Numerical Simulations of Oxy-coal Combustion
in Youngdong 100 MWe Retrofit Boiler
3rd Oxy-coal Combustion Conference9-13 Sept. 2013, Spain
JungEun A. Kim, S. Park, Changkook Ryu
Won Yang*
Young-Joo Kim, Ho-Young Park
Hyuk-Pil Kim
Sungkyunkwan University, Korea
Korea Institute of Industrial Technology
KEPCO Research Institute, Korea
Doosan Heavy Industries and Construction
Introduction : Oxy-fuel combustion Demonstration project of oxy-coal combustion Objective & Subject of Study CFD results Conclusions
Outline
2
Introduction: oxy-fuel combustion
Oxy-fuel combustion One of CCS(Carbon capture and storage) process technology development N2 in the combustion air is replaced with recycled CO2 or CO2/H2O to produce high
concentrations of CO2 in the flue gas Air-fuel combustion : CxHyOz + aO2 + 3.76aN2 → xCO2 + y/2H2O + 3.76aN2
Oxy-fuel combustion : CxHyOz + aO2 + bCO2 + cH2O → (x+b)CO2 + (y/2+c)H2O
Comparison of physical properties for CO2 and N2 (@ 1500 K)Properties at 1500K CO2 N2 Impact on oxy-coal
Molecular weight 44.01 kg/kmol 28.01 kg/kmol
Specific volume 2.793 m3/kg 4.386 m3/kg Lower velocity (swirl)
Specific heat 1.327 kJ/kgK 1.250 kJ/kgK
Heat capacity(ρCp) 0.475 kJ/m3K 0.284 kJ/m3K Lower temperature
Reactivity with char Endothermic reaction inert Faster or slower char burn-out
Radiation Participating Transparent Increased radiation
Flue Gas Recirculation (FGR)
3
Demonstration of oxy-coal combustion in Korea 1
Supported by Korean government: 2007~2012 Design of oxyfuel retrofit of YOUNGDONG-#1 plant (owned by KOSEP)
Conceptual design
Basic design Detailed design & construction
Operation
1st Phase07’-10’ (3 yrs)
2nd Phase10’-12’ (2 yrs)
3rd Phase12’-15’ (3 yrs)
System optimization(KEPRI/KOSEP/DIG
KAIST/PNU)
Boiler/Combustion (KITECH/KEPRI/KOSEP/SKKU/SNU/POSTECH)
Pollutant removal(KIMM/KC Cottrel/KOSEP/
KAIST/Yonsei U.)
Pollutant removal(KIMM/KC Cottrel/KOSEP/
KIER/KAIST)
System optimization & control(KEPRI/KITECH/DIG/DHI/SKKU)
Boiler/Combustion(DHI)
CO2 Storage (KIGAM)KEPRI: Korea Electric Power Research Institute / KOSEP: Korea South-East PowerDIG: Daesung Industrial Gas / DHI: Doosan Heavy IndustryKITECH: Korea Institute of Industrial Technology / KIMM: Korea Institute of Machinery and MaterialsKIER: Korea Institute of Energy Research / KIGAM : Korea Institute of Geoscience and Mineral Resources
Demonstration of oxy-coal combustion in Korea 2
Retrofit of a 125MWe furnace at Young-dong, Korea Demonstration of oxy-coal combustion due in 2017
Furnace design requirement Dual mode operation
Air-mode for commercial operation Oxy-mode for process demonstration
ASU
Coal Yard
FGD
Turbine, Generator
CO2 Recovery facility
Boiler
ESP
Ash Pond
Young-dong plant(Unit 1, 125We)
5
Objective & Subject of Study
Objective To evaluate the combustion and heat transfer
characteristics of retrofit boiler of Young-dong Unit #1
Retrofit boiler of Young-dong Unit #1 Original Boiler
100% TMCR: 125 MWe Anthracite/Bituminous Downshot-firing
Retrofit Design 80% TMCR: 100 MWe Partial Removal of Refractory Operates 12 burners of 16 Opposed-wall firing (12 swirl burners)
