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FluidizationChemical Engneering Practice

Due Date Feb 7, 2012

Lab #2

Farhan Jafri

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To: Rudy Jones

From: Farhan Jafri, Group 3

Date: Jan 31, 2012

Subject: CHG 3122, Fluidization Experiment

Fluidization has been of developed since the 1920s, but commercially it wasn’t success until in

1940s, since it has played critical role in oil refineries where it was used to turn heavy petroleum

products into gasoline which is used as fuel. Fluidization helped removing heavy carbon from petroleum

by using fluidized catalyst particles, where the heavy carbons would be deposited on these particles and

then removed.

The main purpose of this lab is to study pressure drop variation as a gas is passed through when

slowly increasing and decreasing the velocity of gas through bed of particles such as flexi glass and coke

particles. The second part of this experiment is finding the minimum fluidization velocity and to analyze

the bed expansion as a function of gas superficial velocity. Even though the procedure requires us to

use both coke particles and flexolite particles in this experiment but the discussion, calculations and

results will be based on just using flexolite glass as bed particles in this lab report. Other objectives of

this lab would be finding pressure drops in the fixed bed and the fluidized bed will be calculated using

the ergun and bed apparent weight equations.

The experiment was performed by using two columns, each one was either filled with coke particles and

flexolite particles, the flow is these columns was increased incrementally by factor of 2 from 0 to 60

SLPM, and there pressure drop and the height of the column at different air flows were

recorded, and pressure drop was recorded using computer software Labview.

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Equipment and Procedure

The equipment used in this lab as follows, MFC which stands for mass flow controller, windbox, pyrex

glass columns of 3 and 3.5 inches are used .

The mass flow controller measures flow rate going into the wind box which is located beneath the

columns, from here they pass through porous steel plate and into the particles in the columns. The

column with 3.5 inch diameter is used for coke particle and column with 3 inch diameter is used for

flexolite particles, each column was filled with approximately 6 inches of static bed height, or roughly 15

cm. As the air flow leaves the column from the top surface, there are pressure taps located on the wind

box which are connected to the pressure sensors which measure the pressure and transfer the data to

the computer, the labview computes the data by recording and also making a graph of it.

Subsequently, the air flow rate was increased by increments of 2 SPML, and Labview was used to record

data point for each increament, this was performed from range of 0 to 60 SPML.

Both types of particles were subjected to the gas flow rates which passed through the bottom of

columns and flow rate was increased and decreased such that it would be possible to collect data using

Labview, and then be able to find the total pressure drop as well as the bed height as a function of the

gas flow rate. The particles were then removed from column and then they were weighed. At the end

the pressure drop was recorded for the flow rates in empty column.

The mean diameter of the particles also had to be determined. This was performed by doing a

sieve analysis. The flexolite glass were placed into the top of the tray and placed on a shaker. By

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knowing the fraction of weight in each tray, the mean diameter was determined, calculation shown in

appendix A.

Results

Summary of important results in this lab as follows, the theory and explanation is discussed in the

discussion

The mean diameter of flexolite glass is 185 micrometers.

The theoretical pressure drop for flexolite glass in fluidized bed is 2662.84 Pa

Theoretical minimum velocity required for bed to be fluidized is 0.06136 m/s, this can be

determined by looking at table

The experimental fluidization velocity is 0.06814 m/s by looking at figure

The void fraction in the static bed is 0.1469

Minimum fluidization velocity, and bubbling velocity is Vmb=0.01723 m/s, Vmf=0.018m/s

The density if flexolite glass was found out to be 1916.6 kg/m3

Discussion

In order to understand this experiment clearly, one must know what is fluidization: when a static bed of

particles such as flexolite glass which is the focus of this lab report, are applied a strong flow of fluid

such as gas in our case coming from the bottom of the bed, the weight of the particles is then supported

by the drag force which is exerted by the gas on the particles, which causes them to freely suspend or in

other words become fluidized, the fluidized bed characteristics are very similar to that of pure liquid.

The heat and mass transfer rate are increased dramatically by the result of fluidization, this enables

them to be used extensively in gas and solid reactions, for example coal combustion, solid catalysts

reaction i.e. catalytic cracking of petroleum and other applications such as in bioreactors.

