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) ICMSC-15

CFBC PROCESS FLOW DIAGRAM ICMSC-15

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. ICMSC-15

PRINCIPLE OF FBC Buoyancy Force Gravitational Force Solid particle air ICMSC-15

FLUIDIZATION REGIMES Fixed Bed Particulate Regime Bubbling Slug Flow Turbulent Fast Fluidization Pneumatic Conveying Solids Return ICMSC-15

MODEL DEVELOPMENT Description of gas and solid - Eulerian model Multiphase flow Flow simulation - Gidaspow drag model Viscosity - k – ε turbulence model ICMSC-15

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. ICMSC-15

SOFTWARE USED SOLVER – FLUENT MESHING - GAMBIT ICMSC-15

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) ICMSC-15

PHASE PROPERTIES Air PRIMARY VELOCITY [m/s] 1.42 SECONDARY VELOCITY [m/s] 0.05 DENSITY [kg/m3] 1.225 ICMSC-15

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 ICMSC-15

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) ICMSC-15

OPERATING AND BOUNDARY CONDITIONS OPERATING PRESSURE [Pa] 101325 GRAVITY [m/s2] -9.81 in y direction SPECIFIC OPERATING DENSITY [kg/m3] 0.328984 OPERATING TEMPERATURE [k] 1073.15 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] ICMSC-15

FLOW PATTERN ICMSC-15

AXIAL PROFILE – PARTICLE VOLUME FRACTION vs. AXIAL HEIGHT ICMSC-15

AXIAL PROFILE – TRANSITION ZONE ICMSC-15

RADIAL PROFILE - CORE ANNULAR STRUCTURE ICMSC-15

CORE ANNULAR STRUCTURE SOLIDS HOLD UP AND INWARD MIGRATION WITH MODERATE BACK MIXING ICMSC-15

THE RADIAL PROFILE PLOTS AT VARIOUS HEIGHTS ICMSC-15

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SOLIDS HOLDUP AND CLUSTERING ICMSC-15

BACKMIXING ICMSC-15

VELOCITY PROFILE ICMSC-15

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. ICMSC-15

THANKYOU ICMSC-15