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Hindawi Publishing CorporationAdvances in Mechanical EngineeringVolume 2010, Article ID 342357, 13 pagesdoi:10.1155/2010/342357

Research Article

Combustion of Syngas Fuel in Gas Turbine Can Combustor

Chaouki Ghenai

Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science, Florida Atlantic University,777 Glades Road, 36-177, Boca Raton, FL 33134, USA

Correspondence should be addressed to Chaouki Ghenai, [email protected]

Received 20 November 2009; Revised 15 August 2010; Accepted 24 September 2010

Academic Editor: Hyung Hee Cho

Copyright 2010 Chaouki Ghenai. This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Numerical investigation of the combustion of syngas fuel mixture in gas turbine can combustor is presented in this paper. Theobjective is to understand the impact of the variability in the alternative fuel composition and heating value on combustionperformance and emissions. The gas turbine can combustor is designed to burn the fuel eciently, reduce the emissions, andlower the wall temperature. Syngas mixtures with dierent fuel compositions are produced through dierent coal and biomassgasification process technologies. The composition of the fuel burned in can combustor was changed from natural gas (methane)to syngas fuel with hydrogen to carbon monoxide (H2/CO) volume ratio ranging from 0.63 to 2.36. The mathematical modelsused for syngas fuel combustion consist of the k- model for turbulent flow, mixture fractions/PDF model for nonpremixed gascombustion, and P-1 radiation model. The eect of syngas fuel composition and lower heating value on the flame shape, gastemperature, mass of carbon dioxide (CO2) and nitrogen oxides (NOx) per unit of energy generation is presented in this paper.The results obtained in this study show the change in gas turbine can combustor performance with the same power generationwhen natural gas or methane fuel is replaced by syngas fuels.

1. Introduction

Over the past decades domestic and imported oil was usedfor transportation, and domestic coal and natural gas havebeen used as the primary fuels for power generation systems.Today the emission regulations for power plant have becomemore stringent. The concern today with the combustion offossil fuels is the new emission regulations for power plantwith regards to carbon dioxides (CO2) and nitrogen oxides(NOx). Nitrogen oxides (NOx) are responsible for smog andacid rain, and the carbon dioxides (CO2) are one of the maingreen house gases responsible for global warming. Anotherconcern with fossil fuels is the high cost of imported oil.Alternative fuels that can be produced using local feed stocks,burn eciently, and produce low emissions are needed. Withthe development of advanced technologies, coal, biomass,or waste products can be used in power generation systemsto produce low emissions comparable to the ones obtainedwith natural gas fuel. This can be achieved through theIntegrated Gasification Combined Cycle (IGCC). Dierenttypes of gasifiers are used to gasify the solid fuels (coal,biomass or waste products) and produce synthetic gas. The

syngas is then cleaned and burned in gas turbine andthe hot exhaust gas is used to produce steam for steamturbine. Future power generation systems using IntegratedGasification Combined Cycle (IGCC) will have a highereciency and generate lower carbon dioxide and nitrogenoxides emissions. The IGCC systems are used to producesyngas fuel with dierent compositions from solid fuel feedstocks using dierent gasification process technologies. Thesyngas produced through the gasification process consistsmainly of hydrogen (H2) and carbon monoxide (CO) andinert gas such as nitrogen (N2), water vapor (H2O), andcarbon dioxide (CO2). Syngas has also less energy density(KJ/Kg) than natural gas. The main characteristics of thesyngas fuel are the lower heating value, the H2/CO ratio, andthe fraction (up to 50%) of noncombustibles such as steam,carbon dioxide, and nitrogen. For syngas fuels combustion,the eect of hydrogen content is very important. The burningvelocity increases with the hydrogen content because thedensity of the mixture is very low compared to the densityof natural gas. The replacement of methane with syngas withhigh hydrogen content will help to reduce the CO2 emissions.On the other hand, the dilution of fuel with nitrogen, water,

2 Advances in Mechanical Engineering

and carbon dioxide reduces the peak flame temperature andconsequently the NOx emissions.

Gas turbines are designed primarily to be fueled withnatural gas (consisting primarily of methane), and supply-ing them with syngas (fuel gas from biomass, coal, andwaste gasification) presents certain challenges that mustbe addressed. How can we burn eciently syngas fuelwith dierent chemical compositions and heating valuesin gas turbine combustors designed for natural gas? Inorder to meet these challenges, we need to understandthe physical and chemical processes of syngas combustion.Information regarding syngas flame shape, flame speed,gas temperatures and pollutant emissions such as NOxand CO2 for a range of syngas compositions and heatingvalues is needed for the design of gas turbine combustors.Giles et al. [1] performed a numerical investigation on theeects of syngas composition and diluents on the structureand emission characteristics of syngas counterflow diusionflame. The counter flow syngas flames were simulated usingtwo representative syngas mixtures, 50%H2/50%CO and45%H2/45%CO/10%CH4 by volume, and three diluents,N2, H2O, and CO2. The eectiveness of these diluents wascharacterized in terms of their ability to reduce NOx insyngas flames. The results indicated that syngas nonpremixedflames are characterized by relatively high temperatures andhigh NOx concentrations and emission indices. The presenceof methane in syngas decreases the peak flame temperature,but increases the formation of prompt NO significantly.They also concluded that the presence of methane in syngasreduces the eectiveness of all three diluents. Lean premixedcombustion of hydrogensyngas/methane fuel mixtures wasinvestigated experimentally by Alavandi and Agarwal [2].Methane (CH4) content in the fuel was decreased from 100%to 0% (by volume), with the remaining amount split equallybetween carbon monoxide (CO) and hydrogen (H2), thetwo reactive components of the syngas. Experiments fordierent fuel mixtures were conducted at a fixed air flowrate, while the fuel flow rate was varied to obtain a rangeof adiabatic flame temperatures. The CO and nitric oxide(NOx) emissions were measured downstream of the burner,in the axial direction to identify the postcombustion zoneand in the transverse direction to quantify combustion uni-formity. The results show that increasing H2/CO content inthe fuel mixture decreased both the CO and NOx emissions.Experimental study on the fundamental impact of firingsyngas in gas turbines was performed by Oluyede [3]. Thegoal of this study was to determine the appropriate amountof reduction in firing temperature needed to maintain thesame hot section temperatures as experienced with naturalgas firing. The results show that volume fraction of hydrogencontent in syngas fuel significantly impacts the life of hotsections as a result of higher flame temperature for hydrogenrich fuels and also the moisture content of combustionproducts. Correlations were obtained indicating the levelof firing temperature reduction, necessary for hot sectiondurability in terms of hydrogen contents and lower heatingvalue of the fuel. The combustion of hydrogen-enrichedmethane in a lean premixed swirl burner was investigatedby Schfere [4]. The results, using methane/hydrogen fuel