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The wet test meter is used to measure volumes and flow rates of gases, the meter consist of hollow

drum which consists several compartments of known volume, as sufficient amount of gas flows through

the meter causing chamber to hold maximum amount of air, and as gas leaves and enters through the

meter the drum rotates, since the volume of the compartment is known, the rotation of the drum can

be record to find out the total volume of gas flows through the meter.

In order to find the friction pressure drop due to packed bed, first of all we had to perform experiment

consisting of measuring pressure drop in the empty column, the pressure drop data was recorded using

Labview, the pressure given in raw data was in torr, this converted to pressure Pa and this was plotted

against superficial velocity, the graph gave a linear relationship, and using excel‘s trendline function, the

equation of line is obtained.

The next part of analyzing the experimental data was to find theoretical pressure drops across the bed.

The Ergun equation 3 was used to find the pressure drop when the bed height was static, and Ergun

equation 2 was used to come up with pressure drops in fluidized bed. The minimum fluidization velocity

occurred when the bed height changed from its static height, superficial velocity is 0.0613 m/s from

theoretical point of view and the experimental minimum fluidization can be obtained from figure 2,

which is 0.06814 meters per seconds. As velocity as increased beyond the point of minimum fluidization

velocity results in the formation of bubbles which continue to rise through the bed, this causes the bed

height to increase.

As evident from figure 2, in appendix A, the friction pressure drop predicted using Ergun equation barely

resembles the experimental data before and after the fluidization point, but the fluidization pressure

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drop data has wider range over velocity as compare to experimental, this is because as the bed starts to

fluidize, but at this point Ergun equation assumes fixed bed. Also some group members decided to

shake the column for some reason, which affected the fluidized bed and thus gave us inaccurate results.

A graph of height versus the superficial velocity was also constructed, as seen in figure 3 in the appendix

A, by visually looking at this graph, it is evident for velocity of range zero to 0.06 m/s there is no relative

change in the bed height as we increase the flow rate, this process is considered to be fixed bed, thus

glass particles do not move while velocity is increasing. At velocity of 0.0681 m/s, it is visually evident

the bed height starts to expand experimentally but theoretically the bed expands little earlier than this;

at velocity 0.06136 m/s. The rate of height change over superficial velocity is higher when the flow is

increasing as it is evident by looking at the steepness of slope, the graph is more steeper when

fluidization start to begin, and as we go down from maximum velocity of air, the slope descends less

steeper. The maximum superficial velocity applied to the bed is 0.102 m/s, from their we start to

decrease the flow rate and as mentioned before the slope descending has small rate of change. Another

observation that can be noted is the final bed height is higher than initial; the reason for this at the

beginning the particles were tightly packed together, and when particles changing from fluidized state to

static bed had more air between the particles thus giving higher height 17.4 cm compare to before of

16.63 cm.

The classification of glass particles, was determined by finding density and the mean diameter.

The mean diameter of glass particles was found out by; first about fifty grams were measured, and put

into a sieve which distributed glass particles with respect to their diameter, and then the mean diameter

was calculated using mass fractions of different diameters of glass particles which turned out to be 185

micrometers, but calculating the density was a bit trickier because not all the air bubbles in glass particles

were leaving in the graduated cylinder, thus the density1916.6 kg/m3 might be greater than it is suppose to

be. These two above properties help us distinguish them into classification of groups introduced by

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Geldart (1973), since the mean diameter fits the range 90 to 650 micrometer, thus they can be considered

as group B particles.

If mass of bed doubles that would double the height of the bed, but the cross sectional area of the pipe

will be remain the same therefore doubling the mass of the bed means doubling the height. Both sides

of equation 4 in lab handout, includes the height which can be eliminated from both sides so nothing

will change. That means the fluidized bed would be in the same fluidization regime as before.

Conclusion and Recommendations

The mean diameter of flexolite glass is 185 micrometers, and density is found to be 1916.6

kg/m3; this enables us to consider the glass particles to be in group B classification according to

Geldart(1973).

