FlameSheetTM Combustor Engine and Rig … Combustor Engine and Rig Validation for Operational and Fuel Flexibility with Low Emissions Peter Stuttaford, Hany Rizkalla, Khalid Oumejjoud,

Copyright © 2016 ASME1

Proceedings of ASME Turbo Expo 2016: Turbomachinery Technical Conference and ExpositionGT2016

June 13 – 17, 2016, Seoul, South Korea

GT2016-56696

FlameSheetTM Combustor Engine and Rig Validation forOperational and Fuel Flexibility with Low EmissionsPeter Stuttaford, Hany Rizkalla, Khalid Oumejjoud, Nicolas Demougeot, Justin Bosnoian, Fred

Hernandez, Matthew Yaquinto, Afzal Pasha Mohammad, Dwain Terrell, Ryan Weller

Power Systems Mfg, LLC (PSM)

Jupiter, Florida, USA

AbstractFlexibility is key to the future success of natural gas firedpower generation. As renewable energy becomes morewidely used, the need for reliable, flexible generation willincrease. As such, gas turbines capable of operatingefficiently and in emissions compliance from extended lowload to full load will have a significant advantage. A widerrange of gas fuels, including shale gas andrefinery/industrial byproduct gas, is becoming increasinglyavailable, with the opportunity to further reduce the cost ofelectricity. A combustion system capable of operating withwider ranges of heavy hydrocarbons, hydrogen and inertswill have an advantage to accommodate the future fuel gastrends and provide value to gas turbine operators. TheFlameSheetTM combustor incorporates a novel dual zoneburn system to address operational and fuel flexibility. Itprovides low emissions, extended turndown and fuelflexibility. FlameSheetTM is simply retrofittable into existinginstalled E/F-class heavy duty gas turbines and is designedto meet the energy market drivers set forth above. Theoperating principle of the new combustor is described, anddetails of a full scale high pressure rig test and enginevalidation program are discussed, providing insight on rigand engine emissions, as well as combustion dynamicsperformance. The FlameSheetTM implementation andvalidation results on a General Electric 7FA heavy duty gasturbine operating in a combined cycle power plant isdiscussed with emphasis on operational profile optimizationto accommodate the heat recovery steam generator (HRSG),while substantially increasing the gas turbine normaloperating load range.

IntroductionHistorically, the gas turbine power generation market

faced changing market conditions due to fluctuations in gasprices, electricity demand, natural gas inventory, economicand political conditions. The global investment in renewableenergy poses an additional challenge to power generationmarkets. In the 4th quarter 2015 report released by the

American Wind Energy Association (AWEA), electricitygenerated by wind tripled in the last seven years,representing just under 5 percent of the USA’s total end-usedemand. The AWEA reports a total of 69,471 MW ofinstalled wind capacity in the U.S and is aware of 13,250MW worth of construction taking place [1].

70,000

60,000

50,000

40,000

30,000

20,000

10,000

0

Win

dPo

wer

Capa

city

(MW

)

Fig. 1 Installed U.S based wind capacity [1]

According to a report by the IEA (International EnergyAgency), renewable electricity expanded at its fastest rate to130 GW [gigawatts] in 2014 and accounted for more than45% of net additions to world capacity in the power sector[2].

Such penetration of renewable energy sources poses achallenge in the form of volatility in the electricity marketdue to the fluctuation of the energy supply to the grid. Assuch, maximizing turndown capability, while remaining in-emissions compliance allows a gas turbine power plant tofollow market pricing, and can significantly impact powerplant profitability. This is typically achieved by turningdown a gas turbine to the lowest possible, in-emissionscompliance load, during hours of low electricity demand,but remaining online and available to ramp up in load tocapture profits when electricity demand and prices are morefavourable.


An example is presented below based on actual realtime market information in the ERCOT power generatingregion within the U.S.A., in May 2014. As shown in Figure2, in a 24 hour operating period there are certain hours whenprofits turn to losses. For the case where only 50% loadturndown can be achieved the gas turbine is shut down andrestarted, since the fuel cost of a start is still less costly thankeeping the unit running. However, an alternate case with a30% turndown capable combustor, the engine continues tooperate at lower turndown in this period since the losses arebelow those of restarting the turbine.

Fig. 2, Hourly profit comparison at 30% and 50% loadturndown levels

Accumulation of the hourly profit in this 24 hour example isshown in Figure 3 below. Having the ability to run at lowerload and avoid cycling the unit increases the plant profit by30% based on the cost of fuel alone. Adding the associatedmaintenance cost of cycling the power plant increases theprofit margin by more than 50%.

