11stst OxyOxy‐‐fuel combustion conferencefuel combustion conference88thth‐‐1111thth September 2009September 2009
Radisson Hotel, Cottbus, GermanyRadisson Hotel, Cottbus, Germany
SeunghwanSeunghwan Lee, Lee, KaramKaram Han and Kang Y. HuhHan and Kang Y. HuhCombustion LaboratoryCombustion Laboratory
POSTECH, KoreaPOSTECH, Korea
• For a fluctuating variable Φ, there exists a fluctuating variablex which is closely related with fluctuation ofΦ. Flame Structurey
1 1
1 ,n n
i i ii i
P P X
Temperature(K)Temperature(K)
X Probability
1X
2X1X
2X
1P
2P
2X 22P
nX nP nX
Time
• Steady Laminar Flamelet Model2
2 ( )sYN W Y
• Special case of CMC ignoring time derivative & transport terms
2s
• Computationally more tractable• Laminar flamelet structures pre‐calculated and tabulated into a flameletlibrary with mixture fraction and stoichiometric SDR as independentlibrary with mixture fraction and stoichiometric SDR as independent variables
• Accurate at the equilibrium condition with a small SDR
• Difficult to handle long time scale chemical reaction like NOx
• Conditional Moment Closure• Conditional Moment Closure• Klimenko & Bilger [1993]• Key assumption:• Fluctuations of species mass fractions and temperature are primarily associated with fluctuation of the mixture fraction.
• Physically more general than LFM without the laminar flamelet assumption• Numerically more efficient than the PDF transport eq model• Numerically more efficient than the PDF transport eq model• No arbitrary tuning constants involved as in most phenomenological models
• Conditional species mean mass fractions
• Conditional mean reaction rate• Conditional mean reaction rate
• Conditional velocity
.
Optically Thin Limit
Case setupip Partial pressure of species i
,p ia Plank mean absorption coefficient
T Local flame temperature
Extinction limit
Components Primary, daf wt% Secondary, daf wt%Combustion time scale Combustion time scale
Tar 34.9 0
Soot 0 31.5
H2 1.57 4.08
CH4 1 5 0 21
Combustion time scale of devolatilisation product
Combustion time scale of char
CH4 1.5 0.21
C2H2 0 0
C2H4 0.67 0
C2H6 0.24 0
Dominant factor for turbulent combustion characteristics near the burner
Reactant Oxidant
case1 devolatilization gas Air
C3H6 0.56 0
CO 2.5 5.2
CO2 2.5 2.5
H2O 5.2 5.2
Case setup
case2 devolatilization gas 20% O2, 80% CO2
case3 devolatilization gas 30% O2, 70% CO2
HCN 1.02 1.87
H2S 0.33 0.42
Char 49.1
P di t d l i d tPredicted pyrolysis products from a bituminous coal by FLASHCHAIN
[Niksa and others, 2003]
• GRI 3.0 mechanism – 53 species, 325 steps with NOx
• Combined with H2S oxidation mechanism• Combined with H2S oxidation mechanism
Chemical reaction mechanism
case1 Air 175
case2 20% O2, 80% CO2 247
Extinction limit (1/s) Oxidation mechanism of H2S [Kentaro Tsuchiya, The University of Tokyo]
case3 30% O2, 70% CO2 440
OH mass fraction in the mixture fraction space wrt SDROH mass fraction in the mixture fraction space wrt SDR
Air(Extc SDR ‐ 175)
20% O2, 80% CO2(Extc SDR ‐ 247)
30% O2, 70% CO2(Extc SDR ‐ 440)
CO mass fraction in the mixture fraction space wrt SDRCO mass fraction in the mixture fraction space wrt SDR
Air(Extc SDR ‐ 175)
20% O2, 80% CO2(Extc SDR ‐ 247)
