Gas Absorption

UNIVERSITI TEKNOLOGI MARA FAKULTI KEJURUTERAAN KIMIA ENGINEERING CHEMISTRY LAB II (CHE523) STUDENT NAME STUDENT ID GROUP EXPERIMENT DATE PERFORMED SEMESTER PROGRAMME / CODE SUBMIT TO

Remarks: No Title . 1 Abstract/Summary 2 Introduction 3 Aims 4 Theory 5 Apparatus 6 Methodology/Procedure 7 Results 8 Calculations 9 Discussion 10 Conclusion 11 Recommendations 12 Reference 13 Appendix TOTAL MARKS

: MUHAMMAD SHAMIL AZHA IBRAHIM : 2011195429 : EH2203A :GAS ABSORPTION : 11 MARCH 2013 :3 : PURE CHEMICAL ENGINEERING / EH220 : MADAM NUR AZRINI RAMLEE

Allocated Marks (%)

Marks

5 5 5 5 5 10 10 10 20 10 5 5 5 100

Checked by : ---------------------------

Date : 31 MARCH 2013

ABSTRACT

The objective of this experiment was to analyze the absorption of liquid in gas flow to determine a relationship between flow rate of the absorbent and absorbed.Also the loading and flooding of the water. The relationship allows future users of the column to determine the appropriate conditions to achieve the absorption of gas desired. Experimentation consisted of 8 trials, one with gas flow rate as the absorbent and the other with water. The flow rates of air and water were held constant at 2.0 M3, and the absorbent flow rate varied from 2.0 to 5.0 M3/hour. Initial gas concentrations were obtained from the gas analyzer before the absorbent began flowing, and after allowing the flow to reach steady state, the gas concentrations were also collected. The relationship between the absorbent flow rate and concentration change was expected to be linear and have a significant effect on the change in concentration; however, the correlation deviated from the anticipated trend. The data contained outlier points, which when excluded improved the fit of seen correlations. With water as the absorbent, a linear relationship was observed.. The water had a higher average of gas concentration change, a lower average percent error, and a lower standard deviation among the calculated k values. Data, good or bad, proved difficult to obtain mostly due to gas analyzer. Calibration of the analyzer took a majority of the time spent in lab, and in the final lab session the analyzer was never able to be calibrated. We recommend that future users of the absorption column ensure that the carbon dioxide analyzer is properly calibrated to improve precision of the data. The continuous flow process for collecting data is also recommended to obtain better results by lessening fluctuations in the carbon dioxide analyzer readings.

OBJECTIVES I ) To determine the Loading and Flooding Points in the column. II) To model the pressure as a function of gas ( air ) and liquid ( water )

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 (LLE). The packed bed configuration facilitates the intimate contact (mixing) of fluids mismatched densities, such as liquid p = 103kg/m3. The increased surface area for phase contact that packing offers increase the amount of momentum transfer, manifested by an increased vapour- phase pressure drop through column.

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 ) consist 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 ( eg : concentration difference) Na = Ka (Ca1 - Ca2) Packing is a passive device that is designed to increase the interfacial area for vapor-liquid contact. Packing imparts good vapour liquid contact when particular type is a 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 across section and large free volume. Large free across section affects the frictional drop through the tower and therefore the power that is required to circulate the gas. Small free across 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.

PROCEDURE

GENERAL START-UP I ) The manometer calibration ( red-blue) is followed. For calibration of manometers and during operation of the column, the following valves must be in the position stated below :

OPERATION PROCEDURE : 1) The manometer U-tube is filled with water by arranging the values according U-tube arrangement. 2) The values is set to operating arrangement before the operation is started. 3) All valves is checked carefully before the column is safe to use. 4) Valve VR-3 and VR-4 is opened such that the liquid flow rate is set at 20m3/hour. The leverl of liquid is returned to the water reservoir must always be higher than the bottom of the reservoir. This is to avoid air being trapped in line . Valve VR-4 is adjusted accordingly to avoid this phenomena. 5) Valve VR-1 is opened and the airflow is set to be 10m3.hour. 2 minutes is waited and the flow rate of air and water is constant. The pressure drop (ΔP) mmH20 in the monotube. 6) The gas flow rate is increased by adding and extra of 5m3/hour to the column 7) Part 4 is repeated until you reach the Flooding Point. 8) The curve of Ln (V) versus Ln (ΔP/m packing ) 9) Step 2 to 6 is repeated with different kind of liquid flow rate.

