Heat transfer in Rotating Fluidized Beds in a Static Geometry: A CFD study

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1 Heat transfer in Rotating Fluidized Beds in a Static Geometry: A CFD study Nicolas Staudt, Juray De Wilde* * Université catholique de Louvain MAPR / IMAP Réaumur, Place Sainte Barbe Louvain-la-Neuve Belgium juray.dewilde@uclouvain.be THE CONCEPT THEORETICAL INVESTIGATION COMPUTATIONAL FLUID DYNAMICS STUDY STEP RESPONSE TECHNIQUE CONVENTIONAL FLUIDIZED BED ROTATING FLUIDIZED BED IN A STATIC GEOMETRY CONCLUSIONS 1

2 THE CONCEPT FLUIDIZED BED PROCESS INTENSIFICATION IMPROVE EXTERNAL HEAT AND MASS TRANSFER (BETWEEN GAS & SOLIDS) IMPROVE INTERNAL MASS TRANSFER REDUCE GAS-SOLID CONTACT TIME INCREASE RATIO FREEBOARD SURFACE TO BED HEIGHT INCREASE MASS & HEAT TRANSFER COEFFICIENT FLUIDIZE SMALLER PARTICLES REDUCE BED HEIGHT & INCREASE GAS VELOCITY CYLINDRICAL GEOMETRY INCREASE GAS-SOLID SLIP VELOCITY FLUIDIZE IN A CENTRIFUGAL FIELD THE CONCEPT chimney outlet () solids outlet solids 2

MASS & HEAT TRANSFER COEFFICIENT FLUIDIZE SMALLER PARTICLES REDUCE BED HEIGHT & INCREASE GAS VELOCITY CYLINDRICAL

3 THE CONCEPT 36-cm DIAMETER FLUIDIZATION CHAMBER 1G GELDART D HIGH GAS-SOLID SLIP VELOCITIES SHORT GAS-SOLID CONTACT TIMES 1G GELDART B 1G-GELDART D-TYPE: DENSE AND UNIFORM BED 1G-GELDART B-TYPE: SOMEWHAT LESS DENSE AND LESS UNIFORM BUBBLING BED BUBBLING SUPPRESSED AT HIGHER SOLIDS LOADINGS THE CONCEPT CRITERIA FOR STABLE AND UNIFORM OPERATION Chimney: 1000 rpm, S = kg/s 1.6 Solids loading [kg] stable uniform rotating fluidized bed slugging channeling G Geldart D-type particles, 24-cm diameter fluidization chamber Gas flow rate [Nm3/h] (De Wilde & de Broqueville, 2007) 3

STABLE AND UNIFORM OPERATION 2 1.8 Chimney: 1000 rpm, S = 3.56 10-2 kg/s 1.6 Solids loading [kg] 1.4 1.2 1 0.8 0.6 0.4 0.

4 THE CONCEPT FLEXIBILITY IN THE FLUIDIZATION GAS FLOW RATE Force per cubic meter particle bed [N/m3] G-GELDART D-TYPE PARTICLES 24-cm DIAMETER FLUID. CHAMBER Average centrifugal force Average radial -solid drag force Fluidization flow rate [Nm3/h] Average radial (-solid slip) velocity [m/s] LIMITED RADIAL BED EXPANSION, EVEN RADIAL BED CONTRACTION 1600 GAS-SOLID HEAT TRANSFER COEFFICIENT THEORETICAL INVESTIGATION Gas-solid heat transfer coefficient [J/(m^2 s K)] hf: h gs radius at r = 0.12 m hf: h gs radius at r = 0.10 m hf: h gs radius at r = 0.07 m V = m 3 Solids loading = kg h grav gs = J /( m s K) Fluidization flow rate [m3/h] 4

0 850 900 Fluidization flow rate [Nm3/h] 6.5 7.0 7.5 8.0 8.5 Average radial (-solid slip) velocity [m/s] LIMITED RADIAL BED EXPANSION, EVEN RADIAL BED CONTRACTION 1600 GAS-SOLID HEAT TRANSFER

5 GAS-SOLID HEAT TRANSFER ROTATING FLUIDIZED BED IN A STATIC GEOMETRY POTENTIAL: INCREASED SPECIFIC FLUIDIZATION GAS FLOW RATE (i.e. per unit volume particle bed), due to increased width / height -ratio INCREASED FLEXIBILITY IN THE FLUIDIZATION GAS FLOW RATE AND COOLING OR HEATING VIA THE FLUIDIZATION GAS, due to similar effect of the fluidization flow rate on centrifugal and -solid drag force INCREASED GAS-SOLID HEAT AND MASS TRANSFER COEFFICIENTS POSSIBLE, due to increased -solid slip velocity COMPUTATIONAL FLUID DYNAMICS STUDY RESPONSE OF PARTICLE BED TEMPERATURE TO STEP CHANGE IN THE FLUIDIZATION GAS TEMPERATURE FROM 300 K TO 400 K AT TIME t 0 Eulerian-Eulerian approach with Kinetic Theory of Granular Flow Particles: 700 µm, 2500 kg/m 3 Restitution coefficients : - Particle - particle: Particle - wall: 0.9 Specularity coefficient : 0.5 Solids loading : kg/m length fluid. chamber COMPARISON CONVENTIONAL FLUIDIZED BED AND ROTATING FLUIDIZED BED IN A STATIC GEOMETRY 5

the fluidization flow rate on centrifugal and -solid drag force INCREASED GAS-SOLID HEAT AND MASS TRANSFER COEFFICIENTS POSSIBLE, due to increased -solid slip velocity COMPUTATIONAL FLUID DYNAMICS