, this can be determined by looking at table

The experimental fluidization velocity is 0.06814 m/s by looking at figure 2 in appendix A,

theoretical minimum velocity required for bed to be fluidized is 0.06136 m/s.

Though it was not possible in our lab, to control the air flow without manually, but using

a computer to increase or decrease air flow, could have given more consistent data, and

hence better results.

Also the experiment should have been done with smaller intervals of change of air flow,

and increase range, could have given broader scope of data, thus enabling us to better

relate theoretical and experimental data.

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References

Geankoplis,C,N. (2003),Transport Process and Separation process principles” Fourth ed., Prenice

Hall, New Jesey,.

Geldart, D. (1973), “Types of Gas Fluidization”, Powder Tech., 7, 285-292.

Grace, J.R. (1982), “Fluidized Bed Hydrodynamics”, Chapter 8.1 in Handbook of

Multiphase Systems, ed. G. Hetsroni, Washington D.C., Hemisphere Publishing.

Fluidization Experiment Handout

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Appendix A

Table 1- Pressure and temperature of room where experiment was conducted

Pressure (psi) 14.69Pressure (Pa) 101283.6

Room temp.(C) 23Temperature (K) 296.15

Table 2 - The air velocity in the fluidized bed and the pressure drop due to friction.

Column filled with flexilite Empty Column Pressure

(torr)Flow (SLPM) Packed Bed Height

(cm)Pressure (torr)

0 0 15.33 01.8 2.1 15.33 0.13.7 4.1 15.33 0.25.7 6.1 15.33 0.47.7 8 15.33 0.59.8 10.2 15.33 0.7

11.9 12 15.33 0.814.1 14.1 15.33 0.916.5 16.1 15.33 1.118.7 18.1 15.43 1.220.8 20.1 15.4 1.321.2 22.1 15.73 1.521.5 24.1 16.13 1.621.8 26.1 16.33 1.821.9 28.1 16.63 1.922.4 30.1 16.83 2.121.5 28.1 16.63 1.920.9 26 16.43 1.820.3 24 16.33 1.618.7 22 16.23 1.5

17 20 16.2 1.315.3 18 16.13 1.213.4 15.9 16.13 1.111.8 14 16.1 0.910.2 12 16.13 0.8

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8.4 10.2 16.13 0.76.8 8.3 16.1 0.5

5 6.1 16.1 0.43.3 4.2 16.1 0.21.7 2 16.1 0.10.2 0.1 16.1 0

Table 3 – Data of flexilite glass particles in SI units.

Column filled with flexilite Empty Column

Pressure (Pa)

Flow (m^3/s)

Packed Bed Height (cm) Packed Bed Height (m) Pressure (Pa)

0 0 16.63 0.1663 0

239.994 0.000032466

16.63 0.1663 13.333

493.321 0.000063386

16.63 0.1663 26.666

759.981 0.000094306

16.63 0.1663 53.332

1026.641 0.00012368 16.63 0.1663 66.665

1306.634 0.000157692

16.63 0.1663 93.331

1586.627 0.00018552 16.63 0.1663 106.664

1879.953 0.000217986

16.63 0.1663 119.997

2199.945 0.000248906

16.63 0.1663 146.663

2493.271 0.000279826

16.73 0.1673 159.996

2773.264 0.000310746

16.7 0.167 173.329

2826.596 0.000341666

17.03 0.1703 199.995

2866.595 0.000372586

17.43 0.1743 213.328

2906.594 0.000403506

17.63 0.1763 239.994

2919.927 0.000434426

17.93 0.1793 253.327

2986.592 0.000465346

18.13 0.1813 279.993

2866.595 0.000434426

17.93 0.1793 253.327

2786.597 0.00040196 17.73 0.1773 239.994

2706.599 0.00037104 17.63 0.1763 213.328

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2493.271 0.00034012 17.53 0.1753 199.995

2266.61 0.0003092 17.5 0.175 173.329

2039.949 0.00027828 17.43 0.1743 159.996

1786.622 0.000245814

17.43 0.1743 146.663

1573.294 0.00021644 17.4 0.174 119.997

1359.966 0.00018552 17.43 0.1743 106.664

1119.972 0.000157692

17.43 0.1743 93.331

906.644 0.000128318

17.4 0.174 66.665

666.65 0.000094306

17.4 0.174 53.332

439.989 0.000064932

17.4 0.174 26.666

226.661 0.00003092 17.4 0.174 13.333

26.666 0.000001546

17.4 0.174 0

Table 4- Calculated values of for each air velocity, from increase of flow, to decrease.

