Experiment # 01
Objective:
To calculate rate of absorption of CO2 in water from analysis of liquid solutions flowing down
absorption column.
Apparatus:
• Gas Absorption Column Apparatus
• CO2 Cylinder with Integral Pressure Regulator
• Pyrex Bottle
• Pipette
• Burette
• Flask
• Measuring Cylinder.
Figure 6: Schematic Diagram of Gas Absorption Column Apparatus
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Reagents:
• CO2 Gas
• Water
• Air
• Phenolphthalein
• 0.0277 Molar NaOH Solution
• MolarNaHCO3 Solution.
Procedure:
1. Fill the liquid reservoir tank at the base of the column to approximately three-quarters full
with (preferably) deionized water. Note the volume added [VT liters].
2. With gas flow control valves C2 and C3 closed, start the liquid pump and adjust the water
flow through the column to approx. 6 liters/minute on flowmeter F1 by adjusting flow
control valve C1.
3. Start the compressor and adjust control valve C2 to give an air flow of approx. 10% of full
scale on flowmeter F2.
4. Carefully open the pressure regulating valve on the carbon dioxide cylinder, and adjust valve
C3 to give a value on the flowmeter F3 approx., one half of the air flow F2 ensure the liquid
seal at the base of the absorption column is maintained by, if necessary adjustment of control
valve C4.
5. After 15 minutes of steady operation, take samples at 10 minute intervals from S4 and S5.
Take 150ml samples at known times in each case. Analyze the samples according to the
procedure detailed below.
Analysis of Carbon Dioxide Dissolved in Water:
Note: Water used for absorption should be deionized as presence of dissolved salts affect the
analysis described below. If tap water is used, no metal ions should be present in greater
quantities than 1.0 mg/liter and pH should be just alkaline: 7.1 to 7.8.
1. Phenolphthalein indicator prepared from carbon dioxide – free distilled water.
2. Standard 0.0277M NaOH solution, prepared by diluting 27.70ml of 1M NaOH standard
solution to1 liter with carbon dioxide free distilled water. Prepare fresh and protect from
carbon dioxide in the atmosphere by keeping in a stoppered Pyrex bottle.
2
3. Standard 0.01M NaHCO3 solution, prepared by dissolving approximately 0.1 gram of
anhydrous NaHCO3 in carbon dioxide free distilled water to 100ml.
4. Withdraw a sample of liquid S5 from the sump tank with the sampler provided, approximate
volume of 150ml, or from liquid outflow point S4.
5. Discharge the sample at the base of a 100 ml graduated cylinder, flicking the cylinder to
throw off excess liquid above the 100 ml mark.
6. Add 5-10 drops of phenolphthalein indicator solution if the sample turns red immediately, no
free C02 is present. If the sample remains colorless, titrate with standard NaOH solution. Stir
gently with a glass rod until a definite pink color persists for about 30 seconds. This color
change is the end point - note volume VB of NaOH solution added. For best results, use a
color comparison standard, prepared by adding the identical volume of phenolphthalein
solution to 100ml of sodium bicarbonate solution in a similar graduated cylinder.
Observations and Calculations:
Cd = Concentration of dissolved free carbon dioxide (gmol/liter). F = Volumetric Flowrate
(liters/sec).
VB = Volume of NaOH Solution Added in liquid analysis (ml).
Subscripts used:
T = Total
i = Inlet Conditions to Column
o = Outlet Conditions from Column
The amount of free CO2 in the water sample is calculated from:
Note: Solubility of CO2 in water is a strong function of temperature. And the accuracy of this
titrimetric method is approximately ±10%.
F1 =
liters/sec.
VT = Volume of Water in System (liters).
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From Sump Tank S5
From Liquid Outlet Sample Point
(Correspond to conditions at top of
(minutes)
S4
tower)
Time from Start
Cd in tank
VB
ml
[Cdi]
gmol/liter
Cd at outlet
VB
ml
[Cdo]
gmol/liter
10
20
30
40
50
60
4
Experiment # 02
Objective:
To examine the air pressure drop across the column as a function of air flow rate for different
water flow rates through the column.
• To plot the graph of column pressure drop against the air flow rate in a log – log graph.
• To obtain the pressure drop from the generalized correlation chart as in Appendix.
• To compare the experimental value and the correlated value.
