Absorption process

REPUBLIC OF IRAQ
MINISRY OF RESEARCH AND HIEGHER EDUCATION
NORTHERN TECHNICAL UNIVERSITY
TECHNICAL COLLEGE OF KIRKUK
FUEL AND ENERGY ENGINEERING
ABSORPTION
PROCESS
SUBMITTED TO :
 Mrs. Eman Husain
 HOD (HEAD OF DEPARTMENT)
SUBMITTED BY:
 RAMI ALADDIN
 Northern TechnicalUniversity
 Energy & Petrol Engineering

CHEMICAL PROCESS – GAS ABSORPTION
1
CONTENTS
1. INTRODUCTION ------------------------------------------------------------------------ 2
2. THE USES OF ABSORPTION-------------------------------------------------------- 3
3. THEORY OF ABSORPTION ----------------------------------------------------------- 4
4. ABSORPTION IN INDUSTRIAL CORPORATIONS ----------------------------- 6
5. CHOICE OF ABSORPTION SOLVENT --------------------------------------------- 8
6. ABSORPTIN COLUMN TYPES ---------------------------------------------------------9
A. PACKED COLUMN ----------------------------------------------------------------------10
a. Component-----------------------------------------------------------------------10
b. Uses of packed column --------------------------------------------------- 11
c. General information --------------------------------------------------------- 12
d. Equipment design -------------------------------------------------------------12
e. Advantages and disadvantages of packed column--------------- 17
B. PLATE ABSORPTION COLUMN ----------------------------------------------------18
a. Equipment design --------------------------------------------------------------------20
b. Advantages and disadvantages of plate column --------------------------21
c. some advantages and disadvantages for the plate
and the packed columns -----------------------------------------------------------21
COMPARESIMS BETWEEN PLATE & PACKING COLUMNS---------------------21
i. PACKED VS PLATE COLUMNS ------------------------------------------- 22
ii. Conditions favouring packed columns ----------------------------------22
iii. Conditions favouring plate columns --------------------------------------22
iv. Plate contactors ------------------------------------------------------------------23
v. Choice between plate and packing columns ---------------------------24
C. SPRAY COLUMN
a. General informations Equipments design------------------------------------25
b. Usage examples ----------------------------------------------------------------------25
c. Advantages & Disadvantages ----------------------------------------------------25
D. FULLING FILM ---------------------------------------------------------------------------27

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a. General informations Equipments design -----------------------------------28
b. Advantage & Disadvantages -----------------------------------------------------28
E. BUBBLE CUP---------------------------------------------------------------------------28
a. General informations Equipments design---------------------------------28
b. Usage examples--------------------------------------------------------------------28
c. Advantage & Disadvantages --------------------------------------------------29
7. Comparison of Gas Absorption and Distillation Unit Operations ----31
8. REFERENCES----------------------------------------------------------------------------32

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1. Introduction
An Absorption is a technique which commonly used for scrubbing
operation, to separate a component present in a gas mixture by the help
of a solvent which dissolves a particular selected component. Some of
the main characteristics of absorption operation are compared with
distillation operation. Distillation is such a unit operation that uses
thermal energy to separate component into fraction based on their boiling
points:
-In absorption (also called gas absorption, gas
scrubbing, or gas washing), there is a transfer of
one or more species from the gas phase to a
liquid solvent. The species transferred to the
liquid phase are referred to as solutes or absorb
ate. Absorption involves no change in the
chemical species present in the system
ABSORBERS
Absorbers bring gas and liquid phases in contact, so that contaminants in the
gas phase absorb into the liquid phase as a result of their interaction.
ABOUT ABSORPTION
During absorption, soluble components of a gas mixture dissolve into a liquid.
The animation below demonstrates that as the two streams contact, mass
transfer of the soluble components takes place.
The entering gas stream, shown in yellow, contains solutes that are absorbed
into the entering liquid stream, shown in purple. The exiting gas stream shown
in orange leaves the column without the solute, while the exiting liquid
stream, shown in blue, leaves with the solute. Absorption is usually carried out
in vertical and cylindrical columns or towers. The gas and liquid phases can
interact via co-current flow, counter-flow, or cross-flow.
2.BUT WHERE CAN I USE IT ?!!
-Well, here you are ..
Absorption is used to separate gas mixtures, remove impurities, or recover valuable
chemicals.
A common use for an absorption tower is as a scrubber. Scrubbers remove
material from gases vented from factories to reduce pollution. Air quality

