Chapter 6 : Bubbling Fluidized Beds

Example 1, Page 150

In [5]:
z=0.5;     #Height of bed in m
dt=0.5;    #ID of tube in m
rhos=1.6;  #Density of catalyst in g/cm**3
dpbar=60.;  #Averge catalyst diameter in micrometer
umf=0.002; #Velocity at minimum fluidization condition in m/s
uo=0.2;    #Superficial velocity in m/s
dor=2.;     #Diameter of orifice in mm
lor=20.;    #Pitch of perforated plate in mm
g=9.80;    #g=980;#Acceleration due to gravity in m/s**2

#CALCULATION
#Method 1. Procedure using Eqn.(10) & Eqn.(11)
db=(0.035+0.040)/2.;#Bubble size at z=0.5m from Fig.7(a) & Fig.7(b)
ub1=1+1.55*((uo-umf)+14.1*(db+0.005))*(dt**0.32)*0.711*(g*db)**0.5;#Bubble velocity using Eqn.(10) & Eqn.(11)

#Method 2. Werther's procedure
si=0.8;#From Fig.6 for Geldart A solids 
ub2=si*(uo-umf)+(3.2*(dt**(1./3)))*(0.711*(g*db)**0.5);#Bubble velocity using Eqn.(9)

#OUTPUT
print 'Method 1. Procedure using Eqn.(10) & Eqn.(11)'
print '\tDiameter of the bubble=%.4fm'%db
print '\tRise velocity of the bubble=%.4fm/s'%ub1
print 'Method 2. Werthers procedure'
print '\tDiameter of the bubble=%fm'%db
print '\tRise velocity of the bubble=%fm/s'%ub2
Method 1. Procedure using Eqn.(10) & Eqn.(11)
	Diameter of the bubble=0.0375m
	Rise velocity of the bubble=1.4267m/s
Method 2. Werthers procedure
	Diameter of the bubble=0.037500m
	Rise velocity of the bubble=1.253125m/s

Example 2, Page 151

In [2]:
import math

#Variable declaration
z=0.5;      #Height of bed in m
dt=0.5;     #ID of tube in m
rhos=2.6;   #Density of catalyst in g/cm**3
dpbar=100.; #Averge catalyst diameter in micrometer
umf=0.01;   #Velocity at minimum fluidization condition in m/s
uo=0.45;    #Superficial velocity in m/s
dor=2.;     #Diameter of orifice in mm
lor=30.;    #Pitch of perforated plate in mm
g=9.80;     #Acceleration due to gravity in m/s**2
pi=3.142857;

#CALCULATION
#Part(a).Bubble Size
Nor=(2/math.sqrt(3))*(1/lor**2);
dbo=5.5;

#Method 1.Werther's procedure for finding bubble size
z1=[0,5,10,20,30,50,70]
db = [0.,0.,0.,0.,0.,0.,0.]
n=len(z1);
i=0; 
while i<n:
    db[i]=0.853*((1+0.272*(uo-umf)*100)**(1/3.0))*(1+0.0684*z1[i])**1.21;
    i=i+1;    

db1=0.163;#Since bubble size starts at dbo=5.5cm at z=0, we shift the curve accordingly to z=0.5m

#Method 2.Mori and Wen's procedure for finding bubble size
dbm=0.65*((math.pi/4.0)*((dt*100)**2)*(uo-umf)*100)**0.4;
db2=dbm-(dbm-dbo)*math.exp(-0.3**(z/dt));

#Part(b).Bubble Velocity
#Method 1.Procedure using Eqn.(12)
ub1=1.6*((uo-umf)+1.13*db1**0.5)*(dt**1.35)+(0.711*(g*db1)**0.5);

#Method 2.Werther's Procedure
si=0.65;
ub2=si*(uo-umf)+2*(dt**0.5)*(0.711*(g*db1)**0.5);

#Using Eqn.(7) & Eqn.(8)
ubr1=0.711*(g*db1)**0.5;
ubr2=0.711*(g*db2/100.0)**0.5
ub3=uo-umf+ubr1;
ub4=uo-umf+ubr2;