Apparatus:
•
SOLTEQ-QVF Absorption Column BP751-B
Figure 7: The Packed Column Used in The Experiment with Raschig Rings as The Packings
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Theory:
Gas absorption is mass transfer operation where one or more species is removed from a gaseous
stream by dissolution in a liquid. The component that is extracted from the gaseous stream is
known as solute and the component that extracting the solute is known as solvent. Carrier gas is
the insoluble component present in the gas that is not absorbed by the solvent. The transfer is
based on the preferential solubility of solutes in the solvent (Gas Absorption And Desorption).
Packed towers are used for continuous countercurrent contacting of gas and liquid in
absorption.The mechanism in packed tower is the gas and liquid phases flows counter – currently
where they interact on the packings interface. The liquid flows in downward direction, over the
surface of the packing, whereas the gas flows through the space or voids of the packings in
upward direction. The gas flow is driven by pressure while the liquid flow is driven by the gravity
force. The gas undergoes pressure drop due to the liquid occupiedsome part of the open space and
voids of the packing. Thus, reducing the area available for the gas to flow. If the packing is dry
with no liquid feed, then maximum flow gas is available. The pressure drop increases as the
liquid flowrate into the tower increases.
High flux will resulting in flooding. This occurrence happen at the upper limit of the gas flow
rate called flooding velocity since the liquid is blown out with the gas at the flooding point. The
gas start to hinder the liquid flow at loading point where accumulation of liquid start appearing in
the packing. Low flux will resulting in channelling or weeping. There are two types of packings
types which is random and structured.
Figure 8: Typical Packed Tower Packings: (a) Raschig ring, (b) Lessing ring, (c) Berl
6
One of the oldest specially manufactured types of random packings are Raschig rings and still in
general use. (Separation Columns (Distillation, Absorption and Extraction)) They provide a large
surface area within the volume of the column for the interaction between liquid and gas. They
also enhance the contact time between liquid and gas. The generalized correlation for pressure
drops in packed column.
Figure 9: Generalized Correlation for Pressure Drop in Packed Columns
Procedure:
1. All the valves are ensured to be closed except for the ventilation valve, V13.
2. All the gas connections are checked to be properly fitted.
3. All the valve on the compressed air supply line is opened. The supply pressure is set to
between 2 to 3 bars by turning the regulator knob clockwise.
4. The shut-off valve on the CO2 gas cylinder is opened and the pressure is checked.
5. The power for the control panel is turned on.
6. The receiving vessel B2 is filled through the charge port with 50L of water by opening
valve V3 and V5. Then, valve V3 is closed.
7. Valves V9 and V10 is opened slightly. The flow of the water from vessel B1 through
pump P1 is observed. Pump P1 is switched on.
8. Valve V11 is slowly opened and adjusted to give a water flowrate of around 1L/min.
7
9. The water is allowed to enter the top of the column K1, flow down the column and
accumulated at the bottom until it overflows back to vessel B1.
10. The valve V11 is opened and adjusted to give a water flow rate of 1 L/min into column
K1.
11. The valve V1 is opened and adjusted to give and air flow rate of 20L/min into column
K1.
12. The liquid and gas flow in the column K1 is observed. The pressure drop across the
column at dPT-201 is recorded.
13. Steps 3 to 5 is repeated with different values of air flow rate, each time increasing by 20
L/min each time after two minutes while maintaining the same water flow rate.
14. Steps 3 to 6 is repeated with different values of water flow rate, each time increasing by 1
L/min by adjusting valve V11.
15. Pump, P1 is switched off.
16. Valves, V1, V2 and V12 is closed.
17. The valve on the compressed air supply line is closed and the supply pressure is
exhausted by turning the regulator knob counter clockwise all the way.
18. The shut-off valve on the CO2 gas cylinder is closed.
19. All the liquid in the column K1 is drained by opening valve V4 and V5.
20. All the liquid from the receiving vessels, B1 and B2 is drained by opening valves, V7 and
V8.
21. All the liquid from the pump P1 is drained by opening valve V10.
22. The power for the control panel is turned off.
Observations and Calculations:
Density of Air,
ρy = 1.175kg/m3
Density of Water,
ρX = 996kg/m3 (R. H. Perry, 1973)
Packing Factor,
FP = 900m3
Column Diameter,
D = 80mm
Water viscosity,
μX = 0.0008 kg/ms (Bingham, 1922)
*All properties are at T= 30°C
*All calculation is done via excel so the value may vary from calculator.
