stabilizer design(part 2)
DESCRIPTION
Column DesignTRANSCRIPT
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Composition of feed, top and bottom and relative volatilities are:
The key components selected are n-C4 and i-C5 as light and heavy key respctively.
Components Xf Xd Xb K-Values
H2 0.0953 0.5399 0 42.301999852CH4 0.0235 0.1334 0 14.6248911009C2H6 0.0209 0.1148 0.0008 5.2478040536C3H8 0.0375 0.114 0.0212 2.5630552627i-C4 0.031 0.0514 0.0267 1.4622811889n-C4 0.0179 0.0239 0.0166 1.241435261i-C5 0.2959 0.0214 0.3547 0.6927922272n-C5 0.0992 0.0011 0.1202 0.60893354975N5 0.0221 0.1 0.0269 0.47709872372,2 DMC4 0.058 0 0.0704 0.43643681892,3 DMC4 0.0167 0 0.0203 0.37147303972MC5 0.0607 0 0.0737 0.3605294133MC5 0.0372 0 0.0452 0.3362551971NP6 0.0214 0 0.026 0.29825794245N6 0.0396 0 0.0481 0.28752830576N6 0.0362 0 0.044 0.2449354634NP7 0.078 0 0.0947 0.15532483226N7 0.0024 0 0.0029 0.1502743966N8 0.0063 0 0.0076 9.55E-02
K-Value (HK) 0.6927922272Avg Temp T 238 F 114.4 C
Calculation of minimum number of stages Nm:
From Fenske Equation
Nm 5.4386996977Nm 6
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Calculation of minimum reflux ratio:
From Colburn and Underwood we have an expression for minimum reflux ratio
(i * Xif)/(i - )
0.09802927190.02555821020.0269478038
-value can be found by 0.06938135010.15931541650.3489122836
-0.4227142857feed is at boiling point so q=1 -0.1061969101
-0.0150487561therefore at =1.7 -0.0341467626
-0.0076941607-0.0267788426
-0.014864906-0.0072573063
Rm+1 1.689562929 -0.0127902545Rm 0.689562929 -0.0095053132
-0.0118496447-0.0003510153-0.0005556325
Sum 0.0583905457-Value 1.7
Reflux ratio is 1.2 times the minimum reflux ratio
Reflux Ratio 1.2 RmReflux Ratio 0.8274755148
Calculation of Number of theoretical plates:
we first need to find the ratios of (Rm/Rm+1) and (R/R+1)
Rm/Rm+1 0.4081309534
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R/R+1 0.452797046
From Erbar-Maddox correlation Vis A Vis B
Nm/N 0.37 13.82 5.39Nm 6 114.14 57.6N 16.216216216 156.6 95.57
222.67 133.41Number of theoretical plates 302.51 170.2
265.84 160.217 367.32 191.58
313.66 182.48406.69 231.67438.44 226.67
O'Connell's correlation. 444.19 228.86384.13 208.27372.11 207.55362.79 207.09
For Viscosity we have 440.52 243.24653.62 290.84436.73 232.53528.41 271.58506.43 280.76
0.1221891351.7919301232
a*a 0.2189543918
Eo 67.5 %
Actual Number of Trays:
170.675
Actual Plates
Nth
Plate Efficiency calculation (Eo):
Molar avg Viscosity a mNs/m2Relative volatility a
from O'Connell's graph for efficiency of the column (Eo)
NthEo
Nth/Eo
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N 25.185185185N 26
Feed-point location:
Using Krikbride empirical equation
here B 2022 lbmol/hrD 456.5 lbmol/hr
log (Nr/Ns) 0.3386683122Nr/Ns 2.1810635114
Plates in stripping section (Below the feed)
N=Nr+NsNr+Ns 26Ns 8.173367148Ns 9
Plates in rectifying section (Above the feed)
Nr N-NsNr 17Feed-point 18
Column Diameter Calculation:
Flooding velocity can be estimated from the correlation given by Fair
here Uf is the flooding velocity based on net area An
At this stage we need to find the liquid-vapor flow factor FLV for top and bottom for constant K1
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Assume tray spacing of 0.5 m