→ Unusual furnace type(Combustion performance should be guaranteed)
<Original boiler>
Refractory
Mem
bran
ew
all
14.7m
6
Objective To evaluate the combustion and heat transfer
characteristics of retrofit boiler of Young-dong Unit #1
Retrofit boiler of Young-dong Unit #1 Original Boiler
100% TMCR: 125 MWe Anthracite/Bituminous Downshot-firing
Retrofit Design 80% TMCR: 100 MWe Partial Removal of Refractory Operates 12 burners of 16 Opposed-wall firing (12 swirl burners)
→ Unusual furnace type(Combustion performance should be guaranteed)
Objective & Subject of Study
<Retrofit Design>
OFA
BurnersSwirl Refractory
Membranewall
13.4m 34.8m
FRONT WALL
SecondaryS/H
PrimaryS/H
SIDE WALL
14.7m
7
Geometry
Geometry & Mesh Mesh : 620,000 hexahedrons (Symmetry Condition) The upper layer burners of rear wall disused
Burner Inlet conditions determined by separate simulations
symmetryOFA
sym
met
ry
Swirl
8
Operating Conditions
Operating Conditions
* To maintain the swirl strength of the burners in oxy condition, most of the oxidizer is supplied into burner without OFA supplying
Coal Properties
Proximate analysis (%air-dried) Ultimate analysis (%daf)HHV
(MJ/kg)Inherent Moisture
VolatileMatter
Fixed Carbon Ash C H O N S
10.3 40.0 46.2 3.5 75.6 5.7 17.3 1.0 0.5 26.56
CaseO2 in
oxidizer (vol.%)
Stoich. Ratio Coal(air-dried)
(kg/s)
Thermal Input
(MWth)
AdiabaticFlame
Temp. (oC)
Oxidizer (vol.%) Flue gas (vol.%)
Overall Burner CO2 H2O O2 CO2 H2O O2
Air 20.6
1.2
1.00 11.7 284 1927 0 1.6 20.6 14.0 10.5 3.2
Oxy24 24
1.17* 11.46 278
1707 49.1 15.0 24.0 61.1 24.2 3.7
Oxy26 26 1804 48.4 14.3 26.0 61.4 24.2 4.0
Oxy28 28 1899 47.6 13.5 28.0 61.6 24.2 4.2
Oxy30 30 1992 46.8 12.8 30.0 61.7 24.2 4.5
9
Models for CFD
CFD code: FLUENT ver. 6.3
Model Details UDF
Devolatilization FLASHCHAIN [Niksa, 1995] √
Char combustion Shrinking unreacted core model [Wen and Chaung, 1979] √
Turbulence Realizable k–ε model -
Radiation Discrete Ordinate Model with WSGGM[Yin et al., 2010] √
Gas-phase reactions
• Finite rate/Eddy dissipation rate• Reaction scheme based on [Jones-Lindstedt][1] CxHyOz (tar) + aO2 → xCO + 0.5yH2[2] CnHm + 0.5nO2 → nCO + 0.5mH2[3] CnHm + 0.5nH2O → nCO + 0.5(m+n)H2[4] CH4 + 0.5O2 → CO + 2H2[5] CH4 + 0.5H2O → CO + 2.5H2[6] CO + H2O → CO2 + H2[7] H2 + 0.5O2 → H2O
-
Particle trajectories
•Lagrangian tracking of 38,400 particles with turbulent dispersion•Particle size: 1-100 μm, average diameter: 50 μm -
10
FLASHCHAIN (PCCoal Lab, Niksa Energy Associates) Predict composition of volatile matter and rate of devolatilization using Semi-
empirical network model
Devolatilization model (DTF, 1 atm, 1500oC) Develop UDF to apply various composition of volatile matter using FLASHCHAIN
Kinetics: single rate (A=5991 s-1, E=24.02 MJ/kmol)
Coal Devolatilization Model
Coal → Volatiles(Tar, CO, CO2, H2O, H2, CH4, CxHy)+Char(C<s>)
FLASHCHAIN result
CFDinput
C5.29H7.35O0.45 C2.29H4.99
Products CharVolatiles
Tar CO CO2 H2O H2 CH4 C2H4 C2H6 C3H6
(wt.%daf) 37.4 38.3 4.5 5.4 7.1 0.35 3.2 1.33 0.58 1.15
Products Char Tar CO CO2 H2O H2 CH4 CxHy
