Presented at AIChE annual meeting, 2010

1. Simulation of a Steam Coal Gasifier
Presented by
Alireza Abbasi1-3
Paul E. Ege2, Hugo I. deLasa1
(1)Department of Chemical and Biochemical Engineering, University of Western Ontario,
London, ON, Canada
(2) Reactech Process Development Inc., Markham, ON, Canada
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2. Presentation outline
1- Introduction
-Fluidized Bed Modeling
2 - Model
-CFD and Plug Flow
3 - Results
4 - Summary
2

3. Fluidized Bed Properties and
Applications
Introduction
Properties
• Excellent for contacting large gas volumes
effectively with high solid surface area at
near isothermal conditions
• High relative gas/solid velocities
• Strong particle mixing
Applications
• Catalytic processes
• Steam Methane Reforming
• Gasification
• Catalytic Cracking
• CVD processes
• Silicon deposition (SiH4/SiHCl3)
• Uranium coating
• TiO4 coating
• Potassium nitrate granulation
• Other
• Combustion (coal/biomass)
• Thermal Gasification
• Drying
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4. Modeling Principles
Essentially, all models are wrong, but some are useful
(George E. P. Box, 1987)
 All the physics is not understood
 There are lots of assumptions in calculation

5. Simplified Approach Models
Introduction
Pseudo Homogeneous
• Ideal flow (PF/CSTR),
• Dispersion models,
• RTD or CTD models
• Simplified flow
• Single phase assumption
Two-phase modeling
• More advanced = account for bubble/emulsion
• Gas in excess of minimum fluidization = bubbles
• Two distinct phases: bubble & emulsion
• Each phase with has a model for flow & reactions
• Mass interchange between phases
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6. Computational Fluid Dynamics (CFD)
Introduction
1-The Eulerian-Lagrangian approach: The fluid phase is treated as a continuum by solving
the time-averaged Navier- Stokes equations, while the dispersed phase is solved by
tracking a large number of particles through the calculated flow field. (CPFD)
2-The Eulerian-Eulerian approach: It solves a set of n momentum and continuity equations
for each phase. Couplings are achieved through the pressure and inter phase exchange
coefficients. (CFD)
CPFD CFD
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7. Modeling a Coal Gasification Fluidized-
Bed Reactor
Model
(a) The schematic representation of the entrained fluidized bed gasifier. (b) Selected configuration
for the simulation of the entrained fluidized bed gasifier in the near feeding section.
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8. Modeling a Coal Gasification Fluidized-
Bed Reactor
Model
Coal → Char + Volatile + H 2 O + Ash
Volatile + βH 2O → α1CH 4 + α 2 H 2 + α 3CO + α 4 CO2
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9. Mathematical Modeling
Model
∂
CFD
The motion of fluid and dispersed (ρ fθ f ) + ∇ ⋅(ρ fθ f vf ) = S f (1)
∂t   
 
phases are governed by respective Convection Source
Density Chnage
mass and momentum conservation
∂
equations. The volume averaged
fluid mass, momentum and energy
( ρ f θ f v f ) + ∇ ⋅ ( ρ f θ f v f v) = − ∇P + ∇ ⋅θ f + ρ ff g − 
f   f
τ θ F
∂t    Pr essure    Mementum
 
equations are defined as follows: Acceleration
Convection Shear Body Force Exchange
(2)
The trajectory calculation of the ∂
[
( ρ f θ f E ) + ∇ ⋅ρE)ff = −.q + Q
( f + P θ v    ]
∗
discrete phase is made by ∇ (3)
integrating the force balance on ∂t   
  Conduction Source
Convection
the particles. The particle motion Accumulation
is defined as follows:
d
( v p ) = p− v) − ∇P − ∇ ⋅τ p + 
D (v f
p
g (4)
dt
  ρp θ p ρ p Body Force
Acceleration
Drag Force   

Pr essure Stress
Plug Flow
A material balance on the
differential volume of a fluid
vi , j R j
element on species i in a PFR is d
( Fi , x ) = Ac ∑ (5)
calculated as follows: dx
 
 j ν j
molar flow Changing
 r
 ,
Re action
∆H 1 + ∆H 2 + ∆H 3 =Q
 (6)
  
species coming species leaving heat of reaction 0
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10. CFD Modeling
Results
Particle contours after 10S
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11. CFD Modeling
Results
Fluid contours after 10S
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12. CFD Modeling
Results
Gas species contour after 10s
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13. CFD Modeling
Results
Gas species contour after 10s
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14. CFD Modeling
Results
Effluent concentrations
Particle recycle flow at 1150K Particle recycle flow at 1350K
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15. Plug Flow Modeling
Results
Axial Concentration profile
Particle recycle flow at 1150K Particle recycle flow at 1350K
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16. Modeling Results
Results
Temperature Profile
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17. CFD and Plug Flow Comparison
Results
Effluent concentrations
Particle recycle flow at 1150K Particle recycle flow at 1350K
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18. Summary
 Reasonable agreement between CFD and PF effluents
 Methods are complementary, fast general or slow detailed
 PF model set up in few days allow quick investigation
 Useful for wide range of conditions (height, density, flow, temp,
pressure…)
 Possible to apply different kinetics (even parameter fit to
experiments)
 Useful for feasibility, optimization and In Situ calculations ,fast basic
understanding of process
 CFD takes time to set up and run different cases
 Detail understanding of bed hydrodynamics
 Investigate flow/species patterns
 Specify flow related issues (hot spot, bypass)
 Benefit for entrainment and choking
 Useful for scale-up and design
 Also verify changes prior to implementing in practice
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