NO. TITLE ALLOCATED MARKS (%) MARKS
1 ABSTRACT / SUMMARY 5
2 INTRODUCTION 5
3 AIMS 5
4 THEORY 5
5 APPARATUS 5
6 METHODOLOGY / PROCEDURE 10
7 RESULTS 10
8 CALCULATIONS 10
9 DISCUSSION 20
10 CONCLUSION 10
11 RECOMMENDATIONS 5
12 REFERENCE 5
13 APPENDIX 5
TOTAL MARKS 100
REMARKS:
CHECKED BY:
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DATE:
NAME : AHMAD TARMIZI BIN ABD WAHAB STUDENT NO : 2008293356 GROUP : 7 EXPERIMENT : GAS ABSORPTION DATE PERFORMED : 27/07/2010 SEMESTER : 5 PROGRAMME / CODE : DIPLOMA IN CHEMICAL ENGINEERING / EH110 SUBMIT TO : PUAN RABIATUL ADAWIYAH ABDOL AZIZ
2
ABSTRACT / SUMMARY
The packed column is used in industry to produce mass transfer, i.e. gas absorption,
distillation, and liquid extraction while the packed bed represents a workhorse configuration
for a wide variety of mass transfer operations in the chemical process industry. The flow
will be counter-current: gas will move upwards and liquid will move downwards.
This experiment is intended to study and identify the loading and the flooding point
of the column. We will also observe the pressure drop as a function of gas and liquid mass
velocities (m3/hour) using flexi glass column packed with Raschig Ring. Air will be use as the
function of gas while water will be the function of liquid.
3
INTRODUCTION
The packed bed represents a workhorse configuration for a wide variety of mass
transfer operations in the chemical process industry, such as distillation, absorption and
liquid-liquid extraction. The packed bed configuration facilitates the intimate contact
(mixing) of fluids with mismatched surface area for phase contact that packing offers
increases the amount of momentum transfer, manifested by an increased vapour-phase
pressure drop through the column.
4
AIMS
The objective of this laboratory experiment is to determine the Loading and Flooding
Points in the column and to model the pressure drop as a function of gas (air) and liquid
(water) mass velocities (m3/hour) using flexi glass column packed with Raschig Ring.
5
THEORY
Absorption is a mass transfer operation in which a vapour solute A in a gas mixture is absorbed by means of liquid in which the solute is more or less soluble. The gas mixture (Gas Phase) consists of mainly of an inert gas and the solute. The liquid (Liquid Phase) is primarily immiscible in the gas phase; its vaporization into the gas phase is relatively small.
Redistribution of soluble gas as solute in the liquid may involve molecular diffusion in a stagnant medium, molecular diffusion in a smoothly flowing medium (laminar), molecular diffusion and mixing in a turbulent flowing medium or mass transfer between phases.
Total amount of material transferred increased with time allowed for transfer, area through, which transfer can occur and the driving force (e.g. concentration difference).
KA (CA1 CA2)
The device that is designed to increase the interfacial area for the two phases flow through packing imparts good vapour-liquid contact when a particular type is placed together in numbers, without causing excessive pressure-drop across a packed section.
Properties of packing include low weight per unit volume, large active surface per unit volume, large free cross section and large free volume.
Large free cross section affects the frictional drop through the tower and therefore the power that is required to circulate the gas. Small free cross section means a high velocity for a given throughput of gas, and above certain limiting velocities, there is a tendency to blow the liquid out of the tower. Large free volume is to allow for reaction in the gas phase, this factor may be importance.
6
APPARATUS & MATERIAL
1) Gas Liquid Absorption Column [Figure 1] 2) Beaker 0-100 ml
[Figure 1 Gas Liquid Absorption Column]
7
METHODOLOGY / PROCEDURE
The manometer U-tube is filled with water and the value was arranged according to
U-tube arrangement. The values of the operating management were set before the
operation is started. Before the column is safe to be used, all the valves should be checked
carefully (closed). Valve VR-3 and VR-4 is opened at liquid flow rate at 20 m3/hour. (Note:
The level of the liquid returning to the water reservoir must always be higher than the
bottom of the reservoir. This is to avoid air being trapped in line. Adjust valve VR-4
accordingly to avoid this phenomena). Valve VR-1 is opened and the airflow is set at rate to
be 10 m3/hour. Wait for 2 minutes and make sure the flow rate of air and water is constant
throughout all the time. The pressure drop (P) mmH2O in the monotube is read. The gas
flow rate was increased by adding an extra 5 m3/hour to the column. Wait for 2 minute and
the pressure drop is to be read again. Part (4) is repeated until reach the Flooding Point. The
curve of Ln (V) versus Ln (P/m packing) is plotted. Step 2 to 6 is repeated with different
kind of liquid flow rate.
Refer Appendix for the Manometer Calibration to see the U-tube arrangement and
Operation arrangement.
