Absorption & indusrial absorber,Gas Absorption,Equipments,Absorption in chemical Reaction,Absorption in Packed Tower,Absorption for counter current,Choice of Solvent,Continuous Contact Equipment,Height Equivalent to Theoretical Plate,HETP

2.  It is a mass transfer operation in which one or
more gas solutes is removed by dissolution in a
liquid.
 The inert gas in the gas mixture is called “carrier
gas”.
 In the absorption process of ammonia from air-
ammonia mixture by water, air is carrier gas,
ammonia is „solute” and water is absorbent.

3.  An intimate contact between solute gas and
absorbent liquid is achieved in a suitable
absorption equipment, namely, tray tower,
packed column, spray tower, venture scrubber,
etc.
 Desorption or stripping operation is the reverse
of absorption. Absorption operation is of two
types; physical and chemical.
 𝑆𝑆𝑆𝑆𝑆𝑆 +𝑆𝑆𝑆𝑆𝑆𝑆𝑆 𝑆𝑆𝑆
 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 = 𝑆𝑆𝑆𝑆𝑆𝑆 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 𝑆𝑆
𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆
 +
 𝑆𝑆𝑆𝑆𝑆𝑆𝑆 𝑆𝑆𝑆.

4.  Absorption and stripping (as well as
distillation) operations are usually carried out
in vertical, cylindrical columns or towers in
which devices such as plates or packing
elements are placed.
 The gas and liquid normally flow
countercurrently, and the devices provide the
contacting interfacial surface through which
mass transfer takes place (cocurrent flow is also
possible from economic standpoint).

5.  Operations in which one or more components of a
gas phase are absorbed into a liquid phase are
common throughout the chemical process industries
and frequently serve to achieve desired reactions
among components in the two phases (Lee & Tsui,
1999).
 Such operations are often called reactive absorption
because of the combination of reaction and
absorptive mass transport.
 As an example, in the absorption of carbon dioxide
by caustic soda, the carbon dioxide reacts directly
with the caustic soda.

6.  An advantage of absorption plus reaction is the
increase in the mass-transfer coefficient.
 This may be due to a greater effective
interfacial area.
 The process hydrodynamics can also be
directly involved via correlations for the hold-
up, pressure drop, and mass transfer
coefficients, etc.
ADVANTAGE :

8.  Generally , the gas which to be absorbed in the
liquid which is sparged to the bottom of the
column with the help of carrier gas.
 The carrier gas which has insoluble in the liquid
solvent.
 The liquid solvent is entered at the top side
countercurrently.
 At the some height,the packing material is set
for mass transfer operation where absorption
occurs.

9.  The packing either be Regular or Random
based on industrial requirement.
 Abbility of absorption mainly depends on
choice of solvent however it will be good
prefered for gases or not.

10.  Gas solubility
 Volatility
 Corrosiveness
 Cost
 Viscosity
 Miscellaneous

12.  The basic expressions for material balances and
their graphical interpretations will be
presented for countercurrent flow (a similar
method may be used for cocurrent flow).
 The gas stream at any point in the tower
consists of G total moles/hr, made up of
diffusing solute A of mole fraction yA, partial
pressure pA, or mole ratio YA, and non-
diffusing, essentially insoluble gas GS
moles/hr. The relationships among these are:

13.  Similarly the liquid stream consists of L total
moles/hr, containing xA mole fraction soluble
gas, or mole ratio XA, and essentially non-
volatile solvent LS moles/hr. The relationships
among them are:
 Thus the material balance (for y and x subscript
A is omitted):
 which is rearranged for the gas phase mole
fraction of y as:

14.  It is easy to prove that the second parts of the
last two equations are equal, by writing a
material balance on the whole equipment
which can be rearranged as follows:


15.  The liquid and gas compositions in a packed
tower changes continuously throughout the
height.
 The composition of solute from entry to exit of
the packed tower is represented by operating
line and every point indicates some location in
the packed tower.
 On the other hand, in tray tower, few points
(number of trays) in the operating line
represents the conditions in the trays.

16. Height Equivalent to Theoretical Plate::::::
 For a specified separation job, in packed tower,
the height of packing is to be determined and
in tray tower, numbers of ideal trays are
determined.
 The ratio between packing height to number of
trays required for the same separation is called
height equivalent to theoretical plate (HETP)

18. • Relatively low pressure drop
• Capable of achieving relatively high mass-
transfer coefficient and high mass transfer rate
• Increasing the height and/or type of packing or
try numbers capable of improving mass
transfer without purchasing a new piece of
equipment
• Relatively low capital cost
• Relatively small space requirements

19.  • Fiberglass-reinforced plastic construction
permits operation in highly corrosive
atmospheres.
• Ability to collect particles as well as gases
• Collected substances may be recovered by
distillation

20.  • Possibility of creating water (or liquid) disposal
problem (remark: IPPC)
 • Product collected wet
 • Particulates deposition possibly causing
plugging of the bed or the plates
 • Fibreglass-reinforced plastic is sensitive to
temperature
 • Relatively high maintenance cost
 • Must be protected from freezing (if operated in
outside)