mixtures, showed that the addition of up to 41% hydrogensignificantly extended the lean burning limit. For operatingconditions near the lean stability limit, the addition of amoderate amount of hydrogen to the methane/air mixtureresulted in a significant increase in the OH concentrationand a more robust appearing flame. Pater [5] investigatedthe thermo acoustic instabilities during turbulent syngascombustion. He used numerical method to predict acousticfields and instabilities during syngas combustion. The modelwas used to identify frequencies at which instabilities occur.

The challenges of fuel diversity while maintaining supe-rior environmental performance of gas turbine engineswere addressed by Rahm et al. [6]. They reviewed thecombustion design flexibility that allows the use of a broadspectrum of gas and liquid fuel including emerging syntheticchoices. Gases include ultra-low heating value process gas,syngas, ultrahigh hydrogen, or higher heating capabilityfuels. The integration of heavy-duty gas turbine technologywith synthetic fuel gas processes using lowvalue feed stocksin global power generation marketplace was covered byBrdar and Jones [7]. In their paper they summarized theexperience gained from several syngas projects and lessonslearned that continue to foster cost reductions and improvethe operational reliability of gas turbine. They concludedthat further improvements in system performance and plantdesign are needed in the future. The design of combustionsystems using syngas as fuel can take advantage of CFDanalysis to optimize the eciency of the combustion systemwith respect to the limitations of pollutants emission. Theaim of this work is to analyze the fundamental impactsof firing syngas in gas turbine combustor and predict thechanges in the firing temperature and emissions with respectto natural gas or methane combustion.

2. Governing Equations

The mathematical equations describing the syngas fuel com-bustion are based on the equations of conservation of mass,momentum, and energy together with other supplementaryequations for the turbulence and combustion. The standardk- turbulence model is used in this study. The equationsfor the turbulent kinetic energy k and the dissipation rate ofthe turbulent kinetic energy are solved. For non premixedcombustion modeling, the mixture fraction/PDF model isused. The timeaveraged gas phase equations for steadyturbulent flow are:

xj

(ui

) = xi

(

xi

)

+ S. (1)

is the dependent variable that can represent the velocityui, T the temperature, k the turbulent kinetic energy, thedissipation rate of the turbulent kinetic energy, and f themixture fraction. The governing equations are:

2.1. Continuity.

uixi

= 0. (2)

Advances in Mechanical Engineering 3

0 0.05 0.1

0.025 0.075

(m)Z

Y

X

(a)

(m)

X

Y

Z0

0.05

0.1

0.15

0.2

(b)

Figure 1: Geometry of the gas turbine can combustor, (a) primary air (blue) and six fuel inlets, (b) secondary air (blue) and outlet.

0 0.1 0.2

0.05 0.15

(m)

Figure 2: Mesh for the basic geometry of gas turbine cancombustor.

Z

Y

X

0 0.1 0.2

0.05 0.15

(m)

300511722933

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Temperature

(K)

Figure 3: Temperature contours (X-Z Plane, Y = 0): combustionof methane in gas turbine can combustor.

2.2. Momentum Equation.

(uiuj

)

xj= P

xi+(ti j + i j

)

xj, (3)

where ti j is the viscous stress tensor defined as:

ti j = [(

uixj

+ujxi

)

23ukxk

i j

]

,

i j = 1 if i = j, i j = 0 if i /= j.(4)

i j is the average Reynolds stress tensor defined as: i j =ui uj

i j = t[(

uixj

+ujxi

)

23ukxk

i j

]

23

(ki j

), (5)

where k is the average turbulent kinetic energy defined as:k = (1/2)ui uj , t is the turbulent eddy viscosity expressedas: t = ck2/, where C is constant (C = 0.09) and isthe average dissipation rate of the turbulent kinetic energyand defined asfollows : = ui /xjui /xj .

2.3. Turbulent Kinetic Energy Equation.

(kuj

)

xj=

[( + t/k

)(k/xj

)]

xj+ Gk , (6)

where k = 1 and Gk is the production of the turbulentkinetic energy defined as

GK = t[(

uixj

+ujxi

)]uixj

23uixj

i j

[tukxk

+ k]. (7)

2.4. Dissipation of the Kinetic Energy.

(uj

)

xj= C1

kGk +

[( + t/

)(/xj

)]

xj C2

2

k,

(8)

where C1 = 1.44, C2 = 1.92, and = 1.3.


