The experiment is based on pressure drop, the air flow rate , the water flow rate and also
the packed column. The pressure drop is increased when the water flow rate and air flow
rate is increased. This experiment is to examine the air pressure drop across the column as
a function of air flow rate for different water flow rates through the column. The graph of
log pressure drop against log of air flow rate is plotted. The graph of generalized
theoretical pressure drop correlation chart for random packing is also plotted. Both of the
graph have same principle where high flow rate parameter is meant for high liquid flowand
high pressure drop while low flow rate parameter is meant for low liquid flow and low
Absorption is a mass transfer process in which a vapor solute A in a gas mixture is
absorbed by means of a liquid in which the solute more or less soluble. The gas mixture
consists mainly of an inert gas and the soluble. The liquid also is primarily in the gas
phase; that is, its vaporization into the gas phase is relatively slight. A typical example is
absorption of the solute ammonia from an air-ammonia mixture by water. Subsequently,
the solute is recovered from the solution by distillation. In the reverse process desorption
or stripping, the same principle and equations hold.
Gas absorption is the unit operation in which one or more soluble components of a gas
mixture are dissolved in a liquid. The gas phase or gas mixture is inert gas while the
liquid phase is immiscible in the gas phase. Therefore, the liquid phase will vapourize
very slightly in gas phase. 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. 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.
There are 2 types of absorption processes which are physical absorption and chemical
absorption, depending on whether there is any chemical reaction between the solute and
the solvent (absorbent).
When water and hydrocarbon oils are used as absorbents, no significant chemical
reactions occur between the absorbent and the solute, and the process is commonly
referred to as physical absorption.
When aqueous sodium hydroxide (a strong base) is used as the absorbent to dissolve an
acid gas, absorption is accompanied by a rapid and irreversible neutralization reaction in
the liquid phase and the process is referred to as chemical absorption or reactive
More complex examples of chemical absorption are processes for absorbing CO2 and H2S
with aqueous solution of monoethanolamine (MEA), diethanolamine (DEA),
diethyleneglycol (DEG) or triethyleneglycol (TEG), where a reversible chemical reaction
takes place in the liquid phase. Chemical reactions can increase the rate of absorption,
increase the absorption capacity of the solvent, increase selectivity to preferentially
dissolve only certain components of the gas, and convert a hazardous chemical to a safe
1. To determine the pressure drop across the dry column as a function of air flowrate.
2. To examine the air pressure drop across the column as a function of air flow rate for
different water flow rates through the column.
Packed columns are used for efficient gas-liquid contact processes ‘contact interface’ into
the bulk of the liquid. The driving force for absorption involves a concentration gradient
across the gas-liquid interface. Figure 1 provides a visual of the gas-liquid ‘contact
interface’. Packed columns are used for efficient gas-liquid contact processes .It is used
in processes like gas absorption, desorption(stripping) , distillation etc. It mainly consists
of a cylindrical column filled with packings , liquid inlet and distributor at the top, gas
inlet at the bottom, liquid and gas outlets at the bottom and top respectively. Column
packings can be of two types mainly: dumped and structured . A distributor consists of
several perforated pipes used for spreading the liquid uniformly throughout the cross-
section of column.
Figure 1: gas liquid interface
Amount of liquid accumulate in side packed column that generate pressure drop.
Figurer 2 : loading in side packed column
Amount of the liquid flood in the top of column with increasing pressure drop due to
accumulation of liquid in side packed column
Figure 3 :flooding in packed column
Pressure drop is the result of fluid friction between liquid flow and the packings.
The graph above shows the relationship between pressure drop and gas flow rate and
fordry column, a straight line is plotted and wet column three curvy lines are plotted. The
three curves are parallel to the straight line. The point where liquid holdup starts to
increase is the point where the slope starts to change. This point is known as the
loading point. When the gas flow rate is further increased, pressure drop rises
tremendously untilthe lines plotted are almost vertical and at this point, liquid is of
This point is known as the flooding point and happens when liquid accumulates due to hi
ghgas flow rate and this accumulation continues until the packed column is completely
filled with liquid.
Material and apparatus
1. Solteq-QVF absorption column (model: BP 751-B)
1. All valves is ensured are closed except the ventilation valve V13.
2. All the gas connection is checked properly fitted.
3. The power for control panel is on.
4. The receiving vessel B2 is filled through the charge port with 50 L of water by
opening valve V3 and V5.
5. Valve V3 is closed.
6. Valve V10 and V9 is opened slightly. The flow of water from vessel B1 through
pump P1 is observed.
