UNIVERSITY OF SALENTO – SCHOOL OF INDUSTRIAL …

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UNIVERSITY OF SALENTO – SCHOOL OF INDUSTRIAL ENGINEERINGDEPT. OF ENGINEERING FOR INNOVATION – Lecce-Brindisi (Italy)

THE NEW FRONTIERS FOR THE CONTROL THE NEW FRONTIERS FOR THE CONTROL OF COMBUSTION IN GAS TURBINESOF COMBUSTION IN GAS TURBINES

Prof. Eng. Antonio FicarellaUniversity of Salento - [email protected]

REVIEW R30

DATE 27/03/2016

FILE FICARELLAslidesR31.odp

RESPONSIBLE Antonio [email protected]

mailto:[email protected]

mailto:[email protected]

2/44UNIVERSITY OF SALENTO – DEPT. OF ENGINEERING FOR INNOVATION – Lecce-Brindisi (Italy)

SUMMARY

Control of air-fuel mixing

Injection, atomization and vaporization of fuel

Lean combustion

Combustion instabilities

Micro-scale combustion

Active control systems

New combustion concepts


INTRODUCTION

TECHNOLOGICAL TARGETS TO BE ACHIEVED

CURRENT TRENDS OF SCIENTIFIC RESEARCH

INDUSTRIAL DEVELOPMENT AND APPLICATIONS


INJECTION, ATOMIZATION AND VAPORIZATION OF FUEL

EFFECT OF AIR-ASSIST ON LIQUID JET PENETRATION AND DISPERSION IN A CROSS-FLOW OF HOT, HIGH-PRESSURE AIR, Zu Puayen Tan, Eugene Lubarsky, Oleksandr Bibik, Dmitriy Shcherbik, Ben T. Zinn, GT2015-42239.

In many modern jet engines’ combustors , the primary liquid fuel is injected perpendicularly or at an angle into a high pressure and temperature (T) cross-flow of air.

Technique in enhancing the liquid fuel jet’s atomization and penetration involved the use of air-jets to assist/blast the liquid fuel jet as it is being injected into the cross-flow.

The arrangement of the air-jets can take a variety of forms, from a perpendicular fuel-air impingement setup to a coaxial/concentric fuel-air jets setup.

Jet-in-cross-flow (JICF injector) with a plain-orifice fuel nozzle that was recessed into a shallow well.

During their airblast JICF studies, significantly higher spray penetrations was observed in the presence of air-blasting.


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MOTIVATIONSLean premixed combustion systems are commonly employed on heavy duty gas turbines operating on natural gas fuels to achieve regulated low nitrogen oxide (NOx) emissions.

In addition to NOx limits, the design of lean premixed systems systems are constrained by carbon monoxide (CO) emissions at part load, lean blow out (LBO) limit, and combustion instabilities (dynamics).

As gas turbine emissions are being regulated to lower levels and operators are demanding increased operational flexibility and efficiency (translating to higher combustor temperatures) new technologies are required to meet these challenges with lean premixed combustion systems.

Operators of heavy duty gas turbines desire more flexibility of operation in compliance with increasingly stringent emissions regulations.

Delivering low NOx at base load operation, while at the same time meeting aggressive startup, shutdown, and part load requirements for NOx, CO, and unburned hydrocarbons is a challenge that requires novel solutions in the framework of lean premixed combustion systems.

Lean combustion involves some problems:

macroscopic effects: spontaneous oscillations at few Hz (produced when the fuel concentration increases and the flame extends and contracts );

microscopic effects: luminosity variance at high frequencies (produced by local extinguishments).

Lean blowout (LBO) is a major technical challenge for low emission combustion systems.

Different instabilities

Acoustic driven

Chemical driven


Primary air tube Swirler Holes for secondary air supply

Secondary air nozzle

Combustion Chamber

Multipoint injection mode leads to a more fast and efficient mixing with respect to the single injection producing a more homogenous charging of the chamber. Multipoint injection may be realized totally injecting the fuel upstream the swirler inlet or using also the central injector as a “pilot” injection.

In these conditions gas turbines might exhibit strong dynamics that may lead to instabilities, flashback or blowout (LBO).


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Only lean and ultra-lean cases were chosen to underline the abruptly increment of this parameter going toward the LBO limit.

Comparing the different combustion regimes the maximum variance is lower in partially-premixed mode with respect to the non-premixed regime. This is due also to the spray that introduces another source of flame oscillations especially in the zone further away from the injector.

