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Sangmin Choi
KAIST
Thermal Engineering Lab
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Combustion of solid fuel bed
Combustion of the single particle + Interaction between the particles
Major phenomena
Material flow: Gas Solid Multi le Com onenets
Reactions : Solid-gas reaction, Gaseous reaction
Heat transfer : Conduction, Convection, Radiation
ys ca an geome r ca c anges
Generation of internal pore, Change of particle size
Bed structural change : Porosity, height
Melting, Sintering
Reactors containing solid bed Iron-making process
Coke oven, Sintering bed, Blast furnace
Thermal Engineering Lab
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Bed combustion of mixed waste (solid fuel)
Waste heat boiler
y
Rotary kiln
Thermal Engineering LabTraditional stoker-type inc inerator Advanced incinerator : Stoker-type + Rotary ki ln type
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Iron ore sintering process
~90% of inert : Physical changes of inert (iron ore) is important
Self-sustaining combustion (no external heat source) once ignited
No pyrolysis, very slow progress of coke combustion
+COKE, LIME etcPSEUDO-PARTICLES +WATER +COKE, LIME etc+COKE, LIME etcPSEUDO-PARTICLES +WATER
YARD
COG BURNERSTACK
ORE BINREROLLING MIXING YARDYARD
COG BURNERSTACK
ORE BINORE BINREROLLING MIXING
SINTERING BED
EP
HEARTH BED
WIND BOXESSINTERED ORE
SINTERING BED
EPEP
HEARTH BED
WIND BOXESSINTERED ORE
HOT CRUSHING
COOLINGCOLD CRUSHINGSCREENINGRETURN FINE
FAN HOT CRUSHING
COOLINGCOLD CRUSHINGSCREENINGRETURN FINE
FAN
Thermal Engineering Lab
BLAST FURNACEBLAST FURNACE
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Each slice Batch type oven
Charge : 27.8 ton/oven
CHARGING
CAR
Coking t ime : about 20 hours
QUENCHING
COAL
CAR
16.0m
Charging
coal6m . . . .6.7m
Thermal Engineering Lab
0.45m fuel air0.70m More than100 slices
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Blast Furnace
Iron ore+ Coke
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Phenomena in Blast Furnace
Stack zone
Alternate coke/ore layers
Ore layer is heated up and partially reduced
Stack zone
wust te, e .
Cohesive zone
Ore layer is softened and agglomerates. Cohesive zone
Low permeability of ore layer coke slit Wustite is transferred to Fe.
Dripping zoneDripping
zone Ore starts to melt and fall down.
Raceway Reducing gas by coke combustion
-
Deadman
Thermal Engineering Lab
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FINEX Process
Thermal Engineering Lab
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Modeling Approach
Thermal Engineering Lab
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Reactors with bed of solid material : Solid flow: batch or continuous
Common governing mechanism and physical/chemical phenomena but differ
in the dimension, the boundary conditions and additional physical changes
Solidmaterial Oxidizer
Solidmaterial
Solidmaterial Oxidizer
Solidmaterial
Solid
SolidmaterialSolidSolid
materialmaterialmaterial
Fixed bed combustor
Oxidizer
Co-current fixed
Oxidizer
Count-current fixed
Oxidizer
Grate-type incinerator
Fixed bed combustor
Oxidizer
Co-current fixed
Oxidizer
Count-current fixed
Oxidizer
Grate-type incinerator
Thermal Engineering Lab
Direct melting furnace
Coke oven
bed gasifier bed gasifier
Blast furnace
Iron ore sintering bed Direct melting furnace
Coke oven
bed gasifier bed gasifier
Blast furnace
Iron ore sintering bed
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Flexibility in computation - In the model, user can define
Solid components and gaseous species
Combustion/reaction types and their rates
Boundary conditions
Physical and geometric properties
Numerical Scheme
Extension of 1-D, transient model to 2-D model
For moving bed, with constant traveling speed
yy
Thermal Engineering Lab
t=0 tmaxt+ttt=0 tmaxt+tt
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7/27/2019 Choi_Japanese Combustion Symposium
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Governing equations
