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INTRODUCTION : Gas absorption (also known as scrubbing) is an operation in which a gas mixture is contacted with a liquid for the purpose of preferentially dissolving one or more components of the gas mixture and to provide a solution of them in the liquid. Therefore we can see that there is a mass transfer of the component of the gas from the gas phase to the liquid phase. The solute so transferred is said to be absorbed by the liquid. In gas desorption (or stripping), the mass transfer is in the opposite direction, from the liquid phase to the gas phase. The principles for both systems are the same. We will focus on the analysis for gas absorption, for the simple case whereby only one component of the gas solute is being absorbed. The other components of the gas are assumed to be non-soluble in the liquid (the other gas components are inert components), and the liquid is non-volatile, which means that there is no transfer of molecules from the liquid to the gas phase. In addition, we assume there is no chemical reaction in the system and that it is operating at isothermal condition. The process of gas absorption thus involves the diffusion of solute from the gas phase through a stagnant or non-diffusing liquid.
A common instrument used in gas absorption or stripping is a packed tower. A packed tower consists of the following: a cylindrical tube with inert packing material; a gas inlet at the bottom with an exit out the top; and a liquid inlet at the top with its exit out the bottom . In an ideal operation the liquid will descend through the packed column and distribute uniformly over the packing surface in films. The gas will enter the column from below the packed section and rise upward countercurrent to the liquid flow through the small spaces between the packing material. The large amount of intimate contact between the liquid and gas streams allows for an efficient transfer of mass.
OBJECTIVES : 1. To examine the air pressure across the column as a function of air flow rate for different water flow rates down the column.
PROCEDURES : 1. The sump was filled to three-quarters full with tap water. Valves V1, V2, and V3 were set as shown on the diagram so that differential pressures in the top and bottom sections of the column were indicated on the two water manometer. 2. The water pump was switched on and C1 was set to give a flow rate of said 3 litres/minutes down the column. 3. After about 30 second close C1, the pump was switched off and the column was allowed to drain for 5 minutes. 4. The air pressure differential across the wet column was measured as a function of the air flow rate. 5. The air pressure differential across the column was measured as a function of the air flow rate for different water flow rates up to said 5 litres/minute, the appearance of the column was noted at each setting.
RESULT AND DATA : Pressure differential (mm water) Air flow (l/min)
20
40
60
80
100
120
140
160
180
1.0
1
2
5
8
10
16
22
27
32
2.0
4
2
4
8
13
18
24
32
42
3.0
2
3
6
12
17
24
32
42
56
4.0
2
4
5
15
19
24
39
55
75
5.0
9
10
11
19
24
66
6.0
5
11
26
28
32
72
7.0
1
3
8
27
105
8.0
22
25
55
148
9.0
10
30
110
Water Flow (l/min)
10.0
119
CALCULATION : By using theory ∆P = 𝝆 * g * ∆h ∆P = differential pressure. (g/cm.s2) 𝜌 = density constant. (1g/cm2) g = gravity constant. (980 cm/s2) ∆h= height (cm H2O)
Data of flow (air + water) and differential pressure at 1 (L/min) of flow water Wet column Air Flow Rate L/Min