#OUTPUT
print 'Bubble Size'
print 'Initial bubble size from Fig.5.14 for %.2fm/s = %.2fcm'%(uo-umf,dbo)
print '\tMethod 1.Werthers procedure for finding bubble size'
print '\t\tHeight of bed(cm)'
print '\t\t\tBubble size(cm)'
m=len(z1);
j=0;
while j<m:
    print '\t\t%d'%z1[j],
    print '\t\t\t\t%.2f'%db[j]
    j=j+1;

print '\tMethod 2.Mori and Wens procedure for finding bubble size'
print '\t\tMaximum expected bubble size=%.2fcm'%dbm
print '\t\tBubble size=%.0fcm'%db2
print 'Bubble Velocity'
print '\tMethod 1.Procedure using Eqn.(12)'
print '\t\tBubble velocity=%.2fm/s'%ub1
print '\tMethod 2.Werthers procedure'
print '\t\tBubble velocity=%.2fm/s'%ub2
print 'Comparing the above results with the expressions of the simple two-phase theory'
print '\tWerthers bubble size'
print '\tBubble rise velocity=%.2fm/s\tBubble velocity=%.2fm/s'%(ubr1,ub3)
print '\tMori & Wens bubble size'
print '\tBubble rise velocity=%.1fm/s\tBubble velocity=%.2fm/s'%(ubr2,ub4)
Bubble Size
Initial bubble size from Fig.5.14 for 0.44m/s = 5.50cm
	Method 1.Werthers procedure for finding bubble size
		Height of bed(cm)
			Bubble size(cm)
		0 				2.00
		5 				2.86
		10 				3.77
		20 				5.69
		30 				7.73
		50 				12.10
		70 				16.77
	Method 2.Mori and Wens procedure for finding bubble size
		Maximum expected bubble size=61.31cm
		Bubble size=20cm
Bubble Velocity
	Method 1.Procedure using Eqn.(12)
		Bubble velocity=1.46m/s
	Method 2.Werthers procedure
		Bubble velocity=1.56m/s
Comparing the above results with the expressions of the simple two-phase theory
	Werthers bubble size
	Bubble rise velocity=0.90m/s	Bubble velocity=1.34m/s
	Mori & Wens bubble size
	Bubble rise velocity=1.0m/s	Bubble velocity=1.43m/s

Example 3, Page 153

In [6]:
dpbar=53.;      #Average particle size in micrometer
s=[1,2];        #Size of Bermuda rock in cm 
rhosbar=3200.;  #Average solid density of the coke-zircon mixture in kg/m**3
ephsilonm=0.5;  #Void fraction for fixed bed
ephsilonf=0.75; #Void fraction for bubbling bed
rhogbar=0.64;   #Average density of gas in kg/m**3
uo=14.;         #Superficial gas velocity in cm/s
myu=5E-5;       #Viscosity of gas in kg/m s
T=1000.;        #Temperature in degree C
P=1.;           #Pressure in atm
dt=91.5;        #ID of bed in cm
sh=150.;        #Slumped height in cm

#CALCULATION
rhog2=1.2;      #Density of ambient air
myu2=1.8E-5;    #Viscosity of ambient air
rhos2=rhog2*(rhosbar/rhogbar);#For the requirement of constant density ratio
m=((rhogbar*myu2)/(rhog2*myu))**(2./3);#Scale factor by usin Eqn.(16)
u2=(m**0.5)*uo;  #Superficial gas velocity by using Eqn.(17)
#OUTPUT
print 'For the model use'
print '\tBed of ID %.2fcm\tSlumped bed height of %.2fcm\tPacked bed distributor consisting of %.2f-%.2fmm rock'%(m*dt,m*sh,m*s[0],m*s[1])
print 'Fluidizing gas: ambient air at %.2fatm'%P
print 'Solids: \tzirconia, Average particle size=%.2fmicrometers'%(m*dpbar)
print 'Entering gas:\tSuperficial velocity=%.2fcm/s'%u2
For the model use
	Bed of ID 30.45cm	Slumped bed height of 49.92cm	Packed bed distributor consisting of 0.33-0.67mm rock
Fluidizing gas: ambient air at 1.00atm
Solids: 	zirconia, Average particle size=17.64micrometers
Entering gas:	Superficial velocity=8.08cm/s

Example 4, Page 159

In [4]:
import math

#Variable declaration
dtb=20;          #ID of bench-scale reactor
dtp=1;           #ID of pilot reactor
dpbar=52;        #Average particle size in micrometer
ephsilonm=0.45;  #Void fraction for fixed bed
ephsilonmf=0.50; #Void fraction at minimum fluidization condition
ephsilonmb=0.60; #Void fraction 
uo=30;           #Superficial gas velocity in cm/s
Lmb=2;           #Length of fixed bed in m
umf=0.33;        #Velocity at minimum fluidization condition in cm/s
umb=1;           #Velocity at in cm/s
db=3;            #Equilibrium bubble size in cm
g=9.80;          #Acceleration due to gravity in m/s**2
pi=3.142857;