0 0.1

0.025 0.075

(m)0.05Y

XZ

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(K)

Z = 134 mm

(a)

0 0.1

0.025 0.075

(m)0.05Y

XZ

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(K)

Z = 200 mm

(b)

0 0.1

0.025 0.075

(m)0.05

X

Y

Z

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(K)

Z = 300 mm

(c)

0 0.1

0.025 0.075

(m)0.05 X

Y

Z

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(K)

Z = 400 mm

(d)

0 0.1

0.025 0.075

(m)0.05 X

Y

Z

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(K)

Z = 500 mm

(e)

X

Y

Z0 0.1

0.025 0.075

(m)0.05

300511722933

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Temperature

(K)

Z = 590 mm (Exit)

(f)

Figure 4: Temperature contours (X-Y Plane)Combustion of methane in gas turbine can combustor.

2.5. Mixture Fraction f . In non-premixed combustion, fueland oxidizer enter the reaction zone in distinct streams.The PDF/mixture fraction model is used for non premixedcombustion modeling. In this approach individual speciestransport equations are not solved. Instead, equation for theconserved scalar ( f ) is solved, and individual componentconcentrations are derived from the predicted mixturefraction distribution. The mixture fraction equation is givenby

( f uj

)

xj=

[(t/t

)( f /xj

)]

xj+ Sm. (9)

The mixture fraction, f , can be written in terms of elementalmass fraction as

f = Zk Zk,OZk,F Zk,O , (10)

where Zk is the element mass fraction of some element k.Subscripts F and O denote fuel and oxidizer inlet streamvalues, respectively. For the mixture fraction approach, theequilibrium chemistry PDF model is used. The equilibriumsystem consists of 13 species (C, CH4, CO, CO2, H, H2, H2O,N2, NO, O, O2, OH, HO2). The chemistry is assumed to befast enough to achieve equilibrium.


Z

Y

X0 0.1 0.2

0.05 0.15(m)

3113579111416

Velocity w

(ms1)

Figure 5: Contours of the velocity w (z-direction) in the y-z plane:combustion of methane in the gas turbine can combustor.

2.6. Energy Equation.

((E + p

)u j)

xj

=[

(ke)(T/xj

) j h j J j +

(euj

)]

xj+ Sh,

(11)

where E is the total energy (E = h p/ + v2/2, whereh is the sensible enthalpy), ke is the eective conductivity(k + kt : laminar and turbulent thermal conductivity), J j isthe diusion flux of species j, and Sh is the term source thatincludes the heat of chemical reaction, radiation, and anyother volumetric heat sources.

2.7. Equation for the P-1 Radiation ModelRadiation FluxEquation. The P-1 radiation model is used in this studyto simulate the radiation from the flame. The radiationmodel is based on the expansion of the radiation intensityinto an orthogonal series of spherical harmonics (Cheng [8]and Siegel and Howell [9]). The P-1 radiation model is thesimplest case of the P-N model. If only four terms in theseries are used, the following equation is obtained for theradiation flux:

qr = 13(a + S) CSG, (12)

where a is the absorption coecient, S is the scatteringcoecient, G is the incident radiation, and C is the linear-anisotropic phase function coecient (Cheng [8] and Siegeland Howell [9]).

The transport equation for G is

(G) aG + 4aT4 = SG,

= 1(3(a + S) CS) .

(13)

3. Geometry, Boundary Conditions, Mesh, andNumerical Method

The gas turbine can combustor is designed to burn the fueleciently, lower the emissions, and keep the combustor wall

temperatures low. The basic geometry of the gas turbine cancombustor is shown in Figure 1. The size of the combustor is590 mm in the Z direction, 250 mm in the Y direction, and230 mm in the X direction. The primary inlet air is guidedby vanes to give the air a swirling velocity component (seeFigure 1(a)). The boundary conditions of the primary air areas follows: the injection velocity is 10 m/s, the temperatureis 300 K, the turbulence intensity is 10%, mixture fractionf = 0 and the injection diameter is 85 mm. The fuel isinjected through six fuel inlets in the swirling primary airflow (see Figure 1(a)). The boundary conditions of the fuelare as follows: mass flow rate, 0.001 Kg/s, the temperatureis 300 K, the turbulence intensity is 10%, mixture fractionf = 1 and the injector diameter is 4.2 mm. The secondaryair or dilution air is injected at 0.1 meters from thefuel injector to control the flame temperature and NOxemissions. The secondary air is injected in the combustionchamber through six side air inlets each with a diameterof 16 mm (see Figure 1(b)). The boundary conditions ofthe secondary air are as folllows: the injection velocity is6 m/s, the temperature is 300 K, the turbulence intensity is10%, mixture fraction f = 0 and the injection diameter is16 mm. The can combustor outlet has a rectangular shape(see Figure 1(b)) with an area of 0.0150 m2. A quality meshwas generated for the can combustor (see Figure 2). Themesh consists of 106,651 cells or elements (74189 tetrahedra,30489 wedges, and 1989 pyramids), 234368 faces, and 31433nodes. The grid quality was checked, and the results showeda maximum cell squish of 0.94, maximum cell skewness of0.99, and a maximum aspect ratio of 83.17. The finite volumemethod and the first-order upwind method were used tosolve the governing equations. The solution procedure fora single-mixture-fraction system was to (1) complete thecalculation of the PDF look-up tables first, (2) start thereacting flow simulation to determine the flow files andpredict the spatial distribution of the mixture fraction, (3)continue the reacting flow simulation until a convergencesolution was achieved, and (4) determine the correspondingvalues of the temperature and individual chemical speciesmass fractions from the look-up tables. The convergencecriteria were set to 103 for the continuity, momentum,turbulent kinetic energy, dissipation rate of the turbulentkinetic energy, and the mixture fraction. For the energy andthe radiation equations, the convergence criteria were set to106.

