This document presents an experimental study on an airlift packed column with adjustable height and multiple air injection points. The study aims to improve liquid flow rate and total head of the system. Experiments were conducted by varying submersion ratio, air flow rate, and number of air injection nozzles. Results show that liquid flow rate increases with higher submersion ratio, air flow rate, and number of nozzles. Using multiple nozzles distributed along the column maintains both high liquid flow rate due to increased gas holdup and total head. The system offers applications in heat and mass transfer operations with adjustable packed bed height and efficient liquid distribution.

1. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN
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AN EXPERIMENTAL STUDY ON THE AIRLIFT PACKED COLUMN
WITH ADJUSTABLE HEIGHT AND MANY AIR INJECTION POINTS
Adel OUESLATI 1, Ahmed HANNACHI 2, Mohamed ELMAAOUI 3
1. Department of Process Engineering, Higher Technological study Institute of Zaghouan-
Tunisia, +2169759194, adel.oueslati@isetkh.rnu.tn
2. Engineer’s National School of Gabes- Tunisia,+21698660612 amed.hannachi@enig.rnu.tn
3. Faculty of Sciences of Tunis- Tunisia,+21627271789, Mohamed.elmaaoui@fst.rnu.tn
ABSTRACT
A setup consisting of a glass packed with calibrated glass rings has been achieved. It
operates on the principle of an air lift pump with several air jet nozzles. It was designed for
heat and mass transfer operations. Performances of this system were determined by
measuring the displaced water flow rates for different submersion ratios and various air flow
rates. The study shows that the proposed system has high performances and large
environmental industry applications.
Keywords: air-lift pump, packed column, performance
1. INTRODUCTION
Using two machines: compressor and pump to feed a packed column with air and
water is energy intensive. The two machines can be replaced by only one called air lift pump.
An airlifting system is mainly composed of a submerged riser tube in which compressed air is
injected at the base. The buoyancy produced by air bubbles suspended in the fluid causes a
pumping action.
Many researchers have showed that the airlift pump is more energy efficient for low-head
conditions than centrifugal or other standard pumps (Lee et al., 1997; Kumar et al., 2003; Oh,
2000). The air lift pump is made with a minimum of parts, so it requires low maintenance
costs.
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2. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 1, January- February (2013), © IAEME
The airlift pump system is used in the sewage treatment and aquaculture ponds (Parker et al.,
1987), in the petrochemical industry (Baker, 1954) and so on.
The research in the airlift pump field has received considerable attention for not only the
pumping efficiency, but also aeration, sludge displacement (William et al., 1994; Yoon et al.,
1997; Barrut et al., 2011), Carbon dioxide degassing in fresh and saline water (Damian
Moran, 2010), etc.
However, these studies are interested primarily in the effects of operating conditions on the
performance of the air lift pumps.
Many researchers have studied the effect of design characteristics on the air lift pumps
efficiency (G.J. Parker, 1980, Reinenmann, 1987; Oh, 1992; Khalil et al., 1999; Yoon et al.,
2000; CHO Nam-Cheol et al., 2009). However these investigations show that the packed
column operating on the principle of air lift pump has not yet attracted much attention.
Packed column are used in many environmental fields like extraction by liquid solvent,
distillation and gas cleaning. They offer a large contact area and good separation efficiency.
The Rashig rings are known by high void fraction which causes low pressure drop. The up
flow of gas-liquid mixture through a packed bed offers a large opportunity for liquid
distribution and packing particles wettability (Trambouze, 1999). The heat and mass transfer
efficiency of the packed column depend on the packed bed height.
The purpose of this study is to obtain basic information on the characteristics of the airlift
packed column with adjustable height. We propose a new airlift pump system using multiple
air injection points distributed over the air column height to improve both the liquid flow
rate and the total head.
2. MATERIALS AND METHODS
2.1. Experimental system
The experiments were performed on a vertical cylindrical column made up in three
glass tubes 0.072 m diameter and 0.4 m length. The total height of the column and the packed
bed are 1.2 m and 1.0 m respectively. The characteristics of the solid packing are shown in
Table 1. The column is provided with equidistant pressure sensors in order to measure the
local pressure at different heights. Four polypropylene disc diffusers, with 67 circular pores
of 5 mm each, are arranged at the ends of the glass tubes. They have a double role: first they
change the fluid flow direction, second they prevent the exit of solid packing out of tube. The
air jet nozzle is integrated into the disc diffuser.
At the input of the column, a swirl chamber, stainless steel, is designed for the injection of
water and air. At a height equal to 1.02 m of the column, water is recycled through a down
comer and the air continues its path to the cyclone. Water droplets separated at the cyclone
are routed to the swirl chamber. A make-up of water is placed to keep a constant liquid level
in the down comer.
The tests carried out in ambient conditions. The compressor used has a power of 2Kw,
Michelin type and 25 liters of tank, provided with a flow controller valve. The air flow meter
is air float type; brand Tubux whose measuring range is between 0 and 25 m3 / h and the
uncertainty of 4%.
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3. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 1, January- February (2013), © IAEME
The setup is designed in a manner that the amount of water evaporated will be replaced,
automatically, by the same amount of liquid water issued from the tank (7).
The packed column will be used in chemical engineering operations where heat and mass
transfer are involved. The efficiency of these operations depends, mainly, on the liquid flow
rate. In this experiment we will be interested to the basic parameters which influence the
liquid flow rate.
