Disc Bowl Centrifuge

UEMK3431 Chemical Engineering Laboratory II

Exp 8: Disc Bowl Centrifuge

8.0 Disc Bowl Centrifuge Faculty Department: Unit Code and Name Experiment No.: Title of Experiment: Laboratory Room No. and Name: Experiment Duration (hour): Number of Student per Group

Lee Kong Chian Faculty of Engineering and Science Department of Chemical Engineering UEMK3431 Chemical Engineering Lab 2 8 Disc Bowl Centrifuge KB509 Process Control & Reaction Laboratory 4 hours 5 Students

Equipment and Materials Item Description Disc Bowl Centrifuge Weighting scale Deionised water Beaker (1 L) Beaker (500 mL) Measuring cylinder 500 mL Spatula Waste bottle Cooking oil Dish washing detergent *Item category SP Sample or specimen C Consumable CH Chemical W Labware, glassware, tool, and components E Equipment S Software

*Item category E E C W W W W W C C

Quantity estimation (e.g. per set/group of student) 1 1 2.5 LITER 3 2 3 2 5 LITER 2.5 LITER 1 BOTTLE


1.0


OBJECTIVES OF EXPERIMENT

 To understand disc bowl centrifuge working principle.  To demonstrate the separation of heavy phase liquid.  To demonstrate the effect of product type as throughput.  To calculate the separation efficiency.

2.0

INTRODUCTION

Centrifugal separators are used to separate solids from liquid or liquid from liquid using the principle of centrifugal force. Liquid-liquid centrifuge separates two liquids of different densities by spinning at relatively high speeds. Separation occurs as the heavy phase liquid experiences a higher magnitude of centrifugal force causing it to settle on the outer collecting ring while the lighter phase liquid is collected on the inner collecting ring. There are two main types of centrifuge: tube bowl centrifuge and disc bowl centrifuge. Both can be used to separate either solids from liquids or two liquids of different density. The tube bowl is simply a tube rotated about its axis; the liquids are separate as they flow along the centrifuge or the solids are thrown towards the wall. Overflow dams at the outlet end allow the two phases to be collected separately. For disc bowl centrifuge, the feed is admitted near the base and passes up through holes in the disc (which are actually inverted cones). The discs are about 5 mm apart. The solids do not have to travel far before hitting a disc and effectively being separated. Solids then continue to move outwards and are either removed manually or through nozzles on the periphery as concentrated slurry. Disc centrifuges range from 10 cm to 75 cm in diameter, spin speeds are in the 1000's or rpm range. 2.1

Operating Equations for Tube Bowl Centrifuge

The radial velocity, ur of the denser droplets or the particles is given by:

ur 

where  = rotational speed of centrifuge

r 2  1   2  d 2 18

(1)



The liquid layer thickness is small compared to the tube diameter, hence we can treat the radius r of rotation as a constant . This gives the distance traveled in the residence time tres as r 2 u r t res   1   2  d 2 t res 18

(2)

If the feed is homogeneous and the distance moved is equal to half the total thickness of the liquid layer, then half the particles with diameter d will be collected. In this case d = d50 (this only applies if the concentration of one phase in the other is very small), thus

u r t res 

r2  r1 2

(3)

where r1 = radii of the inner overflow dams r2 = radii of the outer overflow dams

In order to compare centrifuges of different design it is convenient to use a relationship which links the throughput with a term which accounts for the nature of the materials and one which accounts for the physical design of the machine. t res 

V Q

(4)

where V = volumetric holdup Q = volumetric throughput 2 d 50 r 2  1   2 V V Q  t res 9   r2  r1 

 2

g  1   2  d 502 V r 2  18 g  r1  r2 

 2u t 50 

where ut = terminal velocity under gravity of the d50 particle

(5)


 =


V r 2 g  r1  r2 

 is a characteristic of the centrifuge design only and is equal to the area of gravitational settler required to do the same duty. For scale up on the same duty

Q1 Q2  1  2

(6)

Values of  are given by manufacturers. 2.2

Operating Equations for Disc Bowl Centrifuge

2n  r23  r13  2  3 g tan  where r1 = inner radii of the disc stack r2 = outer radii of the disc stack n = number of spaces between the discs  = cone half-angle

3.0

EQUIPMENT – DISC BOWL CENTRIFUGE

The disc bowl centrifuge unit is designed to demonstrate the separation of a heavy phase liquid using the principle of centrifugal force. This is a bench top unit comprises of an epoxy coated frame, feed reservoir, collecting vessels, variable speed motor, feed system and control panel mounted on the stainless steel frame. The throughput of the feed system is at least 150 LPH. The speed of the motor can be varied from 8500 to 12000 rpm using an electronic speed controller.

