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142 tons per year.Sieve Plate is chosen because the plating efficiency is high (60- 80%) and its cheaper maintenance compares to bubble cap type and also gives the lowest pressure drop among...

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142

tons per year.Sieve Plate is chosen because the plating efficiency is high (60-
80%) and its cheaper maintenance compares to bu
le cap type and also gives
the lowest pressure drop among others.Unlike Bu
le caps, which are prone to
co
osion and fouling, sieve plates actual have a more stability throughout the
user experiences.
4.1.2 Method of Design and Assumptions
Table 4.1: Method of Design
Method of
Design
Mc-Cabe- Thiele Method
The McCabe–Thiele method is considered to be the
simplest and perhaps most instructive method for the
analysis of binary distillation.
Plate Design
I.Provides a better liquid distribution.
II. Provide sufficient liquid hold-up for good mass
transfer (high efficiency).
III. Have sufficient area and spacing to keep the
entrainment and pressure drop within acceptable limits.
IV. Have sufficient downcomer area for the liquid to
flow freely from plate to plate
Assumptions
Plate spacing = 500 mm
pL (Bottom) = 655 kg/m3
pL (Top) = 570 kg/m3
143

R = 8.314 J/kmol
T top = 65 oC
T bot = 273 oC
Flooding Velocity = 85%
Pressure Top = XXXXXXXXXXpa
Pressure Bottom = XXXXXXXXXXpa
MW (Ethylene) = 28.05 g/mol
MW (Hexane) = 86.15 g/mol
Surface Tension (top) α = 35 x 10-3 N/M
Surface Tension (Bottom) α = 18.43 x 10-3 N/M
Flooding velocity = 0.85
Reflux Ratio = XXXXXXXXXX
Liquid Turndown Rate = 0.7
4.1.3 Step by Step Calculation
Table 4.2: Mole Fraction in Distillation Column
Liquid Molefrac Ethylene Dichloride Vapor Molefrac Ethylene
0 0
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
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XXXXXXXXXX
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144

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1 1
145
Figure 4.1 : Distillation Column
*R = 1.5Rmin
Figure 4.2: Vapour – Liquid Equili
ium Diagram
146

1. Rmin
Y=(
????
????+1
) ? + (
1
????+1
) ?? XXXXXXXXXX)
Intercept C = (
??
????+1
)
C=
0.99
????+1

C through graph above = 0.3
Rmin = (0.99/0.3) -1
= 2.3
R = 1.5Rmin
=1.5(2.3) = 3.45
2. Minimum Number of Stages Nmin
Nmin = 8 stages
3.Number of theoritical Stages N
Y=(
?
?+1
) ? + (
1
?+1
) ?? XXXXXXXXXX)
Intercept C = (
??
?+1
)
C = (
0.99
3.45+1
)
C=0.2224
N = 17 stages
147

4. Overall Column Efficiency Eo
Eo =
? ?????
? ????
XXXXXXXXXX)
Number of ideal stages = XXXXXXXXXXReboiler)
= 16 Stages
Number of Actual Stages =
16
0.60

=27 Stages
5. Column Sizing
Total Feed rate : XXXXXXXXXXkg/h
Mol.Weight of Feed : 0.5 x XXXXXXXXXXx 28.05 = 63.51
In term of Molar flow rate : Total Feed rate / Mol.Weight of Feed : 204 kmol/h
D + B = 204
0.99D + 0.005B = 204
XXXXXXXXXXB XXXXXXXXXXB) = XXXXXXXXXX)
B = XXXXXXXXXXkmol/h
D =102.52 kmol/h
6. Vapour Rate
V=D(1+R XXXXXXXXXX)
V= XXXXXXXXXX)
V = XXXXXXXXXXkmol/h

