EXPERIMENT 1: EFFECT OF WATER AND AIR FLOW CHANGES IN GAS ABSORPTION

1.0 Objective

- Study the relationship between water and air flow rate changes and their effect on

pressure drop of an absorption column.

- Study the effect of an air flow rate on a flooding point in an absorption column.

- Study the effect of water flow rate on flooding point in an absorption column.

2.0 Introduction

Many chemical process materials and biological substances occur as mixture of different

components in the gas, liquid, or solid phase. In order to separate or remove one or

more of the components from its original mixture, it must be contacted with another

phase. When the two contacting phases are a gas and a liquid, the unit operation is

called absorption. A solute or several solutes are absorbed from the gas phase into a

liquid phase in absorption.

3.0 Equipment

C

AA

B

D

E

F G

H

I

J

R S T

O

NM

L K

Q

U VW

XY

Z

A

Legend

A – Control panel O – CO2 flow meter

B – CO2 regulator P – CO2 cylinder valve

C – CO2 cylinder Q - Main ON/OFF & water pump ON/OFF

D – Reservoir with pressure gauge R – CO2 control valve

E – Air compressor S – Water control valve

F – Collecting tank T – Air control valve

G – Water pump U – CO2 sensor (final)

H – Water tank V – CO2 sensor (initial)

I – Berls saddle W – Gas stream incoming valve

J – Tower coloumn X – Gas stream drain valve

K – Manometer (Bottom-middle) Y – Water pump by-pass valve

L – Manometer (Bottom-top) Z – Water stream drain valve

M – Air flow meter AA – Collecting tank inlet valve

N – Water flow meter

4.0 Safety & precaution

1. Place the apparatus on opened air laboratory or good ventilation area.

2. The gas stream incoming valve (W) must always be fully closed unless there is air/gas

flow in the stream line.

3. Do not leave water in the column without air/gas flow. Water will flood the CO2 sensor

and damage the sensor if the gas stream incoming valve (W) is opened.

4. Do not regulate the CO2 flow rate for more than 10 SCFH as too much of CO2 is harmful

to human.

5. Do not leave any pressure in the air/gas stream line after shut down.

6. Do not regulate the water flow rate for more than 3 GPM.

7. Be careful when regulating the CO2 regulator (B). Please report to instructor if there is

any CO2 leakage.

8. No body part should touch any rotating part of the air compressor.

9. The compressor air should not exceed 8.5 bar. Any pressure exceeded 8.5 bar, please

shut off the air compressor immediately.

10. Do not start the water pump if there is no water in the water tank.

11. Do not start the water pump with the by-pass valve (Y) is fully closed.

12. Do not impact the glass column.

13. Shut off the water pump immediately when the water level in the column reached the

highest point on the glass column.

14. Shut off the water pump immediately if there is any water leakage.

15. Shut off the CO2 gas supply immediately if there is any gas leakage.

5.0 Procedure

5.1. Pre-Procedure

1. Only normal air was use in this experiment. CO2 gas was not use in this experiment.

2. LS-32021-GAC Gas Absorption Column Unit was placed on a level floor.

3. The CO2 regulator valve (B) and CO2 cylinder valve (P) was ensure is fully closed.

4. The three valve (R, S and T) was ensure located below the flow meters are fully closed.

5. The gas stream incoming valve (W), gas stream drain valve (X) and collecting tank inlet

valve (AA) was ensured is fully closed. (Caution : The gas stream incoming valve must

always be fully closed unless there is air/gas flow in the stream).

6. The water tank (H) inlet valve, water pump by pass valve (Y) and water stream drain

valve was ensured is fully opened (or alternatively collecting tank inlet valve (AA) is fully

opened).

7. The drain valve for the water tank (H) was ensured is fully closed. Drain valve for the

collecting tank (F) should be open if water is to be discharge directly.

8. The air compressor (E) and the CO2 cylinder was placed next to the unit.

9. The air compressor 3 pin was plug to the 3 pin plug pocket which is located at the side of

the control panel (A) (Reminder : Do not switch on).

10. An air hose from the air compressor outlet was connected to the reservoir inlet (D) which

is located at the bottom of the steel frame. The valve at the air compressor was opened.

11. An air hose from the CO2 regulator (B) was connected to the CO2 inlert port which is

located at the side of control panel (near the 3 pin plug socket). The hose was ensured

is tightening properly.

12. A water hose from the laboratory water supply was connected to the tank (H). the water

tank was filled with clean water.

13. The Gas Absorption Coloumn Unit 3 pin was pluged to the laboratory 240VAC main

power supply.The power was switched ON.

14. The unit main power supply (Q) was switched ON. The MCB/ELCB was ensured is

sitched ON.

15. The air compressor power supply was switched ON. The air compressor was allowed to

compress the air in the tank. The pressure gauge (D) reading was kept an eye the

pressure should not exceed 8.5 bar.

5.2 Experiment procedure

1. The water level in both of the manometers was balanced by pressing the release valves

which is located top of the manometer.

2. The water pump was switched ON by pressing the green push button (Q). The water

stream drain valve was opened (or alternatively collecting tank inlet valve (AA) is fully

opened).

3. The by-pass valve (Y) was closed to half of it original position. The water flow meter (N)

was keep on eye. The water flow rate was set to 1.0 GPM by regulating the water control

valve (S). (Caution : Do not regulate the water flow rate for more than 3 GPM and valve

W must be closed if there is no air/gas flow in the stream line).

4. The air control valve (T) was opened slowly and the gas stream incoming valve (W) was

opened. The air flow meter (M) was keep on eye. The air flow rate was set to 2.0 SCFM

by regulating the air control valve (T). (Reminder : Read the largest diameter to indicate

flow rate).