20
40
60
80
100
120
140
160
180
Water Flow Rate L/Min
1
1
1
1
1
1
1
1
1
∆P(cm H2O)
0.1
0.2
0.5
0.8
1.0
1.6
2.2
2.7
3.2
∆P (g/cm.s2)
98
196
490
784
980
1568
2156
2646
3136
Log Air Flow Rate (L/Min)
1.30103 1.60206 1.77815 1.90309 2.00000 2.07918 2.14613 2.20412
2.25527
Log ∆P (g/cm.s2)
1.99123 2.29226 2.69020 2.89432 2.99123 3.19535 3.33365 3.42259
3.49638
Graph of log pressure differential VS Log air flow 2.5
log air flow
2 1.5 Log Air Flow Rate
1
Linear (Log Air Flow Rate) 0.5 0 0
1
2 log pressure differential
3
4
Data of flow (air + water) and differential pressure at 2 (L/min) of flow water Wet column Air Flow Rate L/Min
20
40
60
80
100
120
140
160
180
Water Flow Rate L/Min
2
2
2
2
2
2
2
2
2
∆P(cm H2O)
0.4
0.2
0.4
0.8
1.3
1.8
2.4
3.2
4.2
∆P (g/cm.s2)
392
196
392
784
1274
1764
2352
3136
4116
Log Air Flow Rate (L/Min)
1.30103 1.60206 1.77815 1.90309 2.00000 2.07918 2.14613 2.20412 2.25527
Log ∆P (g/cm.s2)
2.59329 2.29226 2.59329 2.89432 3.10517 3.24650 3.37144 3.49638 3.61448
Graph of log pressure differential VS Log air flow
2.5
2
log air flow
1.5
Log Air Flow Rate 1
Linear (Log Air Flow Rate)
0.5
0 0
1
2 log pressure differential
3
4
Data of flow (air + water) and differential pressure at 3 (L/min) of flow water Wet column Air Flow Rate L/Min
20
40
60
80
100
120
140
160
180
Water Flow Rate L/Min
3
3
3
3
3
3
3
3
3
∆P(cmH2O)
0.2
0.3
0.6
1.2
1.7
2.4
3.2
4.2
5.6
∆P(g/cm.s2)
196
294
588
1176
1666
2352
3136
4116
5488
Log Air Flow Rate (L/Min)
1.30103 1.60206 1.77815 1.90309 2.00000 2.07918 2.14613 2.20412
2.25527
Log ∆P (g/cm.s2)
2.29226 2.46835 2.76938 3.07041 3.22167 3.37144 3.49638 3.61448
3.73941
Graph of log pressure differential VS Log air flow 2.5
log air flow
2 1.5 Log Air Flow Rate
1
Linear (Log Air Flow Rate) 0.5 0 0
1
2 log pressure differential
3
4
Data of flow (air + water) and differential pressure at 4 (L/min) of flow water Wet column Air Flow Rate L/Min
20
40
60
80
100
120
140
160
180
Water Flow Rate L/Min
4
4
4
4
4
4
4
4
4
∆P(cm H2O)
0.2
0.4
0.5
1.5
1.9
2.4
3.9
5.5
7.5
∆P(g/cm.s2)
196
392
490
1470
1862
2352
3822
5390
7350
Log Air Flow Rate (L/Min)
1.30103 1.60206 1.77815 1.90309 2.00000 2.07918 2.14613 2.20412
2.25527
Log ∆P (g/cm.s2)
2.29226 2.59329 2.69020 3.16732 3.26998 3.37144 3.58229 3.73159
3.86629
Graph of log pressure differential VS Log air flow 2.5
log air flow
2 1.5 Log Air Flow Rate
1
Linear (Log Air Flow Rate) 0.5 0 0
1
2
3
log pressure differential
4
5
Data of flow (air + water) and differential pressure at 5 (L/min) of flow water Wet column Air Flow Rate L/Min
20
40
60
80
100
120
140
160
180
Water Flow Rate L/Min
5
5
5
5
5
5
5
5
5
∆P(cm H2O)
0.9
1.0
1.1
1.9
2.4
6.6
∆P(g/cm.s2)
882
980
1078
1862
2352
6468
Log Air Flow Rate (L/Min)
1.30103 1.60206 1.77815 1.90309 2.00000 2.07918 2.14613 2.20412
Log ∆P (g/cm.s2)
2.94547 2.99123 3.03262 3.26998 3.37144 3.81077
2.25527
Graph of log pressure differential VS Log air flow 2.5
log air flow
2 1.5 Log Air Flow Rate
1
Linear (Log Air Flow Rate) 0.5 0 0
1
2
3
log pressure differential
4
5
Data of flow (air + water) and differential pressure at 6 (L/min) of flow water Wet column Air Flow Rate L/Min
20
40
60
80
100
120
140
160
180
Water Flow Rate L/Min
6
6
6
6
6
6
6
6
6
∆P(cm H2O)
0.5
1.1
2.6
2.8
3.2
7.2
11.9
∆P(g/cm.s2)
490
1078
2548
2744
3136
7056
11662
Log Air Flow Rate (L/Min)
1.30103 1.60206 1.77815 1.90309 2.00000 2.07918 2.14613 2.20412
Log ∆P (g/cm.s2)
2.69020 3.03262 3.40620 3.43838 3.49638 3.84856 4.06677
Graph of log pressure differential VS Log air flow 2.5
