Flow Through Fluidized Beds
University of Illinois
Flow Through Fluidized Beds
Basic diagram of a fluidized bed reactor showing the how the gas entering through the distributor
at the base bubbles up through the packed bed and causes it to become fluidized. The solid
particles are the catalyst for the reaction, fluidization allows for more effective use of the surface
area of the particles as well as achieving more uniform temperature gradient and degree of
mixing while running the reactor in a continuous state.
http://en.wikipedia.org/wiki/File:Fluidized_Bed_Reactor_Graphic.JPG
Unit Operations Lab 3
October 22, 2009
Group 1:
Michael Czepizak
Krista Sutton
Jake Biberstein
Stanley Das
Russell Boyer
Jeff Umbach
Unit Operations ChE-381 Group No. 1
p. 1
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
0. Table Of Contents
0. Table Of Contents .................................................................................................. 2
1. WP&C .................................................................................................................... 3
2. Abstract .................................................................................................................. 4
3. Introduction ............................................................................................................ 5
4. Theory .................................................................................................................... 6
5. Apparatus ............................................................................................................. 12
6. Materials and Supplies ......................................................................................... 17
7. Procedure ............................................................................................................. 18
8. Data Tabulation .................................................................................................... 24
9. Results .................................................................................................................. 30
10. Discussion .......................................................................................................... 33
11. Error Analysis .................................................................................................... 36
12. Conclusion ......................................................................................................... 37
13. References .......................................................................................................... 38
14. Appendix I ......................................................................................................... 40
15. Appendix II ........................................................................................................ 40
Unit Operations ChE-381 Group No. 1
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Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
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Flow Through Fluidized Beds
University of Illinois
1. WP&C
What is the purpose of this experiment?
The purpose of Flow Through Fluidized Beds is to measure the effects of particle size,
packing amount, packing materials, and heated packing materials on flow through a packed
column. We will be working with high-pressure air streams and a heater. Inhalation hazards are
unlikely as there is insufficient airflow for packing material to escape from the column.
What are the hazards associated with the experiment?
Eye and ear damage can result from compressed air streams. Spilled sand or silica can
present a slipping hazard. There is a potential burning hazard from the heater in the silica packed
column. Be prepared to clean up any broken glass.
How will the experiment be conducted in a safe manner?
All valves will remain closed until the apparatus has been checked for leaks, buildup of
materials, and stoppages. The air inlet valve will be opened and the pressure checked before the
valve into the apparatus is opened.
What safety controls are in place?
The high-pressure air first enters the apparatus through a pressure valve that should be set
to approximately 40.0 PSI, not to exceed 100.0 PSI. Each column then has an independent air
flowmeter and shutoff valve.
Describe safe and unsafe ranges of operations.
The range of airflow needed to conduct the experiment is 0.0-1000.0 cc/s of air for the
sand packed column and 0.0-13.9 SCFM for the silica packed column. It is not possible to
increase the flow beyond these values; if it were possible then doing so would risk damage to
sensitive equipment. The pressure range for the apparatus is 0.0-100.0 PSI, which should not be
exceeded.
I have read the relevant background material for the Unit Operations Laboratory entitled:
Flow Through Fluidized Beds and understand the hazards associated with conducting this
experiment. I have planned out my experimental work in accordance to standards and acceptable
safety practices and will conduct all of my experimental work in a careful and safe manner. I
will also be aware of my surroundings, my group members, and other lab students, and will look
out for their safety as well.
Signatures: _Jeff Umbach_______________________________________
_Russell Boyer_______________________________________
_Michael Czepizak___________________________________
_Krista Sutton_______________________________________
_Jake Biberstein______________________________________
_Stanley Das_________________________________________
Unit Operations ChE-381 Group No. 1
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Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
2. Abstract
In this experiment, we measured pressure drop vs. flow rate in two different columns
packed with sand or silica at different heights and temperatures. Theoretically, the superficial
velocity Vs should equal the air velocity at minimum fluidization Vf. For the sand trials, we
found that an average Vs of 0.045 +/- 0.011 meters/second for the large grain sand. The small
grain sand had an average Vs of 0.034 +/- 0.0083 meters/sec. For silica, the Vs values were 0.440
+
/- 0.109 meters/second and 0.321 +/- 0.080 meters/second. The Vf values for the small grain
sand were very close to the theoretical values with an average of 0.035 +/- 0.0082 meters/sec.
The Vf values for the large grain sand did not fit the theoretical values. The Vf values for the
large grain sand averaged out to 0.110 +/- 0.027 meters/second, which is more than twice the Vs
value. The Vf values for silica were 0.50 +/- 0.124 meters/second and 0.48 +/- 0.119
meters/second for unheated and heated silica respectively. These values are close to the Vs
values, but they are not as accurate as the values obtained for the smaller grain size of sand. In
general, the pressure drop in the column was greater when more material was added to the
column bed. Also, the heated silica fluidized much faster than the room temperature, which
would be expected due to lower densities of air particles at higher temperatures.
Unit Operations ChE-381 Group No. 1
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Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
3. Introduction
Fluidized bed reactors are a relatively new tool in the chemical engineering field. Fritz
Winkler developed the first fluidized bed gas generator in Germany in the 1920s. One of the
first United States fluidized bed reactors used was the Catalytic Cracking Unit, created in Baton
Rouge, LA in 1942 by the Standard Oil Company (Exxon Mobil). A fluidized bed is a packed
bed through which fluid flows at such a high velocity that the particles in the bed are loosened
such that the bed behaves as though it is a liquid.
Fluidized beds provide a large surface area for contact between solids and a liquid or a
gas that is conducive for heat and mass transfer.
In this environment, nearly uniform
temperatures can be maintained in the reactor even with highly exothermic reactions. This is
important because a temperature gradient can form in a poorly mixed bed, leading to equipment
failure, product degradation, and decreased efficacy of the reaction. A fluidized bed also
provides uniform mixing, which is important for product quality and efficiency. Fluidized bed
reactors are often a continuous process, meaning they are also very efficient compared to batch
processes.
However, there are some disadvantages to fluidized beds. One disadvantage is that the
cost of a fluidized bed reactor is usually high because the vessels are typically larger than batch
or other processes. Another disadvantage is that sometimes particles may become entrained, or
blown along with the flow, which can be costly and problematic to repair. There is also an extra
power input that is required for the pump to moderate the pressure drop. Finally, the fluid-like
behavior of these fine particles may eventually cause erosion issues.
Fluidized beds can be stimulated by either gas or liquid flows. In either case, the process
of fluidization is a competition between the force of gravity pointing downwards and the upward
Unit Operations ChE-381 Group No. 1
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Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
pointing drag force caused by friction between the flowing fluid and the individual particles that
make up the fluidized bed. As the flow rate of the working fluid is increased, it flows faster
across the individual particles, increasing the magnitude of the drag force. Eventually, at a
certain velocity (called the minimum fluidization velocity, Vf), the drag and gravitational forces
will be in balance, and the bed will begin to fluidize and bubble. As the velocity is further
increased, the drag force becomes more and more dominant over gravity, and the bed bubbles
more furiously. The individual particles are not carried away with the flow, because their settling
velocities are far larger than the minimum fluidization velocity, perhaps 50-75 times larger.
In this experiment, minimum fluidization velocity will be found for several different
types of fluidized beds. The effects of pressure drop, bed height, bed type, grain size, and
temperature will be investigated.
4. Theory
In packed beds the Ergun equation is a very important relation. The Ergun equation
relates the friction factor to numerical constants and the Reynolds Number (Re).
f p  150
Re  1.75
(1)
Where:
fp
=
friction factor of bed (dimensionless)
Re
=
Reynolds number (dimensionless)
The Reynolds number for this scenario is defined as follows:
Re 
D pVs  f
(1 ) 
Unit Operations ChE-381 Group No. 1
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Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
(2)
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
Where:
Re
=
Reynolds number (dimensionless)
Dp
=
Equivalent spherical diameter of the particle (m)
Vs
=
Superficial velocity (m/s)
=
Density of the fluid (kg/m3)
ε
=
Void fraction of the bed (dimensionless)
μ
=
Dynamic viscosity of the fluid (Pa-s)
The equivalent spherical diameter of the particle is defined by:
Vp
D p  6 * SAp
(3)
Where:
Dp
=
Equivalent spherical diameter of the particle (m)
Vp
=
Volume of the particle (m3)
SAp
=
Surface area of the particle (m2)
Notice that the Reynolds number depends on the void fraction (ε). The void fraction is
the ratio of the void volume to the total volume of the bed. Common values for the void fraction
range between 0.4-0.45.
