fluidized bubbling bed reactor model for silane pyrolysis in solar grade silicon production yue...
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Fluidized Bubbling Bed Reactor Model For Silane Pyrolysis In Solar Grade Silicon Production
Yue Huang1, Palghat . A. Ramachandran1, Milorad. P. Dudukovic1, Milind S. Kulkarni2
1 Chemical Reaction Engineering Laboratory (CREL), Department of Energy, Environmental & Chemical Engineering, Campus Box 1198, Washington University in St. Louis, St. Louis, MO 631302 MEMC Electronic Materials, Inc., 501 Pearl Drive, St. Peters, MO 63376
Solar Energy
clean, green, renewable: environmentally friendly tremendous source: sunlight intensity on the earth 1000 W/m2
At some time in the future (50 years or more) fossil fuels will be depleted and humans will have to turn to other energy sources and solar cells will be a big part of generating electricity.
Why Solar Cell Needs Silicon
Semiconductor material in over 95% of all the solar cells produced
worldwide : Silicon
Demand of Solar Grade Silicon [1]
[1] Block et al., Silicon for the Chemical Industry V, 2000
Availability and demand of solar grade (SG)Silicon (Worldwide)
Market development as a function ofprice of modules
Challenge: develop a low cost SG-Si production route
Wp= Watt Peak, which is the Direct Current Watts output of a Solar Module as measured under an Industry standardized Light Test
Price for a 6KW module: 40K USDLife time: 15~20 yrs
Current processes for Silicon
Chlorosilane
s + hydrogen
or silane
cooled bell jar
high temperature Si rods
Siemens (Komatsu) process Fluidized Bed Reactor (FBR) process
Si particles
SiH4+H2
Si seeds
Product
Heater
High energy consumption (1100 C, 800~850 oC)Discontinuity of the processLong duration of the process
High cost: 50~60 $/kg
Lower energy consumption (600~650 oC)Continuous operation
Low cost: <15 $/kg
Objective of research
ONLY MEMC Inc. commercialized FBR process,
because
very expensive and time consuming scale-up
complex reaction mechanism
lack of engineering model for large-scale
reactors
OBJECTIVE
Pathways
SiH4 Si Vapor
Growing Large Si Particles
Si nuclei
Si clusters
(1)
(3)
(2) (6) (5) (4)
(8)(7)
(1)CVD growth on large particles(2)CVD growth on fines(3) Homogeneous silane decomposition (4) Homogeneous nucleation(5) Molecular bombardment of fines(6) Diffusion to growing large particles(7) Coagulation and coalescence of fines(8) Scavenging by large particles on fines
SiH4
Growing Seed Si Particles
Si Fines
(1)(2)
(3)
(1)CVD growth on large particles(2) Homogeneous silane decomposition (3) Scavenging by large particles on fines
Our ModelModel in literatures*
* Caussat et al., 1995Pina et al., 2006White et al. 2006
Model Scheme
Mass&heatexchange
Gas enters buuble phase
Gas in bubble phase
Plug flow
Emulsion gas
Well mixedMass&heatexchange
Gas enters emulsion phase
Feed gas
Gas leaving reactor, from bubble phase
Gas leaving reactor, from emulsion phase
Large Si ParticlesWell mix
edEmulsion
gasWell mixed Mass
exchange
Massexchange
Massexchange
Mass&heatexchange
Massexchange
Mass&heatexchange
Feeding of large Si particles
Discharge of large Si particles
SiH4 + H2
Bubble phase
Emulsion phase
Emulsionphase
Bubblephase
Pathways
),,(/2
2 TCCfsmkmolr HsnHTHT ),,(/2
3 TCCfsmkmolr HsnHDHD
2*5.0
3
3
4exp
2/ Si
A
si
cAHN C
RT
NrmNsmkmolr
(1) & (2): CVD growth on large particles and fines (3): Homogeneous silane decomposition
(4): Homogeneous nucleation
02
2/ SiSi
sisDF CC
M
RTsmkmolr
0,2 2
/ SiSiP
SsiABDL CC
d
Dsmkmolr
20
30, 2
1/1 MsmrCC
(5): Molecular bombardment of fines (6): Diffusion to growing large particles
(7): Coagulation and coalescence of fines
6/16/1
2/5 6
4
32 v
kT
si
where
13/ Msmkgr sisca
mfp
mfmf duPe
2
132 3/2
D
udPe mfSdp,
Fnpd
kTD
,3
(8): Scavenging by large particles on fines.