Fig. 3, Cumulative profit comparison at 30% and 50% loadturndown levels

The above example illustrates the potential tosubstantially increase profit with additional turndown

capability. Clearly, over the period of a year the effect onannual profit is potentially dramatic. The amount ofturndown profit a plant will realize is dependent upon anumber of factors such as cost of gas, price of electricity andoperating profile. Historical plant hourly operatingeconomics will quickly provide an estimate of the potentialturndown profit that could be realized from a specific site.

Due to the potential profitability advantages discussed,gas turbine manufacturers and research institutes have goneto great lengths to optimize combustion systems to enableemissions compliant turn down techniques on modern gasturbine engines.

Typically, the challenge in achieving extendedturndown operation is the generation of high CO (carbonmonoxide) pollutants due to low combustor reaction zonetemperature resulting in an incomplete combustion process.High CO generation during turndown results in emissionsexceedance and fines by the local regulatory authority.Please refer to the introductory section of GT2010-22585[3] for a general description of typical turndownmethodologies, currently employed by various OEM’s.

A common technique utilized on heavy duty gasturbine engines to achieve lower turndown is to restrict theengine airflow (by modulation of the IGV-Inlet GuideVanes) at lower loads, thus forcing the engine operate at ahigher firing temperatures and hence minimizing thegeneration of CO. This methodology, while effective andsimplistic, results in elevated exhaust temperatures and hashistorically posed durability challenges to the latter stages ofthe turbine and downstream exhaust components such as theHRSG (Heat Recovery Steam Generator) in combined cyclepower plants. Excessive IGV closure at part load has alsobeen linked to aerodynamic instabilities in the compressor,as well as harmful inlet icing conditions.

The FlameSheetTM Combustion system utilizes a novelcombustor within combustor technique to control thegeneration of CO at low firing temperatures, thus enablingemissions compliant turndown operation with lower exhausttemperatures to enhance the mechanical integrity of thelatter turbine components and the HRSG.

Increased shale gas production has been credited forreduced NG (natural gas) prices in the U.S.A. Recoverableshale gas abundance in the world wide is shown in thegraphic below.

Fig. 4, Assessed Shale Gas and Shale Oil Basins of theWorld [4]


A normalized measure of fuel flexibility can berepresented using the Modified Wobbe Index (MWI) whichaccounts for variation in fuel heating value and density, andis defined as follows:

( )TSGLHV

´=MWI

Where:LHV = gas lower heating value (BTU/ft3)SG = Specific gravity of fuel gas relative to airT = Fuel gas absolute temperature (oR)

The Modified Wobbe Index is affected by both fuel gastemperature and heating value of the fuel. It is possible tooffset the effect of one of these parameters with the other tomaintain the MWI within an acceptable range.

According to the EIA (U.S. Energy InformationAssociation), shale gas composition varies substantiallyfrom one shale gas region to another across the U.S.A.Calculated MWI variation based on the compositions can beas high as 78%, see Figure 5 below. As such, a combustionsystem capable of operating with large fuel MWI variationis an asset to gas turbine power plants.

Fig. 5, Shale Gas composition variation across the USA [5]

FlameSheetTM CombustorInvented at PSM in 2002, the FlameSheetTM

combustion system has been designed to offer extendedoperational and fuel flexibility ranges to ensure maximumoperating capacity and reduced fuel costs. The design wentthrough multiple prototype design iterations, multiple highpressure rig test campaigns and engine tests throughout thepast 10 years before finalizing a production design for theGeneral Electric 7FA platform in 2014. Figure 6 illustratesthe potential improvements in operational and fuelflexibility that may be realized with a drop-in FlameSheetTM

combustion system.The FlameSheetTM combustion system is designed to:

Ø Provide extended fuel flexibility to allow simultaneousoperation on natural gas, liquefied natural gas, refineryoff-gas, high hydrogen content syngas, and low carboncontent syngas

Ø Extend turndown capability by an additional 20% loadwhilst maintaining emissions compliance.

Ø Operate below 9ppm of NOx and below 9ppm of COacross the load range, from extended turndown tobaseload and overfired operating conditions.

Ø Allow increased firing temperature of at least 50oF(28oC), improving cycle performance whilemaintaining emissions targets

Ø Achieve all targets without the addition of any diluentsuch as water/steam/nitrogen

Ø Provide durability to allow continuous operationwithout inspection for at least 24,000 hours or 900 starts

Ø Be easily retrofitted into existing F and E-class gasturbine platforms.