4
standards usually require the use of scrubbers and other safety devices to trap
pollutants.
In factories using an absorption tower for scrubbing, the waste products captured
by the fluid can be safely collected and properly disposed of, or converted into
use in other industrial processes. These devices can also be used in settings like
refineries to separate out different usable components of gases.
3.THE MECHANISM OF ABSORPTION
The two-film theory
The most useful concept of the process of absorption is given by the two-film theory
due to WHITMAN(1), and this is explained fully in Volume 1, Chapter 10. According to
this theory, material is transferred in the bulk of the phases by convection currents, and
concentration differences are regarded as negligible except in the vicinity of the interface
between the phases. On either side of this interface it is supposed that the currents die out
and that there exists a thin film of fluid through which the transfer is effected solely by
molecular diffusion. This film will be slightly thicker than the laminar sub-layer, because
it offers a resistance equivalent to that of the whole boundary layer. According to Fick’s
law (Volume 1, equation 10.1) the rate of transfer by diffusion is proportional to the
concentration gradient and to the area of interface over which the diffusion is occurring.
Fick’s law is limited to cases where the concentration of the absorbed component is low.
At high concentrations, bulk flow occurs and the mass transfer rate, which is increased by
a factor CT /CB, is governed by Stefan’s law, equation 12.2. Under these circumstances,
the concentration gradient is no longer constant throughout the film and the lines AB and
DE are curved. This question has been discussed in Chapter 10 of Volume 1, but some
of the important features will be given here.
The direction of transfer of material across the interface is not dependent solely on the
concentration difference, but also on the equilibrium relationship. Thus, for a mixture of
ammonia or hydrogen chloride and air which is in equilibrium with an aqueous solution,
the concentration in the water is many times greater than that in the air. There is,
therefore,
a very large concentration gradient across the interface, although this is not the
controlling
factor in the mass transfer, as it is generally assumed that there is no resistance at the
interface itself, where equilibrium conditions will exist. The controlling factor will be the
rate of diffusion through the two films where all the resistance is considered to lie. The
change in concentration of a component through the gas and liquid phases is illustrated
in Figure 12.1. PAG represents the partial pressure in the bulk of the gas phase and PAi
the partial pressure at the interface. CAL is the concentration in the bulk of the liquid
phase and CAi the concentration at the interface. Thus, according to this theory, the
concentrations at the interface are in equilibrium, and the resistance to transfer is centred
in the thin films on either side. This type of problem is encountered in heat transfer across
a tube, where the main resistance to transfer is shown to lie in the thin films on either
side of the wall; here the transfer is by conduction.

5
ABSORPTION OF GASES 659
Figure 12.1. Concentration profile for absorbed component A
4.. ABSORPTION IN INDUSTRIAL CORPORATIONS:
An absorption tower is an industrial tower used to separate out components of a
rising gas with the use of a falling liquid to trap the gas. This equipment is used in
a variety of settings for purification, processing of materials, and other activities.
The absorption tower usually needs to be custom designed for a specific
application to ensure efficient and smooth operation. Like other components of a
factory, it needs regular cleaning and maintenance to function properly and can
be subject to inspection by regulatory officials.

6
In an absorption tower, the gas is pumped in at the bottom of the tower. It, along
with any impurities it contains, begins to float to the top. As it moves toward the
top, aerosolized liquid is sprayed into the tower. The droplets catch impurities in
the gas and carry them to the bottom of the tower for collection. Some towers
can have multiple points where liquid is sprayed out to capture different
impurities or maximize the amount of material trapped.
The flow of fluid and gas has to be carefully controlled, as does the temperature,
as these factors can have an impact on how much the water can absorb. If
conditions in the tower or the factory change, adjustments may need to be made
to compensate. Operators can take steps like shutting off components of a
factory, using shunts to move waste material to different towers, and so forth to
control factory operations and keep conditions as safe and efficient as possible.
For cleaning and maintenance, an absorption tower typically needs to be shut
down to allow workers to access it safely. If the tower handles potentially
hazardous or toxic substances, special gear may be required to enter it and
employees are monitored for signs of exposure. Inspectors can include
absorption towers in the list of factory components they examine to confirm
compliance with the law and verify claims made by the factory about how it

