NAME STUDENT NO GROUP EXPERIMENT DATE PERFORMED SEMESTER PROGRAMME / CODE SUBMIT TO NO. 1 2 3 4 5 6 7 8 9 10 11 12 13
AHMAD TARMIZI BIN ABD WAHAB 2008293356 7 GAS ABSORPTION 27/07/2010 5 DIPLOMA IN CHEMICAL ENGINEERING / EH110 PUAN RABIATUL ADAWIYAH ABDOL AZIZ
TITLE ABSTRACT / SUMMARY INTRODUCTION AIMS THEORY APPARATUS METHODOLOGY / PROCEDURE RESULTS CALCULATIONS DISCUSSION CONCLUSION RECOMMENDATIONS REFERENCE APPENDIX TOTAL MARKS
REMARKS: CHECKED BY:
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ALLOCATED MARKS (%) 5 5 5 5 5 10 10 10 20 10 5 5 5 100
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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.
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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.
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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.
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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.
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APPARATUS & MATERIAL 1) Gas – Liquid Absorption Column – [Figure 1] 2) Beaker 0-100 ml
[Figure 1 – Gas – Liquid Absorption Column]
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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 (ΔP) 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 (ΔP/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.
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RESULTS Liquid Flow, L (m3/hour) Gas Flow, Monotube V Low 3 (m /hour) mm H2O 10 20.1 15 20.2 20 20.3 25 20.4 30 20.7 35 20.7 40 21.3 45 18.6
Liquid Flow, L (m3/hour) Gas Flow, Monotube V Low 3 (m /hour) mm H2O 10 18.0 15 19.1 20 18.3 25 18.3 30 18.4 35 18.4 40 18.4 45 18.7
Liquid Flow, L (m3/hour) Gas Flow, Monotube V Low (m3/hour) mm H2O 10 19.1 15 24.0 20 30.0
20 Monotube High mm H2O 19.9 19.8 19.7 19.6 19.3 19.3 18.7 18.6
(ΔP) mm H2O 0.2 0.3 0.4 0.8 1.4 1.4 2.6 2.8
Ln (V)
10 15 20 25 30 35 40 45
Ln (ΔP/m packing) 0.025 0.0375 0.05 0.1 0.175 0.175 0.325 0.35
30 Monotube High mm H2O 22.0 21.9 21.7 21.7 21.6 21.6 21.6 21.3
(ΔP) mm H2O 4.0 2.8 3.4 3.4 3.2 3.2 3.2 2.6
Ln (V)
10 15 20 25 30 35 40 45
Ln (ΔP/m packing) 0.5 0.35 0.425 0.425 0.4 0.4 0.4 0.325
40 Monotube High mm H2O 19.5 20.0 10.0
(ΔP) mm H2O 0.4 4.0 20.0
Ln (V)
10 15 20
Ln (ΔP/m packing) 0.05 0.5 2.5
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Ln (V) vs. LN (ΔP/m packing) for 20 m3/hour 50 45 40
Ln (V)
35 30 25 20 15 10 5 0 0.025
0.0375
0.05
0.1
0.175
0.175
0.325
0.35
LN (ΔP/m packing)
Ln (V) vs. LN (ΔP/m packing) for 30 m3/hour 50 45 40
Ln (V)
35 30 25 20 15 10 5 0 0.5
0.35
0.425
0.425
0.4
0.4
0.4
0.325
LN (ΔP/m packing)
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Ln (V) vs. LN (ΔP/m packing) for 40 m3/hour 25
Ln (V)
20 15 10 5 0 0.05
0.5
2.5
LN (ΔP/m packing)
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SAMPLE CALCULATIONS To calculate LN (ΔP/m packing) at liquid flow 20 m3/hour and gas flow at 10 m3/hour: ΔP = 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
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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 m /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 m 3/hour and gas flow at 20 m3/hour(TABLE 3). 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 (ΔP/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.
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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 (m 3/hour) using flexi glass column packed with Raschig Ring.
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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.
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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
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APPENDIX
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