Fig. 6, FlameSheetTM operational and fuel flexibility incomparison to other standard F-class dry low emissions

systems

FlameSheetTM Combustor - OperatingPrinciple

The FlameSheetTM name is derived from the methodused for injecting the fuel-air mixture as a continuousuninterrupted sheet into the reaction zone of the combustorwhereupon an aerodynamically generated trapped vortex isutilized to anchor and stabilize the flame.

The combustor consists of two aerodynamic stages andfour fuel stages. The stages are designed for specificoperational aspects such as transient loading and extendedturndown operation. The FlameSheetTM system is acombustor within a combustor. Each of these 2 combustorscan be operated independently of each other. The twoaerodynamic stages consist of a pilot along the axis of thecombustor, and a main stage surrounding the pilot. The pilotand main stages are effectively two independent combustorswith their own robust flame stabilization mechanisms. Thisallows either combustor to be operated with the othercombustor OFF, which allows significant operationalflexibility.

Figure 7 illustrates the overall structure of theFlameSheetTM system. The pilot and main stages are fedfrom the compressor discharge plenum. Pilot air passesthrough the radially outermost circuit to the head end of thecombustor where it enters a radial inflow swirler. Fuel ismixed into the air stream through a row of vanes. The fuel-air mixture then enters the combustor and a flame is swirlstabilized behind a bluff body on the centerline of thecombustor [9, 10]. The main stage air flows along the


backside of the combustion liner and then through a mainfuel injector. The fuel-air mixture is then turned 180 degreesand flows into the combustor. As the flow enters thecombustor it separates off the combustion liner and forms astrong recirculation region, or aerodynamically trappedvortex which stabilizes the flame.

Fig. 7, Overall flow design of FlameSheetTM system [6]

The fundamental design of the main stage flamestabilization mechanism may simply be described incomparison to a commonly used backward facing stepsystem for flame stabilization. Figure 8 illustrates thiscomparison. The aerodynamic point of flow separation islabelled as ‘Equivalent Point 1.’ Since the main stage flowenters the combustor in the opposite direction to the flowwithin the combustor, the flow separates at the end of thecombustion liner. This separation creates a setting in whichan aerodynamically trapped vortex anchors the flame andthen recirculates hot combustion products providingenhanced stability, similar to the backward facing stepscenario. However, the recirculation generated from theFlameSheetTM main stage is significantly stronger than abackward facing step due to the flow turning a full 180degrees about ‘Equivalent Point 1’ in the FlameSheetTM

system. Ultimately, the flow will reattach to the liner at‘Equivalent Point 2,’ the exact position being dependentupon velocity magnitude and swirl magnitude within thecombustor. Computational fluid dynamics (CFD) velocityand temperature contours are shown in Figure 9.

EquivalentPoint 1

EquivalentPoint 2

Fig. 8, Illustration of flame stabilization mechanisms for abackward facing step and the FlameSheetTM combustor

Fig. 9, CFD Velocity contours(top) and TemperatureContours (bottom)

The design of the pilot stage flame stabilizationmechanism is similar to that of a typical swirl stabilizedflame. The center body recirculation region was designedfor stability when the combustor is in pilot-only operation.In addition, the aerodynamic flow area and swirl wereoptimized through testing for optimum emissionsperformance at both the lower operating load andthroughout premix load operation.

The pilot and main stages hence form twoindependent flame stabilization zones resulting in a“combustor within a combustor” configuration, which is keyto enhancing operational flexibility.

Similar to other commercial F-Class combustionsystems, the FlameSheetTM is operated in multiplecombustor modes before reaching the emissions incompliance lower operating load (LOL) point. Thecombustor operating modes are illustrated in Figure 10,below. During the first mode, the combustor is ignited on aportion of the pilot flame stage and the engine is acceleratedbefore mode 2 is reached. During mode 2 another pilotflame stage is introduced and the unit is accelerated throughFull Speed No Load (FSNL) conditions and up to ~10%load. Mode 3 and mode 4 involve introducing the Main 1and 2 stages consecutively until the lower operating load(LOL) point is reached. Once all transfers are completed, theunit falls in emissions compliance and is offered forcommercial dispatch.