7
operates. - The operation of reoving the absorbed solute from the solvent is called
stripping.
Absorbers are normally used with strippers to permit regeneration (or recovery) and
recycling of the absorbent. Since stripping is not perfect, absorbent recycled to the
absorber contains species present in the vapor entering the absorber. When water is used
as the absorbent, it is normally separated from the solute by distillation rather than
stripping.

8
Chemical absorption or reactive absorption is a chemical reaction between the
absorbed and the absorbing substances. Sometimes it combines with physical
absorption. This type of absorption depends upon the stoichiometry of the
reaction and the concentration of its reactants
Some processes involving physical or chemical absorption are listed in Table 1, while.
Industry
Compound to be removed
Solvent
Wood industry (Kraft
and sulphite methods)
Glass production
SO2 Water
Carbon Industry CO2
water, basic liquids
(K2CO3) or other
solvents (acetone, etc.)
HNO3 production NOx
Water (absorption +
chemical
reaction)
H2SO4 production SO3 H2SO4 (98 %)
HCl production HCl water
Explosive manufacture NOx water
Obtaining of Cl2 without
NaOH (American
Cianamid Co Method)
Cl2 SCl2, CCl4
SO2 H2SO4
5.Choice Of Solvent for Absorption
 If the principal purpose of the absorption operation is to produce a specific
solution, as in the manufacture of hydrochloric acid, for example, the
solvent is specified by the nature of the product, i.e. water is to be the
solvent. If the principal purpose is to remove some components (e.g.
impurities) from the gas, some choice is frequently possible.
 The factors to be considered are:
 GAS SOLUBILITY :
The gas solubility should be high, thus increasing the rate of
absorption and decreasing the quantity of solvent required.
Solvent with a chemical nature similar to the solute to be absorbed
will provide good solubility.

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 VOLATALITY :
The solvent should have a low vapour pressure to reduce loss of
solvent in the gas leaving an absorption column.
 CORROSIVENESS :
The materials of construction required for the equipment should not
be unusual or expensive
 COST :
The materials of construction required for the equipment should not
be unusual or expensive.
 VISCOSITY :
Low viscosity is preferred for reasons of rapid absorption rates,
improved flooding characteristics in packed column, low pressure drops on
pumping, and good heat transfer characteristics.
 The solvent should be non-toxic, non-flammable and chemically stable.
Absorption Equipment
Gas absorption at an industrial scale is most commonly practiced in packed
towers,
6.COLUMNS OF ABSORPTION

10
1.PACKED COLUMN:

11
Analyzing a packed tower involves both mass transfer and fluid mechanics. The
mass transfer detailed in the following section determines the height of the
packed tower this mass transfer is described as molar flows partly because of the
chemical reactions that often Occur. The fluid mechanics described in this
section, determines the cross-sectional area of the packed tower. The fluid
mechanics is described as mass flows a consequence of the physics that
control the process. To describe the physics, we discuss the tower packing, the
Flows themselves, and the estimation of the towers cross section
- The packing types can be divided into two broad classes:
structured and random packings. Earlier the random packings were more commonly used
in the industry (Raschig-, Pall- and HyPack rings, and Berl- and Intallox saddles).
USING OF PACKED COLUMN :
Packed columns are used for distillation, gas absorption and liquid-liquid extraction.
The gas-liquid contact in a packed column is continuous, not stage-wise, as in a plate
column. The liquid flows down in the column over a packing surface and the vapor (or
the gas) moves counter-currently, up the column. The performance of a packed column is
very dependent on the maintenance of good liquid and gas distribution through the
packed bed, and this is an important consideration in packed column design.
Packed bed columns use absorption to remove contaminants such as corrosive
gaseous emissions, acidic fumes, and various odors. Distillation columns and
packed bed columns involve essentially the same equipment.