4. Results

The impact of the variability in the syngas fuel compositionand low heating value on the combustion performance andemissions in gas turbine can combustor is performed in thisstudy. Table 1 shows the composition for the five syngasfuel and their lower heating values selected for this CFDanalysis. The syngas fuels were produced using dierentgasification processes (Todd [10]) and using dierent feedstocks (coal, biomass, waste). The range of the constituentsvolume fractions for the selected syngas fuels are hydrogen(1) (H2) = 22.6% 61.6%, (2) carbon monoxide (CO) =23.6%46.6%, (3) methane (CH4) = 0.1%6.9%,(4) carbon


0 0.05 0.1

0.025 0.075

(m)

Z X

Y01723445166888601032120413781548

Velocity.swirling strength

(s1)

Z = 134 mm

(a)

0 0.05 0.1

0.025 0.075

(m)

Z X

Y0163147637994110126142


(s1)

Z = 200 mm

(b)

0 0.05 0.1

0.025 0.075

(m)

Z X

Y01123344557688091102


(s1)

Z = 300 mm

(c)

0 0.05 0.1

0.025 0.075

(m)

Z X

Y091828374655647483


(s1)

Z = 400 mm

(d)

Figure 6: Contours of velocity swirling strength (X-Y plane): combustion of methane in gas turbine can combustor.

dioxide (CO2) = 5.6%17.9%,(5) Nitrogen (N2) = 1.1 %49.3%, and (6) water (H2O) = 0.3%39.8%. The hydrogento carbon monoxide volume ratio for thesefive syngas isbetween 0.63 and 2.36. Table 1 shows also that the lowerheating values for the syngas fuels are smaller comparedto the lower heating value of the methane. It is also notedthat syngas 1 (Schwarze Pumpe) has the highest hydrogenvolume fraction (61.9%), syngas 2 (Exxon Singapore) has thehighest carbon dioxide volume fraction, syngas 3 (Tampa)has the highest carbon monoxide volume fraction (46.6%),and syngas 5 (Sarlux) has the highest water vapor volumefraction (39.8%).

The contours of the predicted gas temperature for thecombustion of methane in gas turbine can combustor areshown in Figures 3 and 4. The maximum gas temperaturefor methane combustion is 2200 K. For the validation ofthe combustion model, the predicted flame temperaturefor methane combustion was compared to the adiabaticflame temperature. For natural gas or methane fuel andwith initial atmospheric conditions (1 bar and 20 C), thetheoretical flame temperature produced by the flame with afast combustion reaction is 2233 K. The predicted maximumtemperature of the combustion products or the adiabaticflame temperature compares well with the theoretical adia-batic flame temperature. The peak gas temperature is locatedin the primary reaction zone. The fuel from the six injectorsis first mixed in the swirling air before burning in theprimary reaction zone. The gas temperature decreases after

the primary reaction zone due to the dilution of the flamewith the secondary air.

Figure 4 shows the temperature contours (X-Y Plane)for methane combustion in can combustor at dierent axialpositions (Z = 134 mm to 590 mm). The first contour(Z = 134 mm) represents the gas temperature near the sixfuel injections. The fuel is injected from the six fuelinletsand mixed with the swirling air before the start of thecombustion. The size of the flame increases downstream andreach a maximum radius at Z = 200 mm. The radius andtemperature of the flame decrease after that with the increaseof the axial distance Z (Z = 300, 400, and 500 mm). Thelowest gas temperature is reached at the exit (Z = 590 mm)of the gas turbine can combustor. A uniform gas temperaturedistribution is obtained at the exit of the can combustor asshown in Figures 3 and 4.

The contours of the velocity w (Z-component) formethane combustion in gas turbine can combustor is shownin Figure 5. The primary air is injected in the Z-directionwith initial velocity of 10 m/s. The primary air is accelerated(up to 16 m/s) at the entrance of the combustors due tothe presence of swirlers vanes (see Figure 1). Swirlers curvedvanes are used to generate recirculation zone at the entranceof the combustion chamber. Strong recirculation regionsare produced in the fuel injection region. This will help toincrease the turbulence and mix very well the fuel and airin the primary reaction zone. This will in turn burn thefuel eciently and reduce the pollutants emissions. Figure 6


(m)Z

Y

X0

0.05

0.1

0.15

0.2

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(K)

CH4

(a)

(m)Z

Y

X0

0.05

0.1

0.15

0.2300476651827100311781354153017051881

Temperature

(K)

Syngas: H2/CO = 2.36

(b)

(m)Z

Y

X0

0.05

0.1

0.15

0.2300484668852103512191403158717711955

Temperature

(K)

Syngas: H2/CO = 1.26

(c)

(m)Z

Y

X0

0.05

0.1

0.15

0.2

300503706909111213151518172119242127

Temperature

(K)

Syngas: H2/CO = 0.8

(d)

Figure 7: Temperature contours for natural gas and syngas fuel mixtures with the same fuel mass flow rate: eect of Syngas composition(H2/CO).

