Distillation is the primary separation process used in the chemical processing industries which approximately consume 40% to 50% of total energy use in the industry. Significant savings in both energy and capital costs can be achieved using Dividing Wall Distillation Column (DWC) compared to the conventional distillation column. DWC can significantly reduce capital and energy expense compared to conventional distillation towers by approximately 30-40% however, implementation of DWC concept is not the optimal solution for every fractionation and each application must be thoroughly reviewed if DWC can bring desirable benefits. This paper elaborates the benefits in terms of capital and energy consumption by reducing additional conventional column and cooling and heating utilities. There are number of tools used in such analysis, including process simulation package, mass transfer equipment hydraulic rating, capital cost estimation, etc. This paper also gives the major highlights on process parameters that need to be considered during modeling of DWC, like column size, metallurgy, operating pressure, pressure balance, etc. as well as important parameters that need to be inspected during column internals installation.

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Divide Your Distillation Column with
Confidence
Anup Elias & Petar Pribic
Sadara Chemical Company
October 2017
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Anup Elias ( Speaker)

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Outline - Dividing Wall Column
➢ Understanding what is a Dividing Wall Column
➢ When to use a Dividing Wall Column
➢ Limitations in using a Dividing Wall Column
➢ Modeling a Dividing wall column
➢ Benefits of using a Dividing wall column vs
conventional column
➢ Inspection of Dividing Wall Column internals

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Ternary Mixture Direct Sequence
Separation
*A-The Most Volatile Component
B-Middle Boiling Component
C-Heavy High Boiling Component
Column 1 Column 2
0 0.2 0.4 0.6 0.8 1
C
o
l
u
m
n
H
e
i
g
h
t Component B composition
Middle Boiler B composition in Direct
Sequence Separation
Column No1
Column No.2
Column 1 Column 2
Column
Thermodynamic
Inefficiency

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What is a Dividing Wall Column
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FEED
TOP
PRODUCT
REFLUX
SIDE
PRODUCT
REBOILER
VAPOR
Vertical wall creates
a feed and draw-off
section
Separation of low
and high boiling
components occurs
in feed section
Medium boiling
component is
concentrated in
draw-off section
BOTTOMS
Dividing Wall Column
Allows separation of 3 component mixture
into pure fractions in single column versus
conventional process with 2 sequential
columns
Particularly suited to obtain pure medium
boiling components
Picture source: MONTZ Dividing Wall Columns

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What is a Dividing Wall Column
FEED
TOP
PRODUCT
REFLUX
SIDE
PRODUCT
REBOILER
VAPOR
Vertical wall creates
a feed and draw-off
section
Separation of low
and high boiling
components occurs
in feed section
Medium boiling
component is
concentrated in
draw-off section
BOTTOMS
Dividing Wall Column
Allows separation of 3 component mixture
into pure fractions in single column versus
conventional process with 2 sequential
columns
Particularly suited to obtain pure medium
boiling components
Picture source: MONTZ Dividing Wall Columns

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When is a Dividing Wall Column Not
Recommended
TOP
PRODUCT
REFLUX
SIDE
PRODUCT
REBOILER
VAPOR
Vertical wall creates
a feed and draw-off
section
Separation of low
and high boiling
components occurs
in feed section
Medium boiling
component is
concentrated in
draw-off section
BOTTOMS
When a DWC is not recommended
– the pressure difference in the
conventional sequence is high
– the conventional sequence
requires utilities at very different
levels
– When the middle boiling
component does not represent
the substantial fraction of the
feed
Picture source: MONTZ Dividing Wall Columns

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ABC
AB
A
B
B
C
BC
ABC
AB
BC
C
B
A
ABC
BC
AB
A
B
C
Evolution of Dividing Wall Column
Concept
Three Column Conventional Layout Two Column linked Layout Two Column Heat integrated Layout

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Vapor and Liquid Splits in Dividing Wall
Columns (DWC)
ABC
A
B
C
Sufficient Staging and
reflux to the prefractionator
side to keep the heavy
component from getting
over the wall.
Sufficient Staging and
vapor to the prefractionator
side to keep the light
component from getting
under the wall.
Sufficient Staging and L/V
to accomplish a clean split
between the light and mid
boiling component.
Sufficient Staging and L/V
to accomplish a clean split
between the mid boiling
and heavy component.
• The vapor split is fixed
by the pressure drop
characteristics of the
internals on each side
of the wall.
• Generally, equal cross
sectional area on both
sides of the wall are
employed.
• The liquid split is best
controlled by removing
all of the liquid from
the top column via a
side draw and
returning the proper
amount to each side of
the wall.
Rectify B from A
Strip A from B
Rectify C from B
Strip B from C