Rectifying Section:
Following are the necessary physical properties for Diameter calculation taken from HYSYS
24.76510
6.37 dyne/cm or 0.00637
Lw 14610 kg/hrVw 18840 kg/hr
0.1708675332
from graph0.06
0.04773
Now the flooding velocity0.2112886239 m/s
Design for 85% flooding at maximum flow rate
Maximum allowable vapor velocity based on the net column cross sctional area
0.1795953303 m/sMaximum volumetric flow rate 760.6
0.211278
Net Area required An 1.2
Take downcomer area as 12% of the total cross sectional area
v Kg/m3L Kg/m3
FLV
K1for values other than 0.02N/m surface tension a correction is applied for K1
K1
Uf
Uv Uf * 0.85Uv
m3/hrm3/s
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Total column cross sectional area Ac 1.34
Diameter of the column D=((At 4)/)Dia 1.3045627066 m or 4.3
Stripping Section:
Following are the necessary physical properties for Diameter calculation taken from HYSYS
40.64466
4.135 dyne/cm or 0.004135
Lw 107300 kg/hrVw 33440 kg/hr
0.9475831828
from graph0.03
0.02
Now the flooding velocity0.0708128106 m/s
Design for 85% flooding at maximum flow rate
Maximum allowable vapor velocity based on the net column cross sctional area
0.060190889 m/sMaximum volumetric flow rate 822.7
0.228528
Net Area required An 3.8
v Kg/m3L Kg/m3
FLV
K1for values other than 0.02N/m surface tension a correction is applied for K1
K1
Uf
Uv Uf * 0.85Uv
m3/hrm3/s
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Take downcomer area as 12% of the total cross sectional areaTotal column cross sectional area Ac 4.31
Diameter of the column D=((At 4)/)
Dia 2.3436334528 m or 7.7
Both diameters differ more than 20%, therefore we will have two different diameters for the column.
Plate Areas:
Ac Total column cross seectional area for top Ac 1.34for bottom Ac 4.31
Ad Cross sectional area of downcomer 12% of Acfor top Ad 0.1604195722for bottom Ad 0.5177341502
An Net area available Ac-Ad (for single pass)for top An 1.18for bottom An 3.80
Aa Active or bubbling area Ac-2Adfor top Aa 1.0159906241for bottom Aa 3.278982951
Ah Hole area normally 10% of Aafor top Ah 0.1015990624for bottom Ah 0.3278982951
Weir Dimensions:
Recommended values for columns operating above atmospheric pressure for Weir Height
hw 40-50mmhw 50 mm
Weir length of 0.77 times Dc is recommended or we can use graph for weir length
Ad/Ac 0.12 or 12
m2m2
m2m2
m2m2
m2m2
m2m2
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From graph the ratiolw/Dc 0.77
for top lw 1.0045132841 m orfor bottom lw 1.8045977587 m
Number of tray passes:
for top sectionliq flow 126.1 gpmweir length lw 39.547788447 inRatio 3.1885474498 gpm/in of weir
for bottom sectionliq flow 1014 gpmweir length lw 71.047194218 inRatio 14.272203303 gpm/in of weir
Both top and bottom liquid flow rate are nearly in the given recommended range.So we have selected singe pass cross flow with sgmental downcomer.
Other tray specifications:
Assumed tray spacing 0.5 mHole diameter 5 mmPlate thickness 5 mm for carbon steel
Tray Hydraulics:
Weep Point:
from HYSYS Maximum liquid rate 107300 kg/hr29.80556 kg/s
Turn down ratio 70 %Min liq rate 20.86389
For one pass design, the liquid flow rate does not exceed 7to 13 gpm/in of outletweir .