It is evident a rapid increase of the variance for equivalent fuel/air ratio lower than about 0.2 towards blowout.


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The variance/mean intensity ratio takes into account the effect of both reduction in heat release rate and rise in the frequency of random local extinction and reignition events occurring in the flame near the blowout.


COMBUSTION INSTABILITIESFEEDBACK CONTROL OF SELF-SUSTAINED NONLINEAR COMBUSTION OSCILLATIONS, Xinyan Li, Dan Zhao, GT2015-42126.

Combustion instability is one of the most plaguing problems in lean-conditioned propulsion systems.

Combustion instability is characterized by a large-amplitude pressure oscillation which may raise some undesirable noise and structural vibration.

Generally, combustion instability is caused by the coupling between the unsteady heat release and the acoustic pressure.

Numerous experimental, theoretical and numerical works have been done to understand the physics behind thermoacoustic instability and to develop effective controller.

The feedback control is widely applied in industry. For example, a controller was applied to stabilize an annular multi-burner combustion system.


COMBUSTION INSTABILITIES/2

COMBINED ACOUSTIC DAMPING-COOLING SYSTEM FOR OPERATIONAL FLEXIBILITY OF GT26/GT24 REHEAT COMBUSTORS, Bruno Schuermans, Mirko Bothien, Michael Maurer, Birute Bunkute, GT2015-42287.

Combustion pulsations occurring in gas turbines can be categorized according to their frequency. On the one hand there are low frequency modes of the order of 100 Hz, on the other high frequencies in the kHz range. Due to their small wavelengths, high frequency modes in annular combustor feature more complex mode shapes.


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Using a sequential combustion system enables the achievement of extremely low NOx emissions and an unmatchable turn-down ratio, by completely switching off the fuel supply to the reheat combustor during very low load operation.

In order to increase the engine’s efficiency and operation range while decreasing emissions it is crucial to overcome high frequency thermoacoustic instabilities and to optimize the cooling features. Both tasks are solved in an integrated new design of the SEV burner front panel.

A highly complex 3-D network of channels and cavities is created. The channels are used to cool the front panel, while the cavities act as acoustic resonators.


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COMBUSTION INSTABILITIES/3

Dynamics and stability of lean-premixed swirl-stabilized combustion, Ying Huang, Vigor Yang, Progress in Energy and Combustion Science 35 (2009) 293–364.

Active control techniques utilize external excitations (such as acoustic forcing and fuel modulation) to attenuate combustion oscillations.

Active control is an attractive strategy because it relies on proper modulation of combustion system parameters, rather than spatial changes of the flowfield as required in passive approaches. Since adjustment of system timing parameters is much simpler and more practical than the potential geometry modification associated with passive control, active control provides flexibility for adaptation and eliminates costly design changes.

Practical applications of active control require reliable sensing and actuation devices with proper time-response characteristics.

The control algorithm is a key element in the success of active instability control.

Practical full-scale implementations present several technological challenges.

First, the active control hardware, i.e., sensors and actuators, must be sufficiently reliable for extended periods of use under the high-temperature and -pressure environment typical of industrial combustors.

Second, the actuators must have sufficient power to damp instabilities without consuming too much energy.

Third, designing actuators that can provide large modulation levels at relatively high frequencies, which might be in excess of 500 Hz or even 1000 Hz, still remains challenging.


...The control system measured the acoustic pressures at the burner flanges as inputs.

Active control was achieved by modulating the pilot gas supply using a Moog direct drive-valve (DDV) actuator. These actuators allow the modulation of flow rate with frequencies of up to 400 Hz.


MICRO-SCALE COMBUSTION/1

A review on microcombustion: Fundamentals, devices and applications, Niket S. Kaisare, Dionisios G. Vlachos, Progress in Energy and Combustion Science 38 (2012) 321-359.

Unlike their conventional-sized counterparts, microburners are no longer governed by bulk behavior; rather, gas-surface interactions play a pivotal role. Small scales enable process intensification (e.g., fast heat and mass transfer), higher efficiency, and faster transients (quick startup).

At the same time, there are challenges in rendering microburners operational, including thermal and radical quenching, thermal management, and susceptibility to failure due to thermal stresses.

Highly efficient, distributed generation of power is critical in meeting our future energy needs.

