Appendix for Absorption Column Design

Author: MUHD HIDAYATULLAH BIN MOHD HUSIN [MH]

Contents

AIV.5 Absorption Column Design Appendix.............................................................................................. 2

AIV.5.1 Chemical Design .......................................................................................................................... 2

AIV.5.2 Calculations ................................................................................................................................. 4

AIV.5.2.1 Vapour pressure (From Perry's Handbook) ............................................................................... 4

AIV.5.2.2 K-value ..................................................................................................................................... 4

AIV.5.2.3 Equilibrium Line ........................................................................................................................ 5

AIV.5.2.4 Operating Line .......................................................................................................................... 5

AIV.5.2.5 Density ..................................................................................................................................... 6

AIV.5.2.6 Average molecular weight ........................................................................................................ 6

AIV.5.2.7 Abcissa ..................................................................................................................................... 7

AIV.5.2.8 Flooding line ............................................................................................................................ 7

AIV.5.2.9 Flooding gas mass flux, Gf , column diameter and column cross sectional area ......................... 8

AIV.5.2.10 Operating gas mass flux and and .......................................................................................... 8

AIV.5.2.11 NOG and HOG........................................................................................................................ 9

AIV.5.3 Mechanical Design .................................................................................................................... 12

AIV.5.3.1 Wall thickness ........................................................................................................................ 12

AIV.5.3.2 Tori spherical head ................................................................................................................. 12

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AIV.5 Absorption Column Design Appendix

AIV.5.1 Chemical Design

Table AIV.5.1 Showing Operating Conditions and Flow rates for Inlet of Absorber

Stream Entering Absorber

Temperature 115C Pressure 1.2 bar

Components Mass Flow rate (kg/hr) Molar Flow rate (kmol/hr)

Methanol 284.4316534 8.877392427

Nitrogen 2212.79 79

Hydrogen 2.931993701 1.45148203

Carbon Dioxide 35.2172863 0.800211004

Carbon Monoxide 7.551210398 0.269589804

Formaldehyde 1888.890157 62.90010513

Water 2266.919789 125.8002103

Total 6698.73209 279.0989907

Table AIV.5.2 Showing Absorber Top Liquid Inlet

Stream Absorber Top Liquid Inlet

Temperature 25C Pressure 1.0 bar

Components Mass Flow rate (kg/hr) Molar Flow Rate (kmol/hr)

Water 1866.777915 103.5947789

Total 1866.777915 103.5947789

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Table AIV.5.3 Showing Absorber Top Outlet

Stream Absorber Top Gas Outlet

Temperature (C) 65 Pressure (bar) 1.3

Components Mass Flowrate (kg/hr) Molar Flow rate (kmol/hr)

Nitrogen 2212.79

79

Hydrogen 2.931993701

1.45148203

Carbon Dioxide 35.21728629

0.800211004

Carbon monoxide 7.551210397

0.269589804

Water 41.33697704

2.293949891

Formaldehyde 11.43636

0.629001051

Methanol 56.88633069

1.775478486

Total 2368.150158

86.21971227

Table AIV.5.4 Showing Absorber Bottom Liquid Outlet

Stream Absorber Bottom Liquid Outlet

99% of Formaldehyde is absorbed Temperature C

= 80

Pressure(bar)= 1.5

Components Mass Flowrate (kg/hr) Molar Flow rate (kmol/hr)

Methanol 227.5453227 7.101914

Formaldehyde 1870.001255 62.2711

Water 4092.360727 227.101

Total 6189.907305 296.4741

Table AIV.5.5 Showing temperature across the absorber

Temperature K

Top 338

Bottom 353

Average 345.5

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Table AIV.5.6 Showing Pressure across the Absorber

Pressure Pa

Top 130000

Bottom 150000

Average 140000

AIV.5.2 Calculations

AIV.5.2.1 Vapour pressure (From Perry's Handbook)

ln P = C1 + C2/T + C3 ln T + C4 T^C5

P in unit Pa T in unit K

Table AIV.5.2.7 Showing Data obtained from Perrys handbook

Name Chemical Formula C1 C2 C3 C4 C5 Tmin

P at Tmin Tmax

P at Tmax

Carbon Monoxide CO 45.698

-1076.6

-4.8814

7.57E-05 2 68.15 1.54E+04 132.92 3.49E+06

Formaldehyde CH20 101.51 -

4917.2 -

13.765 2.20E-

02 1 181.15 8.87E+02 408 6.59E+06

Methanol CH4O 82.718 -

6904.5 -

8.8622 7.47E-

06 2 175.47 1.11E-01 512.5 8.15E+06

Nitrogen N2 58.282 -

1084.1 -

8.3144 4.41E-

02 1 63.15 1.25E+04 126.2 3.39E+06

Water H20 76.945 -

6729.8 -8.179 5.30E-

06 2 178.18 4.75E-02 591.75 4.08E+06

AIV.5.2.2 K-value k value= (Vapour Pressure) / (Operating pressure)

