Al stge CHE 411 Separation Processes II

First semester 1429/1430 H-2008/2009G

ABSORPTION

1. Introduction Choice of solvent for an absorption duty

The two film theory of mass transfer

Mass transfer coefficients and driving forces

The equilibrium data – solubility, effect of temperature on solubility, Antoine equation

The equilibrium stage concept

2. Absorption as a stagewise processAbsorption in plate (tray) columns

Derivation of the operating line equation

Determination of the number of theoretical stages

Graphically

Analytically , absorption factor method, Kremser-Souders-Brown equation

Cases of concentrated and dilute solutions and mixtures

Determination of the minimum flows

Examples: 10.3-1, 10.3-2 and 10.3-3 Geankoplis 3rd edition

Tutorial #1

3. Absorption as a differential processAbsorption in packed columns

Packings, why use packings?, types and properties Characteristics of tower Packings, size, specific surface

, voidage , bulk density , packing factor Derivation of the design equation and Determination of

tower packed height

General equation for the height of packed section , capacity coefficients, Cases of concentrated and dilute solutions and mixtures.

1 1,N NG y

1 1,G y

,N Nx L

0 0,x L

N

1

n

Number of Transfer Units - overall and individual

Height of Transfer Units - overall and individual

Analytical and graphical determination of

Empirical correlations of Height of transfer units , empirical correlations of mass transfer coefficients.

Determination of tower diameter

Fluid flow through packings, pressure drop, loading, flooding, experimental graphical plots used for tower diameter determination.

Examples: 10.6-1, 10.6-2, 10.6-3, 10.7-1, and 10.8-1 Geankoplis 3rd edition

Tutorials #2 and #3

h.m.mustafa

Absorption in Plate Columns

Determination of the Number of Theoretical Stages

Analytically Absorption Factor Method (Kremser-Souders-Brown equation)

Assume dilute solution and linear Equilibrium

Relationship of the form y=mx

Balance for plate n:

Absorption in Packed Columns

Determination of Number of Overall Gas Phase

Transfer Units Analytically

1,G y

2,G y

1,x L

2 ,x L

1

2

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Or

Absorption in Packed Columns

Determination of Number of Overall Gas Phase

Transfer Units Analytically (Absorption Factor

Method)

Material balance:

Equilibrium relationship being straight line passing

Through the origin (0, 0)

By Substituting

For Number of overall gas phase transfer units:

Where:-

Then:

Then:

Absorption in Packed Columns

Height of tower packed section for concentrated solutions: General equation and special cases:

2

1

2

1

(1 )

(1 ) (1 )( )

(1 )

(1 )

(1 )( )

y

lmT

y lm ey

T OG OG

OGy lm

y

lmOG

ey

yGZ dy

K a y y y y

Z H N

GH

K a y

yN dy

y y y

(1 ) (1 )

(1 )ln[(1 ) /(1 )]

elm

e

y yy

y y

i) when (1 )lmy is approximated by the arithmetic average(1 ) (1 )

2ey y

(1 ) (1 )(1 )

2e

lm

y yy

Which can written as: (1 ) (1 ) (1 ) (1 ) ( )

(1 ) (1 )2 2 2

e e ey y y y y yy y

Then substitute in OGN and integrate:

2 2

1 1

2 2

1 1

( )(1 )(1 ) 2

(1 )( ) (1 )( )

( )(1 )

(1 )( ) 2(1 )( )

ey y

lmOG

e ey y

y y

e

e ey y

y yyy

N dy dyy y y y y y

y yydy dy

y y y y y y

2 2 2

1 1 1

2

1

11ln

( ) 2(1 ) ( ) 2 1

y y y

e ey y y

ydy dy dy

y y y y y y

ii) when 0ey as when absorption is accompanied by a fast chemical reaction

(1 ) (1 )(1 )

ln[(1 ) /(1 )] ln(1 )e

lme

y y yy

y y y

2 2

1 1

1 1

2 2

1

2

(1 )

(1 )( ) (1 )( ) ln(1 )

ln(1 )(ln(1 ))ln

(1 ) ln(1 ) ln(1 ) ln(1 )

y y

lmOG

ey y

y y

y y

y yN dy dy

y y y y y y

ydy d y

y y y y