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
AIV.5.1 MH
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 Pressure
115°C 1.2 bar
Components Methanol Nitrogen Hydrogen Carbon Dioxide Carbon Monoxide Formaldehyde Water Total
Mass Flow rate (kg/hr) 284.4316534 2212.79 2.931993701 35.2172863 7.551210398 1888.890157 2266.919789 6698.73209
Molar Flow rate (kmol/hr) 8.877392427 79 1.45148203 0.800211004 0.269589804 62.90010513 125.8002103 279.0989907
Table AIV.5.2 Showing Absorber Top Liquid Inlet Stream Absorber Top Liquid Inlet
Temperature Pressure
25°C 1.0 bar
Components Water Total
Mass Flow rate (kg/hr) 1866.777915 1866.777915
2|P ag e
Molar Flow Rate (kmol/hr) 103.5947789 103.5947789
AIV.5.2 MH Table AIV.5.3 Showing Absorber Top Outlet Stream Absorber Top Gas Outlet
Temperature (˚C) Pressure (bar)
65 1.3
Components Nitrogen Hydrogen Carbon Dioxide Carbon monoxide Water Formaldehyde Methanol Total
Mass Flowrate (kg/hr) 2212.79 2.931993701 35.21728629 7.551210397 41.33697704 11.43636 56.88633069 2368.150158
Molar Flow rate (kmol/hr) 79 1.45148203 0.800211004 0.269589804 2.293949891 0.629001051 1.775478486 86.21971227
Table AIV.5.4 Showing Absorber Bottom Liquid Outlet Stream Absorber Bottom Liquid Outlet 99% of Formaldehyde is absorbed Temperature °C = Pressure(bar)= Components Methanol Formaldehyde Water Total
80 1.5 Mass Flowrate (kg/hr) 227.5453227 1870.001255 4092.360727 6189.907305
Molar Flow rate (kmol/hr) 7.101914 62.2711 227.101 296.4741
Table AIV.5.5 Showing temperature across the absorber Temperature Top Bottom Average
3|P ag e
K 338 353 345.5
AIV.5.3 MH Table AIV.5.6 Showing Pressure across the Absorber Pressure Top Bottom Average
Pa 130000 150000 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 Perry’s handbook Name
Chemical Formula
C1
Carbon Monoxide
CO
45.698
Formaldehyde
CH20
101.51
Methanol
CH4O
82.718
Nitrogen
N2
58.282
Water
H20
76.945
C2
C3
C4
1076.6 4917.2 6904.5 1084.1 6729.8
4.8814 13.765 8.8622 8.3144
7.57E05 2.20E02 7.47E06 4.41E02 5.30E06
-8.179
C5
Tmin
P at Tmin
Tmax
P at Tmax
2
68.15
1.54E+04
132.92
3.49E+06
1
181.15
8.87E+02
408
6.59E+06
2
175.47
1.11E-01
512.5
8.15E+06
1
63.15
1.25E+04
126.2
3.39E+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 Carbon Monoxide Formaldehyde Methanol Nitrogen Water
4|P ag e
Vapour Pressure (Pa) 10591251466 1854748.035 136713.5913 2913148586 29532.10861
K value 75651.79618 0.091724717 0.976525652 20808.20418 0.210943633
AIV.5.4 MH
AIV.5.2.3 Equilibrium Line Table AIV.5.2.9 Showing Equilibrium Line Data x 0.302104888 0 0.1 0.2 0.3 0.4 0.5 0.6
y 0.027710485 0 0.009172472 0.018344943 0.027517415 0.036689887 0.045862358 0.05503483
AIV.5.2.4 Operating Line Table AIV.5.2.10 Showing Operating line Data Operating Line A
x0 0.210038965 xN 0
B
yN 0.225368444 yN+1 0.007295328
Figure AIV. 5.1 Showing Graph of X against Y
Mole Fraction of formaldehyde in Vapour Phase, y
Graph of y vs x 0.25
y = 1.0383x + 0.0073
0.2 0.15 Equilibrium Line
0.1 y = 0.0917x
Operating Line
0.05 0 0
0.1
0.2
0.3
0.4
0.5
0.6
Mole Fraction of Formaldehyde in Liquid Phase, x
5|P ag e
0.7
AIV.5.5 MH 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 Methanol Nitrogen Hydrogen Carbon Dioxide Carbon Monoxide Formaldehyde Water (Steam) Average Density of gas
Density (g/cm3) 1.561486858 1.365082612 0.098445801 2.14485133 1.365082612 1.463528413 0.878214519 1.268098878
Density of water at 337 K can be taken from Perry’s 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 Methanol Nitrogen Hydrogen Carbon Dioxide Carbon Monoxide Formaldehyde Water Total
6|P ag e
