1. CFD ANALYSIS OF MULTIPHASE TRANSIENT FLOW IN A CFB RISER
A. Mercy Vasan, (Asst Professor)
Dr.V.Gopalakrishnan, (Senior Professor)
N.Prasanna, (Asst Professor)
S.Gowtham,(P.G. Student)
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2. CFBC PROCESS FLOW DIAGRAM
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3. OBJECTIVE To analyse and simulate the flow pattern
To study and to analyse the multiphase transient FLOW BEHAVIOUR AND FLOW PATTERN in a 2-D circulating fluidized bed riser and to SIMULATE AXIAL AND RADIAL FLOW PROFILE depicting the particle volume fraction and velocity distribution in a riser.
To analyse and simulate the flow pattern
- radial profile
- vertical profile
To state the importance of flow simulation.
Further to state importance and application of flow modelling and simulation.
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4. PRINCIPLE OF FBC Buoyancy Force Gravitational Force Solid particle air
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5. FLUIDIZATION REGIMES Fixed Bed Particulate Regime Bubbling Slug Flow
Turbulent
Fast
Fluidization
Pneumatic
Conveying
Solids Return
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6. MODEL DEVELOPMENT
Description of gas and solid - Eulerian model Multiphase flow Flow simulation - Gidaspow drag model Viscosity - k – ε turbulence model
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7. MULTIPHASE FLOW Multiphase flow is simultaneous flow of:
Materials with different states or phases (i.e. gas, liquid or solid).
Materials with different chemical properties but in the same state or phase (i.e. liquid-liquid systems such as oil droplets in water).
One of the phases is continuous (PRIMARY) while the other (SECONDARY) are dispersed within the continuous phase.
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8. SOFTWARE USED
SOLVER – FLUENT
MESHING - GAMBIT
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9. SIMULATION PARAMETERS
MATERIALS PHASES
AIR
COAL
PHASE PROPERTIES:
DIAMETER
GRANULAR TEMPERATURE
SOLIDS PRESSURE
GRANULAR VISCOSITY
PHASE INTERACTION:
DRAG - GIDASPOW DRAG MODEL
TURBULENCE CONDITION PARAMETERS
MODEL- k – ε turbulence model
turbulence kinetic energy - k (m2/s2)
turbulence dissipation rate - ε (m2/s3)
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10. PHASE PROPERTIES Air PRIMARY VELOCITY [m/s] 1.42
SECONDARY VELOCITY [m/s]
0.05
DENSITY [kg/m3]
1.225
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11. Coal PARTICLE DIAMETER [m] 70*10-6 PARTICLE DENSITY 1654
PARTICLE COEFF OF RESTITUTION
0.9
WALL COEFF OF RESTITUTION
GRANULAR VISCOSITY [kg/(ms)]
Syamlal-Obrien
GRANULAR BULK VISCOSITY [kg/(ms)]
Lun et al
FRICTIONAL VISCOSITY[kg/(ms)]
Schaeffer
ANGLE OF INTERNAL FRICTION [ °] 30
GRANULAR TEMPERATUE [m2/s2]
algebraic
SOLID PRESSURE [Pa]
RADIAL DISTRIBUTION
ELASTICITY MODULUS
Derived
PACKING LIMIT
0.652
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12. BOUNDARY CONDITIONS & SIMULATION PARAMETERS
OPERATING CONDITIONS:
OPERATING PRESSURE
GRAVITY
BOUNDARY CONDITIONS:
INLET & OUTLET
momentum condition
thermal condition
species condition
WALL
air – no slip condition
particle – slip condition (drag model)
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13. OPERATING AND BOUNDARY CONDITIONS
OPERATING PRESSURE [Pa]
101325
GRAVITY [m/s2]
-9.81 in y direction
SPECIFIC OPERATING DENSITY [kg/m3]
OPERATING TEMPERATURE [k]
TURBULENT KINETIC ENERGY [m2/s2]
0.005
TURBULENT DISSIPATION RATE [m2/s3] 5
PRIMARY AIR VELOCITY [m/s]
1.42
SECONDARY AIR VELOCITY [m/s]
0.05
COAL INLET VELOCITY [m/s]
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14. FLOW PATTERN
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15. AXIAL PROFILE – PARTICLE VOLUME FRACTION vs. AXIAL HEIGHT
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16. AXIAL PROFILE – TRANSITION ZONE
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17. RADIAL PROFILE - CORE ANNULAR STRUCTURE
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18. CORE ANNULAR STRUCTURE
SOLIDS HOLD UP AND INWARD MIGRATION WITH MODERATE BACK MIXING
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19. THE RADIAL PROFILE PLOTS AT VARIOUS HEIGHTS
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24. SOLIDS HOLDUP AND CLUSTERING
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25. BACKMIXING
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26. VELOCITY PROFILE
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27. CONCLUSION
From the computational study of CFB raiser, we came to a conclusion that there is both axial and radial flow is there.
Axial profile indicates that in transition region complete combustion takes place so clustering is less in diluted region.
Core annular radial profile express that riser is very much prone to wear.
Back mixing is a critical property which is useful for proper mixing and increase in turbulence, which in turn increases the combustion efficiency.
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28. THANKYOU
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