Table 1: Syngas compositions.

ConstituentsSyngas 1Schwarzepumpe

Syngas 2Exxonsingapore

Syngas 3Tampa

Syngas 4PSI

Syngas 5Sarlux

Methane(CH4)

H2 61.9 44.5 37.2 24.8 22.7 0

CO 26.2 35.4 46.6 39.5 30.6 0

CH4 6.9 0.5 0.1 1.5 0.2 100

CO2 2.8 17.9 13.3 9.3 5.6 0

N2 1.8 1.4 2.5 2.3 1.1 0

H2O 0.4 0.3 0.3 22.6 39.8 0

Volumetricheating valueKJ/m3

12492 9477 9962 8224 33570

Lowerheating valueMJ/Kg

27.8 12.8 12.7 10.4 50.1

H2/CO 2.36 1.26 0.8 0.63 0.74

shows the contours (X-Y Plane) of the velocity swirlingstrength for Z = 134 mm to 400. Strong recirculation regionswith strong swirling strength are shown at the entranceregions near the fuel injection. The contours show that thevelocity swirling strength decreases downstream with theincrease of the axial distance Z. The velocity swirling strength

contours at Z = 200 shows an annulus region with highswirling strength.

The results of methane combustion in gas turbine cancombustor are used as a baseline for comparison with syngasfuel combustion. The eect of syngas fuel compositions ongas temperature, CO2 and NOx emissions are investigated


0e+007.38e031.48e022.22e022.95e023.69e024.43e025.17e025.91e026.65e027.38e028.12e028.86e029.6e021.03e011.11e011.18e011.26e011.33e011.4e011.48e01

Baseline-CH4

(a)


Syngas 1: Schwarze Pumpe (H2/CO = 2.36)

(b)

Figure 8: Contours of CO2 mass fraction.

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

CO

2m

ass

frac

tion

BaselineCH4

SchwarzePumpe

ExxonSingapore

Tampa PSI Sarlux

Fuel

(a)

0

0.2

0.4

0.6

0.8

1

104C

O2

kg/k

J

NatureGas

SchwarzePumpearpe

ExxonSingapore

Tampa PSI

Fuel

(b)

Figure 9: (a) Average carbon dioxide (CO2) mass fractions at the exit of can combustor. (b) Average mass of carbon dioxide at the exit perunit of energy generation.

first. Table 2 shows the fuel, primary and secondary airinjection conditions, and the power generated for methaneand syngas fuels. It is noted that the first part of theCFD analysis was performed with the same fuel mass flowrate and dierent power generation. The gas temperaturecontours (X-Z plane at Y = 0) for methane and syngasfuels combustion in gas turbine can combustor are shownin Figure 7. The gas temperature for the five syngas tested inthis study shows a lower gas temperature compared to thetemperature of methane. It is noted that all the syngas fuelhave lower heating value than the methane. The volumetricheating value of the methane is 2.68 to 4.08 times higherthan the volumetric heating value of the syngas fuels tested inthis study. In addition to that the flame temperature dependsalso on the syngas fuels compositions. For example, themaximum gas temperature predicted for syngas 5 (Sarlux)

is about 1734 K. The maximum temperature for syngas 5is 466 K less than the maximum flame temperature formethane. This is due to the high volume fraction of water(39.8%) in syngas 5. The maximum temperature for syngas 3is 2008 K compared to 2200 K for methane. Syngas 3 has thehighest volume fraction of carbon monoxide CO (46.6%).The syngas fuel composition and heating value are not onlyaecting the maximum flame temperature but also the shapeand size of the flame. The flame shape and size are changingwhen we switch the fuel from pure methane to syngas fuels.The syngas combustion shows a shorter flame compared tothe one obtained with methane. Replacing methane withsyngas fuels with dierent hydrogen concentration will aectthe combustion process. The reaction zone or the flameis located in the vicinity of the fuel injection region asshown in Figure 7 for all five syngas with hydrogen to



Baseline-CH4

(a)


Syngas 1: Schwarze Pumpe

(b)

0e+005e071e061.5e062e062.5e063e063.5e064e064.5e065e065.5e066e066.5e067e067.5e068e068.5e069e069.5e061e05

Syngas 5: Sarlux

(c)

Figure 10: Contours of NO mass fraction.

0E+00

2E064E066E068E061E05

1.2E051.4E051.6E05

NO

mas

sfr

acti

on

BaselineCH4

SchwarzePumpe

ExxonSingapore

Tampa PSI Sarlux

Fuel

(a)

0E+00

1E082E083E084E085E086E087E08

NO

kg/k

J

NaturalGas

SchwarzePumpearpe

ExxonSingapore

Tampa PSI

Fuel

(b)

Figure 11: (a) Average NO mass fractions at the exit of the can combustor. (b) Average mass of NO at the exit per unit of energy generation.


(m)Z

Y

X0

0.05

0.1

0.15

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(K)

CH4-0.001kg/s-P = 50.1 KW

(a)

(m)Z

Y

X0

0.05

0.1

0.15

0.2300503708909111213151518172119242127

Temperature

(K)

Tampa-0.001kg/s-P = 12.77 KW

(b)

(m)Z

Y

X0

0.05

0.1

0.15

0.2300490680869105912491439162818182008

Temperature

(K)

Tampa-0.0039 kg/s-P = 50.1 KW

(c)

Figure 12: Syngas temperature contours: eect of fuel mass flow rate.

