dynamics. The model has also been used to illustrate the importance of fuel supply system design in controlling combustion stability. It is shown that stability can be a strong function of the acoustic impedance of the fuel supply and that this can lead to enhanced or reduced stability depending on the flame characteristics. [S0742-4795(00)01403-4]

Combustion Instabilities in Industrial Gas Turbines — Measurements on Operating Plant and Thermoacoustic Modelling

1999 ◽  
Author(s):  
David E. Hobson ◽  
John E. Fackrell ◽  
G. Hewitt
Keyword(s):  
Time Delay ◽  
Gas Turbines ◽  
Acoustic Resonance ◽  
Resonant Mode ◽  
Combustion Stability ◽  
Strong Function ◽  
Fuel Supply ◽  
Industrial Gas Turbines ◽  
Observed Behaviour ◽  
Stability Limits

Measurements of vibration and combustion chamber dynamic pressures have been taken on a number of 150MW industrial gas turbines operating on pre-mixed natural gas, both during long periods of base-load operation and during short duration load-swings. The data has been analysed in terms of the frequency and bandwidth of the principle peak in the vibration and pressure spectra as a function of load and other operating parameters. It is observed that bandwidth, which is a measure of the damping of the resonant mode of the combustion chamber’s acoustic resonance, decreases towards zero as the machines approach their combustion stability limits. A theoretical model of the thermoacoustic behaviour of the combustion system has been developed to see to what extent the observed behaviour on the operational machines can be explained in terms of an acoustic model of the ductwork and a flame characterised simply by a time-delay. This time delay is obtained from the frequency response function of the flame in response to unsteady perturbations in inlet velocity and is calculated using computational fluid dynamics. The model has also been used to illustrate the importance of fuel supply system design in controlling combustion stability. It is shown that stability can be a strong function of the acoustic impedance of the fuel supply and that this can lead to enhanced or reduced stability depending on the flame characteristics.

scholarly journals Effects of Ambient Conditions and Fuel Composition on Combustion Stability

1997 ◽  
Author(s):  
Michael C. Janus ◽  
George A. Richards ◽  
M. Joseph Yip ◽  
Edward H. Robey
Keyword(s):  
Gas Turbines ◽  
Pressure Fluctuations ◽  
Field Testing ◽  
Combustion Stability ◽  
Fuel Composition ◽  
Ambient Conditions ◽  
Reaction Region ◽  
Industrial Gas Turbines ◽  
Thermal Nox ◽  
Combustion Oscillation

Recent regulations on NOx emissions are promoting the use of lean premix (LPM) combustion for industrial gas turbines. LPM combustors avoid locally stoichiometric combustion by premixing fuel and air upstream of the reaction region, thereby eliminating the high temperatures that produce thermal NOx. Unfortunately, this style of combustor is prone to combustion oscillation. Significant pressure fluctuations can occur when variations in heat release periodically couple to acoustic modes in the combustion chamber. These oscillations must be controlled because resulting vibration can shorten the life of engine hardware. Laboratory and engine field testing have shown that instability regimes can vary with environmental conditions. These observations prompted this study of the effects of ambient conditions and fuel composition on combustion stability. Tests are conducted on a subscale combustor burning natural gas, propane, and some hydrogen/hydrocarbon mixtures. A premix, swirl-stabilized fuel nozzle typical of industrial gas turbines is used. Experimental and numerical results describe how stability regions may shift as inlet air temperature, humidity, and fuel composition are altered. Results appear to indicate that shifting instability regimes are primarily caused by changes in reaction rate.

An Experimental Study of Effects of Confinement Ratio on Swirl Stabilized Flame Macrostructures

2017 ◽  
Author(s):  
Yiheng Tong ◽  
Mao Li ◽  
Marcus Thern ◽  
Jens Klingmann
Keyword(s):  
Flame Front ◽  
Gas Turbines ◽  
Recirculation Zone ◽  
Operating Conditions ◽  
Combustion Stability ◽  
Reconstruction Method ◽  
Lean Blowout ◽  
Image Reconstruction Method ◽  
Root Position ◽  
Industrial Gas Turbines