log air flow
2 1.5 Log Air Flow Rate
1
Linear (Log Air Flow Rate) 0.5 0 0
1
2
3
log pressure differential
4
5
2.25527
Data of flow (air + water) and differential pressure at 7 (L/min) of flow water Wet column Air Flow Rate L/Min
20
40
60
80
100
120
140
160
180
Water Flow Rate L/Min
7
7
7
7
7
7
7
7
7
∆P(cm H2O)
0.1
0.3
0.8
2.7
10.5
∆P(g/cm.s2)
98
294
784
2646
10290
Log Air Flow Rate (L/Min)
1.30103 1.60206 1.77815 1.90309 2.00000 2.07918 2.14613 2.20412
Log ∆P (g/cm.s2)
1.99123 2.46835 2.89432 3.42259 4.01242
2.25527
Graph of log pressure differential VS Log air flow 2.5
log air flow
2 1.5 Log Air Flow Rate
1
Linear (Log Air Flow Rate) 0.5 0 0
1
2
3
log pressure differential
4
5
Data of flow (air + water) and differential pressure at 8 (L/min) of flow water Wet column Air Flow Rate L/Min
20
40
60
80
100
120
140
160
180
Water Flow Rate L/Min
8
8
8
8
8
8
8
8
8
∆P(cm H2O)
2.2
2.5
5.5
14.8
∆P(g/cm.s2)
2156
2450
5390
14504
Log Air Flow Rate (L/Min)
1.30103 1.60206 1.77815 1.90309 2.00000 2.07918 2.14613 2.20412
Log ∆P (g/cm.s2)
3.33365 3.38917 3.73159 4.16149
2.25527
Graph of log pressure differential VS Log air flow 2.5
log air flow
2 1.5 Log Air Flow Rate
1
Linear (Log Air Flow Rate) 0.5 0 0
1
2
3
log pressure differential
4
5
Data of flow (air + water) and differential pressure at 9 (L/min) of flow water Wet column Air Flow Rate L/Min
20
40
60
80
100
120
140
160
Water Flow Rate L/Min
9
9
9
9
9
9
9
9
∆P(cm H2O)
1.0
3.0
11.0
∆P(g/cm.s2)
980
2940
10780
180 9
Log Air Flow Rate (L/Min)
1.30103 1.60206 1.77815 1.90309 2.00000 2.07918 2.14613 2.20412 2.25527
Log ∆P (g/cm.s2)
2.99123 3.46835 4.03262
log air flow
Graph of log pressure differential VS Log air flow 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0
Log Air Flow Rate Linear (Log Air Flow Rate)
0
1
2
3
log pressure differential
4
5
DISCUSSION : From the theory, at constant liquid rate, gas pressure drop increases with gas velocity while at constant gas velocity, the gas pressure drop is higher at larger liquid rate.Each liquid rate has its own loading and flooding points and at higher liquid rate, the loading and flooding points occur at lower gas pressure drop. In this experiment, the air pressure differential across wet column (gas absorption packed column) need to be find in order to know the relationship between pressure differential and air flow rate. the total pressure differential should be plotted as a function of air flow rate on log-log graph paper for each water flow rate has been plotted. From the graphs, the total pressure differential increased as the air flow rate increased. Other than that, the pressure difference increased when the air flow and water flow increased and the flooding point decreases as the air flow increases (the high water flow the gives less flooding point). Loading point of a column is when the gas velocity is high enough to restrict the flow of liquid. After this point, the pressure drops at a much faster rate till another point, known as the flooding point, when all the liquid is carried away by the gas. It marks the start of entrainment regime in columns, too high a gas velocity will lead to a condition known as flooding whereby the liquid filled the entire column and the operation became difficult to carry out. High pressure will crush and damage the packings in the column.
CONCLUSION : In conclusion, the air pressure across the column as a function of air flow rate for different water flow rates down the column were examined.