Distillation Column Sizing and Configuration
Table 1 Mass Balance for DST-2
    Equipment
    DISTILLATION COLUMN 2
    Operating condition
    T= 80 oC, P= 19 atm
    Input/ Output
    Input
    Output
    Stream name
    S10
    S11
    S12
    Component
    Phase
    kmol/h
    Phase
    Kmol/h
    Phase
    kmol/h
    Methanol
    L
    44.33
    L
    43.88
    L
     0.45
    Recycle Methanol
    -
     -
    -
     -
    -
     -
    Iso Butylene
    -
    -
    -
     -
    -
     -
    Di-isobutylene
    -
    -
    -
     -
    -
     -
    MTBE
    -
    -
    -
     -
    -
    -
    Wate
    L
    376.94
    L
     3.77
    L
    373.17
    SUB-TOTAL (kmol/hr)
    421.27
    47.65
    373.62
    TOTAL (kmol/hr)
    421.27
    421.27
Reference state: Methanol and Water (L, 80oC, 19atm).
Table 2: Energy balance of DST-2
    DST-2
    IN
     
    OUT
    STREAM
    COMPONENT
    PHASE
    T (oC) & P (atm)
    nin (kmol/hr)
    Hin (kJ/mol)
    STREAM
    COMPONENT
    PHASE
    T (oC) & P (atm)
    nout (kmol/hr)
    Hout (kJ/mol)
    10
    Methanol
    L
    80oC; 19 atm
    44.33
    -6.61
    Vapou
    Methanol
    G
    64.7oC; 19atm
    96.55
    35.17
    
    Wate
    L
    
    376.94
    -6.032
    
    Wate
    G
    
    8.29
    41.82
    
     
     
    
     
     
    Liquid
    Methanol
    L
    90oC; 19atm
    1.48
    -0.88
    
     
     
    
     
     
    
    Wate
    L
    
    1242.66
    -0.75
    REFLUX
    Methanol
    L
    50oC; 19atm
    52.66
    2.60
    
    
    
    Total noutHout (kJ/hr)
    2,803.96
    
    Wate
    L
    
    4.52
    2.26
    
    
    
    
    
    
    BOIL UP
    Methanol
    L
    100oC; 19atm
    1.03
    -1.82
    
    
    
    
    
    
    
    Wate
    L
    
    869.49
    -1.51
    
    
    
    
    
    
    
    
    
    Total ninHin (kJ/hr)
     XXXXXXXXXX
Answered Same Day Jun 18, 2021

Solution

Sannidhya answered on Jun 20 2021
144 Votes
Assumptions taken while solving the problem:
· Plate spacing = 500 mm
· ρL,bottom = 1000 kg/m3
· ρL,top = 814 kg/m3
· R = 8.314 J/mol.K
· Ttop = 640C
· Tbottom = 900C
· Flooding velocity = 80%
· Ptop = 101325 Pa
· Pbottom = 1925175 Pa
· MWmethanol = 32.04 g/mol
· MWwater = 18.01 g/mol
· Surface tension (top) = 26.4*10-3 N/m
· Surface tension (bottom) = 72*10-3 N/m
· Reflux ratio = 3.225
· Liquid turndown rate = 0.75
Given,
    Flow rate of methanol in S10 = 44.33 kmol/h
    Flow rate of water in S10 = 376.94 kmol/h
Hence,
    Mole fraction of more volatile component (methanol) in feed, xF = 44.33/(44.33+376.94)
                                     = 0.105
    Flow rate of methanol in S11 = 43.88 kmol/h
    Flow rate of water in S11 = 3.77 kmol/h
Hence,
    Mole fraction of more volatile component (methanol) in distillate, xD =                                                      43.88/(43.88+3.77)
                                     = 0.921
    Flow rate of methanol in S12 = 0.45 kmol/h
    Flow rate of water in S12 = 373.17 kmol/h
Hence,
    Mole fraction of more volatile component (methanol) in bottoms, xB =                                                  0.45/(0.45+373.17)
                                     = 0.0012
At the column temperature of 800C,
    Vapor pressure of methanol, P*methanol = 1354.37 mm Hg
    Vapor pressure of water, P*water = 354.532 mm Hg
Hence,
    Relative volatility, α = P*methanol/ P*water = 3.82
Now, based on the flow rates of methanol and water in the vapor and liquid streams...
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