investigation of liquid-solid and gas-solid fluidized bed

8/12/2019 Investigation of Liquid-solid and Gas-solid Fluidized Bed

1/18

ChE 304

Chemical engineering laboratory - III

Experiment No. 7 Group No. 03 (A2)

Name of the experiment:

I nvestigation of liquid-solid and gas-solid fluidized bed

And

I nvestigation of 2-D and 3-D gas-solid fluidized beds

Submitted by:

Md. Hasib Al Mahbub

Student Id: 0902045

Level: 3; Term: 2

Section: A2

Date of performance: 25/02/2014

Date of submission: 11/03/2014

Partners Student Id. 0902041

0902042

0902043

0902044

Department of Chemical Engineering.

Bangladesh University of engineering and technology, Dhaka.


2/18

Summary

The main objective of this experiment was to verify the Richardson-Zaki equation for liquid-

solid fluidization beds and to study the flow pattern and calculate the pressure drop

characteristics of gas-solid fluidization beds. Water-sand system was used for liquid-solidfluidization & air-resin system was used for gas-solid fluidization. For liquid-solid system, bed

height and superficial velocities were determined. Logarithmic plot of superficial velocity vs.

voidage were plotted for both increasing and decreasing velocities. From the plot values of

terminal settling velocity, minimum fluidization velocity and Richardson-Zaki index were

determined for both increasing and decreasing velocities. From superficial velocity vs. voidage

graph for increasing velocities experimentally found values of terminal settling velocity,

minimum fluidization velocity and Richardson-Zaki index were 0.2642 m/s, 0.0255 m/s, 3.757

respectively and from superficial velocity vs. voidage graph for decreasing velocities

experimentally found values of terminal settling velocity, minimum fluidization velocity and

Richardson-Zaki index were 0.5243 m/s, 0.02305 cm/s, 5.5866 respectively. For gas-solid

fluidized bed, pressure drops for corresponding superficial velocities of air were recorded and

the graphical relation between pressure drop and superficial air velocity were showed in plot.

The flow regimes for different flow rates in gas-solid fluidization bed were shown in neat

sketches.


3/18

Introduction

Fluidization concerns the suspension or transport of solids by liquids and/or gases. The most

common engineering application is in the form of fluidized beds, which are containers of solid

particles through which is passed the fluidizing medium, usually a gas. Fluidized beds are used

in petroleum distillation, coal combustion, polymer production, and heat and mass-transfer

processes, such as food drying.

When a fluid is pumped upward through a bed of fine solid particles at a very low flow rate,

the fluid percolates through the void spaces (pores) without disturbing the bed. This is a fixed

bed process. If the upward flow rate is very large the bed mobilizes pneumatically and may be

swept out of the process vessel. At an intermediate flow rate the bed expands and is in what we

call an expanded state. In the fixed bed the particles are in direct contact with each other,

supporting each others weight. In the expanded bed the particles have a mean free distance

between particles and the particles are supported by the drag force of the fluid. The expanded

bed has some of the properties of a fluid and is also called a fluidized bed. The velocity of the

fluid through the bed opposite to the direction of gravity determines whether the bed is fixed,

expanded, or is swept out


4/18

Experimental Setup

Figure 1: Schematic Diagram of Solid-Liquid Fluidization Bed


5/18

Figure 2: Experimental setup for gas-solid fluidization

Manometer

Flow

meter

Control

Valve

Particles bed


6/18

Flow Regimes

Fixed bed (Observation no. 01)

Bubbling (Observation No. 02) Slugging (Observation No. 03)

Channeling (Observation No. 04) Spouting (Observation No. 05)

Figure 03: Different flow regimes in solid-gas fluidization (2D).


7/18

Observed data

Fixed bed height = 3.95 inch

Room temperature = 24C

Column diameter of liquid-solid tube = 2 inch

Empty bucket weight = 0.3 kg

Table 1: Observed Data for liquid-solid fluidization

No.

Of

Obs.

Increasing Flow Rate Decreasing Flow Rate

Weight of

Water +

Bucket

(Kg)

Time

(s)

Height of

the bed

(inch)

Weight of

Water +

Bucket

(Kg)

Time

(s)

Height of

the bed

(inch)

1 0.6 30 3.95 5.5 30 9.90

2 1.85 30 4.40 5.2 30 9.40

3 2.4 30 4.90 4.95 30 8.90

4 2.8 30 5.40 4.7 30 8.40

5 3.2 30 5.90 4.5 30 7.90

6 3.65 30 6.40 4.25 30 7.40

7 4.0 30 6.90 3.8 30 6.90

8 4.35 30 7.40 3.7 30 6.40

9 4.65 30 7.90 3.2 30 5.90

10 4.9 30 8.40 2.9 30 5.40

11 5.1 30 8.90 2.3 30 4.90

12 5.3 30 9.40 1.7 30 4.40

13 5.55 30 9.90 0.35 30 4.0

14 5.75 30 10.4 5.5 30 9.90


8/18

Table 2: Observed Data for gas-solid fluidization (3D)

No.

