Chemical Engineering August 2014 - 40

Overheads
Cover Story
Feature Report
Reflux
New Horizons
For Dividing
Wall Columns
Feed
How to significantly expand the application window
of DWCs, both as a new design to enhance potential
benefits and as an energy saving retrofit option
Helmut Jansen
Julius Montz GmbH
Igor Dejanovi´c
University of Zagreb
A
dividing wall column (DWC)
is an atypical distillation column
with an internal, vertical
partition wall that effectively
accommodates - within one shell
- two conventional distillation columns
that are connected in series
as required when separating a multicomponent
feed mixture into three
pure products.
DWC components
Figures 1 and 2 show the anatomy
and main components of a conventional
packed DWC, with a centrally
placed partition wall separating the
prefractionator column (feed side)
from the main column (product drawoff
side), each of which contain just
one bed above and below for simplicity.
The prefractionator with a rectification
section above and stripping
section below the feed resembles the
configuration of a typical column.
On the main column side, there
are two binary separation sections
placed above each other. Therefore,
the section above the side-product
draw-off is the stripping section of
the upper column, while the section
Björn Kaibel
BASF SE
Žarko Oluji´c
Delft University of Technology
below the side-product draw-off is
the rectification section of the lower
column. If a conventional column
with an external side-rectifier is replaced
by a DWC, then the partition
wall will extend from around the
middle to the top of the shell, or, in
case of a column with an external
side-stripper, to the bottom of the
shell [1-3].
As shown in Figure 1, the reflux
is distributed over a conventional
bed in the top and upon leaving
this bed it is collected and split, according
to requirements, into two
streams delivered to the distributors
on the prefractionator and
main column sides of the partition
wall, respectively. This is done
using a proprietary device shown in
Figure 2a, which was originally designed
to serve as a reflux/distillate
splitter. Liquid leaving each of two
packed beds in the partitioned part
of the column is collected, mixed
and guided to the distributor of the
lower bed. Here and in all other liquid
redistribution sections, common
chevron- and chimney-type liquid
collectors are used for this pur40
ChemiCal engineering www.Che.Com august 2014
Source:
Julius Montz
Side
product
Vapor
Bottoms
Figure 1. Shown here is a side view
of a simple dividing-wall column (DWC)
that is equipped with structured packing
pose in conjunction with a narrowtrough
distributor, all adapted to fit
into the given cross-sectional area.
On the prefractionator side, this is
the place where the feed stream is
added, and on the main column side
it is where the side product is taken
out of the column.
Figure 2b shows a photograph of
an installed narrow-trough distributor
with predistributor box and a
downpipe coming from the collec
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Chemical Engineering August 2014

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