7. Pump P1 is switch on, valve V11 is open and adjusted slowly to give a water flow
rate of around 1L/min. The water is allowed to enter the top of the column K1, flow
down the column and accumulate at the bottom until it overflows back into vessel B1.
8. Valve V11 is adjusted and open to give a water flow rate of 1L/min into the column
9. Valve V1 is open and adjusted to give an air flow rate of 20L/min into column K1.
10. The pressure drop is recorded .
11. Step 9 is repeated with the different values of air flow rate, each time increasing by
20 L/min while maintaining the same flow rate.
12. Step 8 to 9 is repeated with different values of water flow rate, each time increasing
by 1L/min by adjusting valve V11.
Pressure drop (mm H20)
20 40 60 80 100 120 140 160 180
1 0 1 2 4 8 14 28 51 -
2 0 1 3 5 10 17 73 - -
3 0 4 8 16 48 58 - - -
Table 1: Flow rate and pressure drop
Flow rate Pressure drop (mm H20)
1.3 1.6 1.8 1.9 2.0 2.1 2.15 2.2 2.3
1 0 0 0.3 0.6 0.9 1.1 1.4 1.7 -
2 0 0 0.5 0.7 1 1.2 1.9 - -
3 0 0.6 0.9 1.2 1.7 1.8 - - -
Table 2: Log air flow rate and Log pressure drop
Density of air = 1.175 kg/m3
density of water = 996 kg/m3
Column diameter =80 mm
Area of packed column diameter = 0.005027m2
Packing Factor = 900 m-1
1.3 1.6 1.8 1.9 2 2.1 2.15 2.2
Log Gas Flow Rate, Gy
Graph of Log PressureDrop against
Log Gas Flow Rate
In this experiment, we are going to determine the pressure drop across the dry column as
a function of air flow rate and the air pressure drop across the column as a function of air
flow rate for different flow rates through the column. These two objectives are achieved
by using the same apparatus but different method. The experiment is bases on the flow
rate of liquid and gas in the packed.
Firstly, the water flow rate is kept constant to 1L/min and air flow rate reading is
recorded when achieved 1 minute. The air flow rate is kept rising constantly by 20 L/min
by each minute. All reading of pressure drop is recorded until flooding point is reached.
The pressure drop for flow rate of air are 1, 2, 4, 8 , 14, 28 and 51 mm H20 consequently
to 20, 40, 60, 80, 100, 120, 140, and 160 L/min. It cannot reach 180 of air flow rate,
which the water will sprayed out from the column due to the high flow rate.
The the flow rate is adjusted to 2L/min, by using the same step as recording the 1L/min.
the data recorded are 0, 1, 3, 5, 10, 17 and 73 mm H20 consequently to 20, 40, 60, 80,
0.0154 0.0614 0.1383 0.2459 0.3841 0.5532 0.7531 0.9832
Generalised Thepretical Pressure
Drop CorrelationChart for Random
100, 120, and 140 L/min. Whereby, for flow rate of water 3L/min is 0, 4, 8, 16, 48 and 58
consequently to 20, 40, 60, 80, 100, and 120.
With these data record, the graph of log of pressure drop against the log of air flow rate is
plotted. From the graph plotted, all the log pressure drop is directly proportional log gas
flow rate. We can conclude that the higher the log of gas flow rate the higher the log of
pressure drop. But the higher the water flow rate, the lower the log gas flow rate.
For correlated value of the pressure drop is calculated and the graph of capacity
parameter against flow rate parameter is plotted. The capacity parameter is indirectly
proportional to flow rate parameter. Two of the graph is different as one is directly
proportional while the other one is indirectly proportional.
In conclusion, the aim of experiment which is to determine the pressure drop across the
column as a function of air flow rate for different water flow rate through the column is
achieved. They are some errors made when the experiment is being conducted resulting
in a slight in accuracy of the experimental chart plotted.
When conducting this experiment, there are several recommendations that will produce
better observation which will not differ much from the theoretical observations.
Firstly, safety is very important when doing experiment. Thus, we need to wear
laboratory coat, helmet and fully cover shoes to avoid any danger for safety precaution.
Titration must take place in fume chamber and must be stop when the solution turns to
light pink. Next, when taking the reading of volume of sodium hydroxide solution, make
sure that eyes is directly perpendicular with the level of sodium hydroxide solution inside
the burrette to avoid any parallax error. Before conducting the experiment, we must
ensure that all the apparatus are in good condition and follow all the procedures in order
to get more accurate result.
V. Lab Manual