Use of underutilized energy sources, such as natural gas in remote and offshore locations, presents a true opportunity for providing new energy supplies.



EXPERIMENTAL AND NUMERICAL STUDY ON OPTIMIZING THE DLN MICROMIX HYDROGEN COMBUSTION PRINCIPLE FOR INDUSTRIAL GAS TURBINE APPLICATIONS, H. H.-W. Funke, J. Keinz, K. Kusterer, A. Haj Ayed, M. Kazari, J. Kitajima, A. Horikawa, K. Okada, GT2015-42043.

the Micromix hydrogen combustion principle has been under development at AcUAS and was successfully tested and adapted in conventional gas turbines also at elevated pressures with the prove of significant NOx emission reduction.

Investigations of other researchers on low NOx hydrogen combustion using micro-mixing flames have also shown successful applications for gas turbines even at elevated pressures.


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The Micromix principle significantly reduces the formation of nitric oxides by miniaturizing the reaction zone through the creation of multiple micro diffusion-type flamelets with a typical size of 5-15 mm in length and an inherent safety against flashbacks.

The mixing process is improved using the jet in cross-flow principle.

The flame anchoring, which is essential to low NOx formation, is mostly dominated by the resulting recirculation vortices within the burner geometry and by the momentum flux ratio of the jet in cross-flow.


...Liquid fuel microcombustor using microfabricated multiplexed electrospray sources, Weiwei Deng, James F. Klemic, Xiaohui Li, Mark A. Reed, Alessandro Gomez, Proceedings of the Combustion Institute 31 (2007) 2239–2246.

A miniaturized combustor must rely on a good design of the fuel atomizer, which should yield small, rapidly evaporating droplets to generate the fuel vapor promptly, mix it with the oxidizer and subsequently burn it with the attending heat release.

Use of multiplexed electrosprays and a catalytic reactor for fuel conversion consisting of a pack of catalyst impregnated meshes.

Volumetric heat release rate as large as 270 MW/m3, a value that is of the same order as that of conventional gas turbines.



Experimental investigations on a new active swirl based microcombustor for an integrated micro-reformer system, Gur Partap Singh Sahota, Bhupendra Khandelwal, Sudarshan Kumar, Energy Conversion and Management 52 (2011) 3206–3213.

A new active swirl based concept has been proposed to enhance the flame stability limits in backward facing step microcombustors with premixed methane–air mixtures.

For active swirl case, when precisely controlled secondary flow is used for swirl generation, both upper and lower flame stability limits are significantly enhanced.

A stable flame has been observed to exist for a wide range of mixtures with equivalence ratio varying from 0.6 to 1.3.

heat release density of about 9.75 MW/m3


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NOVEL COMBUSTION CONCEPTS

EXPERIMENTAL INVESTIGATION OF A FLOX®-BASED COMBUSTOR FOR A SMALL-SCALE GAS TURBINE BASED CHP SYSTEM UNDER ATMOSPHERIC CONDITIONS, GT2015-43094, Hannah Seliger, Andreas Huber, Manfred Aigner, German Aerospace Center, Institute of Combustion Technology

EXPERIMENTAL INVESTIGATION OF THE COMBUSTION CHARACTERISTICS OF A DOUBLE-STAGED FLOX®-BASED COMBUSTOR ON AN ATMOSPHERIC AND A MICRO GAS TURBINE TEST RIG, GT2015-42313, Jan Zanger, Thomas Monz, Manfred Aigner, Institute of Combustion Technology, German Aerospace Center.

Newly designed single-stage combustion system based on the flameless oxidation (FLOX®) technology [also termed volume or MILD combustion] for a small scale micro gas turbine (MGT).

It is used for a combined heat and power plant (CHP) with an electrical power output of 3 kW, using natural gas as fuel.

Flameless oxidation is characterized by a flame distributed over a large volume and a high internal recirculation of flue gas.

The FLOX®-combustion concept offers various advantages compared to swirl-stabilized combustion systems in terms of flashback risk and exhaust gas emissions.


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Fuel is injected in the flow direction into a high momentum air flow. Air and fuel are partially premixed. The high jet velocity generates a strong inner recirculation zone. This leads to a homogeneous temperature distribution which is essential for low NOx emissions. Due to the high jet velocity the risk for flashback is significantly reduced.

http://kraftwerkforschung.info/en/hydrogen-gas-turbines/


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Since this path depends exponentially on the temperature, the resulting drop in flame temperature due to the increase in airfuel ratio results in lower NOx emissions.