Table AIV.5.2.8 Showing Vapour Pressure and K-value

Name Vapour Pressure (Pa) K value

Carbon Monoxide 10591251466

75651.79618

Formaldehyde 1854748.035

0.091724717

Methanol 136713.5913

0.976525652

Nitrogen 2913148586

20808.20418

Water 29532.10861

0.210943633

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AIV.5.2.3 Equilibrium Line

Table AIV.5.2.9 Showing Equilibrium Line Data

x y

0.302104888 0.027710485

0 0

0.1 0.009172472

0.2 0.018344943

0.3 0.027517415

0.4 0.036689887

0.5 0.045862358

0.6 0.05503483

AIV.5.2.4 Operating Line

Table AIV.5.2.10 Showing Operating line Data

Operating Line x0 yN

A 0.210038965 0.225368444

xN yN+1

B 0 0.007295328

Figure AIV. 5.1 Showing Graph of X against Y

y = 0.0917x

y = 1.0383x + 0.0073

0

0.05

0.1

0.15

0.2

0.25

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Mo

le F

ract

ion

of

form

ald

ehyd

e in

V

apo

ur P

has

e, y

Mole Fraction of Formaldehyde in Liquid Phase, x

Graph of y vs x

Equilibrium Line

Operating Line

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From graph above, gradient of:

Equilibrium line = 0.0917 Operating line = 1.0383

AIV.5.2.5 Density

Assuming ideal gas,

Table AIV.5.2.11 Showing Component and respective Density

Component Density (g/cm3)

Methanol 1.561486858

Nitrogen 1.365082612

Hydrogen 0.098445801

Carbon Dioxide 2.14485133

Carbon Monoxide 1.365082612

Formaldehyde 1.463528413

Water (Steam) 0.878214519

Average Density of gas 1.268098878

Density of water at 337 K can be taken from Perrys Handbook by interpolation of 2 data.

Thus density of water at 337K = 981.135 kg/m3 and viscosity of water is 0.00044223 Ns/m2

AIV.5.2.6 Average molecular weight

Table AIV.5.2.12 Showing Component, Mole fraction, and Relative Molecular Mass

Component Mole Fraction Molecular Mass (g)

Methanol 0.031807325 32.04

Nitrogen 0.283053693 28.01

Hydrogen 0.005200599 2.02

Carbon Dioxide 0.002867123 44.01

Carbon Monoxide 0.000965929 28.01

Formaldehyde 0.225368444 30.03

Water 0.450736887 18.02

Total 1

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Average molecular weight = 24.00123g

AIV.5.2.7 Abcissa

Lm/Gm is slope of operating line, 1.0383

Therefore, abcissa= 0.028025636

AIV.5.2.8 Flooding line

From generalized pressure drop correlation to estimate column diameter.

Figure AIV. 5.2 Showing Generalized Pressure Drop

Flooding line = 0.21 is based on calculation of abscissa

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Table AIV.5.2.13 Showing Type of packing: Berl Saddle (Ceramic)

Packing Size: 1 in.

Weight: 48 lb/ft2 Surface Area, a: 79 ft2/ft3 packing volume Void Fraction: 68 %

Packing Factor, F: 360.8923885 m2/m3 gc: 9.81 m/s2 : 1

AIV.5.2.9 Flooding gas mass flux, Gf , column diameter and column cross sectional

area

The estimation of % flooding gas mass velocity is 0.5

S = 6.4504 m2

D = 2.8658 m

Packing pressure drop estimation

2 in/ft packing height

AIV.5.2.10 Operating gas mass flux and and

G = 2.884705067

= 0.0525

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Estimated % of Flodding Gas Mass Velocity = 0.5

AIV.5.2.11 NOG and HOG

where,

m, slope of eq. line = 0.0917

and Lm/Gm, slope of op. line = 1.0383

Table AIV.5.2.14 Showing Operating Line Data

Operating Line

Since it is a straight line, y=mx+c

m= 1.0383

c= 0.007295328

At x1= 0.6

y1= 0.630275328

At x2= 0.2

y2= 0.214955328

Now,

m*(Gm/Lm) = 0.088317442

y1/y2 = 2.932122383

Therefore, NOG = 1.114168066

0.088317442

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K3 value and the factor for HG, h are taken to be 0.95 and 60 respectively are taken from Coulson

and Richardson, 5th ed. (Sinnott, 2005)

Table AIV.5.2.15 Showing Data from Sinnott, 2005

h 60

f1 1

f2 1

f3 1

h 2.6

K3 0.95

v, Ns/m2 0.000021986000

L, NS/m2 0.00044223

pv, kg/m3 1.268098878

L, kg/m3 981.135

Table AIV.5.2.16 Showing Data obtained from Ullmann Encyclopedia

Dv (From Ullmann's 6th Ed)

C 16.5

H 1.98

O 5.48

N 5.69

N2 17.9

O2 16.6 Air 20.1

CO2 26.9 H2O 12.7

Formaldehyde (CH2O) is taken as key component. Based on table above, vi and vj are

determined.