Solid phase I : Mass, Energy, Component
( ) ( ), , , ,,
s I V I s I s I
solid gas reactions I Jphase J
f v
Mt y
+ = &
( )( ) ( ), , , , , , ,, , , , , , , , ,
1
V s I s I s I s I s I v I
V s I s I JI s I s J s I conv g I s I g s I rad
J
f h v h T f f k h A T T h A T T q
t y y y
+ = + + +
, , , , , ,s s
s s
I s I r r s I r p I s I
r r
( ) ( ), , , , , , , ,, , , s
s
s I V I s I k s I s I s I k
s I k r
r
f m v mM
t y
+ =
&
Gas phase : Mass, Energy, Species
g g gs I rv M + = &, , s
sI rt y
( ) ( )( ), , , , , , , , ,(1 ) s s s
s s
g g g g
g conv g I s I s I g I s I r r s I r p I s I
I r r
h v h Tk h A T T y M H M C T
t y y y
+ = + + +
& &
Thermal Engineering Lab
( ) ( ), ,, , , , ,s g
s g
g g k g g g k
s I k r g k r r I r
m v m
M Mt y
+ = + & &
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-
Solid gas reactions & Gaseous reactions
Solid- as reactions
solid solid gas gas solid solid gas gas
solid gas solid gas
M M M M + +
Drying : Boling(>373K) and Diffusion(
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Iron ore reduction : Fe2O3(s), Fe3O4, FewO, + CO
2
2
,,
,1,4
6 CO gg CO gi in n m m
mi i CO CO
f
R a Kd W M M
=
=
Solution loss : C+CO2->2CO
Com etitive reactions : Arrhenius rate + diffusion
( ) ( )2 2 2
11 1
, film, 5g CO g CO s COR M A k k = +
Melting ( )1 ,, inflow
j s face facej melt j
n
G AT T
RT M Vol
=
Thermal Engineering Lab
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-
Heat Transfer
Conduction : Included in the energy equations
Convections : Wakao and Kaguei(1982)s equation
or Ranz-Marshall equation
Radiation : 2-flux model(Shin and Choi, 2000)
Among solid phases
( )
, , , ,
, ,,2
where
ss IJ IJ s I s J s I
V I s I s ps g g pgIV JI
IJ
V I s V I
f k C k Cf
hf t t f
+
= +
Geometrical changes
, ,
I
1/ 33 3
Generation of the internal pores , , , ,, , ,
V I ip I s ip I comb i
ip i ip loss I
i i
f v Mf
t y
+ = +
&
&
p u r
Thermal Engineering Lab
Bed structural changes : packing parameter, n
1 n o
V s Vf f f=
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Waste
Incinerator
Iron Ore Sintering
Bed
Coke Oven Blast Furnace
Bed type Moving bed Moving bed Fixed bed Counter-current
Feeding Continuous Continuous Batch Continuous.
Solid
material
Solid waste Iron ore
+Limestone
Coking coal Sintered ore+Coke
+Coke
Mode of
gas/air flow
Blowing air Suction air Discharge of
pyrolized gas
Blowing of
preheated blast
Heat source Volatile/Char
combustion
Coke combustion External Wall
Heating, latent
Heat of Pyrolysis
Coke &
PC(pulverized coal)
combustionPhysical
change
Change of bed
height by
combustion
Melting/sintering
Negligible change
of bed height
Swelling,
shrinkage
Melting of iron ore,
coke diameter
change(combustion)
Thermal Engineering Lab
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Waste Incinerator
Thermal Engineering Lab
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Major phenomena within the bed in waste incinerators
Ignition by radiation from wall/hot gas
Drying Pyrolysis Char combustion
Combined closely with the gas flow in the incinerator
AIRAIR(1) Raw waste(2) Drying(3) Pyrolysis(4) Char reaction
AIRAIR(1) Raw waste(2) Drying(3) Pyrolysis(4) Char reaction
WASTE
WASTE BED
COMBUSTION GAS
WASTE
WASTE BED
COMBUSTION GAS
(1) (2) (3) (4)
(5) Ash
WASTE
WASTE BED
COMBUSTION GAS
WASTE
WASTE BED
COMBUSTION GAS
(1) (2) (3) (4)
(5) Ash
ASHHOPPER
PRIMARY AIR
GRATES ASHHOPPER
PRIMARY AIR
GRATES ASHHOPPER
PRIMARY AIR
GRATES ASHHOPPER
PRIMARY AIR
GRATES
Thermal Engineering Lab
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Single solid phase
Bed height : 0.68 m
The particle size and porosity are not changed during the process
Calculation time : 6000 sec
Bed height (m) 0.68 Type Air
Waste incinerator (Moving bed, Continuous feeding)Ignition by radiation
from hot gas or wall (2)
Waste incinerator (Moving bed, Continuous feeding)Ignition by radiation
from hot gas or wall (2)
x zer o ce s
tmax (sec) 6000 vave 0.136m/st (sec) 1
IgnitionType Radiation
Size 30mm Value CFDresultsa
Solid waste(30~60%
combustible)
gas
Ash
Solid waste(30~60%
combustible)
gas
AshSolid
mat.
