Investigation of Liquid-solid and Gas-solid Fluidized Bed
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Transcript of Investigation of Liquid-solid and Gas-solid Fluidized Bed
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ChE 304
Chemical engineering laboratory - III
Experiment No. 7 Group No. 03 (A2)
Name of the experiment:
I nvestigation of liquid-solid and gas-solid fluidized bed
And
I nvestigation of 2-D and 3-D gas-solid fluidized beds
Submitted by:
Md. Hasib Al Mahbub
Student Id: 0902045
Level: 3; Term: 2
Section: A2
Date of performance: 25/02/2014
Date of submission: 11/03/2014
Partners Student Id. 0902041
0902042
0902043
0902044
Department of Chemical Engineering.
Bangladesh University of engineering and technology, Dhaka.
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Summary
The main objective of this experiment was to verify the Richardson-Zaki equation for liquid-
solid fluidization beds and to study the flow pattern and calculate the pressure drop
characteristics of gas-solid fluidization beds. Water-sand system was used for liquid-solidfluidization & air-resin system was used for gas-solid fluidization. For liquid-solid system, bed
height and superficial velocities were determined. Logarithmic plot of superficial velocity vs.
voidage were plotted for both increasing and decreasing velocities. From the plot values of
terminal settling velocity, minimum fluidization velocity and Richardson-Zaki index were
determined for both increasing and decreasing velocities. From superficial velocity vs. voidage
graph for increasing velocities experimentally found values of terminal settling velocity,
minimum fluidization velocity and Richardson-Zaki index were 0.2642 m/s, 0.0255 m/s, 3.757
respectively and from superficial velocity vs. voidage graph for decreasing velocities
experimentally found values of terminal settling velocity, minimum fluidization velocity and
Richardson-Zaki index were 0.5243 m/s, 0.02305 cm/s, 5.5866 respectively. For gas-solid
fluidized bed, pressure drops for corresponding superficial velocities of air were recorded and
the graphical relation between pressure drop and superficial air velocity were showed in plot.
The flow regimes for different flow rates in gas-solid fluidization bed were shown in neat
sketches.
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Introduction
Fluidization concerns the suspension or transport of solids by liquids and/or gases. The most
common engineering application is in the form of fluidized beds, which are containers of solid
particles through which is passed the fluidizing medium, usually a gas. Fluidized beds are used
in petroleum distillation, coal combustion, polymer production, and heat and mass-transfer
processes, such as food drying.
When a fluid is pumped upward through a bed of fine solid particles at a very low flow rate,
the fluid percolates through the void spaces (pores) without disturbing the bed. This is a fixed
bed process. If the upward flow rate is very large the bed mobilizes pneumatically and may be
swept out of the process vessel. At an intermediate flow rate the bed expands and is in what we
call an expanded state. In the fixed bed the particles are in direct contact with each other,
supporting each others weight. In the expanded bed the particles have a mean free distance
between particles and the particles are supported by the drag force of the fluid. The expanded
bed has some of the properties of a fluid and is also called a fluidized bed. The velocity of the
fluid through the bed opposite to the direction of gravity determines whether the bed is fixed,
expanded, or is swept out
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Experimental Setup
Figure 1: Schematic Diagram of Solid-Liquid Fluidization Bed
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Figure 2: Experimental setup for gas-solid fluidization
Manometer
Flow
meter
Control
Valve
Particles bed
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Flow Regimes
Fixed bed (Observation no. 01)
Bubbling (Observation No. 02) Slugging (Observation No. 03)
Channeling (Observation No. 04) Spouting (Observation No. 05)
Figure 03: Different flow regimes in solid-gas fluidization (2D).
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Observed data
Fixed bed height = 3.95 inch
Room temperature = 24C
Column diameter of liquid-solid tube = 2 inch
Empty bucket weight = 0.3 kg
Table 1: Observed Data for liquid-solid fluidization
No.
Of
Obs.
Increasing Flow Rate Decreasing Flow Rate
Weight of
Water +
Bucket
(Kg)
Time
(s)
Height of
the bed
(inch)
Weight of
Water +
Bucket
(Kg)
Time
(s)
Height of
the bed
(inch)
1 0.6 30 3.95 5.5 30 9.90
2 1.85 30 4.40 5.2 30 9.40
3 2.4 30 4.90 4.95 30 8.90
4 2.8 30 5.40 4.7 30 8.40
5 3.2 30 5.90 4.5 30 7.90
6 3.65 30 6.40 4.25 30 7.40
7 4.0 30 6.90 3.8 30 6.90
8 4.35 30 7.40 3.7 30 6.40
9 4.65 30 7.90 3.2 30 5.90
10 4.9 30 8.40 2.9 30 5.40
11 5.1 30 8.90 2.3 30 4.90
12 5.3 30 9.40 1.7 30 4.40
13 5.55 30 9.90 0.35 30 4.0
14 5.75 30 10.4 5.5 30 9.90
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Table 2: Observed Data for gas-solid fluidization (3D)
No.