The main driving mechanism for the higher CO emissions is the reduction of residence time.


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Double–staged, FLOX®

the margin to lean blow–off is substantially increased by the fuel staging.

Moreover, it is demonstrated that the exhaust gas emissions of the double–staged combustor could be kept at a similar very low level by applying the staging.


NOVEL COMBUSTION CONCEPTS/2

DEVELOPMENT OF THE DLE COMBUSTOR FOR L30A GAS TURBINE, GT2015-42904, Toshiaki Sakurazawa, Takeo Oda, Satoshi Takami, Atsushi Okuto, Yasuhiro Kinoshita, Kawasaki Heavy Industries, Ltd.

DLE combustors consist of three burners, a diffusion pilot burner, a lean premix main burner, and supplemental burners.


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Line A operated by pilot and main burner.

Line B when fuel mass flow of pilot and main burner is kept, and fuel mass flow of supplemental burner is increased up to maximum load.

Plot C when total fuel mass flow is kept, and fuel mass flow of main burner is increased.


NOVEL COMBUSTION CONCEPTS/3

PREMIXED PILOT FLAMES FOR IMPROVED EMISSIONS AND FLEXIBILITY IN A HEAVY DUTY GAS TURBINE COMBUSTION SYSTEM, GT2015-44102, William D. York, Bryan W. Romig, Michael J. Hughes, Derrick W. Simons, Joseph V. Citeno, GE Power & Water.

This program focused on the development of gas turbine technologies required for an Integrated Gasification Combined Cycle (IGCC) power plant with carbon capture and sequestration. For combustion, this meant the development of a combustion system that could burn very high hydrogen fuel with an aggressive emissions target of 2 ppm NOx.

The challenge of ultra-low NOx with the highly reactive fuel led to the development of a new premixer technology called the multi-tube (MT) mixer.

The pilot geometry consists of multiple tubes, a few millimeters in diameter.

A fraction of combustor air is used to feed these tubes and maintain adequate velocities to provide flashback and flame holding margin.

The fraction of air provided to the pilots is fixed.


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NEW 7F DLN2.6+ COMBUSTION SYSTEM

The premixed pilots play a role in enabling the combustion system to feature a shorter liner and associated residence time reduction, while retaining good turndown performance (emissions and LBO margin).

This lower residence time, combined with the excellent premixing capability and air management, allows to achieve lower NOx emissions at base and part load.

To feed the premixed pilots of the outer fuel nozzles, air is extracted from the compressor discharge casing. Bypassing the rest of the combustion system with the pilot air allows higher pressure to feed the pilots and serves to acoustically separate pilot air feed from the combustion system to mitigate combustion dynamics.


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ACTIVE CONTROL OF COMBUSTION

For ground power generation and industrial burners, CO2 capture and NOx emission reduction are the primary drivers to the development of ultra-lean high hydrogen content (HHC) gas turbines, flameless combustion, and oxyfuel combustion.

In the development of ultra-lean HHC gas turbine combustion, combustion instability and flame flashback are among the greatest challenges.

Another challenge is the broad distribution of syngas energy density (5-80 MJ/kg) that further increases the problem of flame instability.

STABILITY

blow-off in aeronautical engines

WIDE RANGE OF OPERATING CONDITIONS

Non-thermal plasmas

low ionization/excitation energy

small temperature rise

permit to dissociate the fuel and to produce free radicals

application of high-voltage pulses to improve the ignition of fuel/air mixtures, to increase flame propagation, enhanced flame stabilization, and extended flammability limits

PLASMA ACTUATORS


-A promising non thermal plasma source is the dielectric barrier discharge (DBD).

A plasma actuator is substantially a device able to change locally the chemical and fluid dynamic state using the action of an high electric field.

It was shown that the plasma created in the recirculation zone permitted to stabilize the lean flame and to reduce the lean extinction limit by about 10-15%, with a power consumption that was less than 1% of the power of the flame.

Nanosecond Repetitively Pulsed (NRP) discharges produced by electric pulses of about 10 kV during 10 ns, and at a frequency of 30 kHz, where applied to stabilize a lean premixed methane/air flame at atmospheric pressure. A repetitive discharge at 9 kHz, with voltage pulse duration of order 100 ms was used to extend the flammability limit of a lean propane/air mixture at atmospheric pressure. [200]

The actuation produces significant change in the flame shape and improves the stability and the homogeneity of the flame. In this condition the effect of actuation is mainly related to the stabilization of the flame and the rise of the blowout limit.