Fig. 10, Mode transfer comparison: FlameSheetTM (bottom)vs. 7FA DLN 2.6 (top)


FlameSheetTMCombustor–MechanicalDescription

The FlameSheetTM combustor is designed as amechanically “drop-in” system, and different versions maybe implemented for cross platform applications. Themodularity in the design of the combustor is unique since itallows the system to be modified for various E and F classengine platforms while the drop-in aspect of the systemallows the combustor to be installed in these platforms withno impact to the mating envelope or mating hardware. TheFlameSheetTM mechanical design also eliminates the needfor internal bellows or fuel seals, which typically limit thereliability of other combustion systems. Only the pilotcartridge configuration is adjusted to switch between gasonly and dual (gas and liquid) fuel operations. Figure 11,illustrates an exploded view of the 7FA FlameSheetTM

Combustor.

Fig. 11, 7FA FlameSheetTM combustion system components

FlameSheetTM Rig testing andBenchmarking to 7FA DLN 2.6 combustionsystem

Rig Test setup/descriptionThe FlameSheetTM combustion system was

benchmarked against the 7FA DLN2.6 combustor at a highpressure combustion rig test facility. The results obtained inthis section are from the PSM high pressure combustion testrig. The full scale test rig (shown in Figure 12 below) iscapable of delivering full F-class base load operatingconditions with the following maximum operatingconditions:

· Air flow = 60 pps (27 kg/s)· Pressure = 350 psia (24 bar)· Inlet Air temp = 1200 oF (920 oK)· Exhaust temp 3500 oF (2200 oK)The test rig provides optical access to the flame as well

as allowing measurement of emissions, combustiondynamics, pressures, and temperatures. Various fuel gasesare provided to the combustion system being evaluatedthrough the facility alternative fuels infrastructure.

Fig. 12, PSM full scale combustion test rig

As shown in Figure 12, air is supplied to the test section intwo locations from a single air feed pipe (blue arrows). Aseries of baffles are installed within the test section tosimulate the engine air flow pattern to the combustor, aswell as the engine equivalent acoustic plenum. The latter isan important consideration to correctly duplicate fieldengine combustion dynamics within the test rig. Thecombustor is exhausted through a slave transition duct toproperly simulate the engine acoustic boundary condition ofthe first stage vane (red arrows). The hot gases then travelthrough the water cooled exhaust duct (red arrows). A quartzwindow is located in the exhaust on the combustorcenterline for observation of the flame (sample flame viewsshown in Figures 12 and 14). The exhaust turns 90 degreesaround the quartz window before entering a back pressurevalve (not shown) which simulates the back pressure effectof a turbine and is used to properly modulate combustionsystem pressure drop.

Emissions measurements are taken inside the testrig at two separate locations. The first emissionsmeasurement, as shown in Figure 11, is taken inside thecombustor transition piece near the AFT end before thecross sectional area begins to decrease at the throat. Thespecific emissions rake used during FlamesheetTM testingtakes emissions samples from 7 different radial locationsthat are equally spaced across the flow path. Reportedemissions values from the test rig are an average of all 7sampling locations.

The second emissions probe is located in theexhaust section of the test rig before the test rig backpressure valve. This emissions rake takes emissions from 3radial locations, also equally spaced. Again, reportedemissions are an average of all of the radial samplinglocations.

Generally, sampling efficiency of the emissionssystems is maintained within 10%, of a verified carbonbalance with fuel input, to confirm accuracy. Whenreporting CO values, the transition piece emissionsmeasurement location, as depicted in Figure 11, is utilizedwith the knowledge that it may result in slightly higher COreadout. Typically, in the engine, the CO burnout reactioncontinues as the combustion products pass through the firstvane. The additional CO burnout in the first vane is nottypically captured in the Rig measurement and as such mayresult in slightly higher CO measurement.

The FlameSheetTM was tested alongside a DLN 2.6combustion system and both combustion systems were runto exact 7FA engine conditions at various loads using thesame emissions and data acquisition systems. Figure 13,


below, illustrates the 7FA FlameSheetTM and DLN 2.6 highpressure combustion test rig setup.

EmissionsMeasurement Plane

7FA DLN 2.6

7FA FlameSheet

Fig. 13, 7FA DLN 2.6 vs FlameSheetTM Rig test setup

Rig Emissions Bench marking vs. 7FARig emissions were obtained for both the

FlameSheetTM and the DLN 2.6 while at true full enginepressures and temperatures. The emissions results showedthat equivalent NOx performance at Baseload firingtemperatures were achieved. However, the FlameSheetTM

was able to maintain lower NOx emissions than the DLN2.6 to sub 6ppm NOx at overfired conditions, see Fig 14below. The results below are for ISO day baseloadconditions (shell temperature and pressure), and the effect ofhot or cold day conditions on emissions for both combustorsmaintain the same trend.

