Post on 10-Nov-2015
description
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