Fluidized Bubbling Bed Reactor Model For Silane Pyrolysis In Solar Grade Silicon Production

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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 63130 2
MEMC Electronic Materials, Inc., 501 Pearl Drive,
St. Peters, MO 63376
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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.
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Why Solar Cell Needs Silicon
Semiconductor material in over 95 of all the
solar cells produced worldwide Silicon
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Demand of Solar Grade Silicon 1
Availability and demand of solar grade
(SG) Silicon (Worldwide)
Market development as a function of price of
modules
Wp Watt Peak, which is the Direct Current Watts
output of a Solar Module as measured under an
Industry standardized Light Test
Challenge develop a low cost SG-Si production
route
Price for a 6KW module 40K USD Life time 1520
yrs
1 Block et al., Silicon for the Chemical
Industry V, 2000
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Current processes for Silicon
Siemens (Komatsu) process
Fluidized Bed Reactor (FBR) process
High energy consumption (1100 C, 800850
oC) Discontinuity of the process Long duration of
the process
Lower energy consumption (600650 oC) Continuous
operation
Low cost lt15 /kg
High cost 5060 /kg
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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
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Pathways
Our Model
Model in literatures

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

1. CVD growth on large particles
2. Homogeneous silane decomposition
3. Scavenging by large particles on fines

Caussat et al., 1995 Pina et al., 2006 White
et al. 2006
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Model Scheme
Feeding of large Si particles
Bubble phase
Emulsion phase
Discharge of large Si particles
SiH4 H2
Emulsion phase
Bubble phase
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Pathways
(1) (2) CVD growth on large particles and 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
where
where
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Bubble Phase Plug Flow
SiH4 mass balance
H2 mass balance
Si vapor mass balance
0th moment of fines
1st moment of fines
2nd moment of fines
Energy balance
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Emulsion Phase Stirring Tank
SiH4 mass balance
H2 mass balance
Si vapor mass balance
0th moment of fines
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Emulsion Phase Stirring Tank
1st moment of fines
2nd moment of fines
Energy balance
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Pathways
Example
(3) 10.89
Si Vapor
SiH4
(2) 0.16
(5) 9.81
(4) 1.08
Si Fines
Bubble Phase
Emulsion Phase
Rate of Various Pathways (kg/hr)
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Reaction or transfer control?

• Unreacted silane mainly in bubbles
• Bubble size strongly affects interphase exchange

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Bed Temperature

• If T ? , conversion ? fines ?
• There is an optimal T profile to maximize the
  productivity

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Silane Concentration

• If Csn ? , fines ?
• If Csn ? , productivity ? but cost of raw
  materials ?

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Bed Height

• If H ? , conversion ?
• If H ? , productivity ? but equipment
  investment ? energy consumption ?

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Conclusions

• A phenomenological model was developed
• Mechanism of the process was investigated
• Enhancement of interphase exchange is the key to
  improve the reactor performance
• This study provides a good basis for optimization
  of operating conditions and for scale-up of
  reactor.

Acknowledgement The financial support provided by