Moisture 45%Pyrolysis
A 1.5104
Volatile 39% E 30kcal/kmol
Char 6% A 2.3
Time = 0 Time = t1 Time = tmaxAirTime = 0 Time = t1 Time = tmaxAir
nc u ngmass-basecomposition)
Ash 10% E 22kcal/kmol
o 0.54
Gaseous
Volatile+O2CO+H2
LHVa 1790 CO+H2OCO2+H
Thermal Engineering Lab
reaction 2n 1 H2+0.5O2H2O
Shrinkage of grid YES
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-
Model is well describing the physico-chemical process in the waste bed
Temperature distribution and gas composition
0.4
0.6
m)
3.73
130.6
m)
3.73
13
COMBUSTION GASCOMBUSTION GASCOMBUSTION GAS
0.3
n
O2
CO2
H2O CO
H2
CxH
yO
z
0.2
.
BedHeight
14
0.2
.
BedHeight
14
0.1
0.2
2
H2
CO2
2
MoleFracti
0 2 4 6 8 10 120.0
Location on the grate (m)
4681
013
0 2 4 6 8 10 120.0
Location on the grate (m)
4681
013
0 1000 2000 3000 4000 5000 6000
0.0
CO
Predicted temperature distribution (x100k) Predicted gas composition (x100k)
me sec
Thermal Engineering Lab
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FURNACE ENCLOSURE
GAS FLOW FIELD :
Mass, Energy, Momentum and
Species Conservation Equations
Temperature, Heat Transfer
Velocity, Turbulent Mixing,
Chemical Species and Reaction
+Turbulence, Radiation, Reaction Models
MGAS, TGAS, VGAS
FUEL BED
QRAD
MODEL
Fuel Components and Temperature
Gas Species and Temperature
Bed Height, etc.
Combustion, Gas Reaction
Heat Transfers
Thermal Engineering Lab
( t = 0 )PRIMARY AIR(x)
x =
(tmax: Fuel Residence Time)
x =
(tmax: Fuel Residence Time)
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12001300
TEMPERATURE
[ UNIT : K ]
1500 Tgas1100
[ UNIT : K ]
700
1100
emperature(K)
0.2
CO2
Mole
1500
Tgas
1400 300
G
asT
0.0
0.1
CxHyOz+CO+H2
Frac
tion
x=0.8m ( t=6.6 min )
1200
700
1100
0.2CO2
1500
1550
SECONDARY
AIR1300
0.35
0.70
Height(m)
0.35
0.70
Height(m)
0.35
0.70
Height(m)
0.35
0.70
Height(m)
0.35
0.70
Height(m)
300
0.0
.CxHyOz+CO+H2
1500 1500
1400
1400
500
0
0.00
4 8 12
Bed
Distance (m)
0
0.00
4 8 12
Bed
Distance (m)
0
0.00
4 8 12
Bed
Distance (m)
0.00
4 8 12
Bed
Distance (m)
4 8 12
Bed
Distance (m)0.70
(m)
0.70
(m)
0.70
(m)
0.70
(m)
0.70
(m)
0.70
(m)
Thermal Engineering Lab
700
1100
0
0.00
4 8 12
0.35
BedHeight
Distance (m)
13
13
12
11
0
0.00
4 8 12
0.35
BedHeight
Distance (m)
0
0.00
4 8 12
0.35
BedHeight
Distance (m)
0
0.00
4 8 12
0.35
BedHeight
Distance (m)
0.00
4 8 12
0.35
BedHeight
Distance (m)
4 8 12
0.35
BedHeight
Distance (m)
13
13
12
11
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Iron Ore Sintering
Thermal Engineering Lab
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Major Phenomena in the sintering bed
SINTERED
IGNITION
SINTERED
IGNITION
COMBUSTION
SINTERED
ZONE
SINTERINGCOMBUSTION
SINTERED
ZONE
SINTERING
RAW MIX ZONE
ZONE ZONEMIX
Hearth Bed
RAW MIX ZONE
ZONE ZONEMIX
Hearth BedRAW MIX
ZONE CHAR COMBUSTION
MOISTURE EVAPORATIONRAW MIX
ZONE CHAR COMBUSTION
MOISTURE EVAPORATION
x
y
COMBUSTION GASx
y
COMBUSTION GASHEARTH BED
MOISTURE CONDENSATIO
HEARTH BED
MOISTURE CONDENSATIO
COMBUSTION GASCOMBUSTION GAS
Thermal Engineering Lab
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Iron ore sintering bed (Moving bed, ContinuousIron ore sintering bed (Moving bed, Continuous
Bed height (m) 0.57Oxidizer
Type Air
# of cells 57 T 300K
tmax(sec) 1500 vave 0.450m/s
Solidmateriala
AirIgnition by burner
Sinteredore
Solidmateriala
AirIgnition by burner
Sinteredore
t (sec) 1Ignition
Type Gas burner
Size(mm) 1.6/3.2 Value 4 m/s, 1400K
Time = 0 Time = t1 Time = tnaxCombustion as
Time = 0 Time = t1 Time = tnaxCombustion as
mat.
