Hydrocarbon Processing - March 2022 - 81

Heat Transfer
A. K. DIXIT, Graham India Pvt. Ltd., India
Modularization of air-cooled heat exchangers:
A " plug and play " solution
An air-cooled heat exchanger-also
called an air fin cooler-is used to reject
the heat from a fluid (liquid or gas, or a
mixture of liquid and gas) directly to the
ambient air. The hot fluid flows inside the
finned tubes of the tube bundle, while the
cold ambient air passes outside the finned
tubes in a cross-flow to exchange the heat.
The ambient air can be forced by using a
fan coupled with a motor, or without fans
(i.e., by natural convection). In general,
the tube bundle assembly is mounted on
its support structure of suitable height,
ensuring sufficient stack for air entrance.
Air-cooled heat exchangers are used in
a wide range of industries and products,
typically including gas compressor packages,
engine cooling, lube oil cooling,
condensing of propane or refrigerants in
liquefied natural gas (LNG), thermic fluid
heating in LNG, steam condensers in
cement and power plants, process cooling
applications in refineries and petrochemicals,
and many others.
The supply of air-cooled heat exchangers
in a " pre-assembled module " is a new
methodology to overcome the challenge
of its long erection time and cost, and the
lack of skilled and experienced personnel
at a project site.
In an air-cooled heat exchanger, a preassembled
module typically comprises
tube bundles with guards, support structure
with top segment columns, temporary
transportation bracings and beams,
header walkways, plenum and fan rings,
a drive structure, fans and motors, and
coupling and vibration instruments-the
loose component may include the bottom
segment of support columns, permanent
bracings, stairs and handrails, and variable
frequency drives (if applicable).
Depending upon the process requirement
and site conditions, an air-cooled
heat exchanger can be in a forced-draft or
an induced-draft configuration. The extent
and outline of the module formation
depends upon the configuration of the aircooled
heat exchanger, in addition to other
factors. Based on learnings from recently
executed projects, the most-effective practice
of module formation for an air-cooled
heat exchanger that avoids numerous interferences
and significantly benefits a
project schedule is presented here.
Module formation of a forced-draft,
air-cooled heat exchanger. In a module
of forced-draft, air-cooled heat exchangers
with direct or belt-driven fans
and motors located at the bottom of the
tube bundles, the supporting structural
columns should be made in two segments
with a splice connection located approximately
300 mm below the bottom of the
motors. The top segment of the columns
will be part of the module, while the lower
segment is to be supplied as loose. FIG. 1
shows this kind of configuration.
In air-cooled heat exchangers with
fans and motors, both located at the top
Air exit
of the tube bundle, the supporting structural
columns are not required to be in
segments. In this case, tube bundles with
plenum, fan ring, fans, motors and drive
assembly should form a module.
Module formation of an induceddraft,
air-cooled
heat exchanger.
The practice of constructing the supporting
structural columns in segments
and locating the splice connection is the
same for 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, as illustrated
in FIG. 2.
Potential benefits in adopting a
modular supply of air-cooled heat
exchangers. The pre-assembled module
can take less than 1 d to erect at a project
site with little to no supervision, while
the older knock-down supply can take
3 d-4 d with the appropriate supervision
of skilled and experienced site personnel.
This savings is exponential with the numHot
fluid in
6
4
5
Hot fluid out
Part of
module
300 mm
Temporary
bracing
Permanent
bracing
1. Fan
2. Fan ring
3. Plenum
4. Nozzle
5. Header
6. Tube bundle
Air entrance
Splice
connection
7. Drive assembly
8. Column support
9. Inlet bell
Bottom segment
of support
column
FIG. 1. A module of forced-draft, air-cooled heat exchangers with direct or belt-driven fans and
motors located at the bottom of the tube bundles.
Hydrocarbon Processing | MARCH 2022 81
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Hydrocarbon Processing - March 2022

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