To calculate DL for CH2O

Table AIV.5.2.17 Showing Data for Formaldehyde

DL for CH20 M of Solvent 18.02 kg/kmol

Viscosity of Solvent 0.00044223 N s/m2

(H20) 2.6 vA (CH20) 0.0296 m3/kg mol

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Dv = 2.13112x 10-5 m2/s

DL = 2.19604x 10-9 m2/s

0.813552217

205.2482308

Value for height is assumed to be 7.45

Therefore, HG= 6.484199667

=7.769051029

HOG = 7.17034238

Z= HOG X NOG

Z= 7.444966493 7.5 m

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AIV.5.3 Mechanical Design

Table AIV.5.2.18 Showing Operating Conditions of Material Choice

Material choice Stainless steel 304

Operating Pressure , atm 1.381692574

Design Pressure (5%) , atm 1.450777202

Operating Temperature , K 345.5

Design Temperature (5%), K 362.775

Design stress of stainless steel is taken from Richardson & Coulson Volume 6

Table AIV.5.2.19 Showing Data from Sinnott, 2005

Design Stress at 80 N/mm2 145

Tensile Strength N/mm2 510

Density of steel g/cm3 7.9

AIV.5.3.1 Wall thickness

Table AIV.5.2.19 Showing Corrosion Allowance & thickness

Corrosion Allowance 2 mm

Minimum wall thickness 9 mm

Total minimum thickness 11 mm

Column diameter, Di 2.865823269 m

2865.823269 mm

Joint Factor 1 Wall Thickness, e 1.453412663 Total min wall thickness 3.453412663 Wall thickness to be use 7 Outer diameter of Column,Do 2879.823269 mm

2.879823269 m

AIV.5.3.2 Tori spherical head

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Table AIV.5.2.20 Showing Wall thickness Data

Wall Thickness, e

Crown Radius

2.872823269

Knuckle Radius

0.287282327

Height of Head

0.557327714

Stress Concentrator Factor

1.540569415

Flange/ Skirt (factor of 1)

0.557327714

Thickness wall used

7

Total Height of Head

1.114655429

Where:

Rc = (Di + Do)/2

Rk = 0.1 X Rc

Dead weight

Height of column = 9.5m

Mean diameter = 2.882689093 m

t is thickness

Cv is a standard approximation

Therefore;-

Table AIV.5.2.21 Showing Column Dimensions

Height of Column Body + Skirt 9.5 m

Head 1.114655429 m

Bottom 1.114655429 m

Total 11.72931086 Stree due to shell side :

Density of material 7900 kg/m3

mean diameter of column 2.882689093 m

Wv 65752.65149 N

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Internal column weight

Weight of berl saddles is 768 kg/m3 and volume of packing is 48.02323787 m3. Therefore weight of

packing is equal to 361810.916N which has been multiplied with gravity force.

Thus

Table AIV.5.2.22 Showing Distributor Data

Type of distributor 10.96573161 kN

Type of support 10.96573161 KN

Total Weight 427563.5675 N

Wind loading

Dynamic wind pressure can be getting by the formula:

where density of air is 1.1kg/m3 and velocity is 9.6km/h.

thus dynamic wind pressure is 469.3333333 N/m2.

To calculate bending moment at the bottom of the column,

Wind pressure x

= 61.0515114 kNm

Analysis of stress

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Bending stress

Table AIV.5.2.23 Showing Bending Stress data

Do 2879.823269 mm2

Di 2865.823269 mm2

lv 65184380392 mm4

b 9.394427672 N/mm2

Resultant stress is

Table AIV.5.2.24 Showing Stress Data

L 15.04557217 N/mm2

h 7.522786084 N/mm2

w (compressive) 6.766865766 N/mm2

Table AIV.5.2.25 Showing Longitudinal stress

Resulting Longitunal stress z z upwind 17.67313407

z downwind -1.11572127

Since the resultant stress is less than 145 N/mm2 which is design stress, thus the thickness is

applicable.

Elastic stability

c = 48.61409431 N/mm2 is gotten after the variable is substitute into the formula. The maximum compressive stress is lower than critical buckling stress.