0E+00

2E05

4E05

6E05

8E05

1E04

CO

2K

g/K

J

Natural Gas Schwarze

PumpearpeSyngas 1a

Schwarze

PumpearpeSyngas 1b

Tampa

Syngas 3a

Tampa

Syngas 3b

Fuel

Figure 13: Average mass of carbon dioxide at the exit per unit ofenergy generationsame power 50.1 KW for all the fuels tested.

carbon monoxide ratio between 0.63 and 2.36. The flametemperature for syngas gas depends not only on the hydrogento carbon monoxide ratio (combustible constituents) butalso on the volume fraction of the noncombustible (CO2, N2,H2O) in the syngas. The higher the hydrogen volume fractionin the syngas is, The higher the gas temperature is and thehigher the volume fraction of inert gas in syngas is, thelower the gas temperature is. The contours of carbon dioxide(CO2) mass fraction for methane and syngas fuel (SchwarzePumpe) combustion are shown in Figure 8. The figure showshigher CO2 concentrations in the reaction zone. It is alsonoted that higher CO2 concentrations are generated with

0E+00

5E091E08

1.5E082E08

2.5E083E08

3.5E084E08

NO

Kg/

KJ

Natural Gas Schwarze

PumpearpeSyngas 1a

Schwarze

PumpearpeSyngas 1b

Tampa

Syngas 3a

Tampa

Syngas 3b

Fuel

Figure 14: Average mass of NO at the exit per unit of energygenerationsame power 50.1 KW for all the fuels tested.

methane when the fuel mass rate was kept constant. With thesame fuel flow rate, the power generated by the syngas fuelstested in this study is about 20% to 55% the power generatedby the methane. For the same power generation, the fuelmass flow rate of the syngas fuel and the CO2 emission willbe higher. With a constant fuel mass flow rate, the syngasfuel combustion shows less carbon dioxide formation insidethe can combustor for all the five syngas tested in this study.The average carbon dioxide mass fractions at the exit of thecombustor generated with methane and syngas fuels withconstant fuel mass flow rate are shown in Figure 9(a). A netreduction (30% to 49%) of CO2 emissions at the exit of


the combustor when methane is replaced with syngas fuel(see Figure 9(a)) but at the same time the power generatedby the syngas gas decreased also by 20% to 55%. Theresults shown in Figure 9(a) are obtained with methane andsyngas fuel with the same mass fuel rate at the injectionand dierent power generated by the can combustor (seeTable 2). For the evaluation of the carbon loading to theenvironment accounted by the can combustor, the resultsshould be presented as the average mass of CO2 emitted perunit of energy generation. The average mass flow rate of CO2emissions (Kg/s) at the exit of the combustor was calculated.The CO2 mass flow rate (Kg/s) was normalized with power(KW or KJ/s) to determine the mass of CO2 emitted perunit of energy generation (Kg/KJ). The results of the massof CO2 per unit energy generation are shown in Figure 9(b).The results show clearly that mass of CO2 emitted per unitof energy generation (Kg/KJ) is higher for the syngas fuels(Exxon Singapore, Tampa, and PSI) with lower heating value(10.412.8 MJ/Kg) or power generation (10.4 to 12.8 KW).The only syngas fuel that shows a reduction of the averagemass of CO2 emitted per unit of energy generation (Kg/KJ)compared to methane fuel is Schwarze Pumpe syngas. TheSchwarze Pumpe syngas fuel ha a lower heating value of27.8 MJ/Kg, and the power generated during the combustionof this fuel in the can combustor is 27.8 KW. The averagemass of CO2 emitted per unit of energy generation (Kg/KJ)for the Schwarze Pumpe syngas fuel decreased by 12%compared to methane fuel.

The NOx emissions from syngas combustion were alsocalculated in this study. The NOx concentrations emittedfrom combustion systems are generally low. The NOx chem-istry has negligible influence on the predicted flow field, tem-perature, and major combustion product concentrations.The NOx model used in this study was a postprocessor tothe main combustion calculation. First the reacting flows aresimulated without NOx emissions until the convergence ofthe main combustion calculation was obtained; after that thedesired NOx models (thermal, prompt, fuel) were enabledto predict the NOx emissions. For NOx emissions prediction(postprocessing), only the equation for NO will be solved,and the solution for the other equations (mass, momentum,energy, radiation, turbulent kinetic energy, dissipation ofthe turbulent kinetic energy, and mixture fraction) will beturned o. The calculation for NOx emissions will continueuntil the NO species residuals are below 106 (convergenceof NO solution). The contours of NO mass fractions insidethe can combustor obtained with the same fuel mass flowrate or dierent power (see Table 2) are shown in Figure 10.Like the gas temperature contours, the NO mass fractioninside the combustor decreases when the baseline fuel (CH4)is replaced with syngas fuel with lower heating value. Thethermal NO emissions are function of the gas temperature.The higher is the temperature, the higher is the NO massfractions. The gas temperature during syngas combustiondepends on the lower heating value of the fuel and fuelcomposition. The temperature increases with the increase ofthe volume fraction of the combustible constituents in thefuel such as hydrogen, carbon monoxides and methane. Onthe other hand, the presence of non combustible constituents

