lecture absorption

1. Unit Operation 1
By: Dr. Amer Aziz
Dr. Farah Talib
Absorption
Lect. No. 3 Part 1+2

2. Packed column
Absorption and stripping are frequently conducted in packed columns, particularly when:
(1) the required column diameter is less than 2 ft.
(2) the pressure drop must be low, as for a vacuum service.
(3) corrosion consideration favour the use of ceramic or polymeric material.
(4) low liquid holdup is desirable.
Structured packing is often favoured over random packing for revamps to overcome capacity limitation of
trayed towers. The counter current packed towers operates in a different manner from plated towers. In packed
towers the fluids are in contact continuously in their path through the tower, while in plated towers the fluids
are contacted occasionally. So, packed columns are continuous differential contacting devices that do not have
the physically distinguishable stages found in tray towers. Thus, packed columns are best analysed by mass
transfer considerations rather than by the equilibrium – stage concept. Nevertheless, in practice packed – towers
performance is often analysed on the basis of equivalent equilibrium stages using a packed height equivalent to
a theoretical (equilibrium) plates (stage), called the HETP or HETS and defined by the equation:

3. G
The most important reason to use packed towers in
absorption is to provide a large contact area as possible as
can. There are many types of packing such as, Rasching
rings, Lessing rings, Bert Saddles, Pall ring, and many
others, most of these types of packing are made of cheep
inert materials such as glass, ceramic, graphite or, plastic,
but some times it may be made of stainless –steal.

14. 1.1-1.5

15. above
(X1)max=X*

16. (X1)max=X*

21. Q2:- In a tower (0.254m) in diameter, absorbing acetone from air at 293K and 1 atm using
pure water. The following experimental data were obtained:-
Height of (25 mm Rashing rings) packings = 4.88 m
Inert gas flow rate 3.3 kmol. Air/hr.
Mole fraction of inlet gas = 0.015 of acetone.
Mole fraction of outlet gas = 0.00072 of acetone.
Pure water flow rate = 9.03 kmole/hr.
Mole fraction of outlet water = 0.00363
Equilibrium equation: y = 1.75 x
Calculate:-
1-Overall M.T.C in gas phase and H.E.T.P.?
2-min. liquid flow rate and percentage of excess liquid used?
3-The relation between HTU)G and HTU)L?
4-If plate tower used, find the No. of stages analytically and graphically?

27. Q3:- Gas from petroleum absorption column has H2S concentration
to be reduced from 0.03 kmol to 1% of this value by scrubbing with
(TEA) solvent. Solvent enters free from H2S and leaves containing
0.013 kmol. The flow rate of inner gas 0.015 kmol/m2.s and the gas
phase resistance controls, KOG.a = 0.04 kmol/m3.s .
Equilibrium relation y = 2 x.
Find ( Z ) and NTU)OG ? all % in mole ratio.

29. Thank You for your
patience