#CALCULATION
ubr=0.711*(g*db/100)**0.5;#Rise velocity of bubble using Eqn.(7)

#Bubble velocity for the bench unit
ubb1=1.55*(((uo-umf)/100.0)+14.1*((db/100.0)+0.005))*((dtb/100.0)**0.32)+ubr;#Bubble velocity using Eqn.(11)
si=1;
ubb2=si*((uo-umf)/100.0)+(3.2*((dtb/100.0)**(1/3.0)))*ubr;#Bubble velocity using Eqn.(9)
ubb=(ubb1+ubb2)/2;#Average bubble velocity

#Bubble velocity for the pilot unit
ubp1=1.55*(((uo-umf)/100.0)+14.1*((db/100.0)+0.005))*(dtp**0.32)+ubr;#Bubble velocity using Eqn.(11)
si=1;
ubp2=si*((uo-umf)/100)+(3.2*(dtp**(1/3)))*ubr;#Bubble velocity using Eqn.(9)
ubp=(ubp1+ubp2)/2;#Average bubble velocity

#Rise velocity of upflowing emulsion
ueb=ubb-ubr;#For the bench unit
uep=ubp-ubr;#For the pilot unit

#Scale-Up Alternative 1.
dteb=20;#Effective bubble diameter
dib=[5,10,15,20];#Different outside diameters
n=len(dib);
li = [0.,0.,0.,0.]
i=0;
while i<n:
    li[i]=math.sqrt(((pi*dib[i]*dteb)/4)+((pi/4)*(dib[i])**2));#Pitch using Eqn.(13)
    i=i+1;

#Scale-Up Alternative 2.
Lmp=Lmb*(ubp/ubb);#Static bed height of commercial unit
dtep=100.0;#Effective bubble diameter
dip=[10,15,20,25];#Different outside diameters
m=len(dip);
i=0;
lip = [0.,0.,0.,0.]
while i<m:
    lip[i]=math.sqrt(((math.pi*dip[i]*dtep)/4.0)+(math.pi/4.0)*dip[i]);#Pitch using Eqn.(13)
    i=i+1;

#Height of Bubbling beds
#For bench unit
deltab=((uo/100.0)-(umb/100.0))/(ubb-(umb/100.0));#Fraction of bed in bubbles using Eqn.(28)
ephsilonfb=deltab+(1-deltab)*ephsilonmb;#Void fraction of bubbling bed using Eqn.(20)
Lfb=Lmb*(1-ephsilonm)/(1-ephsilonfb);#Hieght of bubbling bed usnig Eqn.(19)
#For pilot unit
deltap=((uo/100.0)-(umb/100.0))/(ubp-(umb/100.0));#Fraction of bed in bubbles using Eqn.(28)
ephsilonfp=deltap+(1-deltap)*ephsilonmb;#Void fraction of bubbling bed using Eqn.(20)
Lfp=Lmp*(1-ephsilonm)/(1-ephsilonfp);#Hieght of bubbling bed usnig Eqn.(19)

#OUTPUT
print 'Rise velocity of bubble=%.3fm/s'%ubr
print 'For the bench unit'
print '\tWith Eqn.(11), Rise velocity=%.3fm/s'%ubb1
print '\tWith Werthers procedure, Rise velocity=%.2fm/s'%ubb2
print '\tAverage rise velocity=%.2fm/s'%ubb
print '\tRise velocity of upflowing emulsion=%.2fm/s'%ueb
print 'For the pilot unit'
print '\tWith Eqn.(11), Rise velocity=%.2fm/s'%ubp1
print '\tWith Werthers procedure, Rise velocity=%.2fm/s'%ubp2
print '\tAverage rise velocity=%.2fm/s'%ubp
print '\tRise velocity of upflowing emulsion=%.2fm/s'%uep
print 'Scale-Up Alternative 1.'
print '\tOuter diameter of tube(cm)'
print '\tPitch(cm)'
n=len(dib);
j=0;
while j<n:
    print '\t\t%d'%dib[j],
    print '\t\t\t%.2f'%li[j]
    j=j+1;