(includingmass-base
. Pyrol
ysis
-
Coke 3.8% E -Iron ore 83.2%
CharA 2.3
Limestona : Iron ore + Coke + Limestone (~4% combustible)a : Iron ore + Coke + Limestone (~4% combustible)on)
e .
o 0.4 Gaseousreact
ion
CO+0.5O2CO2n 0.6
Shrinka e of rid No
Thermal Engineering Lab
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IRON ORE SINTERING BED COMPARISON WITH SINTERING POT TEST RESULTS
2000
Computed
25
O2-Computed
1200
1400
1600
1800y=0.11my=0.30m
y=0.49m
ture
(K)
Measured
15
20
ition
(Vol.%)
CO2-Computed
CO-Computed
O2-Measured
CO2-Measured
CO-Measured
600
800
1000
Tempera
5
10
Gascompos
0 200 400 600 800 1000 1200 1400
Time (sec)
0 200 400 600 800 1000 1200 1400
0
Time(sec)
Temperature profile flue gas composition in the sintering bed
4
5
ec
)
Extingushed
m/min) 1600
2000
Sintering timeFlame front speed (FFS) and
Sintering time for various air
velocities and particle
2
3
SinteringTime(s
eFrontSpeed(c
Coke diameter : 1.2mm
800
1200
FFSQuantification of the
Thermal Engineering Lab0.2 0.3 0.4 0.5 0.6 0.7 0.8
1
Fla
Averaged Air Velocity (m/s)
Coke diameter : 1.4mm
Coke diameter : 1.6mm
0
400
(Flame Front Speed,
Sintering Time)
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Flame Front Speed (FFS)
Combustion Zone Thickness (CZT)
Melting Zone Thickness (MZT) : for an Iron Ore Sintering BedCZT : Combustion Zone Thickness
yy35
40MZT : Melting Zone Thickness
CZT(AirV=0.26m/s)
CZT(AirV=0.32m/s)
CZT(AirV=0.45m/s)
CZT(AirV=0.52m/s)
=
1800
2000
)
MaxT(AirV=0.26m/s)
MaxT(AirV=0.32m/s)
MaxT(AirV=0.45m/s)
MaxT AirV=0.52m/s
Sintered Zone
CZT
Sintered Zone
CZT
25
30
s(cm)
.
MZT(AirV=0.32m/s)
MZT(AirV=0.45m/s)MZT(AirV=0.52m/s) 1600
mperature(
.
Melt ing Zone
Combustion Zone
Melt ing Zone
Combustion Zone
10
15Thickne
1200
M
aximumT
Raw Mix
mperature
MZT
MaxT
Raw Mix
mperature
MZT
MaxT
0 400 800 1200 1600 2000
0
5
800
1000
Thermal Engineering Lab
1373K
1000K
T1373K
1000K
T
Time (sec)
Quanti fied resul ts : CZT, MZT, MaxT (for various air
supply)
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Coke Oven
Thermal Engineering Lab
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Plastic
(1) Wet Coal
(
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Height (6m) is much longer than width(0.45m)
1D model
Bed width (m) 0.22
Oxidizer
Type
No oxidizer# of cells 44 T
tmax(sec) 54000 vave
t (sec) 10 Type -
blend but a single coal
Input data - Elemental/Proximate analysis
data
Solidmat.