where
Bubble Phase: Plug Flow bHDbbHTbFnbbsneSnSnbbeb
bSnbG rraCCKdz
Cud,,,,,,
,,
bbSnbH RT
PCC ,,2
bHNbbDFbFnbbHDbbsieSiSibbebbSibG rrarCCK
dz
Cud,,,,,,,
,,
AbHNbbeFnbbebbbbbbG NrMMKM
dz
Mud,,0,0,
2,0
,0,
2
1
SiH4 mass balance
H2 mass balance
Si vapor mass balance
0th moment of fines
1st moment of fines *,,1,1,,3/2
,1,bAbHNbbeFnbbebbbb
bbG vNrMMKMdz
Mud
2*,,2,2,
2,1,3/5
,2, 2 bAbHNbbeFnbbebbbbbbbbbG vNrMMKMM
dz
Mud
bHTbFnrbbHDrbbebbebb
gbbGbp raHrHTTH
dz
dT
RT
PuC ,,,
0,,
2nd moment of fines
Energy balance
Emulsion Phase: Stirring Tank
SiH4 mass balance
H2 mass balance
Si vapor mass balance
0th moment of fines
eHDeHTeFneHTeSd
H
eSnbSnlf
Snbbei
beSnouteineSnine
i
rrara
dzCCH
KV
VCqCq
V
lf
,,,,,
0 ,,,,,,,,
11
e
H
lfeSneH RT
PdzH
CC
lf
0
,,2
1
eDFeFneDLeSdeHN
eHD
H
eSibSilf
Sibbei
beSiouteineSiine
i
rarar
rdzCCH
KV
VCqCq
V
lf
,,,,,
,0 ,,,,,,,,
11
eee
AeHN
H
eblf
Fnbbei
beouteineine
i
MM
NrdzMMH
KV
VMqMq
V
lf
,02
,0
,0 ,0,0,,0,,,0,
2
1
11
Emulsion Phase: Stirring Tank
1st moment of fines
2nd moment of fines
Energy balance
eee
eAeHN
H
eblf
Fnbbei
beouteineine
i
MM
vNrdzMMH
KV
VMqMq
V
lf
,1,3/2
*,0 ,1,1,,1,,,1,
11
eeeee
eAeHN
H
eblf
Fnbbei
beouteineine
i
MMM
vNrdzMMH
KV
VMqMq
V
lf
,22
,1,3/5
2*,0 ,2,2,,2,,,2,
2
11
0
)()(1
ˆ11
,,,,,
0
,1,,,,1,,,,,,,
eHDeHTeFneHTeSdr
eddi
deww
i
wH
eblf
bbei
b
eeouteineineineSiSipi
eeouteineineineepi
rraraH
TThV
ATTh
V
AdzTT
HH
V
V
TMqTMqCV
TCqTCqCV
lf
Pathways
Rate of Various Pathways (kg/hr)
SiH4Si Vapor
Growing Large Si Particles
Si Fines
(1):71.88
(3): 12.02
(2):0.08
(6):6.15(5)
4.72
(4)1.14
(8): 5.18
Emulsion Phase
SiH4Si Vapor
Si Fines
(3): 10.89
(2):0.16 (5)
9.81
(4)1.08
Bubble Phase
Example
Reaction or transfer control?
Silane concentration, Csn, kmol/m3
0.000 0.001 0.002 0.003 0.004
Hei
ght,
m
0
1
2
3
4
Conversion, %
0 20 40 60 80 100
Csn in bubbles
Csn in emulsion phase
Conversion
Bubble size, m
0.0 0.2 0.4 0.6 0.8 1.0H
eigh
t, m
0
1
2
3
4
Mass transfer coefficient, 1/s
0.1 1 10 100 1000
Bubble sizeMass transfer coeff.
Unreacted silane: mainly in bubbles Bubble size strongly affects interphase exchange
Bed Temperature
Temperature, K
750 800 850 900 950 1000
Hei
ght,
m
0
1
2
3
4
-40-20020
If T , conversion & fines
There is an optimal T
profile to maximize the
productivity
Silane Concentration
If Csn , fines If Csn , productivity but
cost of raw materials
Bed Height
If H , conversion
If H , productivity
but equipment
investment & energy
consumption
Conclusions
AcknowledgementThe financial support provided by
A phenomenological model was developed;
Mechanism of the process was investigated;
Enhancement of interphase exchange is the key to im
prove the reactor performance;
This study provides a good basis for optimization of o
perating conditions and for scale-up of reactor.