(4)


Frequency Inverter


Mixing Tank

Disc rpm Meter Disc Bowl Main Power Switch ON/OFF

Liquid Collecting Outlet

AC Motor

Figure 3.1: Disc Bowl Centrifuge

Figure 3.2: Disc Bowl Centrifuge Setup Components


4.0

OPERATING PROCEDURES

4.1

Pre-experiment Procedures


1.

Read and understand the theory of centrifugation.

2.

Read and understand the equipment used in the experiment (disc bowl centrifuge).

3.

Read the safety precautions and chemical hazards before conducting the experiment.

4.

Prepare the following apparatus and materials needed for the experiment: 

Disc bowl centrifuge 1



2 L500 mL beaker  1 2



1 L beaker  4 3



Measuring Cylinder 500 mL  2 3



Weighting scale 1



Deionised water 2.5 L and cooking oil 2.5 L



Spatula 2



Waste bottle 5 L



Dish washing detergent 1 bottle


4.2


General Start-Up Procedures

1.

Place the apparatus on a level table.

2.

Connect the 3-pin plug to main power supply. Turn on the power supply and main power switch at the front of the control panel.

3.

Press the ‘Run’ green button on the frequency inverter. Test run the motor by adjusting the turning knob on the frequency inverter to around 10 Hz. Ensure the motor is running.

4.

Check the disc rpm meter and ensure that there is reading shown in the meter when the motor is running.

5.

The apparatus is ready to use if all the parts and components are working well.

4.3

Cleaning Procedures

1.

Remove the mixing tank, liquid collecting outlet tray and the disc bowl.

2.

Clean it with cleaning detergent and warm water.

3.

Wipe all the parts and dry them.

4.

Place all the parts back to it original position.

5.

Fill the mixing tank with 3 - 4 litres of hot water.

6.

Run the unit by setting the frequency to about 20 Hz.

7.

When all the water is drained out, switch off the machine.

5.0

SAFETY PRECAUTIONS

 Do not use the apparatus for solid-liquid separation.  Do not attempt to change the setting of the speed meter and frequency inverter.  No body part should be inserted to the belt pulley system when the motor is running.  Do not remove the liquid collecting outlet tray when the motor is running.  Be aware of the slipping hazard when handling cooking oil. Avoid oil leaking and spilling on the floor and working surfaces.  Wear gloves when cleaning the solution container.



6.0

EXPERIMENTS

6.1

Experiment 1A: Investigate the Effect of Frequency on Centrifuge Separation

Conduct the experiment with two different solutions at 4 different frequencies (max at 30 Hz).

Reminder: Mix both solutions and determine the density before separation. Allow the apparatus to run for 3 minutes then record down the speed of the bowl.

6.2

Experiment 1B: Investigate the Effect of Density on Centrifuge Separation

By using the same setup as Experiment 1A, repeat the experiment using different ratio (mixture with different density).

6.3

Experiment 2: Density Determination

Determine the density of the test fluid (take note of the unit used).

7.0

RESULTS ANALYSIS AND DISCUSSION

Discuss all your results. The questions below only serve as a guideline. Your discussion should not only limit to these questions. 1.

How does the speed of the bowl affect the separation efficiency?

2.

Can we separate two solutions with densities near to each other using a disc bowl centrifuge? Why?

3.

Is it possible to estimate the separation efficiency using the data you obtained in the experiment? If Yes, show your estimations. If No, explain why it is not possible.

4.

As the proportion of water to oil changes, explain how does this affects the separation efficiency.

Disc Bowl Centrifuge

Recommend Documents