Fig. 14, FlameSheetTM and DLN 2.6 NOx emissions versusfiring temperature

CO emissions are typically the limiting factorgoverning the minimum operating load point on the engine.Maintaining sub 9ppm CO at the lowest possible firingtemperature or load is desired. Figure 15 demonstrates theFlameSheet™ combustor having an additional 15%-20% ofturndown advantage over the 7FA DLN2.6 combustor withboth lean and rich fuel schedule configurations, anddemonstrating down to 30% 7FA engine load condition withsub 9ppm CO compliance. For reference, the reported rigCO values were taken at the TP emissions probe location asshown in Figure 13 above.

Fig. 15, FlameSheetTM showing improved turndownperformance during high pressure rig testing

Engine Testing Validation/Benchmarking.The FlameSheet™ combustor was installed on two

commercially operating “unflared” 7FA heavy duty gasturbine engines. This section focuses on the details of theinstallation and the 7FA engine emissions performance withthe FlameSheetTM combustor at the min load (LOL),baseload and overfired conditions. It is of note that the OEMDLN 2.6 engine operational data was measured on the sameengines and recorded by PSM and the customer before theinstallation outage to install the FlameSheet combustors.

Mechanical installationThe FlameSheet™ combustor installation on the

General Electric 7FA heavy duty gas turbine wasdemonstrated to take approximately one week, similar to atypical Combustor Inspection (CI). During the installation,the 7FA combustors and fuel flex lines were replaced. Sincethe FlameSheetTM is a four stage combustion system, nochanges were required to the fuel skid, and the existing fuelfeed ring manifolds on the engine were utilized. Feedbackfrom the installation efforts were positive due mainly to theFlameSheetTM smaller footprint relative to that of the OEMDLN2.6 combustion system, see Figure 16 below.

Fig. 16, Illustration of FlameSheetTM smaller footprint tothat of a DLN2.6 (red wireframe) combustion system on a

7FA heavy-duty gas turbine


Fig. 17, FlameSheetTM combustion system installation on a7FA heavy duty gas turbine in 2015 [7].

Fig. 18, FlameSheetTM combustion system installation on a7FA heavy duty gas turbine in 2015 [7]

Engine emissions performanceInitial commissioning consisted of finding

optimum settings to reach full speed no load (FSNL) andthen spinning reserve. Then, the flame is systematicallytransferred between different combustor operational modesin order to reach the normal premix, commercial operatingmode. Once in the final combustor mode, combustor designpoints were demonstrated and successfully met.

The FlameSheetTM combustor is designed to be aperformance-neutral, drop-in combustion system. As such,the FlameSheetTM matches the heat rate of the retrofitted gasturbine engine. The FlameSheetTM consistentlydemonstrated similar or lower combustor pressure dropvalues as compared to the baseline, replaced combustionsystem. A low pressure drop variant is also available tofurther increase power output. Furthermore, heat ratecomparison across entire commercial load range forinstalled engines shows that FlameSheetTM meets therequirement of being performance neutral for the gasturbine.

Due to the gas turbine’s specific HRSG liferequirements, the firing curve was adjusted at lower loads toresult in a lower exhaust gas temperature, effectivelylowering firing temperature for the lower operating loadrange. This is particularly important as it also affects thecombustion reaction zone temperature for a givennormalized load which in-turn negatively impacts COperformance. CO is a by-product of incomplete chemicalreactions occurring during the combustion process anddiminishes both with increasing firing temperature andresidence time. In most cases, CO emissions are the limitingfactor which determines a gas turbine’s turndown capability.With this being taken into consideration, the FlameSheetTM

successfully demonstrated sub 9ppm CO corrected to 15%O2 at ~40% load at reduced exhaust temperature on bothinstalled units, representing nearly a 20% load turndownimprovement over the previously installed DLN 2.6, runningin the same machine (see Figure 19).

Fig. 19, FlameSheetTM demonstrating 15-20% additionalturndown over the DLN 2.6 with in-compliance CO

emissions operating at a lower exhaust temperature on a 7FAheavy-duty gas turbine.