(wt.%daf) 36.4 39.2 4.5 5.4 7.1 0.35 3.2 3.06
)( VVkdtdV
oV −= )exp(RTEAk V
VV −=
16
C<s>+O2→CO
C<s>+H2O →CO + H2
C<s>+CO2→2CO
C<s>+H2→CH4
Char Gasification Model
Unreacted core shrinking model [Wen & Chaung (1979)]
( ) ]s cm [g11111
1 1-2-*
,2
,,
, ii
idashisidiff
iC PP
YkYkk
R −
−++
=
( ) ( )2
*
75.03 /1800/10382.1,)/17967exp(8710
Oii
ptdiffss
PPP
dPTkTk
=−
×=−= −
( ) ( )[ ] 3/11/1 fxRrY C −−==
5.2εdiffdash kk =
( ) ( ))]8.1/(30260644.17exp[,/)(
/2000/101,)/21060exp(247
22*
75.03
seqeqCOHOHii
ptdiffss
TKKPPPPP
dPTkTk
−=⋅−=−
×=−= −
( ) ( )2
*
75.04 /2000/1045.7,)/21060exp(247
COii
ptdiffss
PPP
dPTkTk
=−
×=−= −
( ) ( ))]8.1/(18400exp[10041.5,/
/2000/1033.1,)/921127exp(12.06*
75.03
42 seqeqCHHii
ptdiffss
TKKPPPP
dPTkTk−
−
×=−=−
×=−=
rc
R
ε
Ash
Char
Reduction of gas diffusion rate Change of size of char core Variation of reaction rate due to bulk gas composition
Radius ratio: Pi, Pt : Partial & total pressures [atm] Ash film diffusion rate:
12
Boundary Conditions
Membrane Wall section Tout = 603 K (saturation temp. of steam) Overall heat transfer coefficient of membrane wall + fin: 1200 W/m2K Emissivity of inner surface = 0.7
Refractory lined membrane wall Conditions for membrane wall + Refractory: Thickness 20 mm, thermal conductivity 1.5 W/mK
Superheater Avg temperature of in/out steam = 708K Overall heat transfer coefficient 400 W/m2K
13
Result – Gas temperature (1)
1150
1000
1225
1300
Case Oxy30
1525
1150
1375
1225
1000
1150
1000
1225
1300
Case Oxy26Case Air
•Case Air: Low stoichiometry ratio of burner zone & Low N2 specific heat → High Temperature•Case Oxy26: High stoichiometry ratio of burner zone & High CO2 specific heat → Low Temperature•Case Oxy30: High O2 concentration in oxidizer → Increased Temperature
100
1600 oC
1300
1000
700
400
14
Result – Gas temperature (2)
1150
1000
1225
1300
A (Bottom cone)
B (Burner zone)
C (OFA zone)
D (Throat)
E (S/H)
• Lower furnace (A,B) : Temperatures are higher in air case than those in oxy-coal cases due to OFA• Above OFA (C,D) : Temperatures become similar • Average temperature is the highest in air case
Furnace Sections
A B C D AVG
Aver
age
Tem
pera
ture
(o C)
800
900
1000
1100
1200
1300
Air Oxy24 Oxy26 Oxy28 Oxy30
<Volume-averaged temperature>
15
Result – Char burn-out (1)
1.0e-5
1.0e-1
1.58e-2
2.51e-3
6.31e-5
3.98e-4
kg/m3-s(Log scale)
• Case Air : Char slipped through the gaps between the OFA jets or along the side wall→ Residual char remains in the upper furnace
• Case Oxy30 : Increased concentration of CO2 and H2O (char gasification)& Most oxidizer supplied in the burner zone→ Intensive char burn-out
C(s) by O2 C(s) by CO2
C(s) by O2 C(s) by CO2
Case Air Case Oxy30
C(s) by O2 C(s) by CO2
Case Oxy26
16
Result – Char burn-out (2)
1.0e-5
1.0e-1
1.58e-2
2.51e-3
6.31e-5
3.98e-4
kg/m3-s(Log scale)
• The contribution of CO2 increases with an increase in the overall O2 concentration(gas temperature).→ Lowered contribution of oxidation in Case Oxy30
• The char gasified by CO2 is 2~5 times greater than by H2O, since the CO2 concentration is higher.