6 CONVENTIONAL FLUIDIZED BED SOLIDS VOLUME FRACTION 195 m 2 /h 540 m 2 /h 1080 m 2 /h FLUIDIZATION GAS FLOW RATE ROTATING FLUIDIZED BED IN A STATIC GEOMETRY SOLIDS VOLUME FRACTION m 2 /h m 2 /h FLUIDIZATION GAS FLOW RATE (HIGHER THAN WITH CONVENTIONAL FLUIDIZED BED) RADIAL BED EXPANSION LIMITED PARTICLE BED UNIFORMITY BETTER THAN WITH CONVENTIONAL FLUIDIZED BED 6

29800 m 2 /h 59600 m 2 /h FLUIDIZATION GAS FLOW RATE (HIGHER THAN WITH CONVENTIONAL FLUIDIZED

7 PARTICLE BED TEMPERATURE RESPONSE Rotating fluidized bed in a static geometry Fluidization flow rate: Vitesse d'entrée m 3 / (h mdu length gaz fluid. : 39,4 chamber m/s) Vitesse d'entrée m 3 / (h mdu length gaz fluid. : 19,7 chamber m/s) Fluidization temperature Average particle bed temperature [K] Conventional fluidized bed Fluidization flow rate: Vitesse 1080 msuperficielle 3 / (h m length du fluid. gaz chamber : 2 m/s ) Vitesse 540 m 3 superficielle / (h m length du fluid. gaz chamber : 1 ) m/s Time [s] FASTER RESPONSE RFB-SG, DUE TO: INCREASED SPECIFIC FLUIDIZATION GAS FLOW RATE INCREASED GAS-SOLID HEAT TRANSFER COEFFICIENT PARTICLE BED TEMPERATURE UNIFORMITY t = 2 s t = 4 s t = 6 s t = 10 s Conventional fluidized bed Fluidization flow rate = 195 m 3 / (h m length fluid. chamber ) 7

: 19,7 chamber m/s) Fluidization temperature Average particle bed temperature [K] 380 370 360 350 340 330 320 310 Conventional fluidized bed Fluidization flow rate: Vitesse 1080 msuperficielle 3 / (h

8 PARTICLE BED TEMPERATURE UNIFORMITY t = 2 s t = 4 s t = 6 s t = 10 s Conventional fluidized bed Fluidization flow rate = 540 m 3 / (h m length fluid. chamber ) PARTICLE BED TEMPERATURE UNIFORMITY t = 2 s t = 4 s t = 6 s t = 10 s Conventional fluidized bed Fluidization flow rate = 1080 m 3 / (h m length fluid. chamber ) 8

chamber ) Conventional fluidized bed Fluidization flow rate = 1080 m 3 / (h m

9 PARTICLE BED TEMPERATURE UNIFORMITY t = 1 s t = 2 s t = 4 s t = 6 s Rotating fluidized bed in a static geometry Fluidization flow rate = m 3 / (h m length fluid. chamber ) PARTICLE BED TEMPERATURE UNIFORMITY t = 2 s t = 3 s Rotating fluidized bed in a static geometry Fluidization flow rate = m 3 / (h m length fluid. chamber ) IMPROVED PARTICLE BED TEMPERATURE UNIFORMITY, DUE TO TANGENTIAL FLUIDIZATION PARTICLE BED, i.e. THE PARTICLE BED ROTATIONAL MOTION 9

chamber ) PARTICLE BED TEMPERATURE UNIFORMITY t = 2 s t = 3 s Rotating fluidized bed in a static geometry

10 CONCLUSIONS CFD SIMULATIONS CONFIRM THAT ROTATING FLUIDIZED BEDS IN A STATIC GEOMETRY: Offer an increased specific fluidization flow rate Offer increased flexibility with respect to cooling or heating via the fluidization flow rate Offer the potential of -solid heat and mass transfer coefficients one to several orders of magnitude higher than in Conventional Fluidized Bed. Offer improved particle bed temperature uniformity due to excellent mixing resulting from the particle bed rotational motion PERSPECTIVES FOR USE OF ROTATING FLUIDIZED BEDS IN A STATIC GEOMETRY FOR FAST, HIGHLY ENDO- OR EXOTHERMIC REACTIONS OR FOR DRYING APPLICATIONS 10

orders of magnitude higher than in Conventional Fluidized Bed.

Chapter 5 Using Newton s Laws: Friction, Circular Motion, Drag Forces. Copyright 2009 Pearson Education, Inc.

Chapter 5 Using Newton s Laws: Friction, Circular Motion, Drag Forces Units of Chapter 5 Applications of Newton s Laws Involving Friction Uniform Circular Motion Kinematics Dynamics of Uniform Circular