If the flow is very viscous and Re ≤ 1 then the Ergun equation (1) can be approximated to
the Kozeny-Carman Equation:
f p  150
Re
Unit Operations ChE-381 Group No. 1
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Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
(4)
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
Where:
fp
=
friction factor of bed (dimensionless)
Re
=
Reynolds number (dimensionless)
The form of the Ergun equation given in equation (1), while true, is not in terms of
variables that are easily measured. We must derive a relation between the fundamental force
balance of fluidization and the minimum fluidization velocity. Using the force balance, and
starting with the drag force on the bed from the fluid:
F  pA
(5)
Where:
F
p
A
=
Drag force exerted by fluid on the bed (N)
=
Change in pressure across the bed (N/m2)
=
Cross-sectional area of the bed (m2)
This gives us the upward pointing drag force acting on the bed. In fluidization, this force
is balanced with the downward force of gravity, a volumetric force. We must first get the volume
of the particles in the bed:
V p  (1   ) AL
(6)
Where:
Vp
=
Volume of the bed (m3)
ε
=
Void fraction of the bed (dimensionless)
A
=
Cross-sectional area of the bed (m2)
Unit Operations ChE-381 Group No. 1
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Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
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Flow Through Fluidized Beds
L
=
University of Illinois
Height of bed (m)
Knowing that the force of gravity is volume multiplied by density and the gravitational
constant, we can turn equation 6 into:
F  (  p   f )(1   ) ALg
(7)
Where:
F
=
Gravitational force on the bed (N)
=
Density of the bed (kg/m3)
=
Density of the fluid (kg/m3)
ε
=
Void fraction of the bed (dimensionless)
A
=
Cross-sectional area of the bed (m2)
L
=
Height of bed (m)
g
=
gravitational constant (9.8 m/s2)
Knowing that, at minimum fluidization velocity, the drag and gravitational forces are
equal, we can set equations 5 and 7 equal to one another, and rearrange for the pressure drop,
which is something the apparatus can measure:
p  (  p   f )(1   ) Lg
(8)
Where:
p
=
Change in pressure across the bed (N/m2)
=
Density of the bed (kg/m3)
Unit Operations ChE-381 Group No. 1
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Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
=
Density of the fluid (kg/m3)
ε
=
Void fraction of the bed (dimensionless)
L
=
Height of bed (m)
g
=
gravitational constant (9.8 m/s2)
At minimum fluidization velocity, viscous forces dominate, so the Kozeny-Carman
equation (4) can be used to get a useful approximation for the minimum fluidization velocity.
However, we need an expression relating the friction factor to the pressure drop:
fp 
p D p
L Vs2
( 1 )
3
(9)
Where:
fp
=
friction factor of bed (dimensionless)
=
Change in pressure across the bed (N/m2)
L
=
Height of bed (m)
Dp
=
Equivalent spherical diameter of the particle (m)
ρ
=
Density of the fluid (kg/m3)
Vs
=
Superficial velocity (m/s)
ε
=
Void fraction of the bed (dimensionless)
p
Substituting equation 8 into equation 9 (for the delta-p term), then using equation 4 along with
equation 2 yields, after rearrangement:
Vf 
(  p   f ) gD2p
150
(
3
1
)
Unit Operations ChE-381 Group No. 1 p. 10
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
(10)
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
Where:
Vf
=
Minimum fluidization velocity (m/s)
=
Density of the particles (kg/m3)
=
Density of the fluid (kg/m3)
g
=
gravitational constant (9.8 m/s2)
Dp
=
Equivalent spherical diameter of the particle (m)
μ
=
Dynamic viscosity of the fluid (Pa-s)
ε
=
Void fraction of the bed (dimensionless)
Our goal of determining a way to find the minimum fluidization velocity in terms of
variables that can be measured is complete. If we wish not to entrain our particles into the
flowing fluid stream, it’s useful to know the settling velocity of the particles involved.
Vsettling 
(  p   f ) gD2p
18
(11)
Where:
Vsettling =
Settling velocity of the bed (m/s)
=
Density of the bed (kg/m3)
=
Density of the fluid (kg/m3)
g
=
gravitational constant (9.8 m/s2)
Dp
=
Equivalent spherical diameter of the particle (m)
μ
=
Dynamic viscosity of the fluid (Pa-s)
Unit Operations ChE-381 Group No. 1 p. 11
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
It’s also useful to know the maximum value the velocity can be increased to without
entraining particles. Expressed as a multiple of the minimum fluidization velocity:
Vsettling
Vf

25 (1 )
3 3
(12)
Where:
Vsettlin g
=
Vf
The ratio of settling velocity to the minimum fluid fluidization velocity
Vsetting =
Settling velocity (m/s)
Vf
=
Minimum fluidization velocity (m/s)
ε
=
Void fraction of the bed (dimensionless)
In this experiment, we are indirectly finding the minimum fluidization velocity, V f, by
increasing the gas flow rate until the pressure drop no longer increases, then decreasing the flow
rate until the pressure drop returns. From this information, as well as recording the pressure drop,
grain size, and void fraction of the bed used, we can analytically calculate the minimum
fluidization velocity necessary to fluidize the bed, and can draw out any correlations between
this velocity, grain size of the bed used, and temperature of the bed.
5. Apparatus
The Fluidized Bed Apparatus consists of two columns each with a wood packed bottom
(6) and a funnel (9). One is packed with sand (5) and the other with silica pellets (14). Each
Column has an air rotameter (3,18), which monitors the flow rate of the air entering the column.
The air enters though the bottom of the columns and flows upward through the wood beads,
Unit Operations ChE-381 Group No. 1 p. 12
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
which distribute the airflow evenly throughout the width of the column. The air then flows
through the packing where the air manometer (8) measures the pressure drop of the air stream.
The sand column is used for experiments in which the variable if interest is the size of the
packing material or the amount of packing material. The sand is sieved using different grates to
separate the particles by size. A meter stick is used to measure the height of the packed sand in
the column when varying the amount of packing material.
The silica column is used in addition to the sand column to test different packing
materials. It is also used in varying the temperature of the packing media. The peanut heater (20)
is connected to the silica packed portion of the column (16) and is used to heat the packed silica
to different temperatures. The thermocouples (16) and the thermometer (15) are used to make
sure the entire packed portion is uniform in temperature.
Unit Operations ChE-381 Group No. 1 p. 13
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
Figure 1. The figure above shows a flow diagram of the Flow through Packed Beds and
Fluidized Beds Apparatus. The general streams pictured in black represent the air streams. The
yellow stream at the top left is the sieved sand of specific diameter. The grey stream at the top
right is the silica pellets.
Unit Operations ChE-381 Group No. 1 p. 14
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
9 Funnel
9 Funnel
3 Air
Rotameter
8 Air
Mamometer
4 Sand Packed
Column
18 Air
Rotameter
14 Silica Packed
Portion
2 Pressure
Gauge
5 Sand Packed
Portion
6 Wood Packed
Portion
17 Air inlet
Valve
6 Wood Packed
Portion
7 Flask
1 Air Inlet
Valve
Figure 2. The picture above shows the Flow through Fluidized Bed apparatus. Note: there have
been changes made to the apparatus since captured. The top rim on the silica column was loose
and needed to be repaired.
http://images.google.com/imgres?imgurl=http://www.uic.edu/depts/chme/UnitOps/Humidification.jpg
Unit Operations ChE-381 Group No. 1 p. 15
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
No.