Mole Fraction 0.031807325 0.283053693 0.005200599 0.002867123 0.000965929 0.225368444 0.450736887 1
Molecular Mass (g) 32.04 28.01 2.02 44.01 28.01 30.03 18.02
AIV.5.6 MH 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
7|P ag e
AIV.5.7 MH
Table AIV.5.2.13 Showing Type of packing: Berl Saddle (Ceramic) Packing Size: Weight: Surface Area, a: Void Fraction: Packing Factor, F: gc: ψ:
1 48 79 68 360.8923885 9.81 1
in. lb/ft2 ft2/ft3 packing volume % m2/m3 m/s2
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
8|P ag e
AIV.5.8 MH 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= c=
1.0383 0.007295328
At x1= y1=
0.6 0.630275328
At x2= y2=
0.2 0.214955328
Now, m*(Gm/Lm)
= 0.088317442
y1/y2
= 2.932122383
Therefore, NOG = 1.114168066
0.088317442 9|P ag e
AIV.5.9 MH K3 value and the factor for HG, ψh 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 ψh f1 f2 f3 φh K3 µv, Ns/m2 µL, NS/m2 pv, kg/m3 ρL, kg/m3
60 1 1 1 2.6 0.95 0.000021986000 0.00044223 1.268098878 981.135
Table AIV.5.2.16 Showing Data obtained from Ullmann Encyclopedia Dv (From Ullmann's 6th Ed) C H O N N2 O2 Air
16.5 1.98 5.48 5.69 17.9 16.6 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 Viscosity of Solvent φ (H20) vA (CH20)
10 | P a g e
18.02 0.00044223 2.6 0.0296
kg/kmol N s/m2 m3/kg mol
AIV.5.10 MH
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
11 | P a g e
AIV.5.11 MH
AIV.5.3 Mechanical Design Table AIV.5.2.18 Showing Operating Conditions of Material Choice Material choice Operating Pressure , atm Design Pressure (5%) , atm Operating Temperature , K Design Temperature (5%), K
Stainless steel 304 1.381692574 1.450777202 345.5 362.775
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 Tensile Strength N/mm2 Density of steel g/cm3
145 510 7.9
AIV.5.3.1 Wall thickness Table AIV.5.2.19 Showing Corrosion Allowance & thickness Corrosion Allowance Minimum wall thickness Total minimum thickness Column diameter, Di Joint Factor Wall Thickness, e Total min wall thickness Wall thickness to be use Outer diameter of Column,Do
AIV.5.3.2 Tori spherical head
12 | P a g e
2 9 11 2.865823269 2865.823269 1 1.453412663 3.453412663 7 2879.823269 2.879823269
mm mm mm m mm
mm m
AIV.5.12 MH
Table AIV.5.2.20 Showing Wall thickness Data Wall Thickness, e Crown Radius Knuckle Radius Height of Head Stress Concentrator Factor Flange/ Skirt (factor of 1) Thickness wall used Total Height of Head
2.872823269 0.287282327 0.557327714 1.540569415 0.557327714 7 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 Head Bottom Total Stree due to shell side : Density of material mean diameter of column Wv
13 | P a g e
9.5 1.114655429 1.114655429 11.72931086
m m m
7900 2.882689093 65752.65149
kg/m3 m N
AIV.5.13 MH 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 Type of support Total Weight
10.96573161 10.96573161 427563.5675
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 Analysis of stress
14 | P a g e
= 61.0515114 kNm
kN KN N
AIV.5.14 MH Bending stress
Table AIV.5.2.23 Showing Bending Stress data Do Di lv σb
2879.823269 2865.823269 65184380392 9.394427672
Resultant stress
mm2 mm2 mm4 N/mm2
is
Table AIV.5.2.24 Showing Stress Data σL σh σw (compressive)
15.04557217 7.522786084 6.766865766
N/mm2 N/mm2 N/mm2
Table AIV.5.2.25 Showing Longitudinal stress Resulting Longitunal stress σz σz upwind σz downwind
17.67313407 -1.11572127
Since the resultant stress is less than 145 N/mm2 which is design stress, thus the thickness is applicable. Elastic stability
σc = 48.61409431 N/mm2 is gotten after the variable is substitute into the formula. The maximum compressive stress is lower than critical buckling stress.
