Chemical Engineering November 2013 - 22

GEA Heat Exchangers
Newsfront
provides realtime information based on
the actual performance of the heat exchanger
so that the processor can make
informed decisions about which heat
exchangers to clean and when.
" This provides a lot of benefits. First,
it has a great impact on turnaround
because you know which exchangers
to target and when, " says Emerson's
Bishop. " You may end up cleaning
some exchangers every six months
and others every four years, but you
know that is what you should be doing
based upon the analysis. It also saves
time and money spent on unnecessary
cleaning and maintenance and
increases uptime and productivity, because
neglected heat exchangers are
receiving maintenance when needed. "
Improved designs
As with fouling, there are designs in
existence that can be applied in CPI
applications to help improve heat
transfer efficiency and new materials
applied for use in higher temperatures
and corrosive environments.
" Another difficult issue is the efficiency
of the heat recovery in the
very large process flows associated
with the chemical industry, " says Alfa
Laval's Abrahamsson. " In the past,
process engineers might have used
banks of multiple shell-and-tube
units because of the low cost and the
ability to handle high temperatures,
but today's compact technologies can
do the same job, more efficiently and
in a smaller footprint. "
Abrahamsson says gasketed- or
welded-plate heat exchangers are now
being made suitable for such applications.
Previously, he says, this type of
exchanger might not have found use
in the CPI because it couldn't withstand
the high pressures and temperatures,
but today's technologies
are pushing the envelope of temperature
and pressure capabilities. " The
gasket material can withstand many
hundreds of degrees higher than
years ago. Pressures that were not
previously possible in gasketed heat
exchangers are now being achieved.
It's not just new materials, but also
how the gaskets fit in the heat exchangers
and the design of the actual
gasket profile that are allowing these
efficient and compact heat exchangers
to find use in high temperature
and high pressure
chemical applications
today, " says Abrahamsson.
New materials provide
other benefits, as well.
" There are some developments
that allow higher
design pressures and temperatures
to be available
for special geometries than
what was available in the
past, " agrees Bennant J.
Drazner, EPC sales manager
with PHE Systems/
GEA Heat Exchangers, Inc.
(York, Pa.; www.gea.com).
" And in addition to these
benefits, the overall result
is better usage of materials, creating
longer successful operating run
times between required shutdowns
for maintenance, as well as more compact,
smaller-footprint solutions that
lead, in some cases, to higher yields,
faster reaction times through lower
hold up volumes, and reduced surfaces
to maintain. "
In addition, although many proFigure
3. The fully welded construction makes the
GEABloc heat exchanger well suited for applications
that require the high efficiency and compact size of
plate heat exchangers, but where conditions exceed
the capabilities of gasketed-plate heat exchangers
cesses in the chemical industry require
highly corrosion-resistant materials,
the use of these materials was often
cost prohibitive in traditional heatexchanger
solutions, such as shell and
tubes. But the new compact heat exchangers,
such as welded- (Figure 3)
and gasketed-plate products can be
significantly less expensive in these
advanced materials [because they require
less of the material than shelland-tube
heat exchangers would] and
provide a higher degree of heat recovery,
says Drazner.
However, Ron Herman, director of
sales and marketing with Enerquip
(Medford, Wisc.; www.enerquip.com)
says that as the number of options
for corrosion-resistant materials continues
to grow every year, the pricing
for alternative materials used in shelland-tube
exchangers, relative to traditional
carbon- and stainless-steel, has
been declining. He adds that improvements
in the technology behind exchanger
tubing are helping as well.
" Tubing suppliers are developing
varieties of tubing that enhance the
flow and turbulence of fluids flowing
through the exchanger, improving
22 ChemiCal engineering www.Che.Com november 2013
heat transfer by as much as 20 to 40%.
Corrugated tubing and twisted tape
turbulators (static mixers) are both
examples of these technologies, " he
explains. " Although these can increase
pressure drop through the tubes, the
result is improved throughput for
plants, and can often reduce the size
of an exchanger compared to a more
traditional design. Tests are being performed
to validate the cleanability of
these tubing surfaces, since opponents
of these technologies claim that they
can create possible areas where product
buildup can occur, while proponents
claim the increased turbulence
actually cleans the tube naturally
compared to smooth wall tubing. "
Additionally, the use of enhanced
surfaces, be it in tubular, plate or
other geometries, allows for the more
efficient and effective use of materials
and possible economic advantages of
metallurgy upgrades, says Drazner.
" There is also an increase in the possible
use of reduced surface-energy materials,
such as coatings (both polymer
and nanoparticles) or by surface treatment
(ion implantation and nitriding)
to minimize fouling deposition on
heat-transfer surfaces and corrosion
of the heat-transfer wall. "
Obviously there are a lot of choices
when it comes to heat-exchanger type,
design, and material selection. Each
heat-transfer technology offers certain
advantages, and the key is to understand
the need, then match the right
technology to the application.
■
Joy LePree
http://www.gea.com http://www.enerquip.com http://www.Che.Com
Chemical Engineering November 2013

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