Design Of Absorption Column

DESIGN OF ABSORPTION COLUMN PRESENTED BY: ALI SHAAN(016) USAMA SAEED(049) ALI HASSAN(031)

CASE

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

CONTINUE…………… • • • •

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

SOLVENT SELECTION We Selected water(H2O) here:

• Because it is cheap. • Non Toxic. • Easily available.

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 DATA g S02/100 g H2O 0.01 0.05 0.1 0.15 0.2 0.25 0.3

600c

700c

900c

0.43 5.24 13.5 22.7 32.6 42.8 53.3

0.689999997 7.793333308 19.56666661 32.53333324 46.29999986 60.46666649 74.86666645

1.21 12.9 31.7 52.2 73.7 95.8 118

CONTINUED… Mole Fractions X 2.8124E-05 0.000140604 0.000281169 0.000421694 0.000562179 0.000702625 0.000843032 0.001123727 0.001404264 0.00280459

y 0.000908 0.010254 0.025746 0.042807 0.060921 0.079561 0.098509 0.137456 0.177456 0.385088

CONTINUED… Mole Ratios X

Y 2.8125E-05 0.00014062 0.00028125 0.00042187 0.0005625 0.00070312 0.00084374 0.00112499 0.00140624 0.00281248

0.000909 0.010361 0.026426 0.044721 0.064873 0.086439 0.109273 0.159361 0.215741 0.626248

CONTINUED… Conversion is as follows: y x

Pso2 Patm

 (e.g) 

0.6mmHg  7.89x10-4 760mmHg

c / M.Wso2 c / M.Wso2  100 / M .WH 2 0

 (e.g ) 

0.02 / 64  5.625x10-5 0.02 / 64  100 /18

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.

EQUILIBRIUM CURVE Equilibrium curve 0.7 0.65 0.6 0.55 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 0

0

0

0

0

0

0

.

Material Balance Average molecular weight = (mole fr. So2)*(M.W of so2)+( mole fr. Air)*(M.W of Air) M .w  (.2)(64)  (.8)(28.8)  35.84  ρ 

PM 1*35.84   0.07945 ft 3 / h RT 1.31443*343.15

Volumetric flow rate = 40,000 ft3/h 3 3 Mass flow =m 40, 000 ft / h *0.07945lb / ft

CONTINUED… G  3178.38lb / h G  1441.6889kg / h G1  (1441.6889 / 35.84) kmol/ h G1  40.2256kmol / h y1  0.2 Y1 

y1  0.25 1  y1

Gs  G1 (1  y1 )  32.180kmol / h so2 entering  G1 y1  8.04512kmol / h so2 absorbed  so2 entering * (0.96)  7.7233152kmol / h concentration Y2  so2 / Gs  0.01 y2  1  Y2 / Y2  0.001

CONTINUED… As solvent is pure x2=0 (Mole Fraction unit) X2=0 (Mole ratio unit)

MINIMUM LIQUID FLOW RATE By an overall material balance: ( Ls ) min Y1  Y2  Gs ( X 1 ) max  X2 ( Ls ) min  4984.682kmol / h ( Ls )operating  1.3( Ls ) min  6480.0866kmol / h

Molecular weight of solvent =18 Ls  6480.0886 /18 Ls  116641kg / h

LIQUID FLOW RATE AT BOTTOM OF TOWER L1  Ls  so2 absorbed  116641  7.7233  116649.2821kg / h And the x1=0.002462

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 ρ g  0.07945lb / ft 3  1.267 kg / m3

µl=0.4079cp; edition)

surface tension = 64.47 dyne/cm

ρ (liquid)=61.07 lb/ft3 =978.25 kg/m3

(McCabe smith 7 th

(McCabe smith 7th edition)

CONTINUED… Flow parameter

L ρ g 0.5 Flv  ( )  2.91 G ρl As our packing material is Raschig (d p=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 F lv=2.91, the capacity parameter is 0.0075.

CONTINUED… The other parameters are: µl  0.4079cp

ρw 1 ρl

Fp  94.5 / ft g c  4.18x108 ft / h 2

Capacity parameter equation for the first generation. ρw )( µl )0.2 ρl ρ g ρl g c

(G ') 2fl Fp ( cp 

CONTINUED… G 'fl  438.931lb / ft 2 .h G 'op  0.70* G ' fl  307lb / ft 2 .h G 'op  1500kg / m 2 .h

TOWER DIAMETER Tower cross section:  G / G 'op  1441.6889 /1500  0.9611m 2

Diameter 0.9611* 4   1.106 m



TOWER HEIGHT CALCULATION Overall material balance equation: ( Ls ) min Y  Y2  1 Gs X 1  X2

Gs  32.180kmol / h Ls  6480.0866kmol / h y1  0.20 x1  0.001547 y2  0.001 x2  0

CONTINUED… The individual gas and liquid phase mass transfer coefficient are given. The following equation is used to find the height. h  H tG * N tG H tG 

G' k 'y a ' y1

y

1 (1  y )iM N tG   dy   f ( y )dy (1  y ) *( y  yi ) y2 y2

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).

CONTINUED… Equilibrium Curve (mole fr. unit)

0

0

0

0

0

0

0

0

0

0

0

CONTINUED… y

yi 0.2

0.19

0.185

0.175

0.149

0.133

0.1

0.047

0.0569 0.0513 0.0427 0.0376

(1y)im 1-y y-yi f(y) 0.8049 100.62 9 0.8 0.01 37 0.8199 100.61 9 0.815 0.01 22 0.8589 63.085 75 0.851 0.016 72 0.9262 19.418 47 0.9 0.053 18 0.9458 179.10 97 0.9431 0.0056 11 0.9598 196.60 48 0.9573 0.0051 03

CONTINUED… By using trapezoidal rule: y1

y

1 (1  y )iM N tG   dy   f ( y )dy  12.5 (1  y ) *( y  yi ) y2 y2

so N tG  12.5

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

G' k 'y a '

k ' y  0.075*3600  270kmol / h.m 2 G '1  40.2256 / 0.9611  41.85371kmol / h.m 2 G '2  Gs / (1  y2 ) *0.9611  33.4824 kmol/ h .m 2 G '  37.6686 kmol/ h .m 2 H tG  0.311m h  N tG * H tG h  0.311*12.5  3.88m

Specification Sheet Identification: Item: Packed Absorption Column Item No: N/A No. required: 1   Function: To remove SO2 from mixture of gases Operation: Continuous

CONTINUED… Entering gas

Exit gas

Liquid entering

Kg/hr

Kg/hr

Kg/hr

1441.6889

1045.904

116649

Design data: No. of transfer units = 12.5 Height of transfer units = 0.311 m Total height of column = 3.88m Diameter = 1.109m Pressure drop = Neglected

 

CONTINUED… Internals: Size and type = 1.5 in Material of packing:

Rachig ring Ceramic

Packing arrangement: Type of packing support:

Dumped Simple grid & perforated support

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