The pressure difference increased when the air flow and
water flow increased. The flooding point decreases as the air flow increases (the high water flow the gives less flooding point). Therefore, the slope of the flooding curve is decreasing with the increasing of the water flow rate.
REFERENCES :
http://www.separationprocesses.com/Absorption/GA_Chp04a.htm
www.separationprocesses.com/Absorption/GA_Chp03.htm
ttps://www.sciencedirect.com/topics/chemical-engineering/gas-absorption
A common instrument used in gas absorption or stripping is a packed tower. A packed tower consists of the following: a cylindrical tube with inert packing material; a gas inlet at the bottom with an exit out the top; and a liquid inlet at the top with its exit out the bottom . In an ideal operation the liquid will descend through the packed column and distribute uniformly over the packing surface in films. The gas will enter the column from below the packed section and rise upward countercurrent to the liquid flow through the small spaces between the packing material. The large amount of intimate contact between the liquid and gas streams allows for an efficient transfer of mass.
OBJECTIVES : 1. To examine the air pressure across the column as a function of air flow rate for different water flow rates down the column.
PROCEDURES : 1. The sump was filled to three-quarters full with tap water. Valves V1, V2, and V3 were set as shown on the diagram so that differential pressures in the top and bottom sections of the column were indicated on the two water manometer. 2. The water pump was switched on and C1 was set to give a flow rate of said 3 litres/minutes down the column. 3. After about 30 second close C1, the pump was switched off and the column was allowed to drain for 5 minutes. 4. The air pressure differential across the wet column was measured as a function of the air flow rate. 5. The air pressure differential across the column was measured as a function of the air flow rate for different water flow rates up to said 5 litres/minute, the appearance of the column was noted at each setting.
RESULT AND DATA : Pressure differential (mm water) Air flow (l/min)
20
40
60
80
100
120
140
160
180
1.0
1
2
5
8
10
16
22
27
32
2.0
4
2
4
8
13
18
24
32
42
3.0
2
3
6
12
17
24
32
42
56
4.0
2
4
5
15
19
24
39
55
75
5.0
9
10
11
19
24
66
6.0
5
11
26
28
32
72
7.0
1
3
8
27
105
8.0
22
25
55
148
9.0
10
30
110
Water Flow (l/min)
10.0
119
CALCULATION : By using theory ∆P = 𝝆 * g * ∆h ∆P = differential pressure. (g/cm.s2) 𝜌 = density constant. (1g/cm2) g = gravity constant. (980 cm/s2) ∆h= height (cm H2O)
Data of flow (air + water) and differential pressure at 1 (L/min) of flow water Wet column Air Flow Rate L/Min
20
40
60
80
100
120
140
160
180
Water Flow Rate L/Min
1
1
1
1
1
1
1
1
1
∆P(cm H2O)
0.1
0.2
0.5
0.8
1.0
1.6
2.2
2.7
3.2
∆P (g/cm.s2)
98
196
490
784
980
1568
2156
2646
3136
Log Air Flow Rate (L/Min)
1.30103 1.60206 1.77815 1.90309 2.00000 2.07918 2.14613 2.20412
2.25527
Log ∆P (g/cm.s2)
1.99123 2.29226 2.69020 2.89432 2.99123 3.19535 3.33365 3.42259
3.49638
Graph of log pressure differential VS Log air flow 2.5
log air flow
2 1.5 Log Air Flow Rate
1
Linear (Log Air Flow Rate) 0.5 0 0
1
2 log pressure differential
3
4
Data of flow (air + water) and differential pressure at 2 (L/min) of flow water Wet column Air Flow Rate L/Min
20
40
60
80
100
120
140
160
180
Water Flow Rate L/Min
2
2
2
2
2
2
