Chemical Engineering September 2010 - 33

Fractionation Column
Pushing capacity limits
S
tarting around 1970, many new
contacting devices became available
for use in distillation, absorption
and stripping columns. Those
devices included high-performance
random packings, structured packings,
high-capacity structured packings,
augmented crossflow trays, counterflow
trays and cocurrent flow trays.
At the request of FRI's membership,
many of those devices were tested in
FRI's 4-ft and 8-ft test columns.
The FRI test columns, and all of the
ancillary equipment, were designed
in 1952. The original designers of the
unit imagined that the columns would
contain simple single-pass, crossflow
trays at 24-in. spacings. None of those
designers imagined the eventual existence
of today's two-pass, cocurrent
flow trays, which have at least 50%
more capacity. None imagined cocurrent
flow trays at all. Nevertheless,
subsequent to 2004 the following
three cocurrent flow trays were tested
at FRI: Shell ConSep, Koch-Glitsch
Ultra-Frac and UOP SimulFlow. All
worked well, but, it was beginning to
concern the FRI membership that the
capacities of the contacting devices
were near to exceeding the capacities
of the FRI test unit.
In 2007, FRI's Executive Committee,
authorized the use of $2 million to upgrade
the test unit and perform maintenance
work that would extend its life for
an additional 20 years. The first thing
that FRI did was contract with FTS Inspection
& Engineering Services (www.
ftsinspection.com; Bartlesville, Okla.) to
perform a mechanical audit of all vessels
and lines. FTS ultimately concluded
that even after 50 years of operation, the
unit was mechanically sound and safe.
Thereafter, FRI staff engineers attempted
to identify hydraulic and
heat transfer bottlenecks in the unit.
Project money was spent using the
motto " One safe and correct step at a
time " . Over the last two years, many
small and medium-sized projects were
performed, with an overall target of
25% increase in unit capacity. The two
biggest unit bottlenecks proved to be
the steam-generating boiler and the
cooling tower. Even repaired, the boiler's
capacity was stuck at
17 million Btu/h. Meanwhile,
the cooling tower
was also stuck at 17 million
Btu/hr and therefore
needed to be refurbished.
Temperature excursions in the 1990s
had embrittled the plastic fill. Some
areas of the fill were so under-irrigated
that birds had built nests in between
the fill sheets. The cooling tower was
completely refurbished.
FRI's Technical Committee approved
what was called an empty column
test, which took place in October
of 2009. The low-pressure column was
emptied, so that no trays or packings
would limit the unit's capacity. An
auxiliary boiler was rented to run in
parallel with the existing boiler. FRI's
two reboilers were piped-up for parallel
operation; so were the two condensers
and the two reflux pumps. After
about a week of lining out and minor
troubleshooting, FRI's unit was run
steadily at 24 million Btu/h - a 41%
increase over the previous maximum.
FRI's maintenance budgets are annual
and forever. FRI's upgrade project
is now considered to be complete, at a
total cost of only $716,000. FRI stands
ready to test the next generations of
trays and packings. Bring 'em on! ■
Mike Resetarits
Mike Resetarits is the technical director at
FRI (resetarits@fri.org), a distillation research
consortium headquartered in Stillwater,
Okla. Each month, Mike shares his first-hand
experience in this column.
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Chemical Engineering September 2010

Table of Contents for the Digital Edition of Chemical Engineering September 2010