30% O2, 70% CO2(Extc SDR ‐ 440)
Temperature in the mixture fraction space wrt SDRTemperature in the mixture fraction space wrt SDR
Air(Extc SDR ‐ 175)
20% O2, 80% CO2(Extc SDR ‐ 247)
30% O2, 70% CO2(Extc SDR ‐ 440)
Maximum temperature : adiabatic and radiation lossMaximum temperature : adiabatic and radiation loss
Air 20% O2, 80% CO2 30% O2, 70% CO2
Sandia flame D swirl burner
Specification
Case setup for CMC calculation
Sandia flame D ‐ CMC, x/d = 15
0.0020
0.0025
0.0030
0.0035
0.0040
actio
n of
OH
SANDIA FLAMES D calculation
SANDIA FLAMES D exp
0.04
0.05
0.06
0.07ct
ion
of C
O
SANDIA FLAMES D calculation
SANDIA FLAMES D exp
120014001600180020002200
erat
ure
SANDIA FLAMES D calculation
SANDIA FLAMES D exp
0.0 0.2 0.4 0.6 0.8 1.00.0000
0.0005
0.0010
0.0015
Mas
s Fr
a
Mixture Fraction 0.0 0.2 0.4 0.6 0.8 1.00.00
0.01
0.02
0.03
Mas
s Fr
ac
Mi t F ti
0.0 0.2 0.4 0.6 0.8 1.0
200400600800
10001200
Tem
pe
Mixture Fraction
Mass fraction of OH
in mixture fraction space
Mass fraction of CO
in mixture fraction spaceTemperature in mixture fraction space
Mixture Fraction Mixture Fraction
Sandia flame D ‐ CMC, x/d = 15
0.025
0.030
0.035
0.040 SANDIA FLAMES D
calculation SANDIA FLAMES D
exp
n of
CO
0 0010
0.0012
0.0014
0.0016
0.0018
0.0020 SANDIA FLAMES D calculation
SANDIA FLAMES D exp
on o
f OH
1200
1400
1600
1800
atur
e
SANDIA FLAMES D calculation
SANDIA FLAMES D exp
0.000
0.005
0.010
0.015
0.020
0 1 2 3 4 5
Mas
s Fr
actio
n
0 1 2 3 4 50.0000
0.0002
0.0004
0.0006
0.0008
0.0010
Mas
s Fr
actio
r/d200
400
600
800
1000
0 1 2 3 4 5
Tem
pera
r/d
Mass fraction of CO
in mixture fraction spaceTemperature in mixture fraction space
r/d
Mass fraction of OH
in mixture fraction space
Sandia flame D ‐ CMC, x/d = 30
0.03
0.04
air 40% O2, 60% CO2 60% O2, 40% CO2 80% O2, 20% CO2
on o
f OH
100% O2
0.25
0.30
0.35
0.40 air 40% O2, 60% CO2 60% O2, 40% CO2 80% O2, 20% CO2
on o
f CO
100% O2
2000
2500
3000 air 40% O2, 60% CO2 60% O2, 40% CO2 80% O2, 20% CO2
atur
e
100% O2
0.00
0.01
0.02
0 1 2 3 4 5
Mas
s Fr
actio
/
0.00
0.05
0.10
0.15
0.20
0 1 2 3 4 5
Mas
s Fr
actio
0 1 2 3 4 50
500
1000
1500
Tem
pera
Mass fraction of OH
by radial distance
Mass fraction of CO
by radial distanceTemperature by radial distance
r/d r/d r/d
Sandia flame D ‐ CMC, x/d = 30
0.05
0.06
0.07
0.08 air 40% O2, 60% CO2 60% O2, 40% CO2 80% O2, 20% CO2
on o
f OH
100% O2
0.4
0.5
0.6 air 40% O2, 60% CO2 60% O2, 40% CO2 80% O2, 20% CO2
on o
f CO
100% O2
2000
2500
3000
air 40% O2, 60% CO2 60% O2, 40% CO2 80% O2, 20% CO2
atur
e
100% O2
0.00
0.01
0.02
0.03
0.04
0.0 0.2 0.4 0.6 0.8 1.0
Mas
s Fr
actio
0.0 0.2 0.4 0.6 0.8 1.00.0
0.1
0.2
0.3
Mas
s Fr
actio
0
500
1000
1500
0.0 0.2 0.4 0.6 0.8 1.0
Tem
pera
Mass fraction of OH
in mixture fraction space
Mass fraction of CO
in mixture fraction spaceTemperature in mixture fraction space
Mixture Fraction Mixture Fraction Mixture Fraction
k e high Reynolds number model
Turbulent kinetic energy Turbulent dissipation rate
k‐e high Reynolds number model
Turbulence model
Constant rate model Single step modelConstant rate model g p
Specify the time for complete devolatilisation. A constant rate is used to compute the weight loss of coal particles during the specified time.