12
GENERAL INFORMATION
Packed beds are used to clean gas streams. As the animation below shows,
gases flow up through the packed bed, shown by the arrows from orange to
yellow, and the scrubbing liquid flows down the bed, shown by the arrows from
blue to violet. Contaminants are transferred from the gas stream to the liquid
stream. The packing provides a large surface area for gas to liquid mass
transfer to occur.
EQUIPMENT DESIGN
A packed bed column contains a support plate, a liquid distributor, and a mist
eliminator. The liquid stream flows through a liquid distributor and down the
column due to gravity, resulting in counter-flow, cross-flow, or co-current
flow. Contaminants are transferred from the vapor to the liquid, due to
equilibrium or kinetic mechanisms, with the packing providing contact between
phases for this transfer.
(Copyright MikroPul, Inc., Charlotte, NC)
Mist eliminators are used to condense any vaporized scrubbing liquid. The
picture below to the left shows a mesh mist eliminator, and the picture below
to the right shows a vane mist eliminator. For more information, see the mist
eliminators section of this Encyclopedia.

13
(Copyright Amistco Separation Products Inc., Alvin, TX)
Support plates hold the packing in place within the column. The picture below
shows two types of support plates.
(Copyright Sulzer Chemtech Ltd., Switzerland)
The liquid streams flow through distributors to avoid channeling, the uneven
distribution of liquid, which can reduce the transfer of the gas contaminant to
the liquid. A variety of distributors are shown below.

14
Spray-Nozzle Distributor Extraction Distributor Slotted Distributor
Tube Distributor Radial Distributor Bottom-Hole Distributor
The picture in the next page shows a packed tower. The outer shells can be
made out of fiberglass- reinforced plastic, stainless steel, high-nickel alloys,
non-ferrous metals, or thermoplastics. The inside packing can be made of
metals, ceramics, or plastics. Inert ceramics and plastics are commonly used
when operating with corrosive substances. The packing can be
dumped(random) or structured.

15
(Copyright Tri-Mer Corporation, Owosso, MI)
USAGE EXAMPLES
Packed beds are most commonly used in air pollution control, but they are also
used in the chemical, petrochemical, food, pharmaceutical, paper, and
aerospace industries. The beds shown below are used to absorb and eliminate
ethylene gas from a sterilization chamber. The water-soluble ethylene gas is
hydrolyzed to ethylene glycol.

16
(Copyright Croll Reynolds, Inc., Parsippany, NJ)
The packed bed absorption column shown below removes acidic fumes such as
H2SO4, HCl, HNO3, and HF from an inlet gas stream. Packed bed absorption is
commonly used when dealing with corrosive substances such as these.
(Copyright Tri-Mer Corporation, Owosso, MI)

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ADVANTAGES DISADVANTAGES
 Low pressure drop required.
 Small diameters possible.
 Can handle foaming systems.
 Low capital, operating, and
maintenance cost.
 Simple construction.
 Can handle corrosive materials
due to corrosion-resistant
packing.
 Reduces backmixing in
comparison to spray columns.
 Better mass transfer than in
spray columns.
 Fewer stages compared to other
columns.
 Channeling, which must be
controlled by redistributing
liquid.
 Cannot handle extremely high or
low flow rates.
 Cannot handle liquids with high
viscosities.
 Need to be preferentially wetted
to avoid reduction of the
interfacial area to volume ratio.
===============================================================
2. plate (trayed) absorption columns
A plate column (or tray column) is a chemical equipment used to carry out unit
operations where it is necessary to transfer mass between a liquid phase and a
gas phase. In other words, it is a particular gas-liquid contactor. The peculiarity of
this gas-liquid contactor is that the gas comes in contact with liquid through
different stages; each stage is delimited by two plates (except the stage at the
top of the column and the stage at the bottom of the column).
Some common applications of plate columns are distillation, gas-liquid
absorption and liquid-liquid extraction. In general, plate columns are suitable for
both continuous and batch operations.

