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
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
144
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
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XXXXXXXXXX
XXXXXXXXXX
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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