(including
Size 3mm Value -
Moisture 7%Pyrolysis
A 1.5104
Volatile 24.2% E 30kcal/kmol
Char 60.5% A -
Homogeneous porous mediamass-basecomposition)
Ash 8.3% E -
o 0.4Gaseousreaction -
n 1
Shrinkage of grid No
Heat
GasCoke oven (Batch type fixed bed)
Heat
GasCoke oven (Batch type fixed bed)
fromhot wall Raw
cokingcoal
Coke
fromhot wall Raw
cokingcoal
Coke
Thermal Engineering Lab
Time = 0 Time = t1
Time = tmax
Time = 0 Time = t1
Time = tmax
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-
Experimental data Temperature distribution within the oven
Time
700
800
900
1000
1100
e(oC)
300
350
400
450
re(mmH
2O)
#2 charging hole
#3 charging hole
1coke plant No. 2, No. 2 ovenMoisture : 5.8%
200
300
400
500
600
Temperatur
100
150
200
250
ternalgaspress
0 1 2 3 4 5 6 7 8 9 1 0 11 12 13 14 15 16 17 18 19Time (h)
0
100
0
50 In
Temperature change at the center Temperature change at the wall
1000
1200
1400
tu
re(K)
LV(0.15)
MV(0.25)
HV(0.35)1000
1200
tu
re(K)
LV(0.15)
MV(0.25)
HV(0.35)
400
600
800
Tempera
400
600
800
Tempera
Thermal Engineering Lab
0 5 10 15 20200
Time (hour)
0 5 10 15 20
200
Time (hour)
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Blast Furnace
Thermal Engineering Lab
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Modeling
-
Assumptions
2 phases - Gas and solid phases
Layer structure is obtained by Lo/Lc data & solid velocity ape o co es ve zone s e ne y range o so empera ure o ~ o
Shape of deadman(stagnant zone) is assumed
Layer properties (Dp, porosity) are function of locations
Raceway is treated as a boundary condition
# of cells 24x76 Reduction Rate
Size 20.0mma
50.0mmb3Fe2O3+CO
->2Fe3O4+CO2
Sold material : sintered ore + coke + flux(limestone)Blast furnace gas
... .
... .. .
Solidmat. [17]
.
0.45b
0.10c
3 4 ->FeO+CO2FeO+CO->Fe+CO2
Feeding
rate(kg/s)
180.8a
36.7
b
1/4Fe3O4+CO
...
. ... ... .. . . ...
... ...
..
. ... . .. .... .
.. ..
cokeore.
..... .
-> e+ 2
Blast air
T(oC) 1191
P(MPa) 0.42 Solution-loss Rate
V(Nm3/min) 6150 C+CO2->2CO [18]
...
. ..... ..
. .. .. .. . .
.. ... . ..
Solid flow
Thermal Engineering Lab
PCRd(kg/s) 15.9 -asGas
Liquid : pig i ron + slaga: Iron ore, b: Coke, c: Cohesive zone, d: Pulverized coal rate
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29.5
30
30.5
28
28.5
29
Height(m) .
Coke+Ore
O.L
C.COKE
O.S
27
27.5
0 1 2 3 4
COKE
a us m
8
29
29.5
30
(m)
5
6
7Lo/Lc
smoothing of Lo/Lc
27.5
28
28.5
Heigh
1
2
3
4
Lo/Lc
COKE
Thermal Engineering Lab
0 1 2 3 4
Radius(m) 0 1 2 3 4
0
Radius(m)
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7
Case A
5
6
Case C
c
2
3Lo/
0 1 2 3 4 5
0
1
Radius(m)
Lo/Lc data (Case A : Base)
Thermal Engineering Lab
Case A Case B Case C
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-
Thermal Engineering LabCase A Case B Case C
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Thermal Engineering Lab
Fe2O3 Fe3O4 FewO Fe
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=
1.0
Fe O
0.35
0.40 CO2
CO
0.6
.
action
2 3
Fe3O
4
FewO
Fe0.20
0.25
0.30
action
0.2
0.4
Mas
sf
0.10
0.15
Mas
sF
10 15 20 25
0.0
5 10 15 20 25 30
0.00
0.05
Height(m) Height(m)
Mass Fraction of Ore Mass Fraction of Gas
Thermal Engineering Lab
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Reactions of Indirect Reduction
2 3 3 4 23 ( ) ( ) 2 ( ) ( )Fe O s CO g Fe O s CO g+ +
Shrinking Core Model
3 4 2
3( ) ( ) ( ) ( )
4 3 4 3w
wFe O s CO g Fe O s CO g
w w+ +
2we s g w e s g+ +
3 4 21 3( ) ( ) ( ) ( ) ( 848 )4 4
sFe O s CO g Fe s CO g T K + +
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