NETL 2012 Conference on Multiphase Flow Science
Javad Abbasian, Emadoddin Abbasi and Hamid Arastoopour
Sulfur By-Product
Fly Ash By-Product
Slag By-Product
0.01
0.1
1
10
100
250 300 350 400 450 500Temp, C
PC
O2,
atm
AbsorptionMgO+CO2 MgCO3
DecompositionMgCO3 MgO+CO2
°
Advanced Power Plant
CO2 Capture Reactions MgO + CO2 MgCO3 Absorption MgO + CO2 MgCO3 Regeneration
Water-Gas-Shift Reaction CO + H2O CO2 + H2
0
5
10
15
20
25
30
35
40
0 2 4 6 8 10 12 14 16 18Time, min
Con
vers
ion,
%
350 C
500 C
425 C
450 CP= 20 barCO2/N2: 50/50Sorbent: EP44
4
CO2 Capture
0
20
40
60
80
100
0 5 10 15 20 25Time, min
Dec
ompo
sitio
n, %
550 C
500 C
450 CP= 20 barN2: 100%Sorbent: EP44
Sorbent Regeneration
20 µm Scale:
0
5
10
15
20
25
30
35
40
0 5 10 15 20 25 30Time, min
Conv
ersi
on, %
With Potassium Impregnation
Without Potassium Impregnation
200 µmScale: 200 µmScale: 200 µmScale:
Mass balance around the particle for reactant gas (i.e. CO2)
B.C.: (a) @ R = 0 (b) @ R = Rp Mass balance around the grain for reactant gas (i.e. CO2) B.C.: (a) @ r=rg’ (b) @ r=ri
( ) ( ) 01313
22
2 =−−−
∂∂
∂∂ n
eig
iRe CCk
rr
RCRD
RRε
01 22 =
∂
∂
∂∂
rC
rrr
D gg
Rg CC = ( )negg
g CCkr
CD −=
∂
∂.
Rg CC =
Radius at Reaction interface
I.C.: ri = rg @ t=0 Overall Conversion of the particle
( )egMgO
i CCkdtdr
−−=ρ
dRrrR
RX
R
g
ioverall ∫
−=
0
03
32
30
.1.3
0=∂∂
RCR
7
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 5 10 15 20Time, min
MgO
Con
vers
ion
TGA Experimental DataTwo-Zone Reactive ModelOne-Zone Reactive ModelUnifrom Reactivity Model
R2=0.99R2=0.97R2=0.90
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 5 10 15 20Time, min
Con
vers
ion
500 °C
450 °C
425 °C
350 °C
10
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60 70 80 90Time, min
Mol
ar P
erce
nt (M
ole
of C
O2
out/M
ole
of C
O2
in)
350°C
300°C
400°C
425°C
0
10
20
30
40
50
60
70
80
0 10 20 30 40 50 60 70 80 90Time, min
Mol
ar P
erce
nt (d
ry b
ase)
CO2
H2
CO
- For heterogeneous reactive systems: Conservation of species in each phase
- Rj is the heterogeneous reaction rate
- An Ideal reaction model for CFD applications should: - Capture the real physics - Not increase the CPU time significantly - Be easy to implement in CFD codes
- Grain Model:
- Captures the real physics - Is an implicit model (needs 2 additional equations ) - Increases CPU time - Is not easy to implement in commercial CFD codes
jigggigg Ryvyt
=∇+∂∂ ).()( ρερε
Numerical Modeling Species Conservation Equations
Mass balance around the particle for reactant gas (i.e. CO2)
B.C.: (a) @ R = 0 (b) @ R = Rp Mass balance around the grain for reactant gas (i.e. CO2) B.C.: (a) @ r=rg’ (b) @ r=ri
( ) ( ) 01313
22
2 =−−−
∂∂
∂∂ n
eig
iRe CCk
rr
RCRD
RRε
01 22 =
∂
∂
∂∂
rC
rrr
D gg
Rg CC = ( )negg
g CCkr
CD −=
∂
∂.