Another pollutant that is strictly regulated with gasturbine engines are the minor species NO and NO2, oftensimply referred to as NOX. Gas turbine engines whichproduce high levels of NOX are typically outfitted with somemeans to reduce NOX before it reaches the environment.These processes include selective catalytic reduction (SCR),where anhydrous ammonia is utilized with the aid of acatalyst to form Nitrogen gas (N2) and water. The additionof diluents such as water or steam to the reaction zone isalso a common technique used in diffusion stylecombustors. While effective, such NOx abatementtechniques present additional cost and complexity. TheFlameSheetTM however, consistently demonstrates sub 9ppmNOX at 15% O2 from the lower operating load up tobaseload firing temperatures without any form of reductionrequired. Figures 20 & 21 illustrate a significant operatingmargin to sub 9ppm NOx emissions. The tuning marginrefers to the amount of variation in stage fuel splits which


can be achieved while maintaining combustion dynamicsand emissions below targeted values. A margin of at least2% ensures that targets will be maintained across allambient conditions.

Fig. 20, Illustrating 5PPM NOx tuning at F-Class Baseloadconditions on a 7FA unflared heavy-duty gas turbine.

Fig. 21, FlameSheetTM demonstrates sub 9ppm operationacross the extended load range and transfer to premix

operation at 25% engine load.

Also of note, is that the transfer point to full premix(where NOx compliance is achieved) for the FlameSheetTM

occurs near 25% load, whereas for the DLN2.6 the transferto full premix mode (mode 6 or 6Q) occurs typically above45% load. Consequently the DLN 2.6 NOx emissions can beup to an order of magnitude higher at part load thanFlameSheetTM. Figure 21 illustrates the wider range of sub 9ppm NOx emissions for FlameSheetTM operation.

Power plants may overfire the gas turbine foradditional power production when electricity prices arehigh. However, complying with emissions limits becomesincreasingly more challenging when overfiring a unit as theformation of NOX increases exponentially as a function ofreaction zone temperature. The FlameSheetTM providesoperators with the capability to overfire the gas turbineabove baseload while maintaining in compliance emissions.The FlameSheetTM combustor demonstrated sub 9ppm NOXat 15% O2 with up to 50oF (28oC) baseload overfire on anunflared 7FA gas turbine. With additional tuning, thecombustor demonstrated NOX levels as low as 6ppm at 15%O2 at the (+50oF) overfire conditions. Figure 22 illustratesFlameSheetTM combustor tuning at +50oF overfiredoperation on a 7FA gas turbine. This overfire condition wasachieved by keeping combustor inlet air flow constant atISO day baseload levels, and increasing fuel flow to achievethe +50oF increase above baseload firing turbine inlettemperature.

Fig. 22, FlameSheetTM overfire to 50oF (28oC) over baseloadfiring temperature with in-compliance NOx emissions

Rig to Engine benchmarkingTesting the 7FA FlameSheetTM combustion system in a

high pressure test rig and running the same system in acommercially operating 7FA heavy-duty gas turbineprovided a correlation between engine and rig testing resultsfor the same operational load points. Figure 21 belowprovides a comparison of NOx emissions results obtainedbetween different FlameSheetTM rig build configurations andthe 7FA engine.


Turbine Inlet Temperature7F

ABa

seLo

ad+2

50F

Turb

ine

Inle

tTem

pera

ture

7FA

Base

Load

Turb

ine

Inle

tTem

pera

ture

7FA

Base

Load

+50F

Turb

ine

Inle

tTem

pera

ture

Test Rig Build 1Test Rig Build 2Test Rig Build 3Commercial Engine

Fig. 23, FlameSheetTM NOx Emissions comparison enginevs. various rig test builds at base load (100%) and up to

250oF (140oC) overfire conditions

Figure 23 illustrates the lowest achievable NOx atgiven operating points. Therefore this illustrates theFlameSheetTM engine operating below 5ppm for all points atand below baseload. The NOx levels at Baseload matchedclosely between the engine and the rig Although typicallybetter NOx performance should be expected on the rig dueto the absence of can-to-can variability, this variability wasminimized due to the tightly controlled air and fuel flowbalance on the FlameSheetTM hardware.

Also of interest is the FlameSheetTM additional overfirecapability as demonstrated on the high pressure test rig. Asshown in Figure 23 above, the FlameSheetTM was overfiredby ~250oF (140oC) beyond F-class baseload whilemaintaining ~12ppm NOx at 15% O2. Such low NOxcapability at higher turbine inlet temperatures furtherdemonstrates the FlameSheetTM combustor’s capabilitybeyond F-Class and into the H and J class engine platformapplications. These extreme overfire rig tests were also usedto demonstrate the durability margin of the FlameSheetTM.