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9
10
Flow rate
Pressure Drop
(L/min)
(mBar)
Air
20
40
60
80
100
120
140
160
180
1.0
0
0
2
4
5
11
14
25
32 (F)
2.0
0
2
3
6
10
14
25
41(F)
F
3.0
1
2
5
10
18
36(F)
F
F
F
140
160
180
Water
Flow rate
Pressure Drop
(L/min)
(mm H2O/m)
Air
20
40
60
80
100
1.0
0.00
0.00
25.49
50.99
63.73
140.21 178.45 318.66
2.0
0.00
25.49
38.24
76.48
127.46
178.45 318.66
3.0
12.75
25.49
63.73
127.46 229.44
Water
120
458.87
(F)
Flow rate
Theoretical Pressure Drop
(L/min)
(in H2O/ft)
Air
Water
20
40
60
80
100
120
522.60
(F)
407.89
(F)
F
F
F
F
140
160
180
F
F
1.0
0.0000 0.0906 0.2000 0.2917 0.4205
2.0
0.0750 0.2500 0.3958 0.5000 1.0000
F
F
F
F
3.0
0.1600 0.4318 0.7500 1.5000
F
F
F
F
F
0.7500 1.1667
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Flow
Theoretical Pressure Drop
rate
(mm H2O/m)
(L/min)
Air
Water
20
40
60
1.0
0.0000
2.0
6.2483 20.8275 32.9741
3.0
7.5479 16.6620
80
100
120
F
F
41.6550 83.3100
F
Flow rate
Log Pressure Drop
(L/min)
(mm H2O/m)
Water
1.3010 1.6021 1.7782 1.9031 2.0000
1.0
-
2.0
-
3.0
-
1.4064 1.7074 1.8044
1.4064 1.5825 1.8835 2.1054
1.1054 1.4064 1.8044 2.1054 2.3607
F
F
F
F
F
F
F
F
2.0792 2.1461 2.2041 2.2553
2.1468 2.2515 2.5033
2.2515 2.5033
2.6617
(F)
Flow rate
Log Theoretical Pressure Drop
(L/min)
(mm H2O/m)
Air
F
2.7182
(F)
F
1.3010
1.6021 1.7782 1.9031 2.0000
2.0792 2.1461 2.2041
1.0
-
0.8778 1.2217 1.3856 1.5445
1.7958 1.9877
2.0
0.7958
1.3186 1.5182 1.6197 1.9207
F
3.0
1.1248
1.5560 1.7958 2.0968
F
Water
160 180
24.3015 35.0319 62.4825 97.1978
13.3296 35.9733 62.4825 124.9650
Air
140
F
2.6105
(F)
F
F
2.2553
F
F
F
F
F
F
F
F
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Air
Gas
Capacity
Liquid Mass Velocity
Flow Parameter
Flowrat
Mass
Paramete
(𝑮𝒙) 𝐤𝐠/𝐦𝟐𝐬
(x-axis)
e (𝐕𝐲)
Velocity
r(y-axis)
LPM
(𝑮𝐲)
1
2
3
1
2
3
𝐤𝐠/𝐦𝟐𝐬
LPM
LPM
LPM
LPM
LPM
LPM
20
0.0779
0.0011
3.3025 6.6049 9.9074 1.4566 2.9132 4.3698
40
0.1558
0.0046
3.3025 6.6049 9.9074 0.7283 1.4566 2.1849
60
0.2338
0.0103
3.3025 6.6049 9.9074 0.4855 0.9711 1.4566
80
0.3117
0.0184
3.3025 6.6049 9.9074 0.3641 0.7283 1.0924
100
0.3896
0.0287
3.3025 6.6049 9.9074 0.2913 0.5826 0.8740
120
0.4675
0.0414
3.3025 6.6049 9.9074 0.2428 0.4855 0.7283
140
0.5454
0.0563
3.3025 6.6049 9.9074 0.2081 0.4162 0.6243
160
0.6234
0.0735
3.3025 6.6049 9.9074 0.1821 0.3641 0.5462
180
0.7013
0.0931
3.3025 6.6049 9.9074 0.1618 0.3237 0.4855
Water Flow
Theoretical Flooding
Experimental Flooding
Percentage Error
Rate
Air Flow Rate
Air Flow Rate
(%)
(L/min)
(L/min)
(L/min)
1
160
180
12.50
2
120
160
33.33
3
100
120
20.00
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