Of

Obs.

Flow rate

Of air

(L/min)

Height of the manometric fluid(CCl4)

Left

(inch)

Right

(inch)

1 80 21.2 19.6

2 140 21.3 19.5

3 220 21.4 19.4

4 300 21.5 19.4

5 350 21.6 19.3

6 400 21.7 19.2

7 450 21.7 19.2

8 500 21.9 18.9


9/18

Calculated data

Table 3: Calculated data for liquid-solid fluidization.

Obs.

No.

Height

of

Bed, m

Weight

of water,

kg

Mass

flow

rate,

kg/s

Volumetric

flow rate,

m3/s

Superficial

Velocity,

Usm/s

Voidage,

Increasing Flow Rate

01 0.10033 0.3 0.01 1.00271E-05 0.004939465 0.42

02 0.11176 1.55 0.052 5.18068E-05 0.025520568 0.48

03 0.12446 2.1 0.07 7.01898E-05 0.034576253 0.53

04 0.13716 2.5 0.083 8.35593E-05 0.041162206 0.58

05 0.14986 2.9 0.097 9.69288E-05 0.047748159 0.61

06 0.16256 3.35 0.112 0.000111969 0.055157356 0.64

07 0.17526 3.7 0.123 0.000123668 0.060920064 0.67

08 0.18796 4.05 0.135 0.000135366 0.066682773 0.69

09 0.20066 4.35 0.145 0.000145393 0.071622238 0.71

10 0.21336 4.6 0.153 0.000153749 0.075738459 0.73

11 0.22606 4.8 0.16 0.000160434 0.079031435 0.74

12 0.23876 5 0.167 0.000167119 0.082324411 0.76

13 0.25146 5.25 0.175 0.000175474 0.086440632 0.77

14 0.26416 5.45 0.182 0.000182159 0.089733608 0.78

Decreasing Flow Rate

01 0.25146 5.2 0.173 0.000173803 0.085617388 0.77

02 0.23876 4.9 0.163 0.000163776 0.080677923 0.76

03 0.22606 4.65 0.155 0.00015542 0.076561703 0.74

04 0.21336 4.4 0.147 0.000147064 0.072445482 0.73

05 0.20066 4.2 0.140 0.00014038 0.069152506 0.71

06 0.18796 3.95 0.132 0.000132024 0.065036285 0.69


10/18

Obs.

No.

Height

of

Bed, m

Weight

of water,

kg

Mass

flow

rate,

kg/s

Volumetric

flow rate,

m3/s

Superficial

Velocity,

Usm/s

Voidage,

07 0.17526 3.5 0.117 0.000116983 0.057627088 0.67

08 0.16256 3.4 0.113 0.000113641 0.0559806 0.64

09 0.14986 2.9 0.097 9.69288E-05 0.047748159 0.61

10 0.13716 2.6 0.087 8.69016E-05 0.042808694 0.58

11 0.12446 2 0.067 6.68474E-05 0.032929765 0.53

12 0.11176 1.4 0.047 4.67932E-05 0.023050835 0.48

13 0.1016 0.05 0.0017 1.67119E-06 0.000823244 0.43

Table 4: Calculated data for Gas Solid Fluidized bed (3D).

Observation

No.

Air flow rate

(lit/min)

Air flow rate,

Q

(m3/sec)

Air velocity

v, (m/s)

Pressure

drop, m

(in CCl4)

1 80 0.0133 0.741 0.0406

2 140 0.0233 1.296 0.0457

3 220 0.0367 2.037 0.0508

4 300 0.05 2.778 0.0533

5 350 0.0583 3.241 0.0584

6 400 0.0667 3.704 0.0635

7 450 0.075 4.167 0.0635

8 500 0.083 4.630 0.0762


11/18

Sample calculation

For LiquidSolid Fluidization beds:

For observation 5 (increasing velocity)