Swirl stabilized premixed flames are common in industrial gas turbines. The flame shape in the combustor is highly related to the combustion stability and the performance of the gas turbine. In the current paper, the effects of confinement on the time averaged flame structures or flame macrostructures are studied experimentally. Experiments are carried out with swirl number S = 0.66 in two cylindrical confinements with diameters of d1 = 39 mm and d2 = 64 mm and confinement ratio c1 = 0.148 and c2 = 0.0567. All the experiments were carried out in atmospheric. CH∗ chemiluminescence from the flame was recorded to visualize the flame behavior. An inverse Abel image reconstruction method was employed to better distinguish the flame macrostructures. Different mechanisms forming the time averaged M shape flames are proposed and analyzed. It is found that the confinement wall plays an important role in determining the flame macrostructures. The flow structures including the inner and outer recirculation zones formed in the confinement are revealed to be the main reasons that affects different flame macrostructures. Meanwhile, the alternation of flame shapes determines the flame stability characteristics. A smaller confinement diameter forced the flame front to bend upstream into the outer recirculation zone hence forming a M shape flame. A strong noise caused by the interaction of the flame front in the outer recirculation zone with the combustor wall was observed. Another unsteady behavior of the flame in the bigger combustor, which was caused by the alternation of the flame root position inside and outside the premixing tube, is also presented. The V shape flame in the two combustors radiated weaker chemiluminescence but the main heat release zone was elongated than the M shape flame. Other operating conditions, i.e. total mass flow rate of the air flow and the equivalence ratio also affect the flame macrostructures. The flame blowout limits were also altered under different test conditions. The bigger confinement has better performance in stabilizing the flame by having lower lean blowout limits.

Impact of Fuel Supply Impedance on Combustion Stability of Gas Turbines

2008 ◽  
Author(s):  
Andreas Huber ◽  
Wolfgang Polifke
Keyword(s):  
Gas Turbines ◽  
Equivalence Ratio ◽  
Cfd Simulation ◽  
Transfer Functions ◽  
Combustion Stability ◽  
Reacting Flow ◽  
Efficient Manner ◽  
Combustion Dynamics ◽  
Thermoacoustic Instabilities ◽  
Fuel Supply

In the development of gas turbines the prevention of thermoacoustic instabilities plays an important role. The present study analyzes the influence of the acoustic impedance of the fuel supply system on combustion stability in a generic configuration representative of practical lean-premix combustors. Transient Computational Fluid Dynamics (CFD) of turbulent reacting flow and system identification (SI) are combined to obtain a description of the combustion dynamics in terms of two flame transfer functions, which describe the response of heat release rate to fluctuations of velocity and equivalence ratio, respectively. In this way, the mixing and transport of the fuel from the injector to the flame, the kinematic response of the flame to upstream flow fluctuations, and combined effects like the perturbation of flame speed and position due to equivalence ratio perturbations are all captured. The flame transfer functions obtained are combined with a network model for the system acoustics in such a way that results from a single CFD simulation can be used to investigate a wide variety of combustor and fuel supply configurations in a quantitative and very efficient manner. It is demonstrated that a change of the fuel supply impedance can significantly influence the amplitude of equivalence ratio fluctuations as well as the relative phase of the two transfer functions, and thereby provide a means for control of combustion instabilities.

A Study of Parameters Affecting the Combustion Stability and Emissions Behavior of Alstom Heavy-Duty Gas Turbines

2004 ◽  
Author(s):  
Lars O. Nord ◽  
Helmer G. Andersen
Keyword(s):  
Gas Turbines ◽  
Combustion Instability ◽  
Nox Reduction ◽  
Fuel Properties ◽  
Combustion Noise ◽  
Combustion Stability ◽  
Combustion Instabilities ◽  
Heavy Duty ◽  
Ambient Conditions ◽  
Process Data