Rg CC =
Radius at Reaction interface
I.C.: ri = rg @ t=0 Overall Conversion of the particle
( )egMgO
i CCkdtdr
−−=ρ
dRrrR
RX
R
g
ioverall ∫
−=
0
03
32
30
.1.3
0=∂∂
RCR
rc : Radius of the low reactive zone (k2) rp : Initial radius of the particles rp’: Radius of the expanded particle Low Reactive Zone (k2)
Highly Reactive Zone (k1)
Product Layer
Gas Film
rp, k1
rc k2
rp’
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0 200 400 600 800 1000 1200 1400 1600
MgO
Con
vers
ion
Time (s)
Exp 425°C
Variable Dg
SCM
* Abbasi et al., Fuel , 2012
1- There are two distinct reactive zones inside the particles 2- Process is controlled by both surface reaction and product
layer diffusion 3- There is an Expanding product layer 4- Effective product layer diffusivity is a function of conversion
due to expansion ( and increased tortuosity ) 5- Intrinsic reaction rate is Arrhenius type
)exp(0 RTEkk ss −=
)(0βαXDD gg −=
3 )1( ZXXrr pp +−′=
action
s
Layeroduct
gp
iip
gp
i
oMgOebi
kDrrrr
krr
NCCdtdr
RePrfilm
2 1)(/)(
+−
+
−=−
3)(1p
i
rr
X −= dXXr
dr pi
32
)1(3
−−−=
3 )1( ZXXrr pp +−′=
productreact
reactproduct
MM
Z⋅
⋅=ρρ
′−+
−−=
)1(1
)(
p
ii
g
s
eboMgO
si
rr
rDk
CCN
kdtdr
)
111()1(1
)1)((3
331
32
XZXXXr
Dk
XCCN
kr
dtdX
pg
s
eboMgO
s
p
+−−
−−+
−−
−=rp, k1
rc,k2
c
cs rrfork
rrforkk
<≥
=
2
1
)(0βαXDD gg −=
------------------------------------------------------------------------------------------------------------------------------------------- Onischak and Gidaspow, ”Separation of Gaseous Mixtures by Regenerative sorption on Porous Solids. Part II: Regenerative separation of CO2”, Recent Developments in Separation Science, ed. N. Li, 1972
0
5
10
15
20
25
30
0 500 1000 1500 2000 2500 3000 ϕ(
t)
t(s)
Thiele Modulus in our study
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 500 1000 1500
MgO
Con
vers
ion
Time (s)
Exp 350 °C
Exp 425°C
Exp 450°C
Model
0
1E-10
2E-10
3E-10
4E-10
5E-10
6E-10
0 0.5 1
Dg
(m2/
s)
MgO Conversion
Model
Parameter
Without Steam With Steam
350 o C 425
o C 450
o C 425
o C
Dg0 1.1E-10 6.0E-10 1.2E-9 2.1E-9
α 3.5E+2 8.1E+1 5.7E+1 4.6E+1
β 3 3 3 3
)( 30 XDD gg α−=
45 cm
30 cm
Thermocouple
Thermocouple
8 cm
7 cm
T1
Thermowell
Bed of Sorbent
Quartz Beads
SS Annulus
SS Annulus
Frit
Reactor Body
T2
T1
T2
420
425
430
435
440
445
450
455
0 5 10 15 20 25 30 35 40 45 50Time, min
Tem
pera
ture
, C
T11T12T13T14
420 425 430 435Bed Temp., C
Posi
tion
of th
e be
d, c
m
0
8
4 8 cm
2 cm
T11
T12
T14
T13
Thermowell
420 425 430 435Bed Temp., C
Posi
tion
of th
e be
d, c
m
0
8
4 8 cm
2 cm
T11
T12
T14
T13
Thermowell
@ 425°C start 50 min
CO2 Absorption Breakthrough Curve at Different Operating Temperatures
0
0.5
1
1.5
2
2.5
3
3.5
4
0 5 10 15 20 25 30 35 40Time, min
CO
2 Out
let F
low
, mol
/min
*103
Sorbent: EP68System Pressure= 20 atmInlet Total Flow Rate= 200 cm 3 /minCO2 inlet= 50 %molN2 inlet= 50 %mol
450°C
425°C
350°C
Bed Inlet
Bed Outlet
An explicit reaction rate model has been developed which is able to describe the reaction rate data obtained in TGA.
The reaction model is suitable for CFD applications due to its explicit formulation.
The reaction model was validated vs the experimental data obtained in pack-bed.
Future work includes:
Application of the CFD and reaction models in simulations of a bubbling bed and circulating fluidized bed reactors.
Modeling of Regeneration reaction
Modeling of the pr0cess
Financial support for this study was provided by the U.S. Department of Energy (contracts DE-FG26-03NT41798 and DE-FE0003997) and the Illinois Clean Coal Institute (ICCI Project No: 11/US-4).
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