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Skirt thickness

Table AIV.5.2.26 Showing Data for thickness, dead weight stress

Skirt Thickness 11

Ms 5158852.713

bending stress in skirt, bs 71.71778631

dead weight stress in skirt, ws (test) 8.5587488

dead weight stress in skirt, ws (ope.) 4.2793744

s (compressive) 80.27653511

s (tensile) 67.43841191

J factor 0.85

Design Stress of skirt material 165

limiting condition: fs.J.sin(deta) 140.25

Young Modulus E 200000

limiting condition: 0.125E(ts/Ds)sin(deta) 95.49197096

Base Ring and Anchor Bolt Design

To withstand the whole column weight and bending stress, based ring of double plate with gusset is

used.

Calculation of area of one bolt:

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Rough estimation of bolt spacing is around 600mm and pitch circular diameter is 3079.823269mm.

Number of bolt is multiplied with 4 gives the total bolts is 20.

Thus, Ab= 681.9590639mm2

Compressive load

Fb= 2327.810823 kN/m

Table AIV.5.2.27 Showing Maxing Allowable Pressure

Max allowable bearing pressure

5 N/mm2

Minimum width of based ring, Lb

465.5621646 mm

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Base ring thickness

Table AIV.5.2.28 Showing Bolt Dimensions

Bolt size M30 root area 817 mm

Lr 164 mm

Actual bearing pressure f'c 14.19396843 N/mm2

By substitute the values,

tb= 90.44662692 mm

Noxzle

For stainless steel pipe:

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Table AIV.5.2.29 Bottom Gas entering absorber

Components Mass Flowrate (kg/hr)

(kmol/hr)

Mw, Kg mol Mol fraction

Density, kg/m3

Methanol 284.4316534

8.877392427

32.04 0.031807325

1.561573647

Nitrogen 2212.79 79 28.01 0.283053693

1.365158485

Hydrogen 2.931993701

1.45148203

2.02 0.005200599

0.098451272

Carbon Dioxide 35.2172863 0.800211004

44.01 0.002867123

2.144970543

Carbon Monoxide 7.551210398

0.269589804

28.01 0.000965929

1.365158485

Formaldehyde 1888.890157

62.90010513

30.03 0.225368444

1.463609757

Water 2266.919789

125.8002103

18.02 0.450736887

0.878263331

Total 6698.73209 279.0989907

24.00127666 1 1.16978031

Table AIV.5.2.30 Showing Data for inlet Gas Stream

Gas inlet stream 5726.487303 m3/h

velocity 16.5 m/s

area of pipe 26.24640014 m2

d, optimum 0.5825766 m

Table AIV.5.2.31 Showing data for Top liquid inlet

Components Mass Flow rate (kg/hr)

(kmol/hr) Mw, Kg mol Mol fraction Density

Water 1866.777915 103.59478

18.02 1 5.049028608

Total 1866.777915 103.59478

18.02 5.049028608

Table AIV.5.2.32 Showing Data for Liquid Inlet Stream

Liquid inlet stream 2360.021597 m3/h

velocity 1.85 m/s

area of pipe 0.354357597 m2

d, optimum 0.671657362 m

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Table AIV.5.2.33 Showing Data for Top gas outlet

Components Mass Flow rate (kg/hr)

(kmol/hr) Molecular weight

mol fraction Density

Methanol 2212.79 79 32.04 0.916263786 1.561573647

Nitrogen 2.931993701 1.45148203 28.01 0.016834689 1.365158485

Hydrogen 35.21728629 0.800211004 2.02 0.009281068 0.098451272

Carbon Dioxide 7.551210397 0.269589804 44.01 0.003126777 2.144970543

Carbon Monoxide 41.33697704 2.293949891 28.01 0.026605863 1.365158485

Formaldehyde 11.43636 0.629001051 30.03 0.007295328 1.463609757

Water 56.88633069 1.775478486 18.02 0.020592489 0.878263331

Total 2368.150158 86.21971227 31.3203741 1 1.526500339

Table AIV.5.2.34 Showing Gas outlet Data

Gas outlet stream 14052.91363 m3/h

velocity 16.5 m/s

area of pipe 0.236581037 m2

d, optimum 0.548803499 m

Table AIV.5.2.35 Showing Bottom liquid outlet

Components Mass Flow rate (kg/hr)

(kmol/hr) Molecular weight

Mol fraction Density

Methanol 227.54532 7.101913941 32.04 0.023954588 1.561573647

Formaldehyde 1870.0013 62.27110408 30.03 0.210038965 1.463609757

Water 4092.3607 227.1010392 18.02 0.766006447 0.878263331

Total 6189.9073 296.4740572 20.87841129 1.017577305

Table AIV.5.2.36 Showing Gas outlet Data

Gas outlet stream 2378.566855 m3/h

velocity 1.85 m/s

area of pipe 0.35714217 m2

d, optimum 0.674291169 m