5. The water flow rate and air flow rate was leaved to run for about 2 minutes. After 2

minutes, the data was taken for pressure drop ΔP from both manometers. The air flow

rate and water flow rate were make sure are always constant. The reading was recorded

to a table.

6. Step 3 and step 4 was repeated by manipulating the air flow rate (i.e,2.40 – 4.20 SCFM)

until the flooding point was observed (when the water level reached higher than the gas

obserber).

7. Step 3 and step 4 was repeated with a constant air flow rate at 2.0 SCFM and the water

flow rate was manipulated (i.e, 0.60 – 1.40 SCFM).

8. Both of the water flow rate and gas flow rate were converted to liter per minutes (LPM)

unit.

6.0 Results

Useful data :

1 GPM = 3.785 LPM

1 SCFM = 28.316 LPM

1 SCFH = 0.472 LPM

Effect of Water and Air Flow Changes

Constant Water Flow Rate

Time

(min)

Water

flow

rate

(GPM)

Air flow

rate

(SCFM)

Water

flow

rate

(LPM)

Air flow

rate

(LPM)

ΔP

(top-

bot)

ΔP

(bot-

mid)

log

ΔP

(top-

bot)

log

ΔP

(mid-

bot)

log air

flow

rate

1 1.00 2.00 3.785 56.632 75 36 1.88 1.56 1.75

2 1.00 2.40 3.785 67.958 85 37 1.93 1.57 1.83

3 1.00 2.60 3.785 73.622 84 40 1.92 1.60 1.86

4 1.00 3.00 3.785 84.948 85 39 1.93 1.59 1.93

5 1.00 3.40 3.785 96.274 91 42 1.96 1.62 1.98

6 1.00 3.80 3.785 107.601 102 45 2.01 1.65 2.03

7 1.00 4.00 3.785 113.264 94 46 1.97 1.66 2.05

8 1.00 4.20 3.785 118.927 81 38 1.91 1.58 2.08

Constant Air Flow Rate

Time

(min)

Water

flow

rate

(GPM)

Air flow

rate

(SCFM)

Water

flow

rate

(LPM)

Air flow

rate

(LPM)

ΔP

(top-

bot)

ΔP

(bot-

mid)

log

ΔP

(top-

bot)

log

ΔP

(mid-

bot)

log

water

flow

rate

1 0.60 2.00 2.271 56.632 17 14 1.23 1.15 0.36

2 0.80 2.00 3.028 56.632 32 18 1.51 1.26 0.48

3 1.00 2.00 3.785 56.632 84 49 1.92 1.69 0.58

4 1.20 2.00 4.542 56.632 121 84 2.08 1.92 0.60

5 1.40 2.00 5.299 56.632 165 125 2.22 2.10 0.72

GRAPH

CONSTANT WATER FLOW RATE:

1.75 1.83 1.86 1.93 1.98 2.03 2.05 2.081.8

1.85

1.9

1.95

2

2.05

log

ΔP (t

op-

bot)

log ΔP (top- bot) VS log air flow rate

Log Air flow rate

CONSTANT AIR FLOW RATE

0.36 0.48 0.58 0.6 0.720

0.5

1

1.5

2

2.5

log

ΔP (t

op-

bot)

log ΔP (top- bot) VS Log air flow rate

Log Air flow rate

7.0 DISCUSSION

Based on the result, it shows that there is two type of table to be determined which are the

constant air flow rate and the constant water flow rate table. For the constant water flow rate

table, the time that be taken for this experiment is about 8 minutes, while for the constant air

flow rate table, the time that be taken for this experiment is about 5 minutes. Based on the result

table, the air flow rate (SCFM) for constant water flow rate is increasing compared to the

constant air flow rate which is constant. But, for the next table column, its shows that the water

flow rate (LPM) for constant water flow rate table is constant, while the water flow rate (LPM) for

constant air flow rate table is increasing. The reading for both tables is taken for making a

graph. Based on the graph, the constant water flow rate graph shows that the line is fluctuated

which is sometimes increase and decrease while for the constant air flow rate graph shows that

the line is linear which is increasing from starting until to the end of the experiment.

8.0 CONCLUSIONS

The experiment was conducted in order to find out the relationship between water and air flow

rate, as well as the effects on pressure drop of an absorption column. Besides that, the study

also was made to observe the effect of an air flow rate on a flooding point in an absorption

column. Next the effect of water flow rate on the flooding point in the absorption column also is

traced to be the key objectives in the experiment.

What can be concluded is that the CO2 analyzer calibration equation was found to be consistent

with a theoretical relationship called the “non-overlapping line approximation,” which describes

infrared absorption as a function of CO2 mole fraction, pressure and temperature. This

theoretical model and the concept of “equivalent pressure” predicted a form for the water

correction that gives good accuracy over a wide range of conditions using a single physically

meaningful parameter. Theory shows that all CO2 analyzers will show some response to water

vapor because infrared absorption per mole CO2 changes with total pressure and diluents gas

composition. The magnitude of the water effect is larger than those for most other gases.

9.0 REFERENCES

1. Bunce, J. A. and D. A. Ward. 1985. Errors in differential infrared carbon dioxide analysis

resulting from water vapor. Photosynthesis Res. 6: 289 - 294.

2. Ball, J. T. 1987. Calculations related to gas exchange, Ch. 20. In:Stomatal Function, E.

Zeiger, G. D. Farquhar and I. R. Cowan, Eds. Stanford University Press, Stanford,

California.

3. Burch, D. E., E. B. Singleton and D. Williams. 1962. Absorption line broadening in the

infrared. Applied Optics 1: 359 - 363.

4. Jamieson, J. A., R. H. McFee, G. N. Plass, R. H. Grube and R. G.Richards. 1963. Infrared

Physics and Engineering. McGrawHill, New York, 673 pp.