Of
Obs.
Flow rate
Of air
(L/min)
Height of the manometric fluid(CCl4)
Left
(inch)
Right
(inch)
1 80 21.2 19.6
2 140 21.3 19.5
3 220 21.4 19.4
4 300 21.5 19.4
5 350 21.6 19.3
6 400 21.7 19.2
7 450 21.7 19.2
8 500 21.9 18.9
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Calculated data
Table 3: Calculated data for liquid-solid fluidization.
Obs.
No.
Height
of
Bed, m
Weight
of water,
kg
Mass
flow
rate,
kg/s
Volumetric
flow rate,
m3/s
Superficial
Velocity,
Usm/s
Voidage,
Increasing Flow Rate
01 0.10033 0.3 0.01 1.00271E-05 0.004939465 0.42
02 0.11176 1.55 0.052 5.18068E-05 0.025520568 0.48
03 0.12446 2.1 0.07 7.01898E-05 0.034576253 0.53
04 0.13716 2.5 0.083 8.35593E-05 0.041162206 0.58
05 0.14986 2.9 0.097 9.69288E-05 0.047748159 0.61
06 0.16256 3.35 0.112 0.000111969 0.055157356 0.64
07 0.17526 3.7 0.123 0.000123668 0.060920064 0.67
08 0.18796 4.05 0.135 0.000135366 0.066682773 0.69
09 0.20066 4.35 0.145 0.000145393 0.071622238 0.71
10 0.21336 4.6 0.153 0.000153749 0.075738459 0.73
11 0.22606 4.8 0.16 0.000160434 0.079031435 0.74
12 0.23876 5 0.167 0.000167119 0.082324411 0.76
13 0.25146 5.25 0.175 0.000175474 0.086440632 0.77
14 0.26416 5.45 0.182 0.000182159 0.089733608 0.78
Decreasing Flow Rate
01 0.25146 5.2 0.173 0.000173803 0.085617388 0.77
02 0.23876 4.9 0.163 0.000163776 0.080677923 0.76
03 0.22606 4.65 0.155 0.00015542 0.076561703 0.74
04 0.21336 4.4 0.147 0.000147064 0.072445482 0.73
05 0.20066 4.2 0.140 0.00014038 0.069152506 0.71
06 0.18796 3.95 0.132 0.000132024 0.065036285 0.69
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Obs.
No.
Height
of
Bed, m
Weight
of water,
kg
Mass
flow
rate,
kg/s
Volumetric
flow rate,
m3/s
Superficial
Velocity,
Usm/s
Voidage,
07 0.17526 3.5 0.117 0.000116983 0.057627088 0.67
08 0.16256 3.4 0.113 0.000113641 0.0559806 0.64
09 0.14986 2.9 0.097 9.69288E-05 0.047748159 0.61
10 0.13716 2.6 0.087 8.69016E-05 0.042808694 0.58
11 0.12446 2 0.067 6.68474E-05 0.032929765 0.53
12 0.11176 1.4 0.047 4.67932E-05 0.023050835 0.48
13 0.1016 0.05 0.0017 1.67119E-06 0.000823244 0.43
Table 4: Calculated data for Gas Solid Fluidized bed (3D).
Observation
No.