18

19

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EQUIPMENT DESIGN
The geometry of the trays within the column affects the extent and type of
contact between the vapor and liquid streams. The different tray types include
sieve, valve, and bubble cap. Sieve trays contain holes for vapor to flow
through. Valve trays are similar, containing holes with opening and closing
valves. Bubble cap trays contain caps that allow vapor to flow through tiny
openings through the liquid. The three ypes of trays are shown below: sieve,
valve, and bubble cap (left to right).
(Copyright Vendome Copper & Brass Works Louisville, KY)
(Copyright Clean Gas Systems, Inc.,
Hauppauge, NY)

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After the feed mixture enters the column, it flows down the column and across
the trays in either cross flow or counter-flow. In cross flow columns,
downcomers channel the liquid flowing from one tray down to the tray below.
 The liquid/vapor contact in the
cross flow of plate columns is
more effective than the
countercurrent flow in packed
columns.
 Can handle high or low liquid
flow rates cost effectively.
 Can handle solids.
 Easily customized to specific
requirements such as operations
requiring much heat.
 Higher pressure drops than
packed columns.
 Slow reaction rate processes.
 Plugging and fouling may occur.
COMPARESIMS BETWEEN PLATE & PACKING COLUMNS
There are some advantages and disadvantages for the plate and the packed
columns.
1. Plate columns can be designed to handle a wider range of liquid and gas flow rates
than packed columns.
2. Packed columns are not suitable for very low liquid flow rates.
3. The efficiency of a plate can be predicted more accurately than the equivalent terms of
packings (HETP or HTU).
4. For corrosive liquids a packed column will usually be cheaper than the equivalent
plate column.
5. The liquid hold-up is lower in a packed column than in a plate column. This can be
important when the hold-up of toxic or flammable liquids must be kept as small as
possible for safety reasons.
6. Packed columns are more suitable for handling foaming systems.
7. The pressure drop can be lower in a packed column than the equivalent plate column.

22
packed column Vs plate column :
The difference in costbetween plate and packed columns is nottoo great, although packings are
generally more expensive than plates.
In addition, the difference in column heightis not usually significant if the flow rates are such that
efficiencies are near maximum.
Conditions favouring packed columns:
small-diameter columns (less than 0.6m)
more choices in materials ofconstruction for packings especially in corrosive service (e.g. plastic,
ceramic, metal alloys)
lower pressure drop (importantin vacuum distillation)
less liquid entrainment· low liquid hold-up, especially suitable for thermally sensitive material
foaming liquids can be handled more readily (less agitation ofliquid by the vapour)
Conditions favouring plate columns:
variable liquid and/or vapour loads
low liquid rates · large number of stages and/or diameter
high liquid residence time
dirty service (plate columns are easier to clean)

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CHOICE BETWEEN PLATE AND PACKED COLUMN
The choice between use of tray column or a packed column for a given mass transfer
operation should, theoretically, be based on a detail cost analysis for the two types of
contactors. However, the decision can be made on the basis of a qualitative analysis of
relative advantages and disadvantages, eliminating the need for a detailed cost
comparison.
Which are:
1. Because of liquid dispersion difficulties in packed columns, the design of tray column is
considerably more reliable.
2. Tray columns can be designed to handle wide ranges liquid rates without flooding.
3. If the operation involves liquids that contain dispersed solids, use of a tray column is
preferred because the plates are more accessible for cleaning.
4. For non-foaming systems the plate column is preferred.
5. If periodic cleaning is required, man holes will be provided for cleaning. In packed
columns packing must be removed before cleaning.
6. For large column heights, weight of the packed column is more than plate column.
7. Design information for plate column is more readily available and more reliable than
that for packed column.
8. Inter stage cooling can be provided to remove heat of reaction or solution in plate
column.
9. When temperature change is involved, packing may be damaged.
10. Random-packed columns generally are not designed with diameters larger than 1.5 m,
and diameters of commercial tray column are seldom less than 0.67m.