1
2
Equipment
Air Inlet Valve
Pressure
Gauge
University of Illinois
Table 1. Apparatus
Manufacturer
Description
Crane Co. CAT No. 7
Allows air into the sand packed column
N/A
3
Air Rotameter
Gilmont D_6626
4
Sand Packed
Column
N/A
5
Sand Portion
of Column
N/A
6
Bead Packed
Base of
Column
N/A
7
Flask
N/A
8
Air Manometer
Meriam Instrument,
Cleavland OH Mo: RC4615
9
Funnel
N/A
10
Excess Air
Stream
N/A
11
Sieve
Dual Manufacturing Co.
Chicago IL (63-4760
Microns)
12
Sand Entrance
N/A
13
Silica Entrance
N/A
14
Silica Portion
of Column
N/A
15
Digital
Thermometer
Fluke. Omega
Engineering Inc: Stanford
CT. Mo:2166A
16
Thermocouples
N/A
17
Air Inlet Valve
18
Air Rotameter
Crane Co. CAT No. 7
F&P Co. Precision Bore
Flowrator Tube No: FP
Monitors the pressure of the incoming air
Monitors the incoming air flow rate for the sand
packed column
Uses sand as a packing material. The amount of
sand and the diameter of the sand particles can be
varied in this column
This is the portion where the packing material
settles
Allows incoming air into the column and disperses
the air stream using packing to create a relatively
consistent stream though out the diameter of the
sand portion
Connected to the packing material portions of the
columns this filters out excess packing material
from the air
Measures the pressure loss of the air stream
The top of the column. Facilitates adding packing
material to the column and prevents spilling
caused by high pressure air streams
The excess air from the column comes out the top
into the surroundings
Used to filter sand using different grates so that a
certain range in diameters can be obtained
The sand will get sieved then funneled into the
column from the top
the silica packing with be funneled through the top
of the column
this is where the silica will reside while the
experiment is running
Measures the temperature through the packed
portions of the column to make sure temperature
remains the same
Measure the temperature in the silica packed
column. Connected to the digital thermometer.
Allows air into the silica packed column
Monitors the incoming air flow rate for the silica
packed column
Unit Operations ChE-381 Group No. 1 p. 16
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
3/4-21-G-10/83
Pressure
Gauge
N/A
Monitors the pressure of the incoming air
20
Peanut Heater
Superior Electric Co:
Bristol, Conn. Powerstat
Variable transformer
3PN116B 120 V, 10
Amp
Used to heat the air and packing material in the
silica column in order to measure the effects of
temperature on airflow rate
21
Small Air
Valve
Crane Co. CAT No. 7
22
Silica Packed
Column
N/A
19
23
24
Silica Column
Valve
Sand Column
Valve
Located after the Pressure Gauge to protect the air
rotameter from harmful air flows.
Uses silica pellets as a packing material. The
temperature of the packing material can be varied
in this column
N/A
Allows are to flow into the packed column.
N/A
Allows are to flow into the packed column.
6. Materials and Supplies
Table 2. Materials and Supplies
Material
Name
Manufacturer
Description
Safety/Comments
Compressed
Air
UIC
Compressors
Provides a constant stream of
air which flows through the
packed column
The pressure should be
regulated as high pressure
streams are hazardous both to
participants and equipment
Silica
Pellets
Sand
Sieves
N/A
Fisher
Chemical Lot
No. 080318
Dual
Manufacturing
Co: 63
Microns-4760
Microns
Electricity
ComEd
Meter Stick
N/A
Packing material used to
measure affects of temperature
of stream on air flow through
packed beds
Packing material used to
measure affects of particle size
on air flow though packed beds
Avoid spilling to prevent a
tripping hazard
Avoid spilling to prevent a
tripping hazard
These cylinders with different
size grates sift sand according
to range in diameter
Do not leave out as excess
sand may spill creating a
tripping hazard
The heater for the air stream in
the silica bed needs electricity
to heat the air stream
Measures the amount of
Circuits should be avoided if
there is a problem seek an
electrician
Should be put back properly
Unit Operations ChE-381 Group No. 1 p. 17
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
Broom
N/A
Vacuum
Dayton: Mo.
4YE74
University of Illinois
material in the sand packed
column
Used to sweep up any spilled
sand or silica
The vacuum is used to clean
the columns in order to vary
the size or amount of the sand.
as is could fall and cause
injury
Prevents tripping hazards
Spilling may occur while
vacuuming
7. Procedure
Things to Know Before You Start
1. The entire lab shares the air supply. If other experiments requiring the air supply are
being run at the same time as yours then you will have issues with maintaining steady air
pressure. Keep an eye on the flowmeter at all times. You may need to coordinate with
other lab groups in order to secure the amount of airflow that you need.
2. There is insufficient pressure to operate both columns simultaneously, so perform the
experiment on only one column at a time.
a. As it can take a long time for the heater (20) in the right column (22) to achieve
steady state, we recommend first performing the silica experiment at room
temperature and then performing the sand experiments in the left column (4)
while the right column (22) heats up. Make sure that someone keeps an eye on the
temperature of the right column.
Start Up
1. Check all connections for air and electrical supply.
Unit Operations ChE-381 Group No. 1 p. 18
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
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Flow Through Fluidized Beds
University of Illinois
2. Check that all apparatus and materials in the cabinet are accounted for and that nothing is
broken. Make sure that the temperature probes are connected to the digital thermometer
(15). Make sure that you have a Shop-Vac (vacuum cleaner) for cleanup later.
3. Clean out the left (4) and right (22) columns if they have not been already.
4. After making sure that all other airflow valves (1, 17, 21, 23, 24) on the apparatus are
closed, turn on the main air supply valve.
Packing Material Preparation
1. Using the sieve trays (11), prepare separate samples of sand and silica that are of the
approximate diameter required for the experiment. The sand will be placed in the left
column (4) while the silica will be placed in the right column (22).
2. You will prepare two samples of sand that are of two different particle diameters and one
sample of silica. One sand sample should be between 63-297 microns and the other
should be between 297-595 microns. The silica sample should have a grain size ranging
from 500-841 microns. Record the diameter range for each sample in your data.
3. To perform the sifting, choose a two sieve trays (in order from smallest to largest with the
largest on top) and one catch tray. These trays stack atop each other with the bottom sieve
being the of the lowest grain diameter that you need, the top sieve is of the highest grain
diameter that you need. You will use the sifted material that is captured in the bottom
sieve tray (not the catch tray) for your sample. Repeat this step for each sample using the
appropriate sieve trays.
Unit Operations ChE-381 Group No. 1 p. 19
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
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University of Illinois
a. Note: You will at least 2.5 to 3 times as much silica than sand, as you will need to
fill the entire heater assembly (14) in the right column (22) before you will be
able to see enough of the silica bed to visually measure its height.
b. Note: Save at least 5ml of each sample (using a beaker or graduated cylinder to
measure) for the determination of the void fraction.
Determining Void Fraction
1. For each sample, fill a graduated cylinder with up to 5ml of the sample material.
2. Measure separately 5ml of water. Add the water to the graduated cylinder and allow a
few minutes for the water to completely soak into the material.
3. Measure the total volume in the graduated cylinder.
4. Use the dry volume of the packing material, the volume of the water that was added to
the packing material, and the total volume measured after the material has soaked
thoroughly to calculate the void fraction of the packing material.
5. Repeat for all samples.
Experimental Procedure for Sand
1. Load one sample of the sand packing material into the left column (4) using the funnel at
the top to keep from spilling.
a. The height of the packing material in the column should be between 6 to 10 cm.
Accurately measure this height from the base of the bed, just above the gas
distributor (6) at the bottom of the column.
Unit Operations ChE-381 Group No. 1 p. 20
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
b. While pouring the packing material into the column, tap the side of the column to
make sure that the material does not stick to the side. This will also allow for the
packing material to settle more evenly at the base of the column.
2. Open the airflow valve (23) at the base of the left column (4) and make sure that the
airflow valve (24) at the base of the right column (22) is turned off.