Fuel FlexibilityOne of the key features of the FlameSheetTM combustor is toprovide extended fuel flexibility to allow simultaneousoperation on a wide range of fuel types and achieve alltargets without the addition of a diluent, this capability isattributed mainly to the robust mixing techniques and highpremixer exit velocities on the FlameSheetTM. Thecombustor has been tested with MWI variation of up to 30%as shown in Figure 24.

-20%

-15%

-10%

-5%

0%

5%

10%

15%

20%

natural

gas- unhea

ted

natural

gas- hea

ted

11.5%

H2

23%

H2

11.5%

H2,8%

C2H6,

11.2%

C3H8

23%

H2,16

.3%C2H

6,21

.9%C3H

8

8.9%

C2H6,

12.4%

C3H8

20.4%

C2H6,

27.5%

C3H8

23%

H2,23

.3%C2H

6,15

%C4H

10

40%

H2

19.9%

H2,20

%C2H

4,19

.2%C2H

6,

60%

H2

Mod

fied

Wob

beIn

dex

Fig. 24, FlameSheetTM Tested alternate fuel mixtures andModified Wobbe Index variation for fuel [3]

The effect of MWI on emissions is shown in Figure 25 withall points taken at steady state operating conditions [3]. Inall cases, emissions were not significantly affected and NOxemissions were maintained below 6ppm, thus validating theFlameSheetTM design assertion that varying the fuel MWIwould not affect the performance of the system.

0

1

2

3

4

5

6

7

8

9

44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Modified Wobbe Index

NO

xan

dC

O(@

15%

O2)

24% H2

12% H2

NG w/ hot fuel

12% H2,66%CH4,11%C2H6,12%C3H8

71%CH4,15%C2H6,14%C3H8

NG w/ cold fuel

NOx

CO

Fig. 25, Effect of MWI on emissions for a range of fuelconstituents [3]

Hydrogen Testing

Hydrogen operation is of particular interest as it is acommon byproduct of chemical processes and is oftenreadily available at chemical processing facilities andcogeneration gas fired power plants. The benefit ofdisplacing some of the natural gas with freely availablehydrogen can have a significant impact on reducing theoperational costs of the plant. For example, on a typicallybaseloaded 7FA Heavy-duty gas turbine, and assumingtoday’s U.S.A. natural gas price of ~$2.50 MMBtu,displacing 40% of the Natural gas fuel volume with freeavailable Hydrogen can result in ~16.5% reduction inNatural gas utilization and a $5M yearly cost savings.


A challenge with burning hydrogen fuel inpremixed combustors is flashback. Flashback is described asthe process where the flame can propagate into the premixerregion causing damage to a premixed combustion system.Reactive fuels such as hydrogen can put the combustionsystem at risk of flashback due to its higher flame speed,which, with increased concentration, may exceed thepremixer exit velocity causing flame propagation anddamage. The FlameSheetTM combustion has demonstratedhigh tolerance to increased Hydrogen concentrations of upto 65% by volume, this was demonstrated in the highpressure rig facility at F-Class operating conditions, seeFigure 26 below.

0123456789

0% 10% 20% 30% 40% 50% 60% 70%

NO

x15

%O

2(p

pmv)

H2 Volume FractionFig. 26, FlameSheetTM high pressure rig testing with

Hydrogen at F-Class operating conditions.

The ability of the FlameSheetTM to robustly burn highhydrogen fuels also makes this combustion system an idealcandidate for reduced CO2 applications. This is furtherdescribed in [18].

ConclusionsThe F-class engine and rig operational performance of

the 7FA FlameSheetTM combustion system was reviewed inthis paper. The FlameSheetTM low emissions combustiontechnology is modularly designed to allow retrofits ofdifferent FlameSheetTM combustion system versions on E &F class heavy-duty gas turbine platforms, maximizinghardware interchangeability. A fast retrofit on an existing7FA heavy-duty gas turbine and a ‘Plug-in’ approach,reducing plant outage duration was reviewed.

Designed for operational and fuel flexibility, theFlameSheetTM Combustor is positioned to address thecurrent and future energy market conditions which havebeen affected in the recent years by the high penetration ofrenewable energy sources and abundance of Shale gas.

The FlameSheetTM Combustor was rig tested in a highpressure rig test facility at full F-class engine conditionsalongside a 7FA DLN2.6 combustor for benchmarking toother commercially available low emissions combustionsystems. The FlameSheetTM was able to demonstratesuperior overfire NOx emissions and Turndownperformance. Engine testing on a commercial 7FA heavy-duty gas turbine validated the FlameSheetTM Rig results,demonstrating up to 20% improved turndown capability

with reduced exhaust temperatures. Baseload and overfiredemissions performance were shown to be leading theindustry with sub 5ppm baseload and sub 6ppm overfired(+50oF / +28oC) NOx performance.