in the syngas such as water, nitrogen, and carbon dioxidesreduces the temperature of the flame and consequently theNO mass fractions. Figure 11(a) shows the average NO massfraction at the exit of the can combustor. If the fuel mass flowrate is kept constant and the power generated from the syngasfuels is 20% to 55% the power generated by methane fuel, thenet NO mass fraction reduction for syngas 1 and syngas 5 is,respectively, 11.5% and 97.6% compared to methane. Thisreduction is proportional to the amount of inert constituentsin syngas fuel. The volume fraction of inert constituents forsyngas 1 and syngas 5 is, respectively, 5% and 46.5%. Thehigher is the amount on non combustible constituents in thesyngas fuel the lower is the NO mass fraction at the exit of thecan combustor. For non premixed combustion, syngas fuelis used to control the NOx emissions by diluting the syngaswith nitrogen, steam, and carbon dioxides. To assess theamount of NOx loading to the environment accounted by thecan combustor, the results should be presented as the averagemass of NO emitted per unit of energy generation. Theaverage mass flow rate of NO emissions (Kg/s) at the exit ofthe combustor was calculated. The NO mass flow rate (Kg/s)was normalized with power (KW or KJ/s) to determine themass of NO emitted per unit of energy generation (Kg/KJ).The results of the mass of NO per unit energy generation areshown in Figure 11(b). The results show that mass of NO perunit energy generation is higher for most of the syngas fuelstested in this study (Schwarze Pumpe, Exxon Singapore, andTampa). The only syngas fuel that shows a 33% reduction ofthe mass of NO per unit energy generation is the PSI syngasfuel with high water volume fraction (22.6%) as shown inTable 1.

It is noted that all the results presented in Figures 7 to11 were obtained with a constant fuel flow rate. The syngasfuel composition and lower heating values were changedbut the fuel mass flow rate was kept constant at 0.001 Kg/s.In fact when syngas heating value decreases, the mass fuelflow rate should increase to keep the same energy inputin the can combustor. For the same fuel input in the cancombustor, the fuel mass flow is four to five times greaterthan for methane or natural gas, due to the lower heatingvalue of the syngas. Methane has a high lower heating valueof 50.1 MJ/Kg. The lower heating values for the five syngastested in this study is between 10.4 MJ/Kg and 27.8 MJ/Kg.Syngas is primarily composed of carbon monoxide andhydrogen but also contains a significant fraction (up to50%) of non combustibles (nitrogen, steam, carbon dioxide).The volumetric heating values of pure methane, hydrogen,and carbon monoxide are, respectively, 33.5, 10.2, and12.6 MJ/m3. The hydrogen and carbon monoxide has a lowervolumetric heating value about 1/3 of the lower heatingvalue of methane. When combined with nitrogen, water, andcarbon dioxide in the gas stream, the syngas fuel volumetricheating value is even smaller (see Table 1). A comparison ofthe combustion process and emissions between the methaneand syngas fuels with the same power and dierent fuelmass flow rate was investigated (see Table 3). The fuel massflow rate for syngas 1 (Schwarze Pumpe) was increasedfrom 0.001 Kg/s to 0.0018 Kg/s and syngas 3 (Tampa) wasincreased from 0.001 Kg/s to 0.0039 Kg/s to match the same


Table 2: Fuel and air injection conditions and power generated.

ConstituentsSyngas 1SchwarzePumpe

Syngas 2ExxonSingapore

Syngas 3Tampa

Syngas 4PSI

Syngas 5Sarlux

Methane(CH4)

Fuel mass flow rate(Kg/s)

0.001 0.001 0.001 0.001 0.001 0.001

Velocity of primaryair (m/s)

10 10 10 10 10 10

Velocity of secondaryair (m/s)

6 6 6 6 6 6

Total mass flow rate atthe exit (Kg/s)

0.0783 0.0783 0.0783 0.0783 0.0783 0.0783

Lower heating valueMJ/Kg

27.8 12.8 12.7 10.4 50.1

Power KW 27.8 12.8 12.7 10.4 50.1

heat input for the methane. It is noted that the heat inputfrom methane combustion is 50.1 KW with a fuel mass flowrate of 0.001 Kg/s. The heat input from synags 1 (SchwarzePumpe) with a fuel flow rate of 0.001 Kg/s and 0.0018 Kg/sis 27.8 KW and 50.1 KW. The heat input from synags 3(Tampa) with a fuel flow rate of 0.001 Kg/s, and 0.0039 Kg/sis 12.7 KW and 50.1 KW. The fuel mass flow rates for syngas1 and syngas 3 were increased, respectively, by a factor of 1.8and 3.9 to match the same heat input for methane. The heatinput (KW) was obtained by multiplying the lower heatingvalue of the fuel (MJ/Kg) by the fuel mass flow rate (Kg/s).It is also noted that the primary and secondary air mass flowrates were increased accordingly to the increase in the fuelmass flow rate (see Table 3). Figure 12 shows the temperaturecontours of methane and syngas 3 with low and high fuelmass flow rate (same power of 50.1 KW). The results with thehigh fuel mass flow rate for syngas 3 or the same power showthe same eects (lower gas temperature and shorter flame) asthe results obtained with low fuel mass flow rate. The averagemasses of CO2 and NO at the exit of the can combustorper unit of energy generation obtained with the same powerwere calculated, and the results are presented in Figures 13and 14. With the same power, Figure 13 shows a reductionof the mass of CO2 per unit energy generation of about10.7% to 12.5% for Schwarze Pumpe syngas fuel comparedto methane fuel but higher value of CO2 for Tampa syngasfuel. Figure 14 shows a reduction of the mass of NO per unitenergy generated for syngas fuel compared to methane fuelonly when the primary and secondary air mass flow rateswere increased according to the increase in the fuel mass flowrate (Schwarze Pumpe Syngas 1b and Tampa Syngas 3b) ashown in Table 3.

