1.0 TITLE

Fluidized Bed

2.0 OBJECTIVES

-To determine the pressure drop across fluidized bed

-To verify the Carman- Kozeny equation

-To observed the differences between particulate and aggregative fluidization.

3.0 INTRODUCTION

A fluidized-bed reactor (FBR) is a combination of the two most common, packed-bed and

stirred tank, continuous flow reactors. In FBR, the substrate is passed upward through the

immobilized enzyme bed at a high enough velocity to lift the particles. However, the

velocity must not be so high that the enzymes are swept away from the reactor entirely.

This type of reactor is ideal for highly exothermic reaction because it eliminates local hot-

spots, due to its mass and heat transfer characteristics mentioned before.

The increase in FBR use in today’s industrial world is due to the inherent advantages of

the technology. FBR perform uniform particle mixing and temperature gradients and

ability to operate reactor in continuous state. On the other hands, FBR does have its draw-

backs, which must take consideration. FBR need to increased reactor vessel size to solve

the expansion of the bed materials in the reactor. The requirement for fluid to suspend the

solid material necessitates that a higher fluid velocity is attained in the reactor. The high

gas velocities present in this style of reactor often result in fine particles becoming

entrained in the fluid. This may continue is an expensive problem even with other

entrainment reducing technologies. The fluid-like behaviors of the fine solid particles with

the bed eventually result in the wear of the reactor vessel. This can require expensive

maintenance and upkeep for the reaction vessel and pipes. If fluidization pressure is

suddenly lost, the surface area of the bed may be suddenly reduced. This can either be an

inconvenience, such as runaway reaction.

Possible solid particle fluid mixture state are: fixed bed, stationary fluidized bed, bottom

feeding and overflow at the free surface of the bed, or vice versa, vertical conveying in

the dense bed, low density vertical and horizontal conveying, downward particle

movement in the dense bed and spouted bed. Dense phase, non-fluidized solid floe, in

which particles move en bloc, with little relative velocity, has been referred to as moving-

bed flow, packed bed flow or slip-stick flow. The voidage is close to the minimum

fluidization value. Vertical down flow is often used with the fluid moving faster than

solids. Upflow of non-fluidized particles is not common. The spouted bed is a combination

of a jet-like upward moving dilute fluidized phase surrounded by a slow downwards

moving bed through which gas percolates upwards. The use of such system is limited to a

few physical operations with large particles. Using some bed expansion and higher flow

rates will give higher mass transfer rates from the liquid to the particles. Clogging and

dead zones will also be avoided and attrition may help in controlling. Depending on

particle size and density, liquid and gas flow rates, the use of recycle and bed geometry,

several mixing patterns may be obtained in which the liquid phase and the solid phase are

mixed or not.

It is most often applied in immobilized-enzyme catalysis where viscous. Particulate

substrates are to be handled. FBR are used for produce gasoline and other fuels, along

with many other chemicals. Many industrials produced polymers are made using FBR

technology, such as rubber, vinyl chloride, polyethylene, styrenes and polypropylene.

Various utilities also use FBR’s for coal gasification, nuclear power plants, and water and

waste water treatment setting.

4.0 MATERIAL AND EQUIPMENT

5.0 RESULTS AND CALCULATIONS

Column inner diameter = 46 mm

Carbon Height of the bed (Initial) = 135 mm

Length of tube = 470 mm

The results of the experiment is tabulated as below:

Air Flow Rate

(LPM)

Differential Pressure (mbar)

Air Carbon Acrylic

8 0 1 1

10 0 1 1

12 0 1 1

14 0 1 1

16 0 1 1

18 0 1 1

20 0 1 1

22 0 1 1

24 0 2 1

26 0 2 1

28 0 2 1

30 0 2 1

32 0 2 1

34 0 2 1

36 0 2 1

38 0 2 1

40 0 2 1

42 0 2 1

44 0 2 1

46 0 2 1

48 0 2 1

50 0 2 1

52 0 2 1

54 0 2 1

56 0 2 1

58 0 2 1

60 0 3 1

62 0 3 1

64 0 3 1

66 0 3 1

68 0 3 1

70 0 3 1

72 0 3 1

74 0 3 1

76 0 3 1

78 0 3 1

80 0 3 1

82 0 3 1

84 0 3 1

86 0 3 1

88 0 3 1

90 0 3 1

91.2 0 3 1

Table 1.1 Results of the experiment

To calculate the Fluid Velocity, we will use this equation:

� =���

32�

(−∆�)

��

Where,

� = Mean velocity of the tube

� = Viscosity of the fluid = 1.983 × 10�� kg /m s

�� = Diameter of the tube (m)

�� = Length of the tube (m)

∆� = Differential Pressure (Pa)

Thus for carbon grain

Differential

Pressure

(mbar)

Differential

Pressure (Pa)

Mean velocity

(m/s)