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Effect of the plasma actuation on the LBO limits for the activated methane configuration and for different values of Methane flow rate, when the sinusoidal HV amplifier is used (the voltage frequency is set at 20 kHz). [IEEE_SENSORS_submit]

When the plasma actuator is on, it leads to an evident improvement of the LBO limit, with a large increase for low fuel flow rate (low equivalence ratio). [01_manuscript-2]

This could confirm that plasma DBD causes radical production/enhancement and influences the mixing [01_manuscript-2]


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rise in the intensityyellowish in the conical tip

rise in the intensityyellowish in the conical tipINCREASE OF LENGTHINCREASE OF LENGTH

INCREASE OF INTENSITY and yellow/orange regionenhanced anchoring of the flame

INCREASE OF INTENSITY and yellow/orange regionenhanced anchoring of the flame


At standoff distance of 6 mm the yellowish zone is smaller

At standoff distance of 6 mm the yellowish zone is smaller


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The structure of IDF flame and the OH* emission area are greatly influenced by the plasma discharge when the standoff distance is equal to 0.

On the contrary the OH* area keeps almost invariable when the applied voltage and the plasma power increases for the IDF with a standoff distance equal to 6 mm. [01_manuscript-2]

Under plasma actuation, the flame propagation speed is improved, which pushes the thin reaction zone against the upward flow


ACTIVE CONTROL OF COMBUSTION/2

Plasma assisted combustion: Dynamics and chemistry, Yiguang Ju, Wenting Sun, Progress in Energy and Combustion Science 48 (2015) 21e83.

effect of nanosecond pulsed discharge on combustion instabilities at 1 atm

Without plasma, the flame was lifted off and stabilized in the shear layers associated with the recirculation zone.

As the discharges were activated and the pulse repetition frequency was increased, the flame moved successively further upstream and eventually stabilized in the burner passage.

Averaged CH* chemiluminescence intensity for the case without plasma discharges (a), and with f = 5, 10, 15, 20, and 25 kHz (bed); equivalence ratio 0.62, thermal power 50 kW


-The effect of steady pulsed discharges on combustion dynamics was further investigated. It was found that the discharges had a strong effect on the pressure pulsations associated with thermoacoustic dynamics.

Since the discharges affect both the flame shape and the position, they have an influence on the dynamic response of the flame to acoustic perturbations.

This phenomenon was mainly caused by the thermal effect of the plasma. The ultra-fast heating of the flow by plasma was followed by expansion of gas and generation of shockwaves. This aerodynamical impact on transport affects flow velocity and alters vortex structure, and therefore changes the flame transfer function.


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Integrated a DBD actuator into the premixer of a combustor to investigate the effect of ionic wind on flashback.


ACTIVE CONTROL OF COMBUSTION/3NON-EQUILIBRIUM PLASMA ASSISTED COMBUSTION OF LOW BTU FUELS, Hongbin Hu, Gang Xu, Aibing Fang, Weiguang Huang, GT2010-22053.

The measurements of the flame indicate that addition of a very small amount of energy in the form of DBD plasma can provide self-ignition in harsher conditions in contrast to usual spark ignition, and significantly improve the flame stability and combustion efficiency.

The results also show that the effect of DBD plasma on the flame is most efficient in combustion at low equivalence ratios, and the chemical reactions can even occur at the equivalence ratios well below the lean flammability limit.


ACTIVE CONTROL OF COMBUSTION/4

Plasma-Assisted Combustion Technology for NOx Reduction in Industrial Burners, Dae Hoon Lee, Kwan-Tae Kim, Hee Seok Kang, Young-Hoon Song, and Jae Eon Park, Environ. Sci. Technol. 2013.

This new technology uses a simple modification of commercial burners, such that they are able to perform plasma-assisted staged combustion without altering the outer configuration of the commercial reference burner.

Ultimately, the enhanced mixing and removal of hot spots with a widened flame area acted as the main mechanisms of NOx reduction.


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CONCLUSIONS

Deep control of basic chemical and physical phenomena.

High frequency sensors and actuators (MEMS).

Control of small spatial scales (microscale).

Cost is not a problem.

The real challenges are:

Scale-up to industrial size.

Reliability of the control systems.

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