-
A model for black liquor gasification in a fluidized bed
Z. Chena, A.F. Sarofima,b, M.J. Bockeliea and K. Whittyb
a Reaction Engineering International77 W. 200 S., Suite 210,
Salt Lake City, UT 84101
b Department of Chemical and Fuels EngineeringUniversity of
Utah, Salt Lake City, UT 84112
-
Background and Objective Model Development Devolatilization and
Gasification Kinetics Model Results Conclusions Acknowledgement
OUTLINE
-
To develop a model to simulate black liquor gasification in a
bubbling fluidized bed (Big Island steam reformer process)
To examine the effects of operating conditions on syngas
quality, carbon conversion, gas temperature and axial variations of
gas composition and temperature
BACKGROUND AND OBJECTIVE
MTCI process 200 tpd BLS 4 tube bundles
-
MODEL ASSUMPTIONSThe fluidized bed consists of
A particle-free bubble phase A wake-cloud phase A dense
phase
Gas in different phases has the same temperature Particles in
different phases also have the same temperature Drying and
devolatilization are instantaneous
bubble phasedense phase
bubble
cloud
wake
Fluidizing gas
-
Bubble Properties
Bubble size and bubble velocity are determined using
correlations found in the literature.
Bubble fraction is calculated based on the overall gas mass
balance.
Bubble breakup in the tube banks is predicted using a
probabilistic model.
-
Mass Balance Equations Bubble Phase
Exchange Reaction
flow-Cross Convection
0)CA(CKfRAf
dzA)ud(f)CC(dz
)ACud(f
wi,bi,bwbn
1jjb,i,ji,b
bbwi,2bi,1
bi,bb
b =++
+
=
Wake and Dense Phases
Freeboard
0RdzdC
ufn
1jjf,i,ji,
fi,o =+ =
Similar to the above equation
-
Energy Balance EquationsGas Phase
0Q)RH()]f(1f[1)RH(ff
R)(f)]T(Td
6)T(Td
6h)[)](1f(1f[1
T(Td6T(T
d6h)[(1ff
zT
uC
tn
1ige,i,ge,i,mfwb
n
1igw,i,gw,i,mfwb
bi,n
libi,b
4p
4g
ppg
p
emfwb
4p
4g
ppg
p
wmfwb
ggpg
=++++
++++
++
==
=
)])dd
0
Particle Phase
0]H
)H)n
1i
=+++++
++
=
=
watn
1ise,i,se,i,
4g
4p
pgp
p
emfwb
sw,i,sw,i,4g
4p
pgp
p
wmfwb
Q)R(-)T(Td
6)T(Td
6h)[)](1f(1f[1
]R (-T(Td6)T(T
d6h)[(1ff
0R)H(dz
dTCu
i,fi,f
n
li
ggpg0 =+=
Freeboard
-
Devolatilization
Empirical correlations are used to determine C, H, O and S
release (Frederick and Hupa, 1993; Frederick et al., 1995)
Volatiles are represented by a mixture of CH4, CO, H2O and
H2S
ShHOgHfCOeCHSOHC 224dcba +++=
Amount of each gas species is determined from the element mole
balance
Char = BLS - volatiles
-
GASIFICATION KINETICS
Steam gasification (Li and van Heiningen, 1991)
22 HCOOHC +=+ sm/kmolCp42.1pp
T25300exp1056.2Rate 3c
2HOH
OH
p
9
2
2
+
=
CO2 gasification (Li and van Heiningen, 1991)
CO2COC 2 =+ sm/kmolCp4.3pp
T30070exp1030.6Rate 3c
COCO
CO
p
10
2
2
+
=
Other reactions considered (MFIX)
224 H3COOHCH +=+42 CHH2C =+
COOC 221 =+
2221 COOCO =+
OH2COO2CH 2224 +=+OHOH 22212 =+
222 COHOHCO ++
-
PRELIMINARY RESULTS
Product gas composition Particle and gas temperature Bubble
properties Change in gas flow rate in the bed Variation of gas
composition along the height
-
Syngas Composition
0
0.1
0.2
0.3
0.4
0.5
CO CO2 H2O H2
gas species
m
o
l
e
f
r
a
c
t
i
o
n
REI modelUU modelDESIGN
Model results are in good agreement with available data Model
predicts 96% carbon conversion
-
300
400
500
600
700
800
900
0 0.2 0.4 0.6 0.8 1
dimensionless height
t
e
m
p
e
r
a
t
u
r
e
,
K
TgTp
Particle and Gas Temperature
Particle temperature is the same as gas temperature due to a
large contacting area Temperature in the bed is not uniform
-
Bubble Properties
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 0.2 0.4 0.6 0.8 1
dimensionless height
b
u
b
b
l
e
s
i
z
e
,
m
0
0.1
0.2
0.3
0.4
b
u
b
b
l
e
f
r
a
c
t
i
o
n
average db
in the tubebundles
in openspace
tube-free bed
fb
Bubble size is fairly uniform in the tube bundles
-
Gas Flow Rate and Superficial Velocity
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 0.2 0.4 0.6 0.8 1
dimensionless height
s
u
p
e
r
f
i
c
i
a
l
g
a
s
v
e
l
o
c
i
t
y
(
u
0
)
,
m
/
s
1
1.5
2
2.5
3
g
a
s
m
a
s
s
f
l
o
w
r
a
t
e
,
k
g
/
s
Gasification takes place above a dimensionless height of 0.2
-
Gas Species Mole Fraction
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 0.2 0.4 0.6 0.8 1
dimensionless height
m
o
l
e
f
r
a
c
t
i
o
n COCO2H2OH2
Water-gas shift reaction proceeds in forward direction in the
freeboard
-
Gas Species Mole Fraction
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0 0.2 0.4 0.6 0.8 1
dimensionless height
C
H
4
m
o
l
e
f
r
a
c
t
i
o
n
0.00000
0.00005
0.00010
0.00015
0.00020
0.00025
H
2
S
m
o
l
e
f
r
a
c
t
i
o
n
CH4H2S
-
CONCLUSIONS
A three-phase model has been developed to simulate black liquor
gasification in a fluidized bed
Preliminary results are in good agreement with available
data
Predicted carbon conversion is consistent with field data
-
ACKNOWLEGDEMENT
This project has been funded by the DOE under a subcontract
through the University of Utah (DE-FC26-02NT41490). The DOE project
manager is Parrish Galusky. The Georgia-Pacific project manager for
this effort isRobert DeCarrera.