15 | P a g e
AIV.5.15 MH Skirt thickness
Table AIV.5.2.26 Showing Data for thickness, dead weight stress Skirt Thickness Ms bending stress in skirt, σbs dead weight stress in skirt, σws (test) dead weight stress in skirt, σws (ope.) σs (compressive) σs (tensile) J factor Design Stress of skirt material limiting condition: fs.J.sin(deta) Young Modulus E limiting condition: 0.125E(ts/Ds)sin(deta)
11 5158852.713 71.71778631 8.5587488 4.2793744 80.27653511 67.43841191 0.85 165 140.25 200000 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: 16 | P a g e
AIV.5.16 MH
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 Minimum width of based ring, Lb
17 | P a g e
5
N/mm2
465.5621646
mm
AIV.5.17 MH Base ring thickness
Table AIV.5.2.28 Showing Bolt Dimensions Bolt size root area Lr
M30 817 164
mm mm
Actual bearing pressure f'c
14.19396843
N/mm2
By substitute the values, t b=
90.44662692 mm
Noxzle For stainless steel pipe:
18 | P a g e
AIV.5.18 MH
Table AIV.5.2.29 Bottom Gas entering absorber Components Methanol Nitrogen Hydrogen Carbon Dioxide Carbon Monoxide
Mass Flowrate (kg/hr) 284.431653 4 2212.79
(kmol/ hr)
Mw, Kg mol
Mol fraction
Density, kg/m3
8.8773 92427 79
32.04
2.93199370 1 35.2172863
1.4514 8203 0.8002 11004 0.2695 89804 62.900 10513 125.80 02103 279.09 89907
2.02
0.03180 7325 0.28305 3693 0.00520 0599 0.00286 7123 0.00096 5929 0.22536 8444 0.45073 6887 1
1.5615736 47 1.3651584 85 0.0984512 72 2.1449705 43 1.3651584 85 1.4636097 57 0.8782633 31 1.1697803 1
7.55121039 8 1888.89015 7 2266.91978 9 6698.73209
Formaldehyde Water Total
28.01
44.01 28.01 30.03 18.02 24.00127666
Table AIV.5.2.30 Showing Data for inlet Gas Stream Gas inlet stream velocity area of pipe d, optimum
5726.487303 16.5 26.24640014 0.5825766
m3/h m/s m2 m
Table AIV.5.2.31 Showing data for Top liquid inlet Components Water
Mass Flow rate (kg/hr) 1866.777915
Total
1866.777915
(kmol/hr)
Mw, Kg mol Mol fraction
Density
103.5947 8 103.5947 8
18.02
5.049028608
1
18.02
5.049028608
Table AIV.5.2.32 Showing Data for Liquid Inlet Stream Liquid inlet stream velocity area of pipe d, optimum
19 | P a g e
2360.021597 1.85 0.354357597 0.671657362
m3/h m/s m2 m
AIV.5.19 MH
Table AIV.5.2.33 Showing Data for Top gas outlet Components Methanol Nitrogen Hydrogen Carbon Dioxide Carbon Monoxide Formaldehyde Water Total
Mass Flow rate (kg/hr) 2212.79 2.931993701 35.21728629 7.551210397 41.33697704 11.43636 56.88633069 2368.150158
(kmol/hr) 79 1.45148203 0.800211004 0.269589804 2.293949891 0.629001051 1.775478486 86.21971227
Molecular weight 32.04 28.01 2.02 44.01 28.01 30.03 18.02 31.3203741
mol fraction
Density
0.916263786 0.016834689 0.009281068 0.003126777 0.026605863 0.007295328 0.020592489 1
1.561573647 1.365158485 0.098451272 2.144970543 1.365158485 1.463609757 0.878263331 1.526500339
Table AIV.5.2.34 Showing Gas outlet Data Gas outlet stream velocity area of pipe d, optimum
14052.91363 16.5 0.236581037 0.548803499
m3/h m/s m2 m
Table AIV.5.2.35 Showing Bottom liquid outlet Components Methanol Formaldehyde Water Total
Mass Flow rate (kg/hr) 227.54532 1870.0013 4092.3607 6189.9073
(kmol/hr) 7.101913941 62.27110408 227.1010392 296.4740572
Molecular weight 32.04 30.03 18.02 20.87841129
Mol fraction
Density
0.023954588 0.210038965 0.766006447
1.561573647 1.463609757 0.878263331 1.017577305
Table AIV.5.2.36 Showing Gas outlet Data Gas outlet stream velocity area of pipe d, optimum
20 | P a g e
2378.566855 1.85 0.35714217 0.674291169
m3/h m/s m2 m