APPARATUS : I ) Water tank glass absorption ii) Stopwatch iii) Ruler IV) Packing = 10 mm glass Raschig Ring

RESULT AND CALCULATION : Liquid

2.0

3.0

4.0

5.0

6.0

Flow, L M3/Hour Gas Flow in Monotube,

Low,

High

Low

High

Low

High

Low

High

Low

High

mmH20 mmH20 mmH20 mmH20 mmH20 mmH20 mmH20 mmH20 mmH20 mmH20

Vm3 10

20.3

19.7

20

19.7

20.2

19.4

15

20.3

19.7

19.7

20

20.1

19.6

20

20.2

19.6

19.4

20.5

19.9

19.8

25

19.5

20.0

18.9

20.6

18.9

20.8

30

19.0

20.9

18.5

21.2

19.0

20.6

35

17.5

22.3

17.6

22.0

18.5

20.8

40

15.8

24.0

17.2

22.5

45

13.7

26.5

16.8

22.9

FLOODING

Liquid Flow ,L : 20 M3/Hour Gas Flow,

Monotube Low

V (m3/hr)

Monotube High

(mm H2O)

(∆P)

(mm H2O)

ln (V)

ln (∆P/m packing)

(mm H2O)

10

20.3

19.7

0.6

2.30

-2.81

15

20.3

19.7

0.6

2.71

-2.81

20

20.2

19.6

0.6

3.00

-2.81

25

19.5

20.0

0.5

3.22

-2.99

30

19.0

20.9

1.9

3.40

-1.66

35

17.5

22.3

4.8

3.56

-0.73

40

15.8

24.0

8.2

3.69

-0.19

45

13.7

26.5

12.8

3.81

0.25

ln (V) vs ln (∆P/m packing) 4.5 4 3.5 3 2.5 ln (V) vs ln (∆P/m packing)

2 1.5 1 0.5 0 -4

-3

-2

-1

0

1

Liquid Flow ,L : 30 M3/Hour Gas Flow,

Monotube Low

V (m3/hr)

Monotube High

(mm H2O)

(∆P)

(mm H2O)

ln (V)

ln (∆P/m packing)

(mm H2O)

10

20

19.7

-0.3

2.30

-3.50

15

19.7

20

0.3

2.71

-3.50

20

19.4

20.5

1.1

3.00

-2.21

25

18.9

20.6

1.7

3.22

-1.77

30

18.5

21.2

2.7

3.40

-1.31

35

17.6

22.0

4.4

3.56

-0.82

40

17.2

22.5

5.3

3.69

-0.63

45

16.8

22.9

6.1

3.81

-0.49

ln (V) vs ln (∆P/m packing) 4.5 4 3.5 3 2.5 ln (V) vs ln (∆P/m packing)

2 1.5 1 0.5 0 -4

-3

-2

-1

0

Liquid Flow ,L : 40 M3/Hour Gas Flow,

Monotube Low

V (m3/hr)

Monotube High

(mm H2O)

(∆P)

(mm H2O)

ln (V)

ln (∆P/m packing)

(mm H2O)

10

20.2

19.4

-0.8

2.30

-2.53

15

20.1

19.6

-0.5

2.71

-2.99

20

19.9

19.8

-0.1

3.00

-4.61

25

18.9

20.8

1.9

3.22

-1.66

30

19.0

20.6

1.6

3.40

-1.83

35

18.5

20.8

2.3

3.56

-1.47

40 FLOODING

45

ln (V) vs ln (∆P/m packing) 4 3.5 3 2.5 2

ln (V) vs ln (∆P/m packing)

1.5 1 0.5 0 -5

-4

-3

-2

-1

0

Calculation : Liquid flow, L (m3/hr) : 20 Pressure drop at gas flow 10 m3/hr

i)

Pressure drop ∆P mm H2O = Manometer, High - Manometer Low = (19.7-20.2) mm H2O = -0.6 mm H2O

The same step was repeated to calculate the pressure drop at gas flow 15 mm H2O 3

mm H2O in every Liquid flow, L (m /hr) who been experimented yet.

