“Chemical Engineering Equilibrium
Separations”
Lectures 15
22-31 Oct 2012
1
In-Class Problem
benzene (17 mol%)
toluene (66 mol%)
m-xylene (17 mol%)
D
S HO RT Y
DSTWU
FEE D
F = 100 kmol/s
sat’d liquid
1 atm
B
1.0135 bar
Component
Benzene
Toluene
m-Xylene
Tbp oC
80.1
110.7
139.1
Pi star [bar]
80.1 oC 123 oC
1.0135 3.217
0.387
1.42
0.151
0.645
2
In-Class Problem
3
In-Class Problem
4
In-Class Problem
5
In-Class Problem
6
In-Class Problem
7
In-Class Problem
8
Overview
•AspenPlus:
o Shortcut methods: DSTWU
o Rigorous method: RADFRAC
• Efficiencies
• Introduction to multicomponent distillation (Chapter 9)
9
Homework Problem
benzene (17 mol%)
toluene (66 mol%)
m-xylene (17 mol%)
Xbz = 99 mol%
D
S HO RT Y
DSTWU
FEE D
F = 100 kmol/s
sat’d liquid
1 atm
B
Xbz = 0.1 mol%
1.0135 bar
Component
Benzene
Toluene
m-Xylene
Tbp oC
80.1
110.7
139.1
Pi star [bar]
80.1 oC 123 oC
1.0135 3.217
0.387
1.42
0.151
0.645
10
HWK Problem-molefrac specified
11
HWK Problem-molefrac specified
12
Overview
•Review rigorous methods / RADFRAC
• Multicomponent systems:
o Residue curves
o DSTWU / RADFRAC
o Rules of thumb
• Complex (Enhanced) distillation
• Column internals
• Batch distillation
13
Multicomponent
Rigorous Methods
Rigorous Methods: solution of
stage by stage material
balances, energy balances, and
thermodynamic equilibrium
equations.
14
AspenPlus: RADFRAC
Rigorous two- or three-phase fractionation for single columns.
Models absorbers, strippers, reactive distillation, and so forth.
• RadFrac is a rigorous model for simulating all types of multistage vapor liquid
fractionation operations. In addition to ordinary distillation, it can simulate:
o absorption, reboiled absorption, stripping, reboiled stripping, extractive and
azeotropic distillation
15
Rigorous
Model
16
AspenPlus: RADFRAC
Rigorous two- or three-phase fractionation for single columns.
Models absorbers, strippers, reactive distillation, and so forth.
• RadFrac is a rigorous model for simulating all types of multistage vapor liquid
fractionation operations. In addition to ordinary distillation, it can simulate:
o absorption, reboiled absorption, stripping, reboiled stripping, extractive and
azeotropic distillation
• RadFrac is suitable for:
o three phase systems, narrow boiling and wide boiling systems, systems
exhibiting strong liquid phase nonideality
• RadFrac can detect and handle a free water phase or other second liquid phase
anywhere in the column. You can decant free water from the condenser.
• RadFrac can handle solids on every stage.
• RadFrac can model columns where chemical reactions are occurring. Reactions can
have fixed conversions, or they can be:
o equilibrium, rate controlled, electrolytic
• RadFrac can model columns where two liquid phases exist and different chemical
reactions occur in the two liquid phases. RadFrac can also model salt precipitation.
• RadFrac can operate in rating mode or design mode.
• With Aspen Rate-Based Distillation feature, RadFrac can perform rate-based
distillation calculations (packed tower configurations).
17
Rating Mode
18
19
20
Design Mode
21
Rigorous
Model
22
Multicomponent Methods
AspenPlus (methanol, ethanol, 1-propanol):
Component
MeOH
EtOH
1-Propanol
P*i
(64.5 oC)
1.013 bar
0.5709
0.2534
Keys
AspenPlus Txy
23
“Residue” From Batch Distillation
Seader & Henley (2006)
24
Residue Curve Map
25
Residue Curve Map
26
Residue Curve Map
27
DSTWU
Zi = 1/3
MeOH recovery (dist.) = 99.9%
R = 1.2 * Rmin
EtOH recovery (dist.) = 0.1%
28
RADFRAC
Zi = 1/3
F = 100 kmol/h
R = 5.2
N = 63
NF = 31
D = 33 kmol/h
29
Residue Curve Map
30
Plot Wizard
31
NF = 21
32
Set up Scheme 2 (1st column only)
• Run DSTWU
• Run RADFRAC
• Check performance
33
Questions?
34