3. Using the flowmeter (3) on the left side of the apparatus, slowly open the larger valve (1)
below the flowmeter and then gently turn the smaller valve (21) at the bottom of the flow
meter to increase the flow in increments of 5%. (Note: On this meter, each increment is a
percentage of the max flow rate of 2.2 L/s.)
c. Note: The flow meter adjustments can be tricky, if you go past the change you
were attempting for do not go back down or you will skew your results.
4. For each change in airflow rate record: the air flow rate, the pressure drop on the left side
of the manometer (8), the height of the packed bed (5) using the meter Stick, and your
visual observations.
5. Keep increasing the airflow rate until you reach the maximum for this bed of material.
You will know that this has been achieved when the bed is completely fluidized and
further increases in airflow rate do not cause further significant drops in pressure on the
manometer (8). Record the maximum flow rate, bed height, and pressure drop.
6. Decrease the airflow rate in increments of 5 on the flowmeter (3). Record the airflow
rate, bed height, and pressure drop for each change in airflow rate.
7. Once the airflow is turned off, add more of the sand sample that you were testing to the
left column (4) and increase the height of the bed by 3 to 4 cm. Repeat steps 2 through 6.
Unit Operations ChE-381 Group No. 1 p. 21
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
8. Once finished with this sample, remove the funnel and use the Shop-Vac to remove all of
the sand from the left column (4). Then perform steps 1 through 7 using the second sand
sample.
Experimental Procedure for Silica
1. Load one sample of the silica packing material into the right column (22) using the funnel
at the top to keep from spilling.
d. The height of the packing material in the column should be between 6-10 cm
above the top of the heater unit at the base of the column, at least 2-3 cm above
the highest thermal sensor. Accurately measure this height from the base of the
bed, just above the gas distributor (6) at the bottom of the column. This includes
the heater area (14).
e. While pouring the packing material into the column, tap the side of the column to
make sure that the material does not stick to the side. This will also allow for the
packing material to settle more evenly at the base of the column.
2. Open the airflow valve (24) at the base of the right column (22) and make sure that the
airflow valve (4) at the base of the left column (23) is turned off. Make sure that the
electrical heater (20) is turned off.
3. Use the digital thermometer (15) to record the temperatures of the right column (22).
There are temperature probes (16) mounted at multiple positions in the silica bed.
4. Using the flowmeter (18) on the right side of the apparatus, slowly open the valve (17)
below the flowmeter 5%. (Note: On this meter, each increment is a percentage of the
max flow rate of 139.0 SCFM.)
Unit Operations ChE-381 Group No. 1 p. 22
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
f. Note: The flow meter adjustments can be tricky, if you go past the change you
were attempting for do not go back down or you will skew your results.
5. For each change in airflow rate record: the air flow rate, the pressure drop on the right
side of the manometer (8), the height of the packed bed using the meter Stick, the
temperatures of the column, and your visual observations.
6. Keep increasing the airflow rate until you reach the maximum for this bed of material.
You will know that this has been achieved when the bed is completely fluidized and
further increases in airflow rate do not cause further significant drops in pressure on the
manometer (8). Record the maximum flow rate, the temperatures of the column, bed
height, and pressure drop.
7. Decrease the airflow rate in increments of 5 on the flowmeter (18). Record the airflow
rate, the temperatures of the column, bed height, and pressure drop for each change in
airflow rate.
8. Once the air flow is turned off, turn on the heater (20) and allow the silica bed to reach a
steady state at a temperature about 30 to 40 degrees higher than in the previous test. Use
the digital thermometer (15) to monitor the temperatures in the silica bed. (Note: Higher
temperatures than this are more difficult to maintain at a steady state.) Repeat steps 4
through 8.
9. Optional: If you have time to allow the column to cool back down to room temperature,
add more of the silica sample that you were testing to the right column (22) and increase
the height of the bed by 3 to 4 cm. Repeat steps 2 through 8.
Unit Operations ChE-381 Group No. 1 p. 23
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
10. Optional: Once finished with this sample, remove the funnel and use the Shop-Vac to
remove all of the silica from the right column (22). Then perform steps 1 through 9 using
the second silica sample.
11. You will not likely have time for steps 9 and 10.
Shut Down and Clean Up
1. Turn off the air supply. Make sure that the heater (20) is turned off. Turn off the digital
thermometer (15).
2. Remove the funnel from the top of each column. Use the Shop-Vac to vacuum out all
packing material from inside each column. Put the funnel back in place when done.
3. Clean each sieve tray. Do not use water as the trays may corrode!
4. Place all materials in the cabinet below the apparatus and close the door.
8. Data Tabulation
The data presented in Table 3 corresponds to a large sand particle diameter in the range of 297595 microns and an initial bed height of 7.31 cm.
Flow Rate (% of
2.2 L/s, +/- 1%)
0
3.8
7
14.9
19
24.5
34.1
Table 3. Pressure Drop across Large Sand Particles Trial 1
Pressure Drop
Sand Height
Observations
(+/- 0.01 in H2O) (+/- 0.25 cm)
-0.59
47.13
Stable, surface not bubbling at all
-0.46
47.15
Stable, surface not bubbling at all
-0.31
47.15
Stable, surface not bubbling at all
-0.09
47.15
Stable, surface not bubbling at all
0.01
47.15
Stable, surface not bubbling at all
0.19
47.16
Stable, surface not bubbling at all
0.12
47.36
Slight bubbling
Unit Operations ChE-381 Group No. 1 p. 24
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
45
52.7
60.2
69.7
76.9
83.3
91.8
96.9
89.2
82.6
66.8
58.1
49.7
40
32.5
28.1
25.5
12
2.9
0
0.15
0.18
0.22
0.28
0.29
0.31
0.31
0.31
0.31
0.31
0.27
0.23
0.2
0.11
0
-0.02
-0.02
-0.08
-0.43
-0.43
University of Illinois
47.44
47.82
48.27
48.47
48.57
48.68
48.92
49.05
48.87
48.76
48.18
48.12
48.15
47.87
47.8
47.71
47.55
47.4
47.4
47.23
Near even mixing
Slightly higher than even mixing
Slightly higher than even mixing
Low turbulent mixing
Turbulent mixing
High turbulent mixing
High turbulent mixing
Very high turbulent mixing
High turbulent mixing
High turbulent mixing
Just above even mixing
Even mixing
Just less than even mixing
Just above minimum fluidization
Stable, surface not bubbling at all
Stable, surface not bubbling at all
Stable, surface not bubbling at all
Stable, surface not bubbling at all
Stable, surface not bubbling at all
Stable, surface not bubbling at all
The data presented in Table 4 corresponds to a large sand particle diameter in the range of 297595 microns and an initial bed height of 10.19 cm.
Table 4. Pressure Drop across Large Sand Particles Trial 2
Air Flow Rate (%
Pressure Drop
Sand Height
Observations
of 2.2 L/s, +/- 1%) (+/- 0.01 in H2O) (+/- 0.25 cm)
0
-0.62
50.01
Stable, surface not bubbling at all
5
-0.25
50.05
Stable, surface not bubbling at all
10.8
0.06
50.06
Stable, surface not bubbling at all
24.6
0.9
50.17
Stable, surface not bubbling at all
34
1.01
50.2
Slight bubbling
44.9
1.01
50.65
Slightly more bubbling
52.2
1.01
50.87
Almost even mixing
63
1.06
51.21
Slightly turbulent mixing
73
1.11
51.68
Turbulent mixing
85.3
1.2
52.15
High turbulent mixing
93.1
1.2
52.38
Violent mixing
99
1.21
52.48
Violent mixing
85.11
1.2
52.25
Violent mixing
78.8
1.2
52.11
High turbulent mixing
73.8
1.19
51.98
Turbulent mixing
Unit Operations ChE-381 Group No. 1 p. 25
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
66
51.2
44
34
5.9
2.1
0
1.19
1.01
0.8
0.63
-0.31
-0.58
-0.59
University of Illinois
51.83
51.8
51.31
51.18
51.05
50.85
50.45
Just above even mixing
Very slight bubbling
Very slight bubbling
Stable, surface not bubbling at all
Stable, surface not bubbling at all
Stable, surface not bubbling at all
Stable, surface not bubbling at all
The data in Table 5 corresponds to a silica particle diameter in the range of 63 to 297 microns, a
range in temperature from 69F to 78F, and an initial bed height of 6.63 cm.