print '\tSuitable arrangement'
print '\t\tOuter Diameter=%dcm\tPitch:Diameter ratio=%.2f'%(dib[1],(li[1]/dib[1]))
print 'Scale-Up Alternative 2.'
print '\tStatic bed height for commercial unit=%fm'%Lmp
print '\tOuter diameter of tube(cm)'
print '\tPitch(cm)'
n=len(dip);
j=0;

while j<n:
    print '\t\t%d'%dip[j],
    print '\t\t\t%.2f'%lip[j]
    j=j+1;

print '\tSuitable arrangement'
print '\t\tOuter Diameter=%dcm\tPitch:Diameter ratio=%.2f'%(dip[2],(lip[2]/dip[2]))
print '\t\t\t\tFraction of bed in bubbles\tVoid fraction of bed\tStatic bed height(m)\tHeight of bubbling bed(m)'
print '\t\t\t\t---------------------------------------------------------------------------------------------------------'
print 'Bench unit\tID=%fm\t%f\t\t\t%f\t\t%f\t\t%f'%(dtb/100.,deltab,ephsilonfb,Lmb,Lfb)
print 'Commercial unit\tID=%fm\t%f\t\t\t%f\t\t%f\t\t%f'%(dtp,deltap,ephsilonfp,Lmp,Lfp)
Rise velocity of bubble=0.386m/s
For the bench unit
	With Eqn.(11), Rise velocity=1.117m/s
	With Werthers procedure, Rise velocity=1.02m/s
	Average rise velocity=1.07m/s
	Rise velocity of upflowing emulsion=0.68m/s
For the pilot unit
	With Eqn.(11), Rise velocity=1.61m/s
	With Werthers procedure, Rise velocity=1.53m/s
	Average rise velocity=1.57m/s
	Rise velocity of upflowing emulsion=1.18m/s
Scale-Up Alternative 1.
	Outer diameter of tube(cm)
	Pitch(cm)
		5 			9.91
		10 			15.35
		15 			20.31
		20 			25.07
	Suitable arrangement
		Outer Diameter=10cm	Pitch:Diameter ratio=1.54
Scale-Up Alternative 2.
	Static bed height for commercial unit=2.941439m
	Outer diameter of tube(cm)
	Pitch(cm)
		10 			28.16
		15 			34.49
		20 			39.83
		25 			44.53
	Suitable arrangement
		Outer Diameter=20cm	Pitch:Diameter ratio=1.99
				Fraction of bed in bubbles	Void fraction of bed	Static bed height(m)	Height of bubbling bed(m)
				---------------------------------------------------------------------------------------------------------
Bench unit	ID=0.200000m	0.274171			0.709668		2.000000		3.788769
Commercial unit	ID=1.000000m	0.185857			0.674343		2.941439		4.967774

Example 5, Page 161

In [5]:
dtb=20;          #ID of bench-scale reactor
dtp=1;           #ID of pilot reactor
dpbar=200;       #Average particle size in micrometer
ephsilonmf=0.50; #Void fraction at minimum fluidization condition
ephsilonmb=0.50; #Void fraction 
uo=30;           #Superficial gas velocity in cm/s
Lmb=2;           #Length of fixed bed in m
umf=3;           #Velocity at minimum fluidization condition in cm/s
umb=3;           #Velocity at in cm/s
g=9.80;          #Acceleration due to gravity in m/s**2
pi=3.142857;

#CALCULATION
#In the small bench unit
c=1;
ubb=c*((uo-umf)/100.0)+0.35*(g*(dtb/100.0))**0.5;#Velocity using Eqn.(5.22)
zsb=60*(dtb)**0.175;#Height using Eqn.(5.24)

#In the large pilot unit
ubp=c*((uo-umf)/100.0)+0.35*(g*dtp)**0.5;#Velocity using Eqn.(5.22)
zsp=60*(dtp*100)**0.175;#Height using Eqn.(5.24)

#OUTPUT
print 'Condition at which bubbles transform into slugs'
print 'For tha small bench unit\t\tVelocity=%fm/s\t\tHeight above distributor plate=%fm'%(ubb,zsb/100.)
print 'For tha large pilot unit\t\tVelocity=%fm/s\t\tHeight above distributor plate=%fm'%(ubp,zsp/100.);
Condition at which bubbles transform into slugs
For tha small bench unit		Velocity=0.760000m/s		Height above distributor plate=1.013518m
For tha large pilot unit		Velocity=1.365673m/s		Height above distributor plate=1.343233m
In [ ]: