1) The Dividing Wall Column (DWC) technology offers an alternative to traditional distillation column schemes that can save 25-30% in energy usage while improving separation efficiency. 2) A DWC integrates a pre-fractionator column into the main column separated by a vertical baffle, minimizing remixing and improving thermodynamic efficiency over conventional schemes. 3) Case studies show DWC retrofits of naphtha splitter columns can reduce heat input by 28% while improving product yields, with paybacks of less than 1.5 years.

1. Petroleum Federation of India54
Rajeev Ranjan
Sr. Technical Professional
KBR Technology
Samir Saxena
Chief Technical Advisor
KBR Technology
Dividing Wall Column (DWC):
A Smarter Way to Save Energy & Improve Fractionation
Saranraj Pachayappan
Associate Technical Professional
KBR Technology
D
istillation has been the most prominent
separation technology in the refining and
petrochemical industry, and it consumes
a significant share of the total energy required in a
process. In recent years increased cost of energy
and a growing awareness of carbon foot print, have
challenged the hydrocarbon industry to hunt for
alternative technologies for reducing energy usage.
Process units designed several years back
considered a cost of energy which was much lower
than at present, and therefore, these units today
operate sub-optimally, posing challenges to
operators to discover new ways of reducing energy
consumption to remain competitive.
The Dividing Wall Column (DWC) technology offers
an alternative to traditional distillation column
schemes, specifically in naphtha-range hydrocarbon
services, with significant saving in operating cost
due to improved separation efficiency and
substantial reduction in capital expenditure due to
reduced equipment count.
DWC technology is suitable for both revamp and
grass-root applications in various hydrocarbon
separation services. Suitable DWC revamp
scenarios may include i) Converting one of the
existing column from two column sequence to DWC
to provide the same separation performance with
about 25-30% energy saving, ii) Modifying an
existing two-product column to get an additional
side-draw product, e.g. existing two product
reformate splitter can be revamped using DWC
technology to get a concentrated benzene stream
as high-value side draw product whilst meeting
benzene specification for top & bottom products,
iii) Revamping existing three product conventional
column using DWC technology to improve
fractionation quality of products.
Distillation Schemes and DWC
The traditional approach to separate ternary
components is a direct train (Figure 1 (i)) or indirect
train (Figure 1(ii)) i.e. through sequential separation
by arranging columns in series. Such schemes are
successful in separating three or more components
but are energy inefficient due to the inherent remixing
phenomenon and also require higher capital
investment due to the higher equipment count.
A thermally coupled design to perform the same
fractionation is relatively more energy efficient as
compared to a conventional sequential column
design; for example the Petlyuk column, Figure 1(iii).
In a Petlyuk column, the vapor and liquid streams
leaving the first column are directly connected to
the second column. Principally, one condenser and
reboiler are effectively replaced by the thermal
coupling of the pre-fractionator with the main
column, while the required condenser and reboiler
are attached to the main column.
A DWC design represents the next level of
improvement to a Petlyuk column in which the pre-
fractionator column is integrated into the same shell
of the main column. This arrangement is shown in
Figure 2. A vertical baffle/wall is inserted in a column
at the appropriate position and it splits the column

2. Petroleum Federation of India 55
shell into two sections: pre-fractionator and main-
fractionator. DWC technology improves the
thermodynamic efficiency of separation due to the
minimization of remixing phenomenon. This
improvement in thermodynamic efficiency translates
into an improvement in the energy efficiency of the
separation compared to conventional column
separation schemes.
The hydrocarbon industry is now focusing on the
efficient usage of energy to remain competitive and
contribute to a 'greener environment' by reducing
their carbon foot print. The application of such policy
brings an ideal opportunity to apply an efficient and
elegant solution i.e. DWC technology.
Distill-Max™ DWC Technology
The Dividing Wall Column concept has existed for
more than 50 years (first patent in 1949) but
commercialization of this technology was delayed
due to the availability of inexpensive energy, lack of
established design procedures and also industry's
entrenched preference to choose conventional
designs.
KBR began developing DWC technology, known as
Distill-Max, in the late 1980s through pilot-plant
studies. In 1998, KBR in cooperation with BP,
commissioned its first DWC at BP's Coryton Refinery
which was a revamp of a Stabilizer Column to
produce a special gasoline blend component. Since
then KBR has licensed several grassroots and
revamp dividing wall columns which have been
successfully commissioned and are in operation
currently.
Distill-Max DWC Technology
Advantages
Distill-Max DWC technology offers the following
major benefits over conventional distillation column
schemes:
Cost Efficient: DWC can save around 30% capital
cost for grassroots applications due to the
reduced equipment count.
Energy Efficient: Energy savings are in the range
of 25-30% when compared to sequential column
operation for same or improved separation.
Production Efficient: Column throughput can be
increased due to improved fractionation and
energy efficiency as compared to the
conventional scheme.
Plot Area Efficient: It requires less plot space due
to reduced equipment count.
Safe: It reduces hydrocarbon inventory in the
plant due to the reduced number of equipment.
The flare load also decreases due to reduced
heat input and also due to reduced wetted area
for fire case load.
Figure 1 (i) Direct Train (ii) Indirect Train
(iii) Petlyuk Column
Figure 2 Dividing Wall Column

3. Petroleum Federation of India56
Case Study
This study focuses on the energy saving potential
by supplanting two columns with a single DWC
configuration using Distill-Max DWC technology.
The simplified process flow scheme of a FCC
naphtha splitter and a side stripper column with
dedicated reboiler for each column is shown in
Figure 3. The revamp scheme through the
implementation of DWC technology to achieve the
same fractionation objective with reduced heat load
is also presented.
In the existing scheme, full-range naphtha from the
FCC Debutanizer is fed to naphtha splitter column.
The overhead product Light gasoline cut is sent to
the gasoline pool. The Intermediate Cut Naphtha
(ICN) and Heavy Cut Naphtha (HCN) are routed for
further treatment. Some of the notable points after
implementation of DWC in the naphtha splitter
column are as follows:
Improved product distillation of all the three
streams are achieved
Existing main column, reboiler and condenser
are retained
Naphtha side-stripper and its reboiler are
redundant and available to use else-where in the
refinery
Overall heat energy saving is about 28%
(refer to Table-1 below)
Revamp payback less than 1.5 years
Table-1
Conventional Distill-Max
Design Case
Reboiler Duty
(MMKcal/hr)
Naphtha Splitter 10.0 8.7
Naphtha Stripper 2.0 0.0
Total Heat Input 12.0 8.7
Condenser Duty 12.2 9.2
(MMKcal/hr)
Such revamps can be implemented in three weeks
of plant turnaround time with an efficient execution
plan in place.
Conclusion
Distill-Max is a fully-proven and commercialized
DWC technology which offers a cost-effective and
energy efficient solution for a wide range of
hydrocarbon applications where three or more
products are to be separated from a feed stream.
KBR with many years of experience in the design
and pilot testing of commercial units is well
positioned to offer safe & reliable grassroots and
revamp design of an existing column. The rigorous
design procedure and in-house proprietary
thermodynamic data developed by KBR evaluate
the full operating envelope of the column which
enables KBR to guarantee the process performance.
Distill-Max DWC installation is a proven and
technically simple investment with very attractive pay
back for both grass-root designs and revamps of
existing conventional distillation facilities. DWC
installations are growing rapidly for various
hydrocarbon separation applications and DWC has
proven to be a reliable process intensification
distillation technology.
DWC for FCC Naphtha splitter revamp
Figure 3 DWC for FCC Naphtha splitter revamping