Table 5. Pressure Drop across Small Sand Particles Trial 1
Air Flow Rate (%
Pressure Drop
Sand Height
Observations
of 2.2 L/s, +/- 1%) (+/- 0.01 in H2O) (+/- 0.25 cm)
0
-0.6
46.45
Stable, surface not bubbling at all
4.3
-0.45
46.46
Stable, surface not bubbling at all
11.2
-0.28
46.46
Stable, surface not bubbling at all
14.2
-0.2
46.48
Stable, surface not bubbling at all
19.4
-0.08
46.48
Stable, surface not bubbling at all
32
0.01
47.21
Even mixing
36.9
0.01
47.28
Slightly more than even mixing
42.3
0.01
47.32
Slightly more than even mixing
50.3
0.02
47.42
Fairly turbulent mixing
61.8
0.08
47.49
High turbulent mixing
68.8
0.1
47.95
Violent mixing
65.9
0.09
47.74
High turbulent mixing
57
0.08
47.5
Fairly turbulent mixing
50
0.04
47.41
Slightly more than even mixing
38.2
0.01
47.35
Even mixing
27
-0.01
47.2
Slight bubbling
21.8
-0.1
46.95
Very little bubbling
6.7
-0.4
46.6
Stable, surface not bubbling at all
0
-0.58
46.46
Stable, surface not bubbling at all
The data in Table 6 corresponds to a silica particle diameter in the range of 500 to 841 microns, a
range in temperature from 69F to 78F, and an initial bed height of 19.15 cm.
Air Flow Rate (%
of 2.2 L/s, +/- 1%)
Table 6. Pressure Drop across Small Sand Particles Trial 2
Pressure Drop
Sand Height
Observations
(+/- 0.01 in H2O) (+/- 0.25 cm)
Unit Operations ChE-381 Group No. 1 p. 26
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
0
6
14
20
28.1
35
43.2
53.4
65
75.6
70.9
66.1
57.8
51.7
47.2
40.9
33.2
23.3
11
7.6
3.9
0
-0.59
0.31
1
1.51
1.22
1.31
1.33
1.4
1.51
1.51
1.52
1.51
1.49
1.49
1.46
1.41
1.21
0.72
0.5
0.2
-0.07
-0.6
University of Illinois
50.92
50.98
51.08
51.22
52.05
52.45
52.53
53.1
53.56
53.98
53.52
53.42
53.38
53.19
53.05
52.85
52.72
52.6
51.83
51.3
50.97
50.92
Stable, surface not bubbling at all
Stable, surface not bubbling at all
Stable, surface not bubbling at all
Slight bubbling
Slightly more bubbling
Almost even mixing
Just above even mixing
Turbulent mixing
Very turbulent mixing
Very turbulent mixing
Very turbulent mixing
Turbulent mixing
Turbulent mixing
Slightly turbulent mixing
Above even mixing
Even mixing
Slight bubbling
Stable, surface not bubbling at all
Stable, surface not bubbling at all
Stable, surface not bubbling at all
Stable, surface not bubbling at all
Stable, surface not bubbling at all
The data in Table 7 corresponds to a silica particle diameter in the range of 500 to 841 microns, a
range in temperature from 69F to 78F, and an initial bed height of 19.15 cm.
Table 7. Pressure Drop across Silica in the Temperature Range 69F to 78F
Air Flow Rate (%
Pressure Drop
Silica Height (+/of 139 CFM, +/Observations
(+/- 0.01 in H2O)
0.25 cm)
1%)
0
-0.62
59.13
Stable, surface not bubbling at all
7.2
1.63
59.14
Stable, surface not bubbling at all
9
1.8
59.14
Stable, surface not bubbling at all
10
1.9
59.14
Stable, surface not bubbling at all
Very slight movement on silica
12.1
2.32
59.14
surface
More noticeable movement on
14
3.05
59.14
surface
More noticeable movement on
15.1
3.3
59.14
surface
More noticeable movement on
16.4
3.7
59.14
surface
Unit Operations ChE-381 Group No. 1 p. 27
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
19.2
4.04
59.17
21.2
23
27
31.8
35.9
31.5
29.8
26.9
25.2
24
21.8
21
19.1
17.9
14.6
12
9.3
6.8
0
4.04
4.06
4.1
4.1
4.18
4.14
4.11
4.1
4.09
4.08
4.02
3.95
3.98
3.91
3.4
2.87
2.2
1.1
-0.6
59.43
60.01
60.42
61.23
62.65
61.45
60.94
60.45
60.31
60.14
59.87
59.72
59.19
59.13
58.6
58.6
58.57
58.57
58.57
Near even mixing; more bubbling
than before
Slow bubbling but large bubbles
Even mixing
Turbulent mixing
Violent mixing
Extremely violent mixing
Violent mixing
Highly turbulent mixing
Turbulent mixing
Slight turbulent mixing
Just above even mixing
Even mixing
Just above minimum fluidization
Minimum fluidization
Slight movement
Slight movement
Slight movement
Very minimal bubbling
Stable, surface not bubbling at all
Stable, surface not bubbling at all
The data presented in Table 8, corresponds to a silica particle diameter in the range of 500-841
microns and an initial bed height of 18.34 cm.
Table 8. Pressure Drop across Silica in the Temperature Range 88F-108F
Air Flow Rate (%
Silica
Pressure Drop
of 139 CFM, +/Height (+/Observations
(+/- 0.01 in H2O)
1%)
0.25 cm)
Stable, surface not bubbling at
0
-0.6
58.32
all
Stable, surface not bubbling at
7
3.1
58.42
all
9.3
3.89
58.84
Slight bubbling
11.1
3.98
59.31
Bubbling
13.5
4.04
59.71
Fairly turbulent bubbling
16.3
4.1
60.45
Turbulent bubbling
19.7
4.11
61.02
Highly turbulent bubbling
17.2
4.11
60.61
Highly turbulent bubbling
14.4
4.11
60.15
Turbulent bubbling
12.2
4.03
59.57
Just above even mixing
10.1
3.97
58.72
Bubbling
Unit Operations ChE-381 Group No. 1 p. 28
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
T (°F)
100
99
97
94
88
108
105
105
104
104
103
Flow Through Fluidized Beds
University of Illinois
8.7
3.9
58.46
7.1
3.5
58.32
0
-0.62
58.32
Slight bubbling
Stable, surface not bubbling at
all
Stable, surface not bubbling at
all
98
94
94
Table 9. Density of Air Calculation
Pressure
(kPa)
101.325
101.325
101.325
R constant (kPa*m3/kmol*K) Temperature (+/- 0.5 K) rho (kmol/m^3)
8.314
8.314
8.314
Substance
Large Sand
Small Sand
Silica
298
296
311
0.0409
0.0411
0.0392
Table 10. Void Fraction Calculation
Dry Volume (+/- Water Volume(+/Combined
0.1 mL)
0.1 mL)
Volume(+/- 0.1 mL)
5
15
18
5.5
16
18.9
8.8
15.5
20.4
Density of Air
(kg/m^3)
1.19
1.19
1.14
Void Fraction
(dimensionless)
0.40
0.47
0.44
Table 11. Superficial Velocity Calculation
Substance
Large Sand/Trial 1
Large Sand/Trial 2
Small Sand/Trial 1
Small Sand/Trial 2
Substance
Silica / Unheated
Silica / Heated
Flowrate (L/s, +/1%)
1.83
1.88
1.36
1.43
Flowrate (ft^3/min,
+/- 1%)
37.5
27.4
Flowrate (m^3/s)
Area (m^2)
0.00183
0.00188
0.00136
0.00143
0.0408
0.0408
0.0408
0.0408
Superficial
Velocity
(m/s)
0.045
0.046
0.033
0.035
Flowrate (m^3/s)
Area (m^2)
Vs (m/s)
0.0177
0.0129
0.0403
0.0403
0.440
0.321
Table 12. Calculation Summary
Density Density
Particle
Fluidization Superficial
µ
Void Fraction
Substance of Bed
of Air
Diameter
Velocity
Velocity
(Pa*s) (dimensionless)
(kg/m^3) (kg/m^3)
(m)
(m/s)
(m/s)
Large
Sand/Trial
1600
1.19
4.46E-04 1.96E-05
0.40
0.11
0.045
1
Large
Sand/Trial
1600
1.19
4.46E-04 1.96E-05
0.40
0.11
0.046
2
Unit Operations ChE-381 Group No. 1 p. 29
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
Small
Sand/Trial
1
Small
Sand/Trial
2
Silica /
Unheated
Silica /
Heated
University of Illinois
1600
1.19
1.80E-04
1.96E-05
0.47
0.035
0.0333
1600
1.19
1.80E-04
1.96E-05
0.47
0.035
0.0350
2100
1.19
6.71E-04
1.94E-05
0.44
0.50
0.440
2100
1.14
6.71E-04
2.00E-05
0.44
0.48
0.321
9. Results
For this lab, trials were run at two different starting bed heights of sand, each tested
against two ranges of grain size, and two different temperatures of silica at equal starting bed
heights and one range of grain sizes. The grain size ranges of sand were 63-297 microns and
297-595 microns. The range of particle sizes for the silica was 500-841 micrometers. For each
trial, the data collected included bed height, pressure drop, airflow rate, and temperature for the
silica trials. The data collected is best represented in figures 3, 4, and 5.