So, Superficial velocity,

sec90.04774815

00202683.0296.997

sec097.0

2

3

m

mm

kg

g

AmU

H

K1

AH

M1

AH

MAH

V

VVVoidage,know,We

T

PT

mK

K

0581914.0

10033.0142.0

For, bed height, H= 0.14986m;

voidage, 0.6114986.0

0581914.01

Weight of water + bucket = 3.2 kg

Weight of water, w = (3.2-0.3) kg = 2.9 kg

Water collection time , t = 30 sec

Diameter of the column , D = 2 inch = 0.0508 m

The mass flow rate of water, m = w/t = 2.9/30 = 0.097 kg/s

Cross sectional area of the

column ,

A = ( / 4) x D2 = ( / 4) x(0.0508) 2m2

= 0.00202683 m2

Fixed bed height, H = 3.95 inch = 0.10033 m

Fixed bed voidage, = 0.42


12/18

Theoretical Calculation

Fix bed voidage, = 0.42

Diameter of the particle, DP = 0.75mm = 0.7510-3 m

Density of the particle, P = 2.5 kg/m3

Density of water at 240C = 997.296 kg/m3

Viscosity of water at

240C

= 0.89010-3

sec/00655.0

10890.042.01

00075.081.9296.997250042.00055.0

10055.0,

3

23

23

m

gDUow PP

mf

mf

mf

10.5220

10890.03

296.997250081.9296.99700075.02

3

2'''

',

23

3

2

3

2

222

2

2

2

SP gddU

U

RR

U

Rgain

Now for spherical particle from the plot Re'.vs'Re'U

'R 22

we get, 105Re' .

kg/m.s


13/18

Now,

sec/1249.000075.0296.997

10890.0105Re'

Re'

3

md

U

dU

t

t

From Richardson -Zaki equation

398.3

42.0log

1249.0

00655.0log

log

log

loglog

n

U

U

n

U

Un

U

U

UU

t

mf

t

mf

n

t

mf

n

tmf

By graphical method

1. For Increasing velocity :

Umf = 0.0255 m / s

Ut = 0.264 m / s

n = 3.757

2. For decreasing velocity :

Umf = 0.02305 m / s

Ut = 0.5243 m/ sn = 5.5866


14/18

For GasSolid Fluidization beds

Observation 5

Column diameter = 6 inch = 0.1524 m

Cross sectional area = 21524.0

4

= 0.018 cm2

Air flow rate, V = 350 liter/min = 0.0583m3/sec

Air velocity, v =2

3

018.0

sec0583.0

m

m

A

V = 3.241m/s

Pressure drop = (21.6-19.3) in CCl4 = 0.0584mCCl4


15/18

Graphical representation:

Figure 4: Superficial velocity vs. voidage graph (for increasing velocity).

y = 0.2642x3.757

0.01

0.1

0.3

SuperficialvelocityUf(m/s)

Voidage,

Ut=0.2642m/s

=0.779= 0.42

Umf = 0.0255


16/18

Figure 5: Superficial velocity vs. voidage graph (decreasing velocity).

y = 0.5243x5.5866

0.01

0.1

0.3

SuperficialvelocityUf(m/s)

Voidage,

Ut = 0.02305m/s

= 0.769 = 0.49


17/18

Figure 6: Log-log plot of pressure drop vs. air velocity in solid-gas fluidization.

0.03

0.5 5

PressureDropinmanometer(mC

Cl4

Air velocity (m/s)


18/18

Results and Discussions

The experimental values deviate somewhat from the theoretical values. In calculation, it is

assumed that the particles are ideally spherical but it is not true for practical purposes especially

when resin particles are used. When flow of water is increased to a higher value, it has become

increasingly difficult to measure the height of the fluidized bed. This situation led to improper

scaling of the height, which have induced a significant error in the accompanying calculations.

Another reason is that as the velocity approaches the minimum fluidization velocity, some bed

expansion normally occurs before the pressure drop reaches the buoyant weight per unit area

of bed. Therefore, the container walls exert some frictional forces on the bed. For liquid-solid

fluidization the superficial velocity vs. voidage plot in logarithmic scale for both the increasing

and decreasing height shows straight line with a slope which was the Richardson-Zaki index.

In the second part of the experiment (the gas-solid system) the pressure drop behavior was

observed with the change of flow rate of gas. Here the gas was air. And the observation shows

that at less velocity the bed height was increased and the some bubble type voidage was seen.

But as the velocity was increased the continuous big voidage was observed and at the same

time tremendous movement of solid particle was seen. We have plotted pressure drop against

velocity of air on log-log graph.

Experimental ValuesTheoretical Values

Increasing Decreasing

Minimum fluidized bed

velocity, Umf (m/sec)0.0255 0.02305 0.00843

Terminal settling velocity,

Ut (m/sec)0.2642 0.5243 0.1249

n (RZ index) 3.757 5.5866 3.398

investigation of liquid-solid and gas-solid fluidized bed

Documents