Gas Absorption

UNIVERSITI TEKNOLOGI MARA FAKULTI KEJURUTERAAN KIMIA

ENGINEERING CHEMISTRY LAB II (CHE523)

No.

Title Allocated Marks (%) Marks

1 Abstract/Summary 52 Introduction 53 Aims 54 Theory 55 Apparatus 56 Methodology/Procedure 107 Results 108 Calculations 109 Discussion 2010 Conclusion 1011 Recommendations 512 Reference 513 Appendix 5

TOTAL MARKS 100

Remarks:

Checked by :

--------------------------- Date : 31 MARCH 2013

STUDENT NAME : MUHAMMAD SHAMIL AZHA IBRAHIM STUDENT ID : 2011195429

GROUP : EH2203A EXPERIMENT :GAS ABSORPTION DATE PERFORMED : 11 MARCH 2013 SEMESTER : 3 PROGRAMME / CODE : PURE CHEMICAL ENGINEERING / EH220 SUBMIT TO : MADAM NUR AZRINI RAMLEE

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

Flow, L

M3/Hour

2.0 3.0 4.0 5.0 6.0

Gas Flow

in

Monotube

,

Vm3

Low,

mmH20

High

mmH20

Low

mmH20

High

mmH20

Low

mmH20

High

mmH20

Low

mmH20

High

mmH20

Low

mmH20

High

mmH20

10 20.3 19.7 20 19.7 20.2 19.4

15 20.3 19.7 19.7 20 20.1 19.6

FLOODING

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

Liquid Flow ,L : 20 M3/Hour

Gas Flow,

V (m3/hr)

Monotube Low

(mm H2O)

Monotube High

(mm H2O)

(∆P)

(mm H2O)ln (V)

ln (∆P/m packing)

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

-3.5 -3 -2.5 -2 -1.5 -1 -0.5 0 0.50

0.5

1

1.5

2

2.5

3

3.5

4

4.5

ln (V) vs ln (∆P/m packing)



Gas Flow,

V (m3/hr)

Monotube Low

(mm H2O)

Monotube High

(mm H2O)

(∆P)

(mm H2O)ln (V)

ln (∆P/m packing)

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

-4 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 00

0.5

1

1.5

2

2.5

3

3.5

4

4.5




Gas Flow,

V (m3/hr)

Monotube Low

(mm H2O)

Monotube High

(mm H2O)

(∆P)

(mm H2O)ln (V)

ln (∆P/m packing)

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

FLOODING45

-5 -4.5 -4 -3.5 -3 -2.5 -2 -1.5 -10

0.5

1

1.5

2

2.5

3

3.5

4



Calculation :

Liquid flow, L (m3/hr) : 20

i) Pressure drop at gas flow 10 m3/hr

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 until 45

mm H2O in every Liquid flow, L (m3/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.

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, NewYork (2001).

III) R.H. Perry and C. H. Chilton, Chemical Engineers Handbook, 5th edition, McGraw Hill,

New York (1973).

Documents

Gas Absorption