1

Numerical proof of the concept of a rotating chimney

for Rotating Fluidized Beds

* Université catholique de LouvainMAPR / IMAPRéaumur, Place Sainte Barbe 21348 Louvain-la-NeuveBelgiumjuray.dewilde@uclouvain.be

Nicolas Staudt, Juray De Wilde*

• THE CONCEPT

• THEORETICAL

• EXPERIMENTAL

• CFD STUDY

• CONCLUSIONS

2

FLUIDIZED BED PROCESS INTENSIFICATION

IMPROVE EXTERNALHEAT AND MASS

TRANSFER (BETWEENGAS & SOLIDS)

IMPROVEINTERNAL

MASSTRANSFER

FLUIDIZESMALLER

PARTICLES

INCREASE MASS& HEAT TRANSFER

COEFFICIENT

INCREASEGAS-SOLID

SLIP VELOCITY

FLUIDIZE IN ACENTRIFUGAL FIELD

REDUCEGAS-SOLIDCONTACT

TIME

REDUCE BEDHEIGHT &

INCREASE GASVELOCITY

INCREASERATIO

FREEBOARDSURFACE TOBED HEIGHT

CYLINDRICALGEOMETRY

THE CONCEPT

gasinlet

gasinlet

gasinlet

gasinlet

gasinlet

gasinlet

gasinlet

gasinlet

solidsoutlet

solidsinlet

rotatingchimney(outlet)

gas

gas

gas

gasgas

CONCEPT

3

gas tocyclone

centralfixedchimneytube

rotating

chimney

blade

rotatingchimneyblade

fixed

end

plate

fluid

izatio

n

cham

ber

MOTOR

rotatingchimney

axis

fixedend platefluidizationchamber

gas

inle

tslo

tflu

idiz

atio

nch

ambe

r

open endrotatingchimney

closed endrotatingchimney

motion particleinside chimneyrelative to thechimney motion

motion particleinside chimneyrelative to thechimney motion

gas

gas

gas

gas phase motionrelative to thechimney motion

gas phase motionrelative to thechimney motion

axis

open end

chim

ney

CONCEPT

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

200000

650 700 750 800 850 900

Fluidization gas flow rate [Nm3/h]

For

ce p

er c

ubic

met

er p

arti

cle

bed

[N/m

3]

Radial drag force in the rotating particle bed by the fluidization gas near the chimney [N/m3]

Centrifugal force in the rotating particle bed by the fluidization gas near the chimney [N/m3]: gas on averageleaving after 1/24 th of a turn and tangential gas-solid slip velocity = 0.4 * tangential fluidization gas velocity

Centrifugal force by the chimney on the particles at contact with the chimney: tangential particle-chimney slipvelocity = 0.6 * tangential chimney velocity [N/m3]

0 200 400 600 800 1000 1200 1400 1600

Chimney rotational speed [rpm]

(2ndaxis)

εεεεs = 0.6

0

THEORETICAL

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REDUCTION OF SOLIDS LOSSES VIA THE CHIMNEY

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0 0.5 1 1.5 2

Solids loading [kg]

Sol

ids

loss

rat

e [k

g/s]

0 rpm solids loss rate [kg/s] 250 rpm solids loss rate [kg/s]

400 rpm solids loss rate [kg/s] 500 rpm solids loss rate [kg/s]

750 rpm solids loss rate [kg/s] 1000 rpm solids loss rate [kg/s]

1500 rpm solids loss rate [kg/s]

G = 850 Nm3/h, S = 3.56 ⋅⋅⋅⋅10-2 kg/s

chimneyrotational

speed

solids feeding rate (Time: 10 - 80 s)

Rat

eof

sol

ids

loss

esvi

a th

e ch

imne

y[k

g/s]

theo

retic

alm

axim

um s

olid

slo

adin

g

quasi steadystate solids

loading at 0 rpmand given G & S

quasi steadystate solids

loading at 1500 rpm and

given G & S

1G Geldart D-type particles, 24-cm diameter fluidizat ion chamber

EXPERIMENTAL

1G Geldart D-type particles250 rpm 1000 rpm500 rpmChimney:

1G Geldart B-type particles0 rpm 1000 rpm500 rpmChimney:

QUASI STEADY STATE SOLIDS LOADING24-cm diameter fluidization chamber, given fluidizati on gas flow and solids fedding rates

SUPPRESSIONOF BUBBLING

EXPERIMENTAL

5

0

50

100

150

200

250

300

350

400

0 200 400 600 800 1000 1200 1400 1600

Chimney rotational speed [rpm]

Ave

rage

par

ticle

res

iden

ce ti

me

in t

he fl

uidi

zatio

n ch

ambe

r [s

]

