Experimental Study of Conical Fluidized

Bed Using Radioisotope Based Techniques

Lipika Kalo1, H.J.Pant2, and Rajesh K. Upadhyay1

1: Chemical Process Engineering Laboratory (CPEL)

Department of Chemical Engineering

Indian Institute of Technology Guwahati, Assam, India

2: Isotope and Radiation Application Division

Bhabha Atomic Research Centre, Mumbai, India

ID: B01-02

Advantage of Conical Fluidized Bed over Cylindrical Fluidized bed

Applications

Drying

Granulation

Food processing

Coking

Nuclear fuel

particle coating

Crystallization

Gasification and

liquefaction of

coal

Issues• Entrainment

• Poor mixing

• Non-uniform

particle

distribution

• Increases power

requirementGasGas

Peng et al., Chemical Engineering Science, 52(14), 2277-2290 (1997).

Gas

Fixed bed

Gas

Turbulently Fluidized Bed

Gas

Transition Regime

Gas

Partially Fluidized bed

Gas

Fully Fluidized Bed

Increasing velocity

Regimes in Mono Conical Fluidized Bed

Regimes in Binary Conical Fluidized BedComplete

SegregationIncomplete Segregation

Heterogeneous Mixing

Homogeneous Mixing

Increasing velocity

0.6 mm glass particle

1 mm glass particle

Radioactive Particle Tracking (RPT)➢ A gamma ray emitting radioactive particle is

used

➢ Particle resembles the shape, size and densityof the phase of interest

➢ Particle is allowed to move freely inside thecolumn

➢ An array of scintillation detector are placedoutside the vessel of interest to record theintensity of radiation

➢ By using reconstruction algorithm andexperimental data the instantaneous positiontime series of the particle is measured

➢ Instantaneous velocity is calculated by timedifference of two successive position ofparticle.

➢ From the Instantaneous velocity time series arich data base is calculated by applyingsuitable post processing.

Flow chart of Radioactive Particle Tracking (RPT)

RPT Experiments (counts from detector)

Instantaneous Position of the Particle

Instantaneous velocity (time differentiation of two successive position)

Ensemble Average Velocity

Fluctuation Velocity

ReconstructionAlgorithm

Calibration (Distance count map)

Eulerian grid

Limtrakul et al., Chemical Engineering Science, 60, 1889–1900 (2005).

r, θ

r, z

i, j, ki, j, k+1

i, j, k+2

RMS velocities, Kinetic Energy of fluctuation, Granular temperature, diffusivity etc.

Quantities Obtained from RPT Experimental Data

Instantaneous Velocity

Ensemble average velocity

Fluctuating velocity component

RMS velocity

Stress

Fluctuating kinetic energy per unitvolume

Granular Temperature

z

zv

t

( , , )

,

1

1( , , ) ( , , )

( , , )

N i j k

q q n

n

v i j k v i j kN i j k

' ( , , ) ( , , ) ( , , )q q qv i j k v i j k v i j k

'2RMS

q qv v

' '( , , ) ( , , )qs p q sv i j k v i j k

'2 '2 '21[ ]

2p r zKE v v v

2

3s sk

Ks= Kinetic Energy due to solid velocity fluctuation per unit mass

Experimental Setup

Material Size of Solid Umf (m/s)

Glass beads 1mm 1.97

Glass beads 0.6 mm 1.1

Bed Composition Liquid

Velocity

(m/s)

100% 1mm 2, 3, 4Umf

50% 1mm and 50% 0.6mm 2, 3, 4Umf

100% 0.6 mm 2, 3, 4Umf

Sc-46 is used as a gamma-ray sourceActivity = ~ 300 microCi

Tracer particle

Effect of Gas Inlet Velocity on Mean Axial Solid Velocity

Mono 1 mm Glass

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0 0.2 0.4 0.6 0.8 1

Vz

me

an o

f 1

mm

so

lids

[m/s

]

r/R [-]

0.25h expt

0.5h expt

0.75h expt

U=4Umf

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0 0.2 0.4 0.6 0.8 1

Vz

me

an o

f 1

mm

so

lids

[m/s

]

r/R [-]

0.25h expt

0.5h expt

0.75h expt

U=2Umf

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0 0.2 0.4 0.6 0.8 1

Vz

me

an o

f 1

mm

so

lids

[m/s

]

r/R [-]