II)

ln (V) at gas flow 10 m3/hr

ln (V) = ln 10 = 2.30 Repeat the same step to calculate the ln (V) at gas flow 15 mm H2O until 45 mm H2O.

until 45

ln (∆P/m packing)

ln (∆P/m packing) = ln (0.0006 m H2O/0.010 m packing) =-2.81 Repeat the same step to calculate the ln (∆P/m packing) at gas flow 15 mm H2O until 45 mm H2O.

Note : All these steps were repeated to calculate the pressure drop, ln (V) and ln (∆P/m packing) the different liquid flow which are 30 m3/hr, 40 m3/hr and 50 m3/hr.

DISCUSSION :

This experiment uses packed tower that has 10mm glass Raschig Rings. When the liquid flow is at 20 m3/hr and gas flow 10 m3/hr, pressure drop is 0.6mm H2O after 2 minutes, ln (V) = ln 10 which is 2.30 and the ln (∆P/m packing) = ln (0.0006 m H2O/0.010 m packing) which is -2.81. The gas flow increases to15 m3/hr and after 2 minutes operates, the reading of manometer is taken and the pressure drop is still same. it is because the apparatus need to be stable from heating water on the system. Also the gas pass through the system also need to be stable first. Also, in 40 m3/hour at liquid flow, flooding point occurred in 40 m3/hour. it is because flooding point is in a packed or tray column where it have vapor flowing up and liquid flowing down, there is an upper limit to how fast the liquid can drain downwards. The point at which liquid cannot flow down as fast as it is coming into the column. The actual flooding point is partly dependent on how fast the liquid can flow down with no vapor flowing upwards and the rate at which vapor is trying to flow upwards. Cross sections of the column occupied by vapor are not available for liquid flow - effectively reducing the cross-section for downward flow of the liquid. Also get entrainment of liquid in the upward flowing vapor and drag on the liquid as it fights the direction of the vapor flow - the vapor wants to go up while the liquid wants to go down. This additional drag also slows down the flow of liquid trying to drain downward in the column. Then on 50 m3/hour liquid flow, the experiment cannot be conducted because of the flooding point happen too fast and the data cannot be taken. Also, the system also are damaged. V4 valve loosed and experiment cant be conducted.

CONCLUSION : The flooding point and the pressure drop can be determined by using gas-liquid absorption column. At 20 m³/hour liquid flow rate, no flooding point occurs. Then, at 30 m³/hour there is still no flooding point. Also at 40 m³/hour there flooding point at 40 Vm3/hour . However, before the flooding point, the pressure drop will moderately increases and sometimes decreases due to the error during experiment. In the end, the liquid flow rate is increased to 50 m³/hr, the flooding point is achieved at 10 Vm3/hour and experiment cannot be constructed and data cant be taken on 50 m3/hour.

RECOMMENDATION : I)

We recommend that future users of the absorption column ensure that the gas analyzer is properly calibrated to improve precision of the data. The continuous flow process for collecting data is also recommended to obtain better results by lessening fluctuations in the gas flow analyzer readings.

II)

Better location of feed bucket because its hard to access bucket with liquid.

III)

Time constraint because of heater only up for 1.5 kW and more runs would be performed.

REFERENCE I)

Coulson, J.M. and Richardson J.F, Chemical Engineering , Volume 2 , Third Edition ( SI Units) , Pergamon.

II)

W.L. McCabe, J.C. Smith & P. Harriott, Unit Operations of Chemical Engineering, 6th Ed., McGraw-Hill, New York (2001).

III)

R.H. Perry and C. H. Chilton, Chemical Engineers Handbook, 5th edition, McGraw Hill, New York (1973).