Summary,Absorption
Knowledge:
Three main parts:
Part 1,how to achieve an absorption process?
Part 2,how to determine the basic parameters of a
packed column?
Part 3,how to enhance an absorption process?
Part 1,how to conduct an
absorption process?(1)
abs
orpti
on
Rich gas
(solute gas
and inert gas)
Dilute or
lean gas
Weak or
fresh
liquid
Strong
liquid
Regeneration
process
ie,Stripping
or desorption
solute
Plate column
packed column
Part 1,how to
conduct an
absorption
process?(2)
Distributor and redistributor
packings
packing support
packing cover
Part 1,how to conduct an
absorption process?(3)
packings
– dumped packings
– stacked packings
– constructed packings
porosity,60-90%
Part 2,how to determine the basic
parameters of a packed column
(Diameter and Height)?
Diameter of packed tower
– Superficial gas velocity
– flooding velocity
How to determine flooding velocity
L=0
L1
L2
A
A
B
B
Pr
ess
ure
dr
op
of g
as
Velocity of gas
slope,1.8
Counter
current flow and
cocurrent flow
Continous
phase and
dispersed phase
Loading point
and flooding
point
Height of packed tower(1)
limiting gas/liquid ratio
operating line and equilibrium
line
X
Y
X2
Y2
Y1
X1
With the decrease of L….
L=1.1-2 Lmin
V,Y2 L,X2
V,Y1 L,X1
Y,X,
dH
H
*
*
*
*)()(
1
2
1
2
YY
dY
aK
V
YY
dY
aK
V
H
YY
dY
aK
V
dH
YYKd H aNAV d Y
Y
Y
Y
Y
Y
Y
Y
Y

Height of packed tower(2)
Number of transfer units (NTU)
& Height of a transfer unit(HTU)
V,Y2 L,X2
V,Y1 L,X1
Y,X,
dH
H
*
1
2 YY
dY
N
aK
V
H
Y
Y
OG
Y
OG
KYa,overall volumetric mass transfer
coefficient based on gas component
Part 3,how to enhance an
absorption process?
Mechanism of mass transfer between phases
How to reduce resistence
How to enlarge driving force
How to improve apparatus
*)(
AAG
A
ppAK
f o r c e
d r i v i n g
tc o e f f i c i e n
t r a n s f e r
a r e aN

Mechanism of mass transfer between
phases,Two film theory
pA
interface
pAi
cAi cA
diffusion in each boundary layer
convection outside the layer
equilibrium at the interface
How to reduce resistance
dz
dcDJ A
AB
*)(
)(
AAG
AiAG
ppKN
ppkN

LGG HkkK
111
pAi=cAi/H
Diffusivity (diffusion coefficient)
individual mass transfer coefficient
overall mass transfer coefficient
Henry’s Law
resistance
How to enlarge driving force
solvent
temperature
absorption with
chemical
reaction(eg fast and
irreversible )
X
Y OL
EL1
EL2
EL3
How to improve apparatus
new packings
– porosity and area
– flow condition
membrane absorption
– area (area per volume of apparatus)
– flooding,flow condition
Membrane absorption
Summary,Absorption
Methodology
– Differential contact vs stage contact
– D,k,K
0,3 30,3 30,8-0,6 7
1C GaScSh Re?