2
2
2
∆P(cm H2O)
0.4
0.2
0.4
0.8
1.3
1.8
2.4
3.2
4.2
∆P (g/cm.s2)
392
196
392
784
1274
1764
2352
3136
4116
Log Air Flow Rate (L/Min)
1.30103 1.60206 1.77815 1.90309 2.00000 2.07918 2.14613 2.20412 2.25527
Log ∆P (g/cm.s2)
2.59329 2.29226 2.59329 2.89432 3.10517 3.24650 3.37144 3.49638 3.61448
Graph of log pressure differential VS Log air flow
2.5
2
log air flow
1.5
Log Air Flow Rate 1
Linear (Log Air Flow Rate)
0.5
0 0
1
2 log pressure differential
3
4
Data of flow (air + water) and differential pressure at 3 (L/min) of flow water Wet column Air Flow Rate L/Min
20
40
60
80
100
120
140
160
180
Water Flow Rate L/Min
3
3
3
3
3
3
3
3
3
∆P(cmH2O)
0.2
0.3
0.6
1.2
1.7
2.4
3.2
4.2
5.6
∆P(g/cm.s2)
196
294
588
1176
1666
2352
3136
4116
5488
Log Air Flow Rate (L/Min)
1.30103 1.60206 1.77815 1.90309 2.00000 2.07918 2.14613 2.20412
2.25527
Log ∆P (g/cm.s2)
2.29226 2.46835 2.76938 3.07041 3.22167 3.37144 3.49638 3.61448
3.73941
Graph of log pressure differential VS Log air flow 2.5
log air flow
2 1.5 Log Air Flow Rate
1
Linear (Log Air Flow Rate) 0.5 0 0
1
2 log pressure differential
3
4
Data of flow (air + water) and differential pressure at 4 (L/min) of flow water Wet column Air Flow Rate L/Min
20
40
60
80
100
120
140
160
180
Water Flow Rate L/Min
4
4
4
4
4
4
4
4
4
∆P(cm H2O)
0.2
0.4
0.5
1.5
1.9
2.4
3.9
5.5
7.5
∆P(g/cm.s2)
196
392
490
1470
1862
2352
3822
5390
7350
Log Air Flow Rate (L/Min)
1.30103 1.60206 1.77815 1.90309 2.00000 2.07918 2.14613 2.20412
2.25527
Log ∆P (g/cm.s2)
2.29226 2.59329 2.69020 3.16732 3.26998 3.37144 3.58229 3.73159
3.86629
Graph of log pressure differential VS Log air flow 2.5
log air flow
2 1.5 Log Air Flow Rate
1
Linear (Log Air Flow Rate) 0.5 0 0
1
2
3
log pressure differential
4
5
Data of flow (air + water) and differential pressure at 5 (L/min) of flow water Wet column Air Flow Rate L/Min
20
40
60
80
100
120
140
160
180
Water Flow Rate L/Min
5
5
5
5
5
5
5
5
5
∆P(cm H2O)
0.9
1.0
1.1
1.9
2.4
6.6
∆P(g/cm.s2)
882
980
1078
1862
2352
6468
Log Air Flow Rate (L/Min)
1.30103 1.60206 1.77815 1.90309 2.00000 2.07918 2.14613 2.20412
Log ∆P (g/cm.s2)
2.94547 2.99123 3.03262 3.26998 3.37144 3.81077
2.25527
Graph of log pressure differential VS Log air flow 2.5
log air flow
2 1.5 Log Air Flow Rate
1
Linear (Log Air Flow Rate) 0.5 0 0
1
2
3
log pressure differential
4
5
Data of flow (air + water) and differential pressure at 6 (L/min) of flow water Wet column Air Flow Rate L/Min
20
40
60
80
100
120
140
160
180
Water Flow Rate L/Min
6
6
6
6
6
6
6
6
6
∆P(cm H2O)
0.5
1.1
2.6
2.8
3.2
7.2
11.9
∆P(g/cm.s2)
490
1078
2548
2744
3136
7056
11662
Log Air Flow Rate (L/Min)
1.30103 1.60206 1.77815 1.90309 2.00000 2.07918 2.14613 2.20412
Log ∆P (g/cm.s2)
2.69020 3.03262 3.40620 3.43838 3.49638 3.84856 4.06677
Graph of log pressure differential VS Log air flow 2.5
log air flow
2 1.5 Log Air Flow Rate
1
Linear (Log Air Flow Rate) 0.5 0 0
1
2
3
log pressure differential
4
5
2.25527
Data of flow (air + water) and differential pressure at 7 (L/min) of flow water Wet column Air Flow Rate L/Min
20
40
60
80
100
120
140
160
180
Water Flow Rate L/Min
7
7
7
7
7
7
7
7
7
∆P(cm H2O)
0.1
0.3
0.8
2.7
10.5
∆P(g/cm.s2)
98
294
784
2646
10290
Log Air Flow Rate (L/Min)
1.30103 1.60206 1.77815 1.90309 2.00000 2.07918 2.14613 2.20412
Log ∆P (g/cm.s2)
1.99123 2.46835 2.89432 3.42259 4.01242
2.25527
Graph of log pressure differential VS Log air flow 2.5
log air flow
2 1.5 Log Air Flow Rate