24
As my system is non foaming and diameter calculated is larger than 1.5m so I am going
to use tray column.
Also as average temperature calculated for my distillation column is higher that is
approximately equal to 98oc. So I prefer Tray column.
PLATE CONTACTORS:
Cross flow plate are the most commonly used plate contactor in distillation. In which
liquid flows downward and vapours flow upward. The liquid move from plate to plate
via down comer. A certain level of liquid is maintained on the plates by weir. Other
types of plate are used which have no down comer (non-cross flow) the liquid
showering down the column through large opening in the plates (called shower plates).
Used when low pressure drop is required.
Three basic types of cross flow trays used are
(1) Sieve Plate (Perforated Plate)
(2) Bubble Cap Plates
(3) Valve plates (floating cap plates)
I prefer sieve plate because:
(1) Their fundamentals are well established, entailing low risk.
(2) The trays are low in cost relative to many other types of trays.
(3) They can easily handle wide variations in flow rates.
(4) They are lighter in weight. It is easier and cheaper to install.
(5) Pressure drop is low as compared to bubble cap trays.
(6) Peak efficiency is generally high.

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(7) Maintenance cost is reduced due to the ease of cleaning.
3.SPRAY COLUMNS
GENERAL INFORMATION
Spray columns are differential contactors, and as such they use continuous
contact between the two phases, as opposed to the stages used in staged
contactors.
EQUIPMENT DESIGN
As the animation below demonstrates, the liquid stream enters the column
through spray nozzles, shown by the movement of arrows from blue to violet.
Nozzles can be placed at different heights in the column. The droplets that
form provide a large surface area for exposure to the gas stream; smaller
droplets result in a greater exchange area. Gas flows counter-currently with
respect to the liquid in the animation below, as shown by the movement of
arrows from orange to yellow. The gas could also flow co-currently with the
liquid. Low droplet velocities may lead to low contact or turbulence, and high
droplet velocities may cause flooding. Therefore, an optimum droplet velocity
is essential. A mist eliminator (not shown) is used to separate any liquid that is
entrained into the gaseous phase.
USAGE EXAMPLES
One example of a spray column is in the absorption of sulfur dioxide from coal-
fired boiler exhaust gases.
 Low pressure drop.
 Only one stage.
 Most effective for solutes with
high liquid solubility
 High pumping cost.
 Entrainment; gas carries liquid
as mist.
 Poor mass transfer.
 Low residence times.
 Backmixing.
 Droplets may form improperly or
coalesce.

26
In the spray tower, the gas enters at the bottom and the liquid is introduced through a
series
of sprays at the top. The performance of these units is generally rather poor, because the
droplets tend to coalesce after they have fallen through a few metres, and the interfacial
surface is thereby seriously reduced. Although there is considerable turbulence in the gas
phase, there is little circulation of the liquid within the drops, and the resistance of the
equivalent liquid film tends to be high. Spray towers are therefore useful only where the
714 CHEMICAL ENGINEERING
Figure 12.33. Centrifugal spray tower(78)
main resistance to mass transfer lies within the gas phase, and have consequently been
used with moderate success for the absorption of ammonia in water. They are also used
as air humidifiers, in which case the whole of the resistance lies within the gas phase.
Centrifugal spray tower
Figure 12.33, taken from the work of KLEINSCHMIDT and ANTHONY(78), illustrates
a spray
tower in which the gas stream enters tangentially, so that the liquid drops are subjected
to centrifugal force before they are taken out of the gas stream at the top.

27
4. FALLING FILM
GENERAL INFORMATION/EQUIPMENT DESIGN
The image below shows the operation of a falling film absorber. Falling film
absorbers are differential contactors, and are mainly used when a large amount
of heat is removed during absorption. Falling film absorbers are also vertical
shell and tube heat exchangers. As the animation below demonstrates, the
cooling medium falls through the absorber according to the movement of
arrows from teal to green. The vapor rises through the tubes, shown by the
movement of bubbles from orange to yellow, and the solvent falls through the
tubes, shown by the movement of arrows from blue to violet.
The solvent enters at the top and falls down the tube as a film. Gas enters at
the bottom or top to produce counter-current or co-current flow. The
absorption of contaminants from the gas to the solvent depends on gas
velocity, liquid-gas distribution, and the tube surface condition.

