METU Chem. Eng. Dept. Ch.E. 410 Chem. Eng. Lab II

EXPERIMENT 1.1.

FIXED & FLUIDIZED BED

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OBJECTIVE

The objective of this experiment is to investigate the phenomenon of fluidization

in a gas-solid system.

PRELIMINARY WORK

1. Review the fundamental concepts of fluidization (Chapter 7 of McCabe, Smith

and Harriott, Unit Operations and web note on Introduction to Fluidization).

2. Familiarize yourself with the operation of the set-up.

3. Consider the change of ∆P with respect to u roughly on a graph and by

“Ergun Equation”.

4. Familiarize yourself with the force distribution on single particles of the bed

during the fluidization.

5. Prepare a data sheet to record the measurements.

EXPERIMENTAL SET-UP

A schematic diagram of the set-up is shown in Figure below.The set-up consists

of a vertical Plexyglass cylinder of internal diameter 44 mm containing glass

beads of ~ 375 µm as bed material, through which air flows. At the lower end of

the cylinder there is a distributor chamber and a stainless steel sintered plate

distributor which supports the bed. This system ensures uniform fluid flow into the

bed without causing excessive pressure drop.

Upon leaving the bed, the air passes through a stainless steel sintered plate;

then, air escapes to the atmosphere.

An air compressor (P1) with pressure reservoir (D2) is fitted to the unit for the air

supply.

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The air flow rate can be measured with a variable-area flowmeter (FI2). Air flow

rate can be adjusted by using the air bypass valve (V2) and flowmeter (FI2). A U-

tube manometer (PdI2) is used to measure the pressure drop across the fluidized

bed.

If the pressure in the air distribution chamber rises above 0.5 bar above

atmospheric, a pressure safety valve (PSV) will discharge air into the

atmosphere.

EXPERIMENTAL PROCEDURE

1. Be sure that the unit is connected to the electrical supply.

2. Open completely the air by-pass valve, V2 and close completely the valve

of the air flowmeter, Fl2.

3. Start the compressor, P1

4. Adjust the air flow rate through the flowmeter to 200 nL/h and wait till

pressure drop stabilizes. When stabilized make a note of the pressure

drop in mm CCl4 and the bed height.

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5. Increase the air flow rate with increments of 100 nL/h up to 500 nL/h and

following the stabilization period record pressure drop and bed height for

each flow rate.

6. From 500 nL/h onwards increase the flow rate through the flowmeter with

increments of 20 nL/h up to 900 nL/h by decreasing the flow through the

by-pass valve and repeat the recording in step 5.

7. From 900 nL/h to 1600 nL/h increase the air flow rate with increments of

100 nL/h and repeat the recordings in step 5.

8. During the steps given above observe the first movement of particles, first

formation of bubbles and growing bubbles.

9. Decrease the air flow rate to 200 nL/h with the same increments

suggested above and keep on recording the two parameters.

CALCULATIONS

1. Tabulate fluidization velocity, pressure drop and bed height measured at

each air flow rate.

2. Draw the pressure drop (mm H2O) versus fluidization velocity (cm/s) curve

for both increasing and decreasing air flow rates by using the recorded

data and the bed bulk density, 1.5 g/cm3.

3. Plot the variation of bed height against the fluidization velocity and

comment on the variation.

4. Determine the minimum fluidization velocity by using the experimental

data.

5. Calculate the theoretical minimum fluidization velocity and compare it with

the experimental one. Discuss your findings.

SUGGESTED READING

1. McCabe, W.L.,.Smith, J.C and Harriott P., "Unit Operations of Chemical

Engineering", 7th ed., McGraw Hill, N.Y., 2005, Ch.7.

2. Kunii, D. and Levenspiel, O.,”Fluidization Engineering”, 2nd ed.,

Butterworth-Heinemann, 1991, Ch.3.

3. Web Note on Introduction to Fluidization.