Hydrocarbon Processing - March 2022 - 82

Heat Transfer
ber of bays or modules of air-cooled heat
exchangers required in a project.
the supplier's factory works to the project
site-is essential to ensure the safe transThe
transportation of modular air-cooled heat
exchangers from factory works to the project site-
by sea, inland transportation or both-is critical
and numerous factors impact costs.
The dismantling of air-cooled heat
exchangers that have been assembled to
conduct factory/shop run-in tests is not
required in the case of modular supply-
a single module or a bay saves approximately
250 work hours, as well as wear
on machinery.
Transportation costs associated with
the modular supply of small- to mediumsize
air-cooled heat exchangers (i.e., not an
over-dimensional consignment) are less
than its knock-down supply, as the number
of trucks and trailers required to transport
dismantled supporting structures, plenum
and fan rings, tube bundles, etc., is reduced.
For projects where the site location has
limited approachability for plant erection
due to adverse climate conditions in one
or more seasons, or when a fast-tracked
project faces challenges in the availability
of skilled and experienced site personnel,
adopting a modular supply of air-cooled
heat exchangers becomes essential to
overcome these challenges.
A checklist and general direction
for the modular supply of air-cooled
heat exchangers. A route survey-from
Air exit
Part of
module
Hot fluid in
4
5
4
Hot fluid out
300 mm
Air entrance
Permanent
bracing
Temporary
bracing
Air entrance
Splice
connection
Bottom segment of support column
FIG. 2. An induced-draft, air-cooled heat exchanger with the direct or belt-driven fans located
at the top and motors located at the bottom of the tube bundles.
82 MARCH 2022 | HydrocarbonProcessing.com
6
7
8
portation of the modules. The transportation
limitations in length, width and height
of the module are determined based on
this route survey. A thermal engineer must
consider these transportation limitations
while sizing the air-cooled heat exchangers.
In the case of modular supply of aircooled
heat exchangers, each individual
bay (typically a module) has its independent
supporting structure. Therefore, a
gap of approximately 450 mm should be
between two adjacent bays. The piping
engineer preparing the plot plan must
account for this: ideally, this gap should
also be sealed with air sealing plates at the
top of the steel elevation level to avoid
any air recirculation.
The air-cooled heat exchanger supplier
will perform an additional structural
calculation of the module to determine
the optimum sizes of temporary bracings
and beams required for transportation
purposes.
A local junction box for vibration instruments
and a local control station for
the motor are often installed on support
structure columns of the air-cooled heat
exchanger. Due to the splice connec1
9
2
3
tion
of the support structure columns
in modular supply, the air-cooled heat
exchanger supplier must ensure
that these junction boxes and local
control stations do not interfere
with splice connection fasteners.
Otherwise, the engineering, procurement
and construction (EPC)
contractor should be informed in
advance to find another suitable
location for the junction box and
local control station.
The tube bundle is the heaviest part of
an air-cooled heat exchanger to be lifted
in case of knock-down supply. However,
a module is much heavier and larger than
its tube bundle alone. Therefore, the aircooled
heat exchanger supplier must carefully
design and use a proper certified lifting
arrangement for a module.
During the onsite erection of the
module, permanent bracings should be
assembled before dismantling the temporary
transportation bracings. This
must be specifically highlighted by the
air-cooled heat exchanger supplier in its
erection manual.
Takeaway. The modular supply concept
of air-cooled heat exchangers in any project
can save substantial factory and site activities,
while minimizing the supervision
of skilled and experienced site personnel.
Many reputed EPC contractors, project
managing companies and owners of leading
refineries, petrochemical and LNG
projects have already sourced air-cooled
heat exchangers in modular condition to
enable faster plant erection. LNG projects
require numerous air-cooled heat exchangers
in both of their terminals (i.e., liquefaction
terminals and regasification terminals).
Considering the potential benefits
and ease in adoption, the modular supply
of air-cooled heat exchangers in LNG projects
has become an industry train. A structural
engineer can further add value to
this concept by optimizing the structural
design to avoid the scraping of temporary
transportation bracings and beams by utilizing
them as permanent equipment.
AJAY KUMAR DIXIT is a Mechanical
Engineer with more than 11 yr of
working experience in the thermal
engineering of air-fin coolers and
vacuum ejector systems. He now
works for Graham India Pvt. Ltd.
as an Application Engineer.
Previously, he has worked for L&T Chiyoda and
Fluor Daniel India Pvt. Ltd.

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