C(s) by O2 C(s) by CO2
C(s) by O2 C(s) by CO2
Case Air Case Oxy30
Case Air Oxy24 Oxy26 Oxy28 Oxy30
by O2 73.2 73.9 72.5 70.7 67.5
by CO2 17.4 19.9 21.5 22.9 26.4
by H2O 8.8 6.1 5.9 6.2 5.9
Total 99.4 99.9 99.9 99.9 99.8
<Proportion of char converted by O2, CO2, H2O>
17
100
1650oC
1340
1030
720
410
Result – Char conversion
<100MWe Front wall-firing>
•Lack of mixing between char and O2 due to unusually wide horizontal cross-section→ Lower oxidation & higher gasification
proportion of char burn-out comparing to front wall-firing boiler
Front wallSide wall
3x 4 burners(40MWth each)
OFA nozzles
33.5m
9.0m
<Proportion of char converted by O2, CO2, H2O>
<Temperature>
Case Air Case Oxy28
[wt.%] Young-dong FWF boilerAir Oxy28 Air Oxy28
by O2 73.2 70.7 90.89 76.89
by CO2 17.4 22.9 5.31 17.52
by H2O 8.8 6.2 2.75 5.03
18
Result – O2 concentration
• Young-dong retrofit boiler : The region of O2 depleted is significantly large (Case Air) and stretched to the upper part of the furnace (Case Oxy26) → Insufficient mixing between char and O2 due to the wide horizontal cross-section
Young-dong unit#1MoleFraction
0
0.25
0.20
0.15
0.10
0.05
Front wall-firing boiler
Case Air Case Oxy26 Case Air Case Oxy26
19
Result – Wall Heat flux
• Air mode : Lower stoichiometric ratio & Higher gas temperature in the burner zone→The largest heat transfer rate
• Oxy mode : Heat transfer rate increases with an increasing O2 concentration
Adiabaticflame temp. (oC)
Total heattransfer (MW)
Average heat flux (kW/m2)
Air-mode 1927 154.5 79.7
Oxy24-mode 1707 129.2 66.6
Oxy26-mode 1804 136.8 70.6
Oxy28-mode 1899 143.1 73.8
Oxy30-mode 1992 146.5 75.6
0
250kW/m2
200
150
100
50
Case Oxy30Case Oxy26
Case Air
Sym
met
ry
Sym
met
ry
Sym
met
ry
20
Conclusions
Retrofit of Young-dong Unit #1 for oxy-coal combustion The retrofit boiler is expected to achieve stable combustion performance
under both combustion modes Supply most oxidizers to the burner zone in the oxy-coal cases
Helps to achieve stable flame formation and fast char conversion Lowers the gas temperature and heat flux in the burner zone
The proportion of char gasified by CO2 and H2O was significantly higher than in the front wall-firing boiler Due to the insufficient mixing between char and O2 which was caused by the wide
horizontal cross-section of the burner zone
21
Acknowledgement
Oxy-fuel Combustion R&D Organization, Korea Energy Efficiency & Resources Program
(KETEP Grant No. 2010201010108A)
22
Radiation and WSGGM
Radiative transfer equation(RTE)
Weight Sum of Gray Gases Model (WSGGM) Gas emissivity(ε) and absorption coefficient(κi), weighting factor(aε,i) and mean beam length(L)
From the gas emissivity, the effective absorption coefficient for gases is calculated as,
Three different WSGGMs WSGGM of Smith et al. : Not valid for large furnaces and dry/wet FGR of oxy-fuel conditions Yin et al.’s WSGGM: Improved for oxy-fuel conditions → FLUENT UDF developed
( )( )PLI
igi
ieTa κεε −
=
−=∑ 10
,
∑=
=J
j
jgjii Tca
0,,ε
AVL 49.0=
( )Lεα −
−=1ln
( ) ( ) ( ) ( ) ( ) '',',4
,4
0
42 Ω++=+++⋅∇ ∫ dssΦsrIETnsrIsI p
ppp
π
πσ
πσασαα
I :radiation intensity, α: absorption coefficient,αp: absorption coefficient of particles,σp: scattering factor of particles,n: refractive index, T: temperature
P: Pw + Pc, I : the number of gray gases
WSGGM Smith et al.(1982) Yin et al.(2010)
Valid ranges PL : 0.001 ~ 10 atm·m,600 < T < 2400K
PL : 0.001 ~ 60 atm·m,500 < T < 3000K
Number of gray gases 3 4
Coefficients available for aε,i and ki 5 ranges 10 ranges
23
Gas reaction model
Gas phase reactions
Reaction rate: Finite rate/Eddy dissipation rate model The slowest rate between kinetic rate(Rkinetic) and mixing rate (Rmixing) controls the
whole gas reaction rate
1.C(s) + O2 → CO2.C(s) + CO2 → 2CO3.C(s) + H2O → CO + H2
4.C(s) + 2H2 → CH4
1. Tar+ O2 → a CO + b H2
2. Tar + H2O → a CO + c H2
3. CxHy+ 0.5x O2 → x CO + (y/2) H2
4. CxHy + x H2O → x CO + (y/2+x) H2
5. CH4+ 0.5 O2 → CO + 2 H2
6. CH4+ H2O → CO + 3 H2
7. H2 + 0.5 O2 → H2O8. CO + H2O ↔ CO2 + H2
=
∑∑
PP
P
RR
RRkinetic M
Yk
ABM
Yk
ARRν
ερν
ερ ,minmin,min
Rmixing
Solid-Gas ReactionsGas phase Reactions
Tar:C5.29H7.35O0.45N0.13CxHy:C2.29H4.99
24
