Hydrocarbon Processing - July 2021 - 49

Process Optimization
recovery. The high-pressure receiver also
provides the settling time necessary to
remove water from the system that otherwise
can lead to water entrapment issues.
These and other similarities are utilized to
provide an effective and reliable design.
The DWC design utilizes two advanced
separation units.b,c
These units are based
on well-proven designs that optimize plant
CAPEX and maximize product purity to
achieve maximum recovery. In comparing
FIGS. 1 and 2, seven conventional vessels are
combined into three vessels, using DWC
technology to provide significant savings
in CAPEX and plot space. Not only are the
number of vessels reduced, but also the
number of foundations is reduced by having
fewer columns. The amount of vessel
metal is reduced significantly, as is foundation
load and material cost. A significant
reduction in column insulation, ladders,
platforms, etc., is achieved. The number
of condenser systems (exchangers, drum,
pumps, controls) is reduced from five to
two, and the number of reboiler systems is
reduced from six to five.
The DWC SGP design can easily operCDU
gas
Reformer stabilizer gas
Reformer stripper gas
Other gas streams
Offgas
Lean oil
Compressor
section
Rich oil
Propane
Advanced separation unitb
Sponge absorber/
Absorber/
Deethanizer/
Depropanizer
Crude unit overhead liquid
Reformer stabilizer overhead liquid
Reformer stripper overhead liquid
Other saturated liquid streams
Debutanizer/
deisobutanizer
nC4
iC4
iC5
Depentanizer/
deisopentanizer
ate over the typical range of SGPs and is
a lower-CAPEX solution. The simplistic
design configuration helps achieve equal
or better product recoveries and purities,
as compared to any conventional system,
but at lower CAPEX. This SGP design
can be used without the addition of a
high-cost refrigeration system to provide
propane recovery of greater than 97%.
Molecular management and light ends
recovery will become more important
than ever to enable shifts to petrochemical
feedstock and higher-octane gasoline
production. DWCs offer lower-CAPEX
means of attaining these demands.
DWC internals design. Some in the industry
have expressed reluctance to use
DWC technology. However, the introduction
of packing internals has been a
topic of interest over the past century and,
as with DWCs, there was a reluctance to
use packing at that time. Great success
has been experienced in using packing
instead of trays. At the same time, some
significant failures have been experienced
by those who did not possess adequate
design knowledge. DWC internals are no
different. Hundreds of applications using
DWC designs with success already exist.
However, to create this success requires
detailed knowledge in designing the process
and the column internals.
While a DWC tray can be similar to
a conventional tray, it also has some distinctive
features that allow proper tray operation.
FIG. 3 shows a shop setup of twopass
trays for a DWC that has since been
installed. To some degree, the tray is no
different than a standard tray design, but
here each tray is segmented on each side
of the dividing wall.
The basic tray operation is essentially
no different than a conventional design.
However, there are many enhancements
in the design, especially in the transition
areas. The proper splitting of vapor and
liquid to the two sides of the wall, and how
to achieve this, are also important. In addition,
the shape of the tray leads to changes
in operating parameters, such as weir loadings,
which must be taken into consideration.
While a DWC tray has similarities
to a conventional tray, it also has differnC5
HN
FIG.
2. SGP utilizing proprietary LPGb
and GWCc
technologies.
Hydrocarbon Processing | JULY 2021 49
Hydrocarbon Processing - July 2021

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