Air veloci

ty (m/s)

Void Fraction ԑ

Experimental (Pa)

Theoretical (Pa)

Sphericity (Φ)

Fluid Viscosi

ty (Pa*s)

Mean Diameter dv (m)

Fluid Densit

y (kg/m^

3)

1-ԑ Φ*dv

0 0.147 0 0(fixed bed)

0.82 0.000018

0.000185

1.2 0.853

0.0002

0.0071

0.147 226.661 37.079272

0.82 0.000018

0.000185

1.2 0.853

0.0002

0.0139

0.147 466.655 140.74189

0.82 0.000018

0.000185

1.2 0.853

0.0002

0.0207

0.147 706.649 311.08649

0.82 0.000018

0.000185

1.2 0.853

0.0002

0.0271

0.147 959.976 534.67805

0.82 0.000018

0.000185

1.2 0.853

0.0002

0.0346

0.147 1213.303 868.75746

0.82 0.000018

0.000185

1.2 0.853

0.0002

0.0407

0.147 1479.963 1202.1089

0.82 0.000018

0.000185

1.2 0.853

0.0002

0.0478

0.147 1759.956 1659.2847

0.82 0.000018

0.000185

1.2 0.853

0.0002

0.0546

0.147 2053.282 2163.0392 (fixed

bed)

0.82 0.000018

0.000185

1.2 0.853

0.0002

0.061 0.152 2333.275 2662.842 0.82 0.0000 0.0001 1.2 0.8 0.00

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4 7(fluidized

bed)

18 85 48 02

0.0681

0.151 2599.935 2662.8427

0.82 0.000018

0.000185

1.2 0.849

0.0002

0.0749

0.167 2626.601 2662.8427

0.82 0.000018

0.000185

1.2 0.833

0.0002

0.0817

0.186 2653.267 2662.8427

0.82 0.000018

0.000185

1.2 0.814

0.0002

0.0885

0.195 2666.6 2662.8427

0.82 0.000018

0.000185

1.2 0.805

0.0002

0.0953

0.209 2666.6 2662.8427

0.82 0.000018

0.000185

1.2 0.791

0.0002

0.102 0.218 2706.599 2662.8427

0.82 0.000018

0.000185

1.2 0.782

0.0002

0.0953

0.209 2613.268 2662.8427

0.82 0.000018

0.000185

1.2 0.791

0.0002

0.0881

0.2 2546.603 2662.8427

0.82 0.000018

0.000185

1.2 0.8 0.0002

0.0814

0.195 2493.271 2662.8427

0.82 0.000018

0.000185

1.2 0.805

0.0002

0.0746

0.191 2293.276 2662.8427

0.82 0.000018

0.000185

1.2 0.809

0.0002

0.0678

0.189 2093.281 2662.8427

(fluidized bed

0.82 0.000018

0.000185

1.2 0.811

0.0002

0.061 0.186 1879.953 1398.9515 (fixed

bed)

0.82 0.000018

0.000185

1.2 0.814

0.0002

0.0539

0.186 1639.959 1092.1199

0.82 0.000018

0.000185

1.2 0.814

0.0002

0.0475

0.185 1453.297 864.99014

0.82 0.000018

0.000185

1.2 0.815

0.0002

0.0407

0.186 1253.302 622.94043

0.82 0.000018

0.000185

1.2 0.814

0.0002

0.0346

0.186 1026.641 450.52743

0.82 0.000018

0.000185

1.2 0.814

0.0002

0.0281

0.185 839.979 305.00607

0.82 0.000018

0.000185

1.2 0.815

0.0002

0.0207

0.185 613.318 165.21364

0.82 0.000018

0.000185

1.2 0.815

0.0002

0.0142

0.185 413.323 78.701448

0.82 0.000018

0.000185

1.2 0.815

0.0002

0.0068

0.185 213.328 18.149848

0.82 0.000018

0.000185

1.2 0.815

0.0002

0.0003

0.185 26.666 0.072916(fixed

0.82 0.000018

0.000185

1.2 0.815

0.0002

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bed)

Table 5 - Properties of two different particles.