A number of factors can influence the combustion instability region and emission behavior of a heavy-duty gas turbine. Changes in the composition of the natural gas supplied have an impact that was studied in a prior investigation, which focused on parameters such as fuel temperature and composition. To further investigate the fuel sensitivity additional plants were included in this study. In addition to the fuel properties the distribution of the fuel inside the combustor was examined. To expand the fuel properties study, additional parameters were examined. Ambient conditions were paid special interest, specifically ambient temperature and humidity. Included in this study was also the effect on combustion of changes in compressor discharge pressure. With the growing interest in inlet chilling a pulsation/emission study was included to specifically look for NOx and combustion instability effects due to inlet chilling. Also, influences from special occurrences such as on-line compressor washing were examined. The turbines in this study utilize a silo-type combustor with either the DLN [Dry Low NOx] EV [EnVironmental] burners or with single diffusion burners using water or steam as NOx reduction medium. The rated power output of the gas turbines was in the range of 50–120 MW. The data acquired included frequency-analyzed combustion instabilities, various process data, as well as ambient conditions and fuel composition. The collected data shows the magnitude of the changes in the emissions and combustion noise with changes in the parameters studied. The conclusion is that some key parameters are very important for both the pulsations and the emissions, whereas others can be neglected. Some parameters affect the combustion instabilities only, without noticeable effect on emissions, and vice versa.

scholarly journals Characterization of Oscillations During Premix Gas Turbine Combustion

1997 ◽  
Author(s):  
George A. Richards ◽  
Michael C. Janus
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Pressure Fluctuations ◽  
Combustion Stability ◽  
Published Data ◽  
Operating Pressure ◽  
Reference Velocity ◽  
Air Temperatures ◽  
Industrial Gas Turbines ◽  
Fuel Nozzle

The use of premix combustion in stationary gas turbines can produce very low levels of NOx emissions. This benefit is widely recognized, but turbine developers routinely encounter problems with combustion oscillations during the testing of new pre mix combustors. Because of the associated pressure fluctuations, combustion oscillations must be eliminated in a final combustor design. Eliminating these oscillations is often time-consuming and costly because there is no single approach to solve an oscillation problem. Previous investigations of combustion stability have focused on rocket applications, industrial furnaces, and some aeroengine gas turbines. Comparatively little published data is available for premised combustion at conditions typical of an industrial gas turbine. In this paper, we report experimental observations of oscillations produced by a fuel nozzle typical of industrial gas turbines. Tests are conducted in a specially designed combustor, capable of providing the acoustic feedback needed to study oscillations. Tests results are presented for pressures up to 10 atmospheres, and with inlet air temperatures to 588 K (600 F) burning natural gas fuel. Based on theoretical considerations, it is expected that oscillations can be characterized by a nozzle reference velocity, with operating pressure playing a smaller role. This expectation is compared to observed data, showing both the benefits and limitations of characterizing the combustor oscillating behavior in terms of a reference velocity rather than other engine operating parameters. This approach to characterizing oscillations is then used to evaluate how geometric changes to the fuel nozzle will affect the boundary between stable and oscillating combustion.

Characterization of Oscillations During Premix Gas Turbine Combustion

1998 ◽  
Vol 120 (2) ◽  
pp. 294-302 ◽  
Author(s):  
G. A. Richards ◽  
M. C. Janus
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Pressure Fluctuations ◽  
Combustion Stability ◽  
Published Data ◽  
Operating Pressure ◽  
Reference Velocity ◽  
Air Temperatures ◽  
Industrial Gas Turbines ◽  
Fuel Nozzle

The use of premix combustion in stationary gas turbines can produce very low levels of Nox emissions. This benefit is widely recognized, but turbine developers routinely encounter problems with combustion oscillations during the testing of new premix combustors. Because of the associated pressure fluctuations, combustion oscillations must be eliminated in a final combustor design. Eliminating these oscillations is often time-consuming and costly because there is no single approach to solve an oscillation problem. Previous investigations of combustion stability have focused on rocket applications, industrial furnaces, and some aeroengine gas turbines. Comparatively little published data is available for premixed combustion at conditions typical of an industrial gas turbine. In this paper, we report experimental observations of oscillations produced by a fuel nozzle typical of industrial gas turbines. Tests are conducted in a specially designed combustor capable of providing the acoustic feedback needed to study oscillations. Tests results are presented for pressure up to 10 atmospheres, with inlet air temperatures up to 588 K (600 F) burning natural gas fuel. Based on theoretical considerations, it is expected that oscillations can be characterized by a nozzle reference velocity, with operating pressure playing a smaller role. This expectation is compared to observed data that shows both the benefits and limitations of characterizing the combustor oscillating behavior in terms of a reference velocity rather than other engine operating parameters. This approach to characterizing oscillations is then used to evaluate how geometric changes to the fuel nozzle will affect the boundary between stable and oscillating combustion.

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