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8 9
LIQTOSPL
TOP-PROD
14
17
FEED
10
13
16
11
MID-PROD
VAPTOSPL
BOT-PROD
TOP
MID-1
MID-2
BOT
SPL-LIQ
SPL-VAP
Rigorous Simulation
•4 RADFRAC Blocks
•2 Split Blocks
There are alternatives
•This seems the most intuitive
Getting Started
•Perform a 2-column sequence
•Arrange the simulation as seen
on the left with those numbers
•Optimize from there
DWC Rigorous Simulation

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Different DWC Layouts
Alpha A
Alpha B
> Alpha B
Alpha C
Alpha A
Alpha B
< Alpha B
Alpha C
Mb<<Ma,Mc Mb>>Ma,Mc
• Alpha-Relative Volatility
• M – Mass Flow rate
A
B
C
A
B
C
A
B
C
A
B
C
A-The Most Volatile Component
B-Middle Boiling Component
C-Heavy High Boiling Component

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Dividing Wall Column (DWC) Internals
Distributor
DWC Model Layout
Liquid
Collector
DWC Packing Fabrication
Picture source: SULZER CHEMTECH

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Dividing Wall Column (DWC) Internals
DWC Industrial Column
Wall starts here ( wall is
positioned off-center)
Liquid Ring Channel
Liquid draw-off nozzle
From undivided section
above
Chimney Tray
Support Ring
Reflux return line
To divided section
Picture source: SULZER CHEMTECH

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Dividing Wall Column (DWC) Internals
DWC with Trays
Off-center Partition Wall
Side Downcomers
( 2-Pass Trays)
Side Downcomers
( 2-Pass Trays)
Center Downcomer
( 2-Pass Trays) Tray weir
Clearance under DowncomerPicture source: SULZER CHEMTECH

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Dividing Wall Column (DWC) Internals
DWC with Middle Positioned Wall
(Distributor Layout)
Catalytic DWC
(Packing Filled with Catalyst))
Picture source: SULZER CHEMTECH

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Dividing Wall Column (DWC) Internals
DWC with weld-ins
DWC distributor
DWC Top view

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C
B
Feed
T:80C
P:4 bar a
F:180,000 kg/hr
Comp ( mass fr.)
A: 0.26
B:0.47
C:0.27
A
B top: 50ppm
BC
A bottom:500ppm
Lights Column Finishing Column
C
C top: 100ppm
Conventional Column for Ternary
Mixture Separation

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Composition Profile in Conventional
Column
Lights Column Composition Profile
Column
Bottoms
Column
Top
Component A
Component B
Component(s) C
Re - Mixing
CONCENTRATION
COLUMN HEIGHT

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Hydraulic Design
Lights Column
Upper Diameter,m:4.2m
Lower Diameter,m:4.5m
Packing: High Efficiency,250m2/m3
Upper Section: 2 Beds ( 4.1m/4.1m)
Bottom Section:2 Beds( 4.1m/3.1m)
Reboiler Duty, kW: 17,950
Finishing Column
Upper Diameter,m:3.9m
Lower Diameter,m:4.3m
Packing: High Efficiency,250m2/m3
Upper Section: 2 Beds ( 4.1m/3.6m)
Bottom Section:2 Beds ( 5.1m/5.1m)
Reboiler Duty,kW: 17,920
Lights Column Finishing Column
B top: 50ppm
BC
A bottom:500ppm
C top: 100ppm
B bottoms:
1000 ppm
Feed
Hydraulic Design of Conventional
Column

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Design of Dividing Wall Column (DWC)
DWC Rigorous Modelling
Pre-fractionator
Non-sharp split
Of middle boiling
component
No more mixing
inefficiency
Vapor split is determined
by wall position
Best Draw-off
Location
Liquid split is determined
by separation requirements
B top:50ppm
C in side Draw:100ppm
B bot:1000ppm
TOP
BOTTOM
FEED STAGE
Stage Number
(Top to Bottom)
Draw-off
LiquidProduct
Concentration

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Hydraulic calculations in DWC
Vapor Split – By Hydraulic Calculation of Internals
Prefractionator
Equivalent
Diameter
Pressure Drop
Upper Section
Pressure Drop
Lower Section
Wall Split: 60:40
Total Pressure Drop: 9.22mbar

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Hydraulic calculations in DWC
Vapor Split – By Hydraulic Calculation of Internals
Product Side
Equivalent
Diameter
Pressure Drop
Upper Section
Pressure Drop
Lower Section
Wall Split: 60:40
Total Pressure Drop: 9.15 mbar

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Hydraulic calculations in DWC
Rectification Section
Full
Diameter
Stripping Section
Full
Diameter

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Inspection of Dividing Wall Column (DWC)
Proper Column Inspection
Collars in packing
Proper Packing Installation
Importance of leveling
Improper bolting
Missing Tray Valves
Packing Support Grid
Level checking

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Conclusion
➢ Dividing wall columns are an alternative to multi-
column circuits, which reduces
• Investment
• Energy consumption,
• Plot area
• operational and maintenance costs.
➢ In our case, investment costs were reduced by 28 %
and utility costs were reduced by 24 %.

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Q & A
Thank you for your attention