5. Conclusions

Three-dimensional CFD analysis of syngas fuel combustionin gas turbine can combustor is presented in this study.Five Syngas fuel mixtures with dierent fuel compositions(H2/CO = 0.63 to 2.63) and low heating values (8224 KJ/m3

to 12492 KJ/m3) were tested in this study. The syngas fuels areproduced by dierent gasification processes using dierent

feed stocks (coal, biomass, waste). The k- model wasused for turbulence modeling, mixture fractions/PDF modelfor non premixed gas combustion and P-1 for radiationmodeling. The eect of the syngas fuel composition (H2, CO,CO2, CH4, N2, H2O) and fuel heating values on syngas flameshape, gas temperature, carbon dioxide (CO2), and nitrogenoxides (NOx) emissions was determined in this study

(i) Baseline fuel (methane) combustion: the results ofthe gas temperature, velocity field, swirling strengthand CO2 and NOx emissions show that gas turbinecan combustor burns the fuel eciently, reducesthe emissions, and, lower the wall temperature.The predicted maximum temperature of methanefuel combustion compares well with the theoreticaladiabatic flame temperature.

(ii) The gas temperature for the all five syngas showsa lower gas temperature compared to the temper-ature of methane. The gas temperature reductiondepends on the lower heating value and the com-bustible constituents (hydrogen, carbon monoxide,and methane) and non combustibles (inert) con-stituents in the syngas fuel.

(iii) The results show a reduction (30% to 49%) of CO2mass fraction at the exit of the can combustor whenmethane is replaced with syngas fuel that producesless power (20% to 55% power reduction with syngasfuel). The reduction of CO2 concentrations dependson the carbon monoxide and methane volume frac-tions in syngas fuel. For the same power generatedby the methane and syngas fuels combustion, theresults show a higher mass of CO2 emitted per unitof energy generation (Kg/KJ) for Exxon Singapore,Tampa, and PSI syngas fuels compared to methanefuel. Schwarze Pumpe was the only syngas fuel thatshows a reduction of about 12% of the average massof CO2 emitted per unit of energy generation (Kg/KJ)compared to methane fuel.

(iv) With the same fuel mass flow rate but less powergenerated for the syngas fuel, the results show areduction (11.5% to 97.6%) of the average NO mass


Table 3: Fuel and air injection conditionssame power generated.

ConstituentsSyngas 1aSchwarzepumpe

Syngas 1bSchwarzepumpe

Syngas 3aTampa

Syngas 3bTampa

Methane

Fuel mass flow rate (Kg/s) 0.0018 0.0018 0.0039 0.0039 0.001

Velocity of primary air (m/s) 10 18 10 39 10

Velocity of secondary air (m/s) 6 10.8 6 23.4 6

Total mass flow rate at the exit (Kg/s) 0.079 0.141 0.081 0.305 0.078

Lower Heating value MJ/Kg 27.8 27.8 12.7 12.7 50.1

Power KW 50.1 50.1 50.1 50.1 50.1

fraction for synags fuel compared to methane. Syngasis used in non premixed combustion to controlthe NOx emissions by diluting the synags gas withnitrogen, carbon dioxide, and steam. The diluentsreduce the flame temperature and consequently theformation of NOx. For the same power generated bythe methane and syngas fuels combustion, the resultsshow a reduction of the mass of NO per unit energygenerated for syngas fuel compared to methane fuelonly when the primary and secondary air mass flowrates were increased according to the increase in thefuel mass flow rate to keep the same power.

The results obtained in this study show the change ingas turbine can combustor performance (temperature, flameshape, CO2 emissions, and NO emissions) when natural gasor methane fuel is replaced by syngas fuels with lower heatingvalue and fuel compositions.

References

[1] D. E. Giles, S. Som, and S. K. Aggarwal, NOx emissioncharacteristics of counterflow syngas diusion flames withairstream dilution, Fuel, vol. 85, no. 12-13, pp. 17291742,2006.

[2] S. K. Alavandi and A. K. Agrawal, Experimental study ofcombustion of hydrogen-syngas/methane fuel mixtures in aporous burner, International Journal of Hydrogen Energy, vol.33, no. 4, pp. 14071415, 2008.

[3] E. O. Oluyede, Fundamental impact of firing syngas in gasturbines, gas turbine industrial fellowship program, ProjectReport, Electric Power Research Institute, Charlotte, NC, USA,2006.

[4] R. W. Schefer, Combustion of hydrogen enriched methanein a lean premixed swirl burner, in Proceedings of the DOEHydrogen Program Review, 2001.

[5] S. Pater, Acoustics of turbulent non-premixed syngas com-bustion, Ph.D. thesis, University of Twente, Enschede, TheNetherlands, 2007.

[6] S. Rahm, J. Goldmeer, M. Moilere, and A. Eranki, Addressinggas turbine fuel flexibility, in Power-Gen Middle East confer-ence, Manama, Bahrain, February 2009.

[7] R. D. Brdar and R. M. Jones, GE IGCC Technology andExperience with Advanced Gas Turbines, GE Power Systems,New York, NY, USA, 2000.

[8] P. Cheng, Two-dimensional radiating gas flow by a momentmethod, AIAA Journal, vol. 2, pp. 16621664, 1964.

[9] R. Siegel and J. R. Howell, Thermal Radiation Heat Transfer,Hemisphere, Washington, DC, USA, 1992.

[10] D. Todd and M. Gas, Turbine Improvements enhanceIGCC viability, in Gasification Technologies Conference, SanFrancisco, Calif, USA, October 2000.

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