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Weir crest
Maximum how 80.92484 mm of liqMinimum how 63.799 mm of liq
At minimum rate hw+how 113.799 mmFrom graph 31
minimum design vapor velocity 1.9827603442Actual minimum vapor velocity Minimum Vapor rate/Ah
0.4878629954
Plate pressure drop:Plate pressure drop is given by
first we calculate dry plate pressure drop
Plate thickness/Hole diameter 1Percent perforated area
0.1 or
from graph 0.84maximum vapor velocity through holes 0.6969471363now 3.0618158187
Residual head is given by
hr 26.824034335 mm of liq
The total plate drop is given by ht=hd+hr+(hw+how)
ht 160.81069162 mm of liq
now P 735.13964434 orfor total pressure drop across all trays
K2
for orifice coefficient Co we use graph
CoUhhd
N/m2
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Downcomer liquid backup:
here
Am is either the downcomer area or clearance area under the downcomer Aap, whichever is smaller
Taking height of Apron hap=hw-10hap 40 mm
Area Aap hap*lw
Aap 0.0721839103 m less than downcomer area
130.3316481 mm of liq
downcomer liquid backup 422.0672 mm of liq0.422067 m
Residence time calculation:
tr 3.4164659109 s 3s
Entrainment Check:
percentage flooding = Un (act velocity based on net area)/Uf (flooding velocity based on net area)
Un 0.060190889 m/sUf 0.0708128106 m/spercentage flooding 0.85
85 %0.9475831828
from graph
fractional entrainment 0.001 well below 0.1
hdc
hb
FLV
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Total Number of holes:
Number of holes = Ah/ah
here ah area of one hole
dh 5 mmahah 1.96375E-005
Number of holes 5173.72692095174 holes
Height of Distillation Column:
Number of plates 26Tray spacing 0.5Distance between 26 plates tray space*N
13
Top and bottom clearance usually amount to 15% of that required by trays
Top and Bottom Clearance 1.95Tray thickness 5total thickness 0.13
Total height of the column 15.0849.4750672
50
* dh2/4m2/hole
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Composition of feed, top and bottom and relative volatilities are:
The key components selected are n-C4 and i-C5 as light and heavy key respctively.
Relative Volatility
61.060153666521.1100681079
7.57485988953.69960164392.11070669031.7919301232
10.87895551630.68866061860.6299678342
0.5361968930.52040048790.4853622543
0.4305157170.41502819230.35354822670.22420117620.21691120380.1377809003
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From Colburn and Underwood we have an expression for minimum reflux ratio
(i * Xid)/(i - )
0.55536205570.14508362720.14801951560.21091930420.26415523890.4658661216
-0.0305714286-0.0011775867-0.0680939189
0000000000
1.689562929
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Viscosity Xf * Viscosity
0.00296246 0.00028232240.020555101 0.0004830449
0.0582756837 0.00121796180.0804438475 0.00301664430.1007373902 0.00312285910.1062978504 0.00190273150.1072707083 0.03174140260.1231593616 0.01221740870.1967505846 0.00434818790.1574151096 0.00913007640.1604235033 0.00267907250.1402137612 0.00851097530.1469910158 0.00546806580.1528496492 0.00327098250.2116548985 0.0083815340.2749104037 0.0099517566
0.177310109 0.01383018850.261682442 0.0006280379
0.3183940376 0.0020058824
Sum 0.122189135
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for top and bottom for constant K1
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Following are the necessary physical properties for Diameter calculation taken from HYSYS
N/m
Maximum allowable vapor velocity based on the net column cross sctional area
m2
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ft
Following are the necessary physical properties for Diameter calculation taken from HYSYS
N/m
Maximum allowable vapor velocity based on the net column cross sctional area
m2
m2
-
ft
Both diameters differ more than 20%, therefore we will have two different diameters for the column.
Recommended values for columns operating above atmospheric pressure for Weir Height
Weir length of 0.77 times Dc is recommended or we can use graph for weir length
%
m2
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39.5477884471 in71.0471942183 in
Both top and bottom liquid flow rate are nearly in the given recommended range.
For one pass design, the liquid flow rate does not exceed 7to 13 gpm/in of outletweir .
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m/s
m/s
10
m/smm of liq
0.7351396443 KPa19.1136307527 KPa
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Am is either the downcomer area or clearance area under the downcomer Aap, whichever is smaller
less than downcomer area
Setisfactory
percentage flooding = Un (act velocity based on net area)/Uf (flooding velocity based on net area)
Setisfactory
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mm
mmm/platem
mftft
Sheet1