Flexolite Particles Coke particlesDiameter of the bed (cm) 7.8 9.2Height of Static Bed (cm) 16.63 15.24Weight of Particles (Kg) 1.24 1.12

0 0.02 0.04 0.06 0.08 0.1 0.120

50

100

150

200

250

300

f(x) = 2730.07278603018 x − 5.57663779441472R² = 0.997633382548514

Velocity m/s

Empty Column Pressure (Pa)

Figure 1 – The pressure drop in the empty column used in the fluidization bed experiment versus air

velocity. Using excel trendline function it can be found that it follows the equation delta P =y = 2730x -

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5.576.

0 0.02 0.04 0.06 0.08 0.1 0.120

500

1000

1500

2000

2500

3000

Series2Series4

Velocity (m/s)

Pressure (Pa)

Figure 2 – A comparison between the experiment’s results for the pressure drop due to friction and

those would be obtained using Ergun equation for fixed, and fluidized bed.

0 0.02 0.04 0.06 0.08 0.1 0.120.155

0.16

0.165

0.17

0.175

0.18

0.185

Velocity m/s

Bed Height (m)

Figure 3 – The change in height of the fluidized bed versus the air velocity for flexi glass particles.

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Appendix B

Sample Calculations:

The mean diameter is defined in this experiment as the surface-to-volume mean diameter,

approximated from sieve analysis as:

d sv=1

∑ (xi /d pi)

d sv=1

( 0 . 0834500μm )+( 0 .057

425μm )+( 0.596300μm )+( 0 .237

212 μm )

where,

dsv: The mean diameter. It could be defined as dsv=φdv, it is in μm.

Φ: The sphericity of the particles.

xi: The mass fraction collected between two trays.

dpi: The mean diameter between two trays of the sieve anlalysis in μm.

The flexolite Density ρ is given by:

ρ=mV

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m is the mass of particles

And V is the volume of particles

The mass of the particles is: 9.584 g

The volume of the particles is:

V=5mL

Therefore:

ρ=9 .584 g

5cm3=1 . 9166g /cm3

In order to carry out this experimental calculations; the air velocity should be found. The devices

measured the air flow in SLPM. That should be changed to velocity unites for calculation required. It

is known:

P1Q1

T 1

=P2Q2

T 2

Where;

P is the pressure in Pa.

Q is the volumetric flow rate in LPM.

T is the temperature in K.

Subscripts 1&2 indicate Standard and Lab conditions respectively.

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After finding the volumetric flow rate of air with respect to lab conditions; the air velocity will be found.

That could be obtained easily by dividing the air flow rate by the cross-sectional area of the pipe.

Q2=P1Q1T 2

P2T 1

¿(101325 Pa ) (2 . 1LPM ) (298 .15o K )(101283Pa ) (273 . 15o K )

=2 .3LPM

∴ v=Q2

A=

(2.3 Lmin)(m3

1000 L )(min60 sec )

(0 .076m )2 π4

=0.0007m / s

The pressure drop across the bed is due to two main factors. The hydrostatic pressure drop and the

friction pressure drop which is due to the fluidized solid. The Labview reads the total pressure drop. In

order for us to find which fraction of the pressure is due to which factor; we carried out the experiment

in an empty column with various air velocities Figure (1), where x is the superficial velocity 2730.x -

5.576.