Figure 3 shows the relation between airflow rate and the overall pressure drop in the
column for a bed height of approximately 10.5 cm, and both sand sieve ranges. The portion
where pressure drop starts levels off is the point of minimum fluidization. We can see that for the
large sieve size, minimum fluidization occurs at a flow rate of approximately 85% of 2.2L/s.
Similarly, for the small sieve size, minimum fluidization occurs at a flow rate of approximately
65% of 2.2L/s. Fluidization occurs when the superficial velocity equals the minimum fluidization
velocity, and superficial velocity is directly proportional to the flowmeter reading. Tables 3 and 5
show that fluidization for the smaller bed height occurs at 83.3% and 61.8% of 2.2L/s, for large
and small sieve sizes, respectively.
Unit Operations ChE-381 Group No. 1 p. 30
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
1.7
1.45
Pressure Drop (in H2O)
1.2
0.95
0.7
0.45
Large Sand Size
0.2
Small Sand Size
-0.05
0
10
20
30
40
50
60
70
80
90
100
-0.3
-0.55
-0.8
Flowmeter Reading, percentage of 2.2 L/S
Figure 3. Pressure drop vs flowmeter reading for large bed heights of sand. Superficial velocity
increases as flowmeter reading increases. Fluidization occurs when the slope of the graph levels
off.
Figure 4 shows the same correlation of air flow rate to pressure drop for the silica column
at both room temperature and the increased temperature average of about 103° F. The data
displayed below shows this correlation for both increasing and decreasing flow rates. For cool
silica, fluidization occurred at 27% of 139 CFM, and for hot silica, fluidization occurred at
16.3% of 139 CFM.
Unit Operations ChE-381 Group No. 1 p. 31
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
4.3
3.79
Pressure Drop (in H2O)
3.28
2.77
2.26
1.75
Cool Silica
1.24
Hot Silica
0.73
0.22
-0.29 0
5
10
15
20
25
30
35
40
-0.8
Flowmeter Reading, percentage of 139 CFM
Figure 4. Pressure drop vs flowmeter reading for silica. Silica bed was heating to approximately
103°F. The pressure drop was the same magnitude for both cases.
Figure 5 illustrates the correlation between airflow rate and bed height of the larger sand
particles from both increasing and decreasing flow rates. When the experiment began, the bed of
sand was 47.13 centimeters above the workbench that apparatus was mounted on. Increases in
flow rate lead to an increase of the bed height and a decrease in the flow rate leads to a decrease
in bed height. This makes sense since the air flowing through the bed applies a force in the
vertical direction causing the bed height to change. This graph is representative for all tested
scenarios.
Unit Operations ChE-381 Group No. 1 p. 32
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
50
49.65
49.3
Bed height (cm)
48.95
48.6
48.25
47.9
47.55
Large Sand Size
47.2
46.85
46.5
0
10
20
30
40
50
60
70
80
90
100
Flowmeter Reading, percentage of 2.2 L/S
Figure 5. Bed height vs flowmeter reading for large sand size at the small bed height. Bed
height increases with increasing flow rate. This figure is representative for all tested scenarios.
10. Discussion
A fluidized bed can be created by a gas flowing through a bed of solid particles that are in
some kind of vessel, for our experiment inside a column. Under the appropriate conditions the
gas will cause the solid to begin to behave as a fluid and when this occurs the bed is fluidized.
Fluidized beds are useful because they create a large contact surface area between the solid and
gas, which allows for an increase in the overall heat or mass transfer. Some of uses of this
technique in chemical engineering are in the processes of fluid catalytic cracking and fluidized
bed combustion, both of which are widely used in the energy industries today.
For this experiment we had two columns, one filled with sand and the other with silica.
For the silica we only used one height and grain size range, 500-841 microns, but varied the
Unit Operations ChE-381 Group No. 1 p. 33
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
temperature to determine any effect this has on rate of fluidization. For sand we used two grain
size ranges, 63-297and 297-595 microns, at two different bed heights. We then measured the
change in pressure as the flow rate of the air was increased until fluidization occurred, and then
decreased back down to zero.
For the silica column, in addition to pressure drop, the
temperature was also recorded at every flow rate. We also took note of any observations
regarding the surface of the silica or sand bed as the flow rate of air was changed. The void
fraction was also calculated for silica and both grain size ranges of sand. For every tested
scenario, as the flow rate was increased, the height of the bed also increased, because the air
flowing through the bed forced the solid to move vertically.
With respect to the silica column, we can see that an increased temperature decreases the
flow rate required to cause fluidization, and, by extension, the minimum fluidization velocity. At
high temperatures, because of this decrease in flow rate, the pressure changes at a faster rate for
hot silica than it changes for cooler silica. This temperature effect on minimum fluidization
velocity cannot be explained as a viscosity effect, as minimum fluidization velocity is inversely
proportional to viscosity, and the viscosity of air increases with increasing temperature, implying
that minimum fluidization velocity should increase with increasing temperature, not the opposite
as shown in the experiment. The temperature effect on minimum fluidization velocity could be
due to convective heat transfer between the air and heated silica: the hot silica at the top of the
bed transfers heat by convection to the air around it, which rises due to its own buoyancy. If the
velocity of this convective hot air is non-negligible with respect to the forced airflow through the
bed, it could be a sizable effect on minimum fluidization velocity.
With respect to the sand column, using smaller grain sizes of sand increased the
magnitude of the pressure drop at fluidization, as well as decreasing the necessary flow rate
Unit Operations ChE-381 Group No. 1 p. 34
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
required to fluidize the bed. The rise in the magnitude of the pressure drop is unexpected, as the
pressure drop is directly proportional to the amount of material that is not void space. It was
shown that the smaller grains of sand had more void, implying less non-void space, implying a
lesser pressure drop. For this increased pressure drop to occur, that would mean the bed of
smaller sand grains must have had a higher density. The decrease in the minimum fluidization
velocity is expected however, as minimum fluidization velocity is directly proportional to the
square of the equivalent spherical diameter of the bed grains, and, as such, smaller grains
decrease the minimum fluidization velocity.
The major reason for errors in this experiment derives from a lack of true knowledge of
the equivalent spherical diameter of the bed grains. Minimum fluidization velocity is directly
proportional to the square of the equivalent spherical diameter of the bed grains. In this
experiment, it is assumed that the simple average of the sieve size is a good approximation for
this equivalent spherical diameter, but this could be problematic, as having more small grains
than large grains would mean the true equivalent diameter would be less than the simple average.