28
 Low pressure drop.
 Minimal static head and
residence time.
 Ideal for heat-sensitive fluids.
 Easy cleanup.
 Continuous heat removal.
 Flooding.
 Restricted by pressure drop.
 Film breakup.
 Need continuous heat removal.
 Evaporation may deteriorate
components.
 Liquid must be uniformly
supplied.
5.BUBBLE COLUMNS
GENERAL INFORMATION/EQUIPMENT DESIGN
Bubble columns are a type of sparged tank. In a sparged tank, the gas stream is
introduced in the form of small bubbles and acts as the agitator. As shown in
the animation, gas enters at the bottom through a gas distributor or sparger,
shown by the movement of arrows from orange to yellow, and is dispersed in
the form of bubbles through the liquid stream, shown by the movement of
arrows from blue to violet. The liquid can be introduced at the top or the
bottom, resulting in either counter-flow or co-current flow, respectively. The
bubbles rise at a velocity determined by the bubble size: the larger the
bubbles, the faster they rise. Spargers are designed to produce consistent
bubble sizes, so that all the bubbles rise at the same velocity. The bubbles may
contain entrained liquid, which may result in more hold up at high velocities.
USAGE EXAMPLES
Bubble columns can be used to purify nitroglycerin with water; in the chemical
industry for hydrogenation, oxidation, chlorination, and alkylation; and in the
biotechnology field for effluent treatment, single-cell protein production,
animal cell culture, and antibiotic fermentation. Bubble columns can be used
for radioactive elements because there are no moving parts.

29
 High thermal stability.
 Uniform distribution because of
high liquid circulation.
 Low energy input requirements.
 Two gases that form an
explosive mixture may be used.
 Long liquid residence time.
 Low investment cost.
 Large mass transfer area.
 Can handle radioactive materials
because there are no moving
parts.
 Low contact efficiency.
 Backmixing.
 Short gas residence time.
 High gas pressure drop.

30
Comparison of Gas Absorption and Distillation Unit Operations
Comparison of Gas Absorption and Distillation:
ABSORPTION
 Gas absorption is operation which deals with the separation of constituent present
in a gas mixture.
 A liquid is used for separation of gas mixture
 The solvent in liquid form is below it boiling point
 The principle of solute diffusion governs the absorption operation that is a
component from gas phase diffuse into liquid phase
 Pure products are not obtained further purification operations are required
 Heat of solution will dominate the heat effect caused by dissolved gas
 High performance of gas absorption column is attained when it operates below
dew point temperatures conditions
 The best equipment for gas absorption is packed bed column
 The degree of separation depend on the selection of solvent and solubility of gas
in that solvent
 Example:
1. Separation of ammonia from air using water
2. Separation of sulphur dioxide from flue gas using base solutions
DISTILLATION
 A liquid mixture can be separated into individual components
 Thermal energy influence the separation of liquid mixture
 The liquid exist at bubble point
 Equimolar counter diffusion take place that is mass is transferred between liquid
phase and gas phase simultaneously

31
 Pure products are produced nearly 99.99%
 Latent heat of vaporisation and condensation are dominating heat effect of
distillation tower
 All vapour should be at dew point temperature for continuous operation of
distillation column
 High performance of distillation operation is obtained by a plate tower equipment
 Separation of component by distillation depends on the volatility of individual
component present in the feed liquid mixture. The large the difference of
volatility between them the higher the separation can be done
 Example :
1. Separation of crude petroleum into fuels as gasoline, diesel etc.
2. Separation of methanol and water

32
REFERENCES
1. .wikipedia.org/wiki/Absorption
2. www.cpp.edu
3. http://www.absorbtion in chemical industry
4. chemical engineering Volume 2
5. http://www.separationprocesses.com
6. http://neweducation-plus.blogspot.com
7. Gas Liquid Absorption (Theory) _ Chemical Engineering _ Chemical
Engineering _ IIT Bombay Virtual Lab
8. www.separationprocesses.com/Absorption/GA_Chp03.htm
9. faculty.ksu.edu.sa/malik/Documents/absorption.doc
10.www.che.iitb.ac.in
11.portal.unimap.edu.my
12.www.ivt.ntnu.no
13.www.slideshare.net
14.www.linkedin.com

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Absorption process