Numerical Simulations of Oxy - coal Combustion in Youngdong 100 MWe Retrofit Boiler 3 rd Oxy-coal Combustion Conference 9-13 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
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Numerical Simulations of Oxy-coal Combustion in Youngdong ...
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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
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
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