Similarly, having more large grains than small grains would mean the true equivalent diameter
would be more than the simple average.
Other reasons for error in our data and calculations came from the fact that the flow rate
of the air fluctuates, due to the source being shared, so we had to take approximate values for the
flow rates in our calculations. The air flow meters were extremely sensitive so we could not
change our flow rates at a constant interval, which would have helped the usefulness of the
calculated values. Another factor that contributed to the error was the heights of the beds of sand
and silica, which were measured with a meter stick, from the outside of the column. A more
accurate way of measuring the heights of the beds would include graduations being marked on
Unit Operations ChE-381 Group No. 1 p. 35
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
the column, perhaps with a black marker. There was also some error associated with the beds
themselves. Since we had air flowing through the beds the heights changed and while the change
was only slight with low flow rates at higher flow rates the height changed dramatically, making
it difficult to get an accurate value for the height of the bed. The turbulent mixing associated with
fluidization also changed the distribution of mass between any two points in the column.
11. Error Analysis
Each piece of equipment contributes to uncertainties in the measured data. These
uncertainties affect the calculations in such a way that causes uncertainties in the results
produced. The uncertainty in the results is calculated by propagation of errors from the measured
uncertainties. The uncertainties associated with each piece of equipment are as follows:
The airflow used for silica is measured with a flow meter that reads in percentage of
139.0 SCFM with markings at each 1% interval. Since the flow meter level remained constant
throughout the experiment, one extra significant digit could be approximated which would create
an uncertainty of 0.1%. The air flow meter used for sand reads in a percentage of 2.2 liters per
second in intervals of 1%. As with the silica side air flow meter, one extra significant digit could
also be approximated to an uncertainty of 0.1% of max flow.
The manometer used for
measuring the difference in pressure reads in intervals of 0.1 inches of water. Since the level of
water in the manometer remained level at each flow rate, the last digit can accurately be
measured to an uncertainty of 0.01 inches of water. The digital thermometer used to measure the
temperature in the silica column only reads in integer values. We read the values in Fahrenheit
because the scale is more sensitive than the Celsius scale; however, since the first decimal is
rounded off, each reading has an uncertainty of 0.5° F. The height of material in each column
was measured using a meter stick, which reads in increments of 1 mm. The height of the column
could not be read as accurately due to bubbling and mixing of material at higher flow rates which
caused the uncertainty of each measurement to be 0.25 cm at high flow rates.
Unit Operations ChE-381 Group No. 1 p. 36
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
Equipment
Air Rotameter
(Silica)
Air Rotameter
(Sand)
University of Illinois
Table. 13 - Error Analysis
Units
Uncertainty
SCFM (Standard
± 0.1 % of
Cubic Feet per
139 scfm
Minute)
L/s (cubic
± 0.1% of
centimeters per
2.2 L/s
second)
Monometer
Inches of Water
± 0.01
inches H2O
Digital
Thermometer
°F or °C
± 0.5 °F or
°C
Bed height
measurements
with meter stick
cm (centimeters)
± 0.25 cm
Reason
Lowest readable increment is
1%. Last digit approximated.
Lowest readable increment is
1%. Last digit approximated.
Lowest readable increment is
0.1 inch. Last digit
approximated.
Only reads integer values
which are rounded off to the
nearest value
Height of material fluctuates at
higher flow rates
12. Conclusion
Fluidized beds provide a large surface area for contact between solids and a liquid or a
gas that is conducive for heat and mass transfer providing for an environment where nearly
uniform temperatures can be maintained in the reactor even with highly exothermic reactions.
This is important because hot or cold spots may develop in beds where there is a temperature
gradient or the temperature is not uniform. These hot spots can cause equipment failure and
product degradation while the cold spots decrease the efficiency of the reaction. A fluidized bed
also provides uniform mixing, which is important for product quality and efficiency.
Consequently, the study of fluidized beds is valuable to the chemical engineering field.
In this experiment we analyzed the effects of grain size and temperature to determine the
minimum fluidization velocity (Vf ). The trials were run at two different starting bed heights of
sand each for two ranges of grain size, and two different temperatures of silica at equal starting
bed heights and one range of grain sizes. The grain size ranges used for sand were 63-297 µm
Unit Operations ChE-381 Group No. 1 p. 37
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
and 297-595 µm. For the silica the particle size ranged from 500-841 µm. For the 297-595
micrometer range sand the bed heights were 7.31 cm and 10.19 cm and for the 63-297
micrometer range the bed heights were 6.63 cm and 11.10 cm. Finally for the silica we used bed
heights of 19.15 cm and 18.34 cm. The temperature range for the silica trials was 69-78˚F for
the colder trial and 88-100˚F for the warmer trial. The void fraction was also calculated for the
large sand (0.40), small sand (0.47), and silica (0.44). For each trial, the data collected included
bed height, pressure drop, airflow rate, and temperature for the silica trials.
As expected when the flow rate increased the bed height also increased. As the flow rate
increased the sand and silica exhibited different behaviors. At very low flow rates there was no
appreciable impact on the silica and sand. As the flow rate gradually increased the bed began to
bubble and eventually reached the minimum fluidization velocity. Beyond this point the beds
began to exhibit turbulent behavior with severe bubbling and mixing.
The minimum fluidization velocity was experimentally determined to be 0.45 and 0.46
m/s for the large sand trials, 0.0333 and 0.0350 m/s for the small sand trials, and 0.44 and 0.321
m/s for the silica trials. These values are determined by identifying the point in the flow rate vs
pressure drop curves where the graph first flattens out; this is the point where the derivative is
equal to zero. Therefore as grain size decreases, the minimum fluidization velocity also
decreases. This result makes sense because a fluid is essentially composed of several tiny
particles condensed together. From the silica trials it can be inferred that as bed temperature
increases the minimum fluidization velocity decreases; that is hotter beds fluidize faster.
13. References
1. Flow Through Fluidized Bed Lab Manual.
2. Fluidized Bed Reactor. http://en.wikipedia.org/wiki/Fluidized_bed_reactor
Unit Operations ChE-381 Group No. 1 p. 38
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
3. Material Safety Data Sheet: Sand. Fisher Scientific.
http://fscimage.fishersci.com/msds/09890.htm
4. Material Safety Data Sheet: Silica Gel Desiccant. Fisher Scientific.
http://www.atmos.umd.edu/~russ/MSDS/silicagel28200.html
5. Fogler, Scott H. Elements of Chemical Reaction Engineering. 4th Ed. Boston: Pearson.
2006.