1
Linear (Log Air Flow Rate) 0.5 0 0
1
2
3
log pressure differential
4
5
Data of flow (air + water) and differential pressure at 8 (L/min) of flow water Wet column Air Flow Rate L/Min
20
40
60
80
100
120
140
160
180
Water Flow Rate L/Min
8
8
8
8
8
8
8
8
8
∆P(cm H2O)
2.2
2.5
5.5
14.8
∆P(g/cm.s2)
2156
2450
5390
14504
Log Air Flow Rate (L/Min)
1.30103 1.60206 1.77815 1.90309 2.00000 2.07918 2.14613 2.20412
Log ∆P (g/cm.s2)
3.33365 3.38917 3.73159 4.16149
2.25527
Graph of log pressure differential VS Log air flow 2.5
log air flow
2 1.5 Log Air Flow Rate
1
Linear (Log Air Flow Rate) 0.5 0 0
1
2
3
log pressure differential
4
5
Data of flow (air + water) and differential pressure at 9 (L/min) of flow water Wet column Air Flow Rate L/Min
20
40
60
80
100
120
140
160
Water Flow Rate L/Min
9
9
9
9
9
9
9
9
∆P(cm H2O)
1.0
3.0
11.0
∆P(g/cm.s2)
980
2940
10780
180 9
Log Air Flow Rate (L/Min)
1.30103 1.60206 1.77815 1.90309 2.00000 2.07918 2.14613 2.20412 2.25527
Log ∆P (g/cm.s2)
2.99123 3.46835 4.03262
log air flow
Graph of log pressure differential VS Log air flow 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0
Log Air Flow Rate Linear (Log Air Flow Rate)
0
1
2
3
log pressure differential
4
5
DISCUSSION : From the theory, at constant liquid rate, gas pressure drop increases with gas velocity while at constant gas velocity, the gas pressure drop is higher at larger liquid rate.Each liquid rate has its own loading and flooding points and at higher liquid rate, the loading and flooding points occur at lower gas pressure drop. In this experiment, the air pressure differential across wet column (gas absorption packed column) need to be find in order to know the relationship between pressure differential and air flow rate. the total pressure differential should be plotted as a function of air flow rate on log-log graph paper for each water flow rate has been plotted. From the graphs, the total pressure differential increased as the air flow rate increased. Other than that, the pressure difference increased when the air flow and water flow increased and the flooding point decreases as the air flow increases (the high water flow the gives less flooding point). Loading point of a column is when the gas velocity is high enough to restrict the flow of liquid. After this point, the pressure drops at a much faster rate till another point, known as the flooding point, when all the liquid is carried away by the gas. It marks the start of entrainment regime in columns, too high a gas velocity will lead to a condition known as flooding whereby the liquid filled the entire column and the operation became difficult to carry out. High pressure will crush and damage the packings in the column.
CONCLUSION : In conclusion, the air pressure across the column as a function of air flow rate for different water flow rates down the column were examined.
The pressure difference increased when the air flow and
water flow increased. The flooding point decreases as the air flow increases (the high water flow the gives less flooding point). Therefore, the slope of the flooding curve is decreasing with the increasing of the water flow rate.
REFERENCES :
http://www.separationprocesses.com/Absorption/GA_Chp04a.htm
www.separationprocesses.com/Absorption/GA_Chp03.htm
ttps://www.sciencedirect.com/topics/chemical-engineering/gas-absorption
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