0.25h expt

0.5h expt

0.75h expt

U=3Umf

• h represents the static bed height=25 cm

• Observed upward motion of solid particles inthe center and downward motion near thewall

• Increase in velocity increases the solid axialvelocity as the momentum through the liquidincreases

• Velocity of the solid increases with the height

Effect of Gas Inlet velocity on Mean axial solid velocity

Mono 0.6 mm Glass

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0 0.2 0.4 0.6 0.8 1

Vz

me

an o

f 0

.6m

m s

olid

s [m

/s]

r/R [-]

0.25h expt

0.5h expt

0.75h expt

U=2Umf

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0 0.2 0.4 0.6 0.8 1

Vz

me

an o

f 0

.6m

m s

olid

s [m

/s]

r/R [-]

0.25h expt

0.5h expt

0.75h expt

U=4Umf

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0 0.2 0.4 0.6 0.8 1

Vz

me

an o

f 0

.6m

m s

olid

s [m

/s]

r/R [-]

0.25h expt

0.5h expt

0.75h expt

U=3Umf

• Same trend observed for both 1mm and0.6 mm particle

• Velocity of bigger particle is lower thansmaller particle for a particular velocityas both the bed have been operated atsame velocity

Mean axial velocity ofbinary fluidized bed

50% 1mm-50s 0.6 mm Glass beads

• For binary mixture velocity profile is same as of mono dispersed bed

• With increse in level inside the bed solid velocity increases which shows thattop section is more violent compared to bottom section

• In binary bed the velocity of bigger particle is higher as compared to unary bedof same size it means smaller particles helps the fluidization of bigger particles

• Homogeneous distribution and mixing of solids are not observed

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0 0.2 0.4 0.6 0.8 1

Vz

me

an o

f 1

mm

so

lids

[m/s

]

r/R [-]

0.25h expt

0.5h expt

0.75h expt

U=4Umf

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0 0.2 0.4 0.6 0.8 1

Vz

me

an o

f 0

.6m

m s

olid

s [m

/s]

r/R [-]

0.25h expt

0.5h expt

0.75h expt

U=4Umf

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

0 0.2 0.4 0.6 0.8 1

Vz

rms

of

1m

m s

olid

s [m

/s]

r/R [-]

0.25h expt

0.5h expt

0.75h expt

U=4Umf

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

0 0.2 0.4 0.6 0.8 1

Vz

rms

of

0.6

mm

so

lids

[m/s

]r/R [-]

0.25h expt

0.5h expt

0.75h expt

U=4Umf

• With increase in air velocity fluctuation at the top section increases andbed become more violent for both the particles

• Fluctuation in smaller particle is higher than bigger particle as the u/umf ofsmaller particle is higher than bigger particle.

• Similar trend is observed for all the air inlet velocities

RMS velocities in mono dispersed bed of two different sizes

Mono Bed 1 mm Glass beads Mono Bed 0.6 mm Glass beads

RMS velocities in binary bed of 50% 1mm and 50% 0.6 mm particle

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

0 0.2 0.4 0.6 0.8 1

Vz

rms

of

1m

m s

olid

s [m

/s]

r/R [-]

0.25h expt

0.5h expt

0.75h expt

U=4Umf

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

0 0.2 0.4 0.6 0.8 1

Vz

rms

of

0.6

mm

so

lids

[m/s

]

r/R [-]

0.25h expt

0.5h expt

0.75h expt

U=4Umf

• Profile of axial rms velocity remains same for binary and mono dispersed bed

• fluctuation in smaller particle is only marginally higher than bigger particle in binarybed.

• However compared to mono bed of smaller particle fluctuation in binary bed is lowerwhich confirms that smaller particles are transferring some of the momentum tobigger

Conclusions➢Velocity of solid increases with increase in fluid velocity in conical

bed

➢Axial mean velocity of bigger particle is lower than smallerparticle for a particular gas velocity as both the bed are operatedat same velocity

➢The fluctuation in case of smaller particle is more than biggerparticle which is expected as smaller particle bed is operated athigher u/umf ratio

➢ Increase in fluctuation for bigger particle in binary bed isobserved which confirms that smaller particles transfer some ofits momentum to bigger particle to ease the fluidization.

➢Homogeneous distribution of particle is not observed even at avelocity of 4umf of bigger particle

➢These information are very critical for designing the industrialcoater