G = 850 Nm3/h

Solids loading = 1.0 kg

AVERAGE PARTICLE RESIDENCE TIME CONTROL1G Geldart D-type particles, 24-cm diameter fluidizat ion chamberGiven fluidization gas flow rate and solids loading in th e fluidization chamber

EXPERIMENTAL

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 200 400 600 800 1000 1200 1400 1600

Chimney rotational speed [rpm]

Solid

s lo

adin

g [k

g]

Minimum solids loading no high frequency slugging [kg]Minimum solids loading no low frequency slugging [kg]Minimum solids loading no channeling [kg]Maximum solids loading in the fluidization chamber [kg]

G = 850 Nm3/h,S = 3.56 ⋅⋅⋅⋅10-2 kg/s

stable uniformrotating fluidized bed

slugging

channeling

theoretical maximum solids loading

Quasi steady state solids loading in the fluidization chamberat the given G and S [kg]

CRITERIA FOR STABLE AND UNIFORM OPERATION1G Geldart D-type particles, 24-cm diameter fluidizat ion chamber

EXPERIMENTAL

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CFD STUDY

• EFFECT ON ROTATING FLUIDIZED BEDS• INFLUENCE CHIMNEY DESIGN• IMPROVED UNDERSTANDING FLOW PATTERNS• BEHAVIOR WITH MICRO-SCALE PARTICLES ?

CFD STUDY

• Fluidization chamber: 24-cm diameter (2D)• Gas inlet slots: 24, 2.3 mm width tangential (30°)• Gas injection velocity: 35 m/s• Rotating chimney: 16-cm diameter, 32 blades, 1000 rp m• Rotating chimney: two different designs• Operating pressure (outlet): 101300 Pa• Particles: 350 µm, 2100 kg/m 3

• Particles: continuously fed

chimneyblade

chimneyrotationsense

chimneyrotationsense

chimneyblade

design 1 design 2

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CFD STUDY

design 1 design 2

Solids volume fractiont = 10 s (after start solids feeding)

chimney:1000 rpm

chimney:1000 rpm

CFD STUDY

design 1 design 2

Solids volume fractiont = 35 s (after start solids feeding)

chimney:1000 rpm

chimney:1000 rpm

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CFD STUDY

design 1 design 2

Solids volume fractiont = 70 s (after start solids feeding)

• No solids losses via the chimney, despite high solids l oading• Design 2 results in improved particle bed uniformity an dreduced radial bed expansion

chimney:1000 rpm

chimney:1000 rpm

CFD STUDY

design 1 design 2

Solids velocity magnitudet = 10 s (after start solids feeding)

chimney:1000 rpm

chimney:1000 rpm

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CFD STUDY

design 1 design 2

Solids velocity magnitudet = 35 s (after start solids feeding)

chimney:1000 rpm

chimney:1000 rpm

CFD STUDY

design 1 design 2

Solids velocity magnitudet = 70 s (after start solids feeding)

chimney:1000 rpm

chimney:1000 rpm

Design 2 results in:• improved gas-solid momentum transfer (vicinity gas inle t slots)• slightly increased average particle bed rotational spee ds (effect limited)

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CFD STUDY

design 1 design 2

Gas velocity,colored by tangential gas velocityt = 70 s (after start solids feeding)

Effect chimney design limited

CFD STUDY

design 1 design 2

Solids velocity relative to the chimney,colored by the tangential solids velocity

t = 70 s (after start solids feeding)

Effect chimney design limited

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CFD STUDY

• Fluidization chamber: 36-cm diameter (2D)• Gas inlet slots: 12, 4.0 mm width tangential (35°)• Gas injection velocity: 20 m/s• Rotating chimney: 14-cm diameter, 4 blades, 1500 rpm• Operating pressure (outlet): 101300 Pa• Particles: 10 µm, 2100 kg/m 3

• Particles: continuously fed

Behavior with micro-scale particles ?

Solids volume fraction Solids velocity vectors relativeto the chimney rotational motion,

colored by the absolute solidsvelocity magnitude

CFD STUDY

• Rotating fluidized bed around a rotating chimney• Solids entrained into the chimney can be refed to the

fluidization chamber via the opening of the next blade

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CONCLUSIONS

• CONCEPT OF ROTATING CHIMNEY FORROTATING FLUIDIZED BEDS STUDIED

• CFD CONFIRMS EXPERIMENTALLY OBSERVEDFEATURES

• REDUCTION OF THE SOLIDS LOSSES VIATHE CHIMNEY

• INCREASED SOLIDS LOADING IN THEFLUIDIZATION CHAMBER

• CFD ALLOWS TO STUDY CHIMNEY DESIGN• CFD DEMONSTRATES USE WITH

MICRO-SCALE PARTICLES⇒⇒⇒⇒ ROTATING FLUIDIZED BED AROUND

A ROTATING CHIMNEY