Reaction rate proportional to the amount of volatile matter
*( )dV K V V*
devol
dV Vdt T
*
0
( )
1 exp
exp
v
t
v
vv v
V K V Vdt
V V K dt
EK ART
* : the volatile matter content (kg) after Q-factor adjustmentV
: devolatilisation timedevolT
pv vPRT
1
: rate constant
: pre-exponential factor(s ): activation energy for devolatilisation(J/kmol)
v
v
K
AE
Devolatilization model ‐ Aachen Devolatilization model ‐ KITECH
: activation energy for devolatilisation(J/kmol)vE
0.7512 2 2 124 5 06 10 ( )mTDK kgm Nm
1st order combined model5.06 10 ( )m
dp m p
K kgm Nmd RT d
: diffusion rate coefficient : mechanism factor (1 for CO2 & 2 for CO)T : mean particle/gas temperature
d
m
K
( )K P P
d : particle diameter
D : diffusion coefficientp
exp( )charc char
P
EK ART
( )d g sq K P P
: consumption rate per unit external surface areaq
: partial pressure of oxygen in the bulk gasgP
A : pre-exponential factorE : activation energy for char oxidation
char
char
( ) : overall ratec dg
c d
K Kq PK K
Char combustion model
: partial pressure of oxygen at the char surfacesP2 : char burning rate
c d
pdchar q d
dt
EBU 2‐step
Eddy Break-Up by Magnussen
Assumption
3min , , /
: fuel consumption rate
O PF ebu F ebu
O P
F
Y YR A Y B kg m sk s s
R
Assumption- The reaction is a single-step irreversible one
involving fuel, oxidant and product, plusbackground inert species
- The reaction time scale is so small that the rate-
p
//
F
O O O F F
P P P F F
s n M n Ms n M n M
controlling mechanism is turbulent mixing , : dimensionless empirical coefficientsebu ebuA B
Gas combustion model
Radiative transfer equationDiscrete Ordinate Method
Solves field equations for radiation i t it i t d ith fi d
4
( ) ( )4
sa s p a b p p
dI kk k k I k I k I I dds
Boundary conditionintensity associated with fixed directions s, represented by discrete solid angles. (24 directions)
Gas emissivity by WSGGM ( ' 0)
( ) ( ') ' bn s
I s I I s n s d
Discretized RTE
y y
Constant temp wall bounaries
1( )
4
ns
i i a s p i a b p p i ii
ks I k k k I k I k I I
Radiation model
1i
RWTH Aachen 0.1MW OXY‐PC pilot furnace – 170,000 polyhedral cells
Specification
Detailed investigation of a pulverized fuel swirl flame in CO2/O2 atmosphere, D. Toporov, P. Bocian, P.Heil, Combustion and Flame 155 (2008) 605 ‐ 618
Specification
#1 #2 #3 #4 #5 #6 #7
Swirl rato 1.2 1.2 1.2 1.2 1.2 1.5 2.0
EBU Amix 4.0 6 3 4.0 4.0 4.0 4.0
EBU Bmix 0.5 0.75 0.375 0.5 0.5 0.5 0.5
Devolatilization ‐ 0.0833 0.0833 0.0708 0.0958 0.0833 0.0833
ReferenceHigh EBU Low EBU Fast Slow
High swirl High swirlReferenceg
constants constants devolatilisation devolatilisation High swirl High swirl
Effect of EBU constant
Effect of devolatilization Effect of swirl ratio
0.05 m 0.3 m 0.5 m
1500 0.05 m
1200
Exp
0.05 m
900
Tempe
rature 'C
Exp
Ref
case2
case3
case4Higher devolatilization speed
600case5
case6
case7
& higher EBU constants
Higher swirl ratio
300
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
Radius
Temperature distribution in radial direction at 0.05m from burner
13001500
0 3 m 0 5 m
1200
1300
1200
0.3 m 0.5 mHigher swirl ratio
1100
mpe
rature 'C
900
empe
rature 'C
1000
Tem
600Te
Higher devolatilization speed & higher EBU constant s
900
0 0.05 0.1 0.15 0.2
Radius
300
0 0.05 0.1 0.15 0.2
RadiusRadius RadiusTemperature distribution in radial direction
at 0.3m from burnerTemperature distribution in radial direction
at 0.5m from burner
Korea institute of industrial technology (KITECH) 0.4MW OXY‐PC furnace
Excess air ratio 1.2
Temperature of the primary oxidizer (oC) 150
Temperature of the secondary oxidizer (oC) 300
Ratio of the primary oxidizer (%) 20Ratio of the primary oxidizer (%) 20
Ratio of the secondary oxidizer(%) 80
Flowrate of the primary oxidizer (Nm3/hr) 89.89
Flowrate of the secondary oxidizer (Nm3/hr) 359.6
LHV (kcal/kg) 5258.99
Coal consumption rate (kg/sec) 0.018
C 58.220 % water 18 %
H 4.100 %
O 15.580 %
N 0.820 %
S 0.410 %
Ash 2.87 %
Combustible
matter79.13 %
Specification CAD data of KITECH 0.4MW OXY‐PC furnace
• RANS simulation by STAR‐CD 4.08• 150,000 polyhedral cells• dense mesh near the burner
Model
Swirl vane angle 2nd inlet 30 degree
Particle size 80 um
Turbulence K‐ε high reynolds number
Devolatilization Single step
Ch b ti 1st dChar combustion 1st order
Gas combustion EBU 2 step
Radiation DOM
#1 #2 #3 #4 #5 #6
Flow rate ofFlow rate of primary oxidizer (Nm3/hr)