The Fuel flexibility aspect of FlameSheetTM was alsodiscussed with emphasis on heavy hydrocarbon andhydrogen fuel operation. The ability to burn up to 65% H2by volume fuels positions power plant users to takeadvantage of available cost effective alternative fuels.

The new dual fuel capable FlameSheetTM combustionsystem provides extended operational and fuel flexibility formodern gas turbine power plants.

References

1. American Wind Energy Association, “U.S. Wind IndustryThird Quarter 2015 Market Report”, October 22, 2015.

2. International Energy Agency, “Renewable Energy Mid-Term Market Report 2015”, IEA publications, 2015 ISBN:978-92-64-24367-5.

3. Stuttaford, P. Rizkalla, H., Chen, Y., Fawcet, J, Copley,B., “Extended Turndown, Fuel Flexible Gas TurbineCombustion System”, ASME Turbo Expo 2010, Glasgow,Scotland GT2010-22585

4. U.S. Energy Iformation Administration, “TechnicallyRecoverable Shale Oil and Shale Gas Resources: AnAssessment of 137 Shale Formations in 41Countries Outsidethe United States”, June 2013, U.S Dept. of Energy

5. Bullin, Keith, Krouskop, Peter, “Composition VarietyComplicates Processing Plans for US Shale Gas”, AnnualForum, Gas Processors Association—Houston Chapter, Oct.7, 2008, Houston

6. Stuttaford, P., Jorgensen, S., Hui, T. Chen, Y., Rizkalla,H., Oumejjoud, K., “FlameSheetTM Combustor Dome”,2014, United States Patent Application number US2014/0090390

7. Combined Cycle Journal, “World-class competition fromthird-party suppliers”, CCJ Publications August 19, 2015.

8. Stuttaford, P., “Alternative fuel considerations for gasturbine combustion”, ASME Turbo Expo 2007, Montreal,Canada, GT2007-27549.

9. Stuttaford, P.J., Jennings, S., Green, A. McMahon, R.,Chen, Y., Rizkalla, H., Carella, J., Duraibabu, V., Spalding,M., “FlameSheetTM Combustor”, 2005, United States Patentnumber 6,935,116


10. Stuttaford, P.J., Margarit-Bel, N., Chen, Y., Oumejjoud,K., Jennings, S., “Method of operating a combustion systemfor increased turndown capability”, 2006, United StatesPatent number 7,137,256

11. Leiuwen, T., McDonell, V., Petersen, E., Santavicca, D.,2006, “Fuel Flexibility Influences on Premixed CombustorBlowout, Flashback, Autoignition, and Stability,” ASMETurbo Expo 2006, Barcelona, Spain, GT2006-90770.

12. "Specification for Fuel Gases for Combustion in Heavy-Duty Gas Turbines", GEI 41040j, GE Energy, April 2007.

13. Nag, P., “LNG Flexibility Solutions for Siemens’ GasTurbines”, Electric Power Conference and Exhibition 2007.

14. Nag, P., Little, D., Teehan, D., Wetzl, K., Elwood, D.,“Low Load Operational Flexibility for Siemens G-class GasTurbines”, Power-Gen International, Orlando, Florida,December 2008.

15. Vandervort, G.L., “9ppm NOx/CO Combustion systemfor “F” Class Industrial Gas Turbines”, Journal ofEngineering for Gas Turbines and Power, Vol. 123, April2001.

16. “Gas Turbine Upgrades for Enhancing OperationalFlexibility”, EPRI, Palo Alto, CA: 2007, 1012720

17. “The tuning methodology of GE 7FA + e DLN-2.6 gasturbine combustor”, Jeongseog Oh, Minki Kim, YoungbinYoon, Applied Thermal Engineering 36 (2012) 14-20

18. Stuttaford, P. and Oumejjoud, K. “Low CO2Combustion System Retrofits for Existing Heavy Duty GasTurbines”, ASME Turbo Expo 2008, Berlin, GermanyGT2008-50814

Documents

FlameSheetTM Combustor Engine and Rig … Combustor Engine and Rig Validation for Operational and Fuel Flexibility with Low Emissions Peter Stuttaford, Hany Rizkalla, Khalid Oumejjoud,