8
RESULTS
Liquid Flow, L (m3/hour)
20
Gas Flow, V (m3/hour)
Monotube Low mm H2O
Monotube High mm H2O
(P) mm H2O
Ln (V) Ln (P/m packing)
10 20.1 19.9 0.2 10 0.025
15 20.2 19.8 0.3 15 0.0375
20 20.3 19.7 0.4 20 0.05
25 20.4 19.6 0.8 25 0.1
30 20.7 19.3 1.4 30 0.175
35 20.7 19.3 1.4 35 0.175
40 21.3 18.7 2.6 40 0.325
45 18.6 18.6 2.8 45 0.35
Liquid Flow, L (m3/hour)
30
Gas Flow, V (m3/hour)
Monotube Low mm H2O
Monotube High mm H2O
(P) mm H2O
Ln (V) Ln (P/m packing)
10 18.0 22.0 4.0 10 0.5
15 19.1 21.9 2.8 15 0.35
20 18.3 21.7 3.4 20 0.425
25 18.3 21.7 3.4 25 0.425
30 18.4 21.6 3.2 30 0.4
35 18.4 21.6 3.2 35 0.4
40 18.4 21.6 3.2 40 0.4
45 18.7 21.3 2.6 45 0.325
Liquid Flow, L (m3/hour)
40
Gas Flow, V (m3/hour)
Monotube Low mm H2O
Monotube High mm H2O
(P) mm H2O
Ln (V) Ln (P/m packing)
10 19.1 19.5 0.4 10 0.05
15 24.0 20.0 4.0 15 0.5
20 30.0 10.0 20.0 20 2.5
9
0
5
10
15
20
25
30
35
40
45
50
0.025 0.0375 0.05 0.1 0.175 0.175 0.325 0.35
Ln (
V)
LN (P/m packing)
Ln (V) vs. LN (P/m packing) for 20 m3/hour
0
5
10
15
20
25
30
35
40
45
50
0.5 0.35 0.425 0.425 0.4 0.4 0.4 0.325
Ln (
V)
LN (P/m packing)
Ln (V) vs. LN (P/m packing) for 30 m3/hour
10
0
5
10
15
20
25
0.05 0.5 2.5
Ln (
V)
LN (P/m packing)
Ln (V) vs. LN (P/m packing) for 40 m3/hour
11
SAMPLE CALCULATIONS
To calculate LN (P/m packing) at liquid flow 20 m3/hour and gas flow at 10 m3/hour:
P = P2-P1
= 20.1 19.9
= 0.2 mm H2O
0.2 mm x
= 0.0002m.
Packing = 8 mm glass Raschig Rings change to meter packing
8 mm x
= 0.008m.
Thus,
LN =
= 0.025
12
DISCUSSION
In this experiment we need to determine the loading and flooding points in the
column. Furthermore we need to model the pressure drop as a function of gas (air) and
liquid (water) mass velocities (m3/hour) using flexi glass column packed with Raschig Ring.
Based on the result, the point which the water starts to load into the column is at 20
m3/hour and gas flow at 10 m3/hour(TABLE 1). In contrast, the water starts to flood over the
column at certain flow rate. This is the flooding point for the column which is at 40 m3/hour
and gas flow at 20 m3/hour(TABLE 3).
Based on manometer, we can observe that as the mass velocities of air and water
increase, the pressure drop in manometer will also increase. Furthermore, from the graph
we can say that the flow rate of gas Ln in directly proportional to LN (P/m packing).
There are precautions that have to be concerned. Firstly, the gas-liquids absorption
column should be check carefully to avoid any accident from occurring. Next, we need to
ensure that all the valves are free from air bubble so that the reading at the manometer is
free from parallax error. In addition, the manometer calibration is in the right order. Last but
certainly not least, the level of water at the bottom VR 4 should always be adjusted. This is
to avoid air from trapped in the line.
13
CONCLUSION
As for the conclusion, the loading point of the gas-liquid absorption column, by using
raschig rings which at liquid flow of 20 m3/hour and gas flow at 10 m3/hour, while flooding
point is at of 20 m3/hour and gas flow at 10 m3/hour. Furthermore, we manage to visualize
pressure drop as a function of gas (air) and liquid (water) mass velocities (m3/hour) using
flexi glass column packed with Raschig Ring.
14
RECOMMENDATIONS
Do not proceed with different phases of the experiment until you understand how each
piece of apparatus works. Do not be afraid to ask for help, for this experiment is rather
complex and requires attention to detail to get good results.
When starting up the system, always use low initial air and water velocities. Be sure the
recycle valve to the sump pump is always at least partially open to prevent build-up of liquid
and flooding. An extension has been added to the top of the column to help prevent spillage
of caustic.
The gas cylinder regulator handle should be loose (easy to turn) before opening the tank.
See safety instructions in the auxiliary section notebook. Open the tank valve slowly.
Remember to plug in the gas heater 5 minutes before turning on the gas. Turn off the gas at
the end of the day, or else you will not be able to operate during the next lab period!!
Relieve the spring pressure on the regulator diaphragm by backing out the regulator handle
to its original loose position.
15
REFERENCE
Online Journal
1. J. H. Perry, Ed., Chemical Engineer's Handbook, 5th or 6th ed., p. 14.2 - 14.40, McGraw-Hill Publishing Co., New York, NY, 1973.
2. W. L. McCabe and J. C. Smith, Unit Operations of Chemical Engineering, 4th ed., p. 617-631, McGraw-Hill Publishing Co., New York, NY., 1985.
3. http://en.wikipedia.org/wiki/absorption.com
16
APPENDIX