Air flow rate
(lit/min)
Air flow rate,
Q
(m3/sec)
Air velocity
v, (m/s)
Pressure
drop, m
(in CCl4)
1 80 0.0133 0.741 0.0406
2 140 0.0233 1.296 0.0457
3 220 0.0367 2.037 0.0508
4 300 0.05 2.778 0.0533
5 350 0.0583 3.241 0.0584
6 400 0.0667 3.704 0.0635
7 450 0.075 4.167 0.0635
8 500 0.083 4.630 0.0762
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Sample calculation
For LiquidSolid Fluidization beds:
For observation 5 (increasing velocity)
So, Superficial velocity,
sec90.04774815
00202683.0296.997
sec097.0
2
3
m
mm
kg
g
AmU
H
K1
AH
M1
AH
MAH
V
VVVoidage,know,We
T
PT
mK
K
0581914.0
10033.0142.0
For, bed height, H= 0.14986m;
voidage, 0.6114986.0
0581914.01
Weight of water + bucket = 3.2 kg
Weight of water, w = (3.2-0.3) kg = 2.9 kg
Water collection time , t = 30 sec
Diameter of the column , D = 2 inch = 0.0508 m
The mass flow rate of water, m = w/t = 2.9/30 = 0.097 kg/s
Cross sectional area of the
column ,
A = ( / 4) x D2 = ( / 4) x(0.0508) 2m2
= 0.00202683 m2
Fixed bed height, H = 3.95 inch = 0.10033 m
Fixed bed voidage, = 0.42
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Theoretical Calculation
Fix bed voidage, = 0.42
Diameter of the particle, DP = 0.75mm = 0.7510-3 m
Density of the particle, P = 2.5 kg/m3
Density of water at 240C = 997.296 kg/m3
Viscosity of water at
240C
= 0.89010-3
sec/00655.0
10890.042.01
00075.081.9296.997250042.00055.0
10055.0,
3
23
23
m
gDUow PP
mf
mf
mf
10.5220
10890.03
296.997250081.9296.99700075.02
3
2'''
',
23
3
2
3
2
222
2
2
2
SP gddU
U
RR
U
Rgain
Now for spherical particle from the plot Re'.vs'Re'U
'R 22
we get, 105Re' .
kg/m.s
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Now,
sec/1249.000075.0296.997
10890.0105Re'
Re'
3
md
U
dU
t
t
From Richardson -Zaki equation
398.3
42.0log
1249.0
00655.0log
log
log
loglog
n
U
U
n
U
Un
U
U
UU
t
mf
t
mf
n
t
mf
n
tmf
By graphical method
1. For Increasing velocity :
Umf = 0.0255 m / s
Ut = 0.264 m / s
n = 3.757
2. For decreasing velocity :
Umf = 0.02305 m / s
Ut = 0.5243 m/ sn = 5.5866
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For GasSolid Fluidization beds
Observation 5
Column diameter = 6 inch = 0.1524 m
Cross sectional area = 21524.0
4
= 0.018 cm2
Air flow rate, V = 350 liter/min = 0.0583m3/sec
Air velocity, v =2
3
018.0
sec0583.0
m
m
A
V = 3.241m/s
Pressure drop = (21.6-19.3) in CCl4 = 0.0584mCCl4
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Graphical representation:
Figure 4: Superficial velocity vs. voidage graph (for increasing velocity).
y = 0.2642x3.757
0.01
0.1
0.3
SuperficialvelocityUf(m/s)
Voidage,
Ut=0.2642m/s
=0.779= 0.42
Umf = 0.0255
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Figure 5: Superficial velocity vs. voidage graph (decreasing velocity).
y = 0.5243x5.5866
0.01
0.1
0.3
SuperficialvelocityUf(m/s)
Voidage,
Ut = 0.02305m/s
= 0.769 = 0.49
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Figure 6: Log-log plot of pressure drop vs. air velocity in solid-gas fluidization.
0.03
0.5 5
PressureDropinmanometer(mC
Cl4
Air velocity (m/s)
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Results and Discussions
The experimental values deviate somewhat from the theoretical values. In calculation, it is
assumed that the particles are ideally spherical but it is not true for practical purposes especially
when resin particles are used. When flow of water is increased to a higher value, it has become
increasingly difficult to measure the height of the fluidized bed. This situation led to improper
scaling of the height, which have induced a significant error in the accompanying calculations.
Another reason is that as the velocity approaches the minimum fluidization velocity, some bed
expansion normally occurs before the pressure drop reaches the buoyant weight per unit area
of bed. Therefore, the container walls exert some frictional forces on the bed. For liquid-solid
fluidization the superficial velocity vs. voidage plot in logarithmic scale for both the increasing
and decreasing height shows straight line with a slope which was the Richardson-Zaki index.
In the second part of the experiment (the gas-solid system) the pressure drop behavior was
observed with the change of flow rate of gas. Here the gas was air. And the observation shows
that at less velocity the bed height was increased and the some bubble type voidage was seen.
But as the velocity was increased the continuous big voidage was observed and at the same
time tremendous movement of solid particle was seen. We have plotted pressure drop against
velocity of air on log-log graph.
Experimental ValuesTheoretical Values
Increasing Decreasing
Minimum fluidized bed
velocity, Umf (m/sec)0.0255 0.02305 0.00843
Terminal settling velocity,
Ut (m/sec)0.2642 0.5243 0.1249
n (RZ index) 3.757 5.5866 3.398