DESIGN OF ABSORPTION COLUMN

PRESENTED BY: ALI SHAAN(016) USAMA SAEED(049) ALI HASSAN(031)

CASE

It is required to design a packed tower to treat 40000 ft3 /h of an air stream containing 20 mole% of so2 at 700c and 1 atm total pressure. It is necessary to recover 96% of the so2 using water at a rate 30% more than the minimum. The column may be

packed with 112

-inch Raschig rings and may be operated at 60% of the flooding

velocity. The individual mass transfer coefficients are / 3xk a=1.25kmol/m s and

/ 3yk a=0.075kmol/m s . Design the tower.

STEPS USED DURING DESIGN OF ABSORPTION COLUMN

• Selection of solvent• Selection of column type• Selection of packing• Equilibrium data• Material balance• Minimum solvent flow rate

CONTINUED…

• Operating solvent flow rate• Flooding/Diameter calculation• Pressure drop• Height of packing

SOLVENT SELECTION

We Selected water(H2O) here: • Because it is cheap.• Non Toxic.• Easily available.• Universal solvent

SELECTION OF PACKING

We have selected random packing here:• Because pressure drop is nearly negligible in our case.• It is cheap as compare to structured .

MATERIAL AND TYPE OF PACKING

Raschig ring 1.5 inches.Ceramic material.Because they have:• High Strength.• High Fracture Toughness.• High Hardness.• Excellent Wear Resistance.• Good Frictional Behaviour.

EQUILIBRIUM DATAg S02/100 g H2O 600c 700c 900c

0.01 0.43 0.689999997 1.210.05 5.24 7.793333308 12.90.1 13.5 19.56666661 31.7

0.15 22.7 32.53333324 52.20.2 32.6 46.29999986 73.7

0.25 42.8 60.46666649 95.80.3 53.3 74.86666645 118

CONTINUED…Mole Fractions

X y2.8124E-05 0.000908 0.000140604 0.0102540.000281169 0.0257460.000421694 0.0428070.000562179 0.0609210.000702625 0.0795610.000843032 0.0985090.001123727 0.1374560.001404264 0.1774560.00280459 0.385088

CONTINUED…Mole Ratios

X Y2.8125E-05 0.0009090.00014062 0.0103610.00028125 0.0264260.00042187 0.0447210.0005625 0.064873

0.00070312 0.0864390.00084374 0.1092730.00112499 0.1593610.00140624 0.2157410.00281248 0.626248

CONTINUED…Conversion is as follows:

The equilibrium (x, y) data are converted to mole ratio unit (X, Y) and plotted on X-Y plane. As shown below. The cure is slightly convex upward. So the operating line corresponding to the minimum liquid rate will not touch the equilibrium line. It will rather meet the equilibrium line at the point having an ordinate Y1 (0.25). This is the pinch point having abscissa = (X1)max = 0.0015.

2

2

2 2

-4

so -5

so 0

0.6( .g) 7.89x10760

/ M.W 0.02 / 64( . ) 5.625x10/ M.W 100 / . 0.02 / 64 100 /18

so

atm

H

P mmHgy eP mmHg

cx e g

c M W

EQUILIBRIUM CURVE

0 0.0005 0.001 0.0015 0.002 0.0025 0.0030

0.050.1

0.150.2

0.250.3

0.350.4

0.450.5

0.550.6

0.650.7

Equilibrium curve

Material BalanceAverage molecular weight = (mole fr. So2)*(M.W of so2)+( mole fr. Air)*(M.W of Air)

Volumetric flow rate = 40,000 ft3/hMass flow =m

. (.2)(64) (.8)(28.8)35.84

M w

31*35.84  0.07945 /1.31443*343.15

PM ft hRT

ρ

.

3 340,000 / *0.07945 / ftft h lb

CONTINUED…

1

1

1

11

1

1 1

2 1 1

2 2

2

3178.38 /1441.6889 /(1441.6889 / 35.84) kmol/ h40.2256 /0.2

0.251

(1 ) 32.180 /8.04512 /

*(0.96) 7.7233152 /

s

G lb hG kg hGG kmol hy

yYy

G G y kmol hso entering G y kmol hso absorbed so entering kmol hso leaving

2 2

2 2 2

0.32180 /

/ 0.011 / 0.001

s

kmol hconcentrationY so Gy Y Y

CONTINUED…As solvent is pure x2=0 (Mole Fraction unit)

X2=0 (Mole ratio unit)

MINIMUM LIQUID FLOW RATEBy an overall material balance:

Molecular weight of solvent =18

min 1 2

1 max 2

min

min

( )( ) X

( ) 4984.682 /( ) 1.3( ) 6480.0866 /

s

s

s

s operating s

L Y YG XL kmol hL L kmol h

6480.0886 /18116641 /

s

s

LL kg h

LIQUID FLOW RATE AT BOTTOM OF TOWER

And the x1=0.002462

1 2 116641 7.7233 116649.2821 /sL L so absorbed kg h

FLOODING VELOCITY CALCULATION

Total pressure in the tower =1atm ( I have neglected the pressure drop in the tower); temp= 303 k L1=116649.2821 kg/h

G1=1441.6889 kg/h

M.Wav=35.84

µl=0.4079cp; surface tension = 64.47 dyne/cm (McCabe smith 7 th edition) (liquid)=61.07 lb/ft3 =978.25 kg/m3 (McCabe smith 7th edition)

3 30.07945 / 1.267 /g lb ft kg m ρ

ρ

CONTINUED…Flow parameter

As our packing material is Raschig (dp=1.5 inch);

By using Eckert’s GPDC Chart ( Figure 5.33, principle of mass transfer and separation by Binay k. dutta). Since it good enough for first generation packing. At flooding Flv=2.91, the capacity parameter is 0.0075.

0.5( ) 2.91g

llv

LFG

ρρ

The other parameters are:

Capacity parameter equation for the first generation.

1w

l

ρρ

8 2

0.407994.5 /

4.18x10 /

l

p

c

µ cpF ft

g ft h

CONTINUED…

2 0.2

l

( ') ( )( )wlfl p

pl

g c

G F µc

g

ρρ

ρ ρ

CONTINUED…

2fl

2

2

' 438.931 / .

' 0.70* ' 307 / .

' 1500 / .op fl

op

G lb ft h

G G lb ft h

G kg m h

TOWER DIAMETERTower cross section:

Diameter

2

/ ' 1441.6889 /1500

0.9611opG G

m

0.9611*4 1.106 m

TOWER HEIGHT CALCULATIONOverall material balance equation:

min 1 2

1 2

( )X

s

s

L Y YG X

1

1

2

2

32.180 /6480.0866 /0.200.0015470.0010

s

s

G kmol hL kmol hyxyx

CONTINUED…The individual gas and liquid phase mass transfer coefficient are given. The following equation is used to find the height.

Now we have plotted the equilibrium data on x-y plane (mole fr. Unit). Then we fined the interfacial concentrations on the gas side. ( By Following the procedure describe in the Section 6.4.1 ( principle of mass transfer and separation process By Binay K.Dutta).

1 1

2 2

*'

' '

(1 ) ( )(1 )*( )

tG tG

tGy

y yiM

tGiy y

h H NGHk a

yN dy f y dyy y y

CONTINUED…

0 0.0003 0.0006 0.0009 0.0012 0.0015 0.0018 0.0021 0.0024 0.0027 0.0030

0.06

0.12

0.18

0.24

0.3

0.36

0.42Equilibrium Curve (mole fr. unit)

CONTINUED…

y yi(1-y)im 1-y y-yi f(y)

0.2 0.190.8049

9 0.8 0.01100.62

37

0.185 0.1750.8199

9 0.815 0.01100.61

22

0.149 0.1330.8589

75 0.851 0.01663.085

72

0.1 0.0470.9262

47 0.9 0.05319.418

18

0.0569 0.05130.9458

97 0.9431 0.0056179.10

11

0.0427 0.03760.9598

48 0.9573 0.0051196.60

030.0088

70.0063

30.9923

990.9911

30.0025

4394.20

50.0033

50.0017

80.9974

350.9966

50.0015

7637.44

42

CONTINUED…By using trapezoidal rule:

1 1

2 2

(1 ) ( ) 12.5(1 )*( )

12.5

y yiM

tGiy y

tG

yN dy f y dyy y y

soN

CONTINUED…The height of a gas-phase transfer unit:

2

21

22 2

2

'' '

' 0.075*3600 270 / .

' 40.2256 / 0.9611 41.85371 / .

' / (1 )*0.9611 33.4824 kmol/ h .m

' 37.6686kmol/ h .m0.311

*0.311*12.5 3.88

tGy

y

s

tG

tG tG

GHk a

k kmol h m

G kmol h m

G G y

GH mh N Hh m

Specification Sheet

Identification:Item: Packed Absorption ColumnItem No: N/ANo. required: 1

 Function: To remove SO2 from mixture of gasesOperation: Continuous

CONTINUED…Entering gas Kg/hr

Exit gasKg/hr

Liquid entering Kg/hr

1441.6889 1045.904 116649  

Design data: No. of transfer units = 12.5Height of transfer units = 0.311 mTotal height of column = 3.88mDiameter = 1.109mPressure drop = Neglected

CONTINUED…Internals: Size and type = 1.5 in Rachig ringMaterial of packing: CeramicPacking arrangement: DumpedType of packing support: Simple grid & perforated support

THANK YOU