Unit Operations ChE-381 Group No. 1 p. 39
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
14. Appendix I
In this appendix, it will be shown how the minimum fluidization velocity and interstitial
velocity for the first trial of the large sand size was calculated. Starting from the minimum
fluidization velocity equation:
Vf 
(  p   f ) gD2p
150
(
3
1
)
Where:
Vf
,
=
Minimum fluidization velocity (m/s)
=
Density of the bed (kg/m3)
=
Density of the fluid, air (kg/m3)
g
=
gravitational constant (9.81 m/s2)
Dp
=
Equivalent spherical diameter of the bed particles (m)
μ
=
Dynamic viscosity of the fluid, air (Pa-s)
ε
=
Void fraction of the bed (dimensionless)
, Dp, μ, and ε are our unknowns of interest. We will start with void fraction ε. Void
fraction is defined as:
Void Volume

Dry Volume
From our preliminary data for the large sand size, 5 mL of sand were mixed with 15 mL of water
in a graduated cylinder, yielding an 18 mL solution. Thusly, two mL of the water added filled the
void space in the sand, so:
Unit Operations ChE-381 Group No. 1 p. 40
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
(20  18)

 0.4
5
From the void fraction, we can obtain the density of the bed. We postulate that sand is simply
made up of silicon dioxide (SiO2) particles and void space, so:
 p   s (1   )
Where:
=
Density of the bed (kg/m3)
s
=
Density of pure SiO2 (kg/m3)
ε
=
Void fraction of the bed (dimensionless)
Knowing that pure SiO2 has a density of 2634 kg/m3, and using our previously found void
fraction:
 p  2634 * (1  .4)
 p  2634 * 0.6
kg
 p  1580.4  1600 3
m
, the density of the air, can be easily obtained from the ideal gas law:
P   f RT
Where:
P
=
Ambient Pressure (101.325 kPa)
=
Density of the air (kmol/m3)
R
=
Gas constant (8.314 kPa*m^3/kmol*K)
T
=
Absolute Temperature (298 K)
Unit Operations ChE-381 Group No. 1 p. 41
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
Solving for
University of Illinois
:
(101.325)
0.0409 kmol
f 

(8.314)( 298)
m3
0.0409 kmol 29 kg 1.19 kg
*

3
m
kmol
m3
Dp is taken as the simple average of the size of the sieve used. This trial corresponded to a sieve
range of 297-595 microns. Thusly:
(595  297)
* 10 6 m
2
Dp  4.46 *104 m
Dp 
μ, the viscosity of the air, is linearly interpolated between two known values of μ at 250K and
300K. μ for a temperature of 298K is:
  1.9632 *105 Pa* s
We have solved for all of our unknowns and can find Vf, the minimum fluidization velocity:
(1600  1.19) * (9.81) * (4.46 *104 )2 0.43
Vf 
(
)
150(1.9632 *105 )
1  0.4
0.11 m
Vf 
s
This will be compared to the interstitial velocity, calculated using the flow rate, Q. Minimum
fluidization occurs when the pressure drop across the fluidized bed stops increasing. In this trial,
the flowmeter read 83.3% of 2.2 L/s when the pressure drop stabilized. As such:
Q
83.3
* 2 .2
100
Unit Operations ChE-381 Group No. 1 p. 42
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
1.83 L 1 m3
0.00183 m3
Q
*

s
1000 L
s
From this flow rate, we can calculate the interstitial velocity by dividing the flow rate, Q, by the
cross sectional area, A. Knowing the diameter of the column is 0.114 m:
A  0.0408 m 2
Q 0.00183 0.045 m
Vs  

A 0.0408
s
Unit Operations ChE-381 Group No. 1 p. 43
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
15. Appendix II
The lab group members and their contributions are presented below
13 hrs 45 min
Krista Sutton
Time Spent in Lab
Section
1 – WP&C
2 – Abstract
3 – Introduction
4 – Theory
5 – Apparatus
6 – Materials and Supplies
7 – Procedure
8 – Data Tabulation/Graphs
9 – Results
10 – Discussion
11 – Error Analysis
12 – Conclusion
13 – References
14 – Appendix I
4 hrs
Time Spent
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15 min
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4 hrs
30 min
30 min
1 hr 45 min
30 min
15 min
15 min
15 min
0 hrs
0 hrs
Unit Operations ChE-381 Group No. 1 p. 44
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Comments
Review
Review
Review
Review
Writing initial Drat
Writing initial Draft
Review
Reformatting Tables
Review
Review
Review
Review
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
16 hrs 0 min
Jake Biberstein
Time Spent in Lab
Section
1 – WP&C
2 – Abstract
3 – Introduction
4 – Theory
5 – Apparatus
6 – Materials and Supplies
7 – Procedure
Time Spent
0 hrs
15 min
1 hr
2 hrs
0 hrs
0 hrs
0 hrs
8 – Data Tabulation/Graphs
5 hrs
9 – Results
10 – Discussion
11 – Error Analysis
12 – Conclusion
13 – References
14 – Appendix I
4 hrs
1 hr
30 min
0 hrs
15 min
15 min
1 hr 45 min
Unit Operations ChE-381 Group No. 1 p. 45
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Comments
Group Section
Edited Mike’s First Version
Edited Mike’s First Version
Did the master Excel file which
contained all graphs, calcs, tables…
Edited Russ’s First Version
Edited Stan’s First Version
Group Section
Provided the things I used
Wrote the section
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
10 hrs 0 min
Stanley Das
Time Spent in Lab
Section
1 – WP&C
2 – Abstract
3 – Introduction
4 – Theory
5 – Apparatus
6 – Materials and Supplies
4 hrs
Time Spent
0 hrs
30 min
0 hrs
0 hrs
0 hrs
30 min
7 – Procedure
0 hrs
8 – Data Tabulation/Graphs
1 hr
9 – Results
10 – Discussion
11 – Error Analysis
0 hrs
3 hrs
30 min
12 – Conclusion
30 min
13 – References
14 – Appendix I
0 hrs
0 hrs
Unit Operations ChE-381 Group No. 1 p. 46
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Comments
N/A
Helped write this section with the rest
of the group
N/A
N/A
N/A
Reviewed this section for errors and
typos
N/A
Input all data collected into excel
spreadsheets, increased font size of
axes, legend. Collected data.
N/A
Wrote first draft of this section
Wrote first draft of this section
Reviewed this section for errors and
typos
N/A
N/A
Fall 2009
10/22/2009
Flow Through Fluidized Beds
Michael Czepizak
Time Spent in Lab
Section
1 – WP&C
2 – Abstract
3 – Introduction
4 – Theory
5 – Apparatus
6 – Materials and Supplies
7 – Procedure
8 – Data Tabulation/Graphs
9 – Results
10 – Discussion
11 – Error Analysis
12 – Conclusion
13 – References
14 – Appendix I
University of Illinois
13 hrs 0 min Total Time Spend on this Lab
4 hrs
Time Spent
10 min
10 min
2 hrs 30 min
2 hrs 30 min
0
0
0
0
10 min
10 min
0
3 hrs
10 min
10 min
Unit Operations ChE-381 Group No. 1 p. 47
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Comments
Reviewed the section
Reviewed
Wrote this section
Wrote this section
Reviewed this section
Reviewed this section
Wrote this section
Add references
Reviewed section
Fall 2009
10/22/2009
Flow Through Fluidized Beds
Jeff Umbach
Time Spent in Lab
Section
1 – WP&C
2 – Abstract
3 – Introduction
4 – Theory
5 – Apparatus
6 – Materials and Supplies
7 – Procedure
8 – Data Tabulation/Graphs
9 – Results
10 – Discussion
11 – Error Analysis
12 – Conclusion
13 – References
14 – Appendix I
University of Illinois
13 hrs 10 min Total Time Spend on this Lab
4 hrs
Time Spent
45 min
10 minutes
30 min
1 hr
30 min
20 min
4 hrs
10 min
15 min
15 min
30 min
10 min
20 min
15 min
Comments
Revised and proofread.
Formatted and proofread
Revised and proofread.
Edited, revised, and proofread.
Revised and proofread.
Revised and proofread.
Wrote original and revised as issues
were found during the lab experiment.
Proofread
Proofread and fixed grammar.
Proofread and fixed grammar.
Revised and proofread. Fixed grammar.
Formatted, revised, and proofread.
Tracked down some references.
Proofread
Unit Operations ChE-381 Group No. 1 p. 48
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Fall 2009
10/22/2009
Flow Through Fluidized Beds
University of Illinois
10 hrs 55 minutes
Russ Boyer
Time Spent in Lab
Section
1 – WP&C
2 – Abstract
3 – Introduction
4 – Theory
5 – Apparatus
6 – Materials and Supplies
7 – Procedure
8 – Data Tabulation/Graphs
9 – Results
10 – Discussion
11 – Error Analysis
12 – Conclusion
13 – References
14 – Appendix I
4 hrs
Time Spent
30 min
20 min
30 min
30 min
15 min
15 min
30 min
45 min
1 hr 30 min
15 min
1 hr 15 min
10 min
10 min
0 hrs
Unit Operations ChE-381 Group No. 1 p. 49
Biberstein, Boyer, Czepizak, Das, Sutton, Umbach
Comments
Writing and revisions
Writing and revisions
Proofreading and editing
Proofreading and editing
Gathering apparatus specifications
Gathering specifications
Editing and revisions
Data gathering and reduction
Wrote initial draft
Proofreading and editing
Writing and proofreading
Proofreading and editing
Gathering references
Fall 2009
10/22/2009