89.89 62.62 89.89 92.62 32.62 69.58
Flow rate of secondary
359 6 250 5 359 6 220 5 280 5 278 3y
oxidizer(Nm3/hr)
359.6 250.5 359.6 220.5 280.5 278.3
O2 (vol %) 20.9 30 30 30 30 27
N2 (vol %) 79.1 ‐ ‐ ‐ ‐ ‐
CO2 ‐ 70 70 70 70 73
Air Reference Oxy Reference Same flow rate with Air Ref case
Flow rate ratio Flow rate ratio
Effect of Air & Oxy combustion Effect of inlet flow Effect of oxygen
concentration
Case 1 Air reference Case 2 Oxy reference
Case 4 High primary inlet flow rateCase 3 same flow rate with Air Ref
Case 6 Low oxygen concentrationCase 5 High secondary inlet flow rate
Case 1 Air reference Case 2 Oxy reference
Case 4 high primary inlet flow rateCase 3 same flow rate with Air Ref
Case 6 Low oxygen concentrationCase 5 High secondary inlet flow rate
Case 1 Air reference Case 2 Oxy reference
Case 4 High primary inlet flow rateCase 3 Same flow rate with Air Ref
Case 6 Low oxygen concentrationCase 5 High secondary inlet flow rate
•• Flame Stability Flame Stability ‐‐Methane Methane –– Stability of air combustion is similar to that of aboutStability of air combustion is similar to that of about 70% CO2 fraction.70% CO2 fraction.
–– Peak flame temperature of air combustion is similar to that of 80% CO2 fraction.Peak flame temperature of air combustion is similar to that of 80% CO2 fraction.
•• Flame Stability Flame Stability –– DevolatilizationDevolatilization gasgas–– Negligible difference in the SDR extinction limit between adiabatic and radiation heat loss.Negligible difference in the SDR extinction limit between adiabatic and radiation heat loss.
–– With CO2 recirculation the maximum With CO2 recirculation the maximum stoichiometricstoichiometric temperature decreases and flames temperature decreases and flames b bl h l l lb bl h l l lbecome more unstable with a lower extinction limit SDR In general. become more unstable with a lower extinction limit SDR In general.
•• Sandia Flame D ValidationSandia Flame D Validation–– The CMC modelThe CMC model validated against Sandia Flame D data.validated against Sandia Flame D data.
–– SLFM results are generally similar with those by CMC, however, CMC is more accurate for slow SLFM results are generally similar with those by CMC, however, CMC is more accurate for slow species such as OH and NO.species such as OH and NO.
•• Parametric Study Parametric Study –– Aachen BurnerAachen Burneryy–– Temperature profile underestimated near the burner, but not due to model constants. Temperature profile underestimated near the burner, but not due to model constants.
–– When the When the devolatilizatondevolatilizaton rate and the EBU constants increase, the temperature profile is rate and the EBU constants increase, the temperature profile is shifted to the left at the burner exit as expected. Tuning required for any given data set. shifted to the left at the burner exit as expected. Tuning required for any given data set.
Hi h i l l d t b d fl i ith h d i i b t b lHi h i l l d t b d fl i ith h d i i b t b l–– Higher swirl leads to a broader flame region with enhanced mixing by turbulence.Higher swirl leads to a broader flame region with enhanced mixing by turbulence.
•• KITECH Burner KITECH Burner SimulationSimulation–– Flame stabilized by swirl and recirculation in the upstream regionFlame stabilized by swirl and recirculation in the upstream region
–– Mixing with oxidizer increases by swirl. The flame length decreasesMixing with oxidizer increases by swirl. The flame length decreases and the flame radius and the flame radius g y gg y gincreases.increases.
–– OxyOxy‐‐fuel combustion has a shorter flame length due to a smaller flow rate in Case2. fuel combustion has a shorter flame length due to a smaller flow rate in Case2.
–– The primary inlet flow influences the flame length whileThe primary inlet flow influences the flame length while thethe secondary inlet flow secondary inlet flow influences the flame radiusinfluences the flame radiusinfluences the flame radius.influences the flame radius.
–– The highThe high temperature region and PC region do not match with each other. temperature region and PC region do not match with each other.
–– TheThe PCPC region seems to be primarily influenced by turbulent mixing due to high inlet region seems to be primarily influenced by turbulent mixing due to high inlet velocity and swirl. velocity and swirl.