Table 1: Physical characteristics of the packing
Type of solid Glass rings
Density : ρS 2.187 (kg/m3)
Average diameter: dp 0.008 (m)
Average length : lp 0.008 (m)
fixed bed porosity: ε 77.3
Form Factor: φp 0.681
2.2 Airlift pump system
The air from the compressor can be injected in one or three points of the riser. Some
valves are placed for air flow rate modification. The height of the packed column is
adjustable by adding or removing of glass tubes of diameter 0.072 and 0.4m length to the
riser.
2.3 Experimental procedure
Two adjustable variables are: the submersion ratio, Sr, and the air flow rate, QG (m3/h).
But this later can be injected in the bottom or in the middle of the column. The only
measured parameter is the liquid flow rate. In the first we will measure the influence of the
influence of gas flow rate injected only in the bottom and the submersion ration on the liquid
flow rate. In the second time, we will experiment the influence of the number of air injections
points on the liquid flow rate.
The submerged depth, Zs, is in the range 0.4 - 0.7 m; the total head (Ha) is in the range 1m;
air flow rate (QG) is in the range: 0.5-1.8 m3 /h.
3 RESULTS AND DISCUSSION
3.1 Submergence ratio
Submergence ratio (Sr) is the ratio of the length of the tube submerged in the water per total
length of the vertical tube.
Sr = Zs / Ha (1)
Where, Zs is the submerged depth, Ha is the total head. According to Cho-Nam-Cheol, the
limits of Sr are 40% -90%. If Zs equal to Ha that means there ‘is no lifting, But if Sr is low
means that Zs is low and the lifting head is high.
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4. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 1, January- February (2013), © IAEME
3.2 Water flow rate
The water flow rate is measured by calibrated liquid flow meter. The error of this instrument
is below 5%. We measure liquid flow rate for each submersion ratio (Sr) value with different
gas flow rate and one or three air injection points.
The experimental results are shown in fig.2, 3, 4 and 5.
Fig.1. Experimental set up
(1)Riser, (2) down comer, (3) buffer tank, (4) cyclone, (5) compressor, (6 water flow
meter, (7) water make up, (8), (9) Air flow meter, (10) Temperature control
Fig.2. Effect of the Gas flow rate, submersion ratio and the number of the air injection
nozzles on the water flow rate
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5. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 1, January- February (2013), © IAEME
Fig.3. Effect of the Gas flow rate, submersion ratio and the number of the air injection
nozzles on the water flow rate
Fig.4. Effect of the Gas flow rate, submersion ratio and the number of the air injection
nozzles on the water flow rate
Fig.5. Effect of the Gas flow rate, submersion ratio and the number of the air injection
nozzles on the water flow rate
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6. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 1, January- February (2013), © IAEME
The curves illustrated by fig. 2, 3, 4 and 5 show that the liquid flow rate increases when the
submersion ratio (Sr), gas flow rate and the number of air injection nozzles increase.
It is known that the liquid flow rate decreases with the increase of total head value. This
explained by friction energy degradation.
According to Merchuk et al., Circulation of liquid and gas is facilitated by the difference in
gas hold up between the riser and the down comer, which creates a pressure difference at the
bottom of the equipment:
∆Pୠ = ρ୐ gሺεୖ − εୈ ሻ (2)
Where ∆Pୠ is the pressure difference, ρ୐ is the density of the liquid (the density of the gas is
considered to be negligible), g is the gravitational constant, and εୖ and εୈ are the fractional
gas holdup of the riser and down comer, respectively. The pressure difference forces the fluid
from the bottom of the down comer toward the riser, generating fluid circulation. Since εୖ and
εୈ are both average values integrated along the height of the packed column.
Generally, the global gas hold up, ߝீ , is defined as follows:
௏ಸ
ߝீ = ௏ (3)
ಸ ା௏ಽ ା௏ೄ
Where:
ܸீ , ܸ௅ and ܸௌ are the Volume of Gas, Liquid and Solid respectively.
The average density of the fluid mixture in the riser is given by the following equation
(Trambouze, 1999):
ߩ̅ = ߩ௅ ߝ௅ + ߩீ ߝீ (4)
With:
ߝ௅ : Liquid hold up
ߝீ and ߩீ are the hold up and density of the gas.
Gas hold up and liquid hold up are linked by the following relation:
ߝ௅ + ߝீ +ߝௌ = 1 (5)
ߝௌ is the volume fraction of packing.
So, if the gas flows rate increases then the Gas volume and the gas hold up, ߝீ . The pressure
difference, ∆Pୠ , increases and the average density of the mixture fluid decreases, then the
liquid flow rate increases immediately. Therefore, the gas hold up must have a high value for
a high liquid flow rate value. For this purpose we propose many air injection points. This
proposition can maintain both high values of liquid flow rate and total head because the
liquid flow rate is proportional to the gas holdup and the total head can be insured by the use
of several air jet nozzles.
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7. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 1, January- February (2013), © IAEME
4 CONCLUSIONS
In the present paper, experiments were conducted on an air lift packed column using one
or three air jet nozzles. From the above mentioned results and discussion, the following
conclusions are obtained.
(1) The use of many air jet nozzles placed in different levels of the column can increase
both the total head and the liquid flow rate.
(2) The average fluid mixture density decreases and can be maintained in a low value
when the number of air jet nozzles used is high.
(3) The height of the packed column can be adjusted by adding or removing tubes with
heat and mass transfer efficiency needed. So the number of air jet nozzle used can
also be adjusted.
(4) The use of several air jet nozzles can improve the air lift pump efficiency because the
quantity of consumed air can reduced.
ACKNOWLEDGEMENTS
This work was supported by Science Faculty of Tunis. El MANAR University-
Tunisia, 2012.
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