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−ΔPhydrostatic=2730x−5 . 576

−ΔPhydrostatic=2730. 7 (0 . 007m /s )−5 .576=−13 . 5389−ΔPfriction=−ΔPtotal+ΔPhydrostatic

¿−13. 54 Pa+239 Pa=226 Pa

where;

−ΔPhydrostatic : Is the pressure drop due to connections and taps. (Pa)

−ΔPfriction : Is the pressure drop due to packing material. (Pa)

−ΔPtotal :: Is the total pressure drop. (Pa)

The void fraction can be calculated by simply ignoring the mass of air in the packing solid: thus

static bed porosity is

m=ρ p Δ xA (1−ε )Therefore ;

ε=1−mAρp Δx

=1−1240 g

(45 . 6cm2 )(1 .9166gcm3 )(16 . 63cm )

=0 . 1469

where;

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m: The total mass of the packing (g)

ρp: The density of the packing particles=2.5g/cm3

A: The cross-sectional area of the bed = 45.6 cm2

Δx: The height of the bed at the flow of interest. (cm)

ε: The void fraction.

In a fluidized bed, the friction force would be equal to the buoyant weight. That will tell equation (2)

in the class handout which is:

A (−ΔPfriction)fluidizedbed

=Ag Δx (ρp− ρf ) (1−ε )

(−ΔPfriction)fluidizedbed=gΔx (ρ p− ρf ) (1−ε )

¿( 9. 8m /s2 )(0 . 1663m ) (1916 .6−1.2 ) kgm3

(1−0 . 1468 )=2663 .35Pa

where;

g: The gravitational constant = 9.8 m/s2

ρf: The density of air = 1.2 kg/m3

Equation 3 in the handout is called Ergun equation. It describes the frictional pressure drop in a

fixed bed.

−( ΔPfriction)fixedbed

=150vμ (1−ε )2 Δx

(φdv )2ε3+1 .75

v 2 ρf (1−ε ) Δx

(φdv ) ε3

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=150(0 . 007 ) (1 . 8×10−5 ) (0 .85 )2 (0 .1663 )(0 . 000152 )2 (0 .1469 )3

+1. 75(0. 007 )2 (1. 2 ) (0 . 85 ) ( 0. 1663 )(0. 000223 )2 (0. 1469 )3

−( ΔPfriction)fixedbed

=37 .08 Pa

where;

μ: The air viscosity=1.8x10-5 Pa.s

ΔP friction=150vμ (1−ε )2 Δx

(φdv )2 ε3

+1. 75v2 ρ f (1−ε )Δx

(φdv )ε3

−gΔx ( ρp−ρ f )(1−ε )

To calculate the minimum fluidization velocity, equation (4) in the handout becomes under

dimensionless form:

Remf=√C12+C2⋅Ar−C1

Remf is the Reynolds number at the minimum fluidization velocity

Coefficients according to Grace: C1 = 27.2 and C2 = 0.0408

Ar is the Archimedes number

Archimedes number is given by Eq. (7) in the lab manual:

Ar=g . ρ f ( ρ p−ρf )(φdv )3 / μ2

Ar=9 .8m / s2⋅1.2kg /m3⋅(1916 .6−1.2)kg /m3(0 .000152)3

(1.8⋅10−5 Pa . s )2

Ar=244 .15

Substitute into Eq. (4)

Remf=√27 . 2 2+0 . 0408⋅244 . 15−27 .2

Remf=0. 1825

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Rearrange Reynold number equation to solve for Vmf:

Remf=Vmf p f φd v

μ f

Thus minimum fluidization velocity:

Vmf=Remf μf

p f φdv

=0. 1825⋅1 .8⋅10−5 Pa . s1. 2kg/m3⋅0 .000152m

Vmf=0 . 018m /s

The minimum bubbling velocity Vmb is given by eq 10 in the lab manual

Vmb=2 .07 exp (0 .716∗F45)( d p ρg0. 06

μ0 . 347 )F45 is the mass fraction of coke less than 45μm in diameter.

d p is the diameter of the particles

ρg is the density of the air

μ is the viscosity of the air

Since sieve analysis was used, we will assumeF45 to be 1% the mass fraction

V mb=2 .07 exp (0 .716⋅0 . 01)(185 x10−6m⋅(1 . 2kg/m3 )0. 06

(1 . 8x 10−5 Pa . s )0.347 )=0 . 01723m /s