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

2 200 14.18976191

2 200 14.18976191

2 200 14.18976191

2 200 14.18976191

2 200 14.18976191

2 200 14.18976191

2 200 14.18976191

2 200 14.18976191

2 200 14.18976191

2 200 14.18976191

2 200 14.18976191

2 200 14.18976191

2 200 14.18976191

2 200 14.18976191

2 200 14.18976191

2 200 14.18976191

2 200 14.18976191

2 200 14.18976191

3 300 21.28464287

3 300 21.28464287

3 300 21.28464287

3 300 21.28464287

3 300 21.28464287

3 300 21.28464287

3 300 21.28464287

3 300 21.28464287

3 300 21.28464287

3 300 21.28464287

3 300 21.28464287

3 300 21.28464287

3 300 21.28464287

3 300 21.28464287

3 300 21.28464287

3 300 21.28464287

3 300 21.28464287

The graph of Pressure drop Against Fluid Velocity for Carbon:

y = 1

R² = #N/A

0

0.2

0.4

0.6

0.8

1

1.2

0 1 2 3 4 5 6 7 8

Pre

ssu

re (

mb

ar)

Mean velocity (m/s)

Graph of Pressure Drop Vs Fluid Velocity

For Acrylic

Differential

Pressure

(mbar)

Differential

Pressure (Pa)

Mean velocity

(m/s)

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

1 100 7.094880956

The Graph of Pressure drop against Fluid velocity for Acrylic

y = 1

R² = #N/A

0

0.2

0.4

0.6

0.8

1

1.2

0 1 2 3 4 5 6 7 8

Pre

ssu

re (

mb

ar)

Mean velocity (m/s)

Graph of Pressure Drop Vs Fluid Velocity

By combining both Graphs for both materials:

0

0.5

1

1.5

2

2.5

3

3.5

0 5 10 15 20 25

Pre

ssu

re D

rop

Mean Fluid Velocity

Graph of Pressure drop Vs Mean Fluid Velocity

Carbon grain Acrylite Linear (Carbon grain)

6.0 DISCUSSION

Figure 6.1: Schematic Diagram of Fluidized Bed Unit

Calculation of this experiment is done by using the Carmen-Kozeny equation

which is given below,

where u = mean velocity of the tube

µ = viscosity of the fluid

dt = diameter of the tube

lt = length of the tube

Wate

r C

olu

mn

Air

Co

lum

n

dp dp

Digital Water

Flow Meter

Main ON/OFF

Switch

Water Bypass

Valve

Water Flow

Control Valve

Water

Pump

Water

Tank

Digital Air

Flow Meter

Air Flow Control

Valve

Digital Pressure

Drop Meter

(Water Column)

Digital Pressure

Drop Meter (Air

Column)

Based on the equation, pressure drop, ∆P is directly proportional to the velocity, u. The

higher the velocity, the higher the pressure drop or vice versa. In this experiment, carbon

grain and acrylic are being used to test the differential pressure for air system across the

tube. Based on the graphs that we have plotted, they showed a direct relationship between

differential pressure and velocity across the tube. When the differential pressure is

increases, the velocity increases too. The experiment for carbon grain is successful as the

velocity across the tube increases as the differential pressure increases. However, for

acrylic, it is not successful because the pressure remains constant in the whole experiment.

The pressure indicator might encounter some errors during the process.

During the experiment, we can observe that when the air is passing upwards

through the particle at a very low flow rate, which is also at low fluid velocities, the bed

will remain packed and the particles would not move. When the air flow rate is increased

sufficiently, a point will be reached at which the drag force on a particle will be balanced

by the net weight of the particle. The particles are suspended in the upward moving air

and it will move away from one another and this is the point of incipient fluidization at

and beyond which the bed is said to be fluidized.

On the other hand, we also observe that the initial and final height of the test

material in the column before and after experiment is different. This means that there is

some air trapped between the test materials or the test materials are held loosely in the

column or not compressed. When we are testing for acrylic, there are some black particles

which are believed to be carbon grains left in the column. Hence, this might gives us

inaccurate results for this experiment. Besides, the digital flow meter and pressure drop

meter are not sensitive to give small reading of flow rate. This will cause inaccurate result.

There are few precaution steps need to be taken. It is important to open the compressor

valve slowly to avoid excess strong air flow pressure from entering the column. Opening

compressor valve in sudden will trigger the material in the column to burst out from the

air outlet. While changing the test materials from the column, make sure that the column

is perfectly cleaned to avoid any contamination for the next test material.

7.0 CONCLUSION

The experiments shows that the Pressure drop is having a direct proportional relationship

to the air velocity, however it will come constant when it reaches a ‘maxiumum’ point of

the air velocity. From the experiment, the variation of the pressure drop for carbon grain

is greater than acrylic, this can be explain as the mass of the acrylic and volume of acrylic

is greater than the carbon grain. The Carmen-Kozerny Equation verified.

8.0 REFERENCES

Rhodes, M. (2008). Introduction to particle technology (1st ed.). Chichester, England:

Wiley.