Hydrocarbon Processing - October 2021 - GP-23

SPECIAL FOCUS: LNG TECHNOLOGY
surfaces. Closely spaced fins may create
resistance in the release of condensed water
and may also lead to the formation of
a thick boundary layer on the fin and tube
surfaces, creating resistance to heat transfer.
As shown in FIG. 4, it is recommended
to establish a minimum fin spacing of 2.54
mm for extruded aluminium fins, which
enables sound mechanical bonding with
base tubes and efficient heat transfer.
A higher number of finned tube rows
in the AAH is to be avoided. Four finned
tube rows are ideal for the easy release of
condensed water in both high-humidity
and relatively colder sites. In the case of
limited available plot area, one or two additional
tube rows can be used, preferably
with higher fin spacing or without fins
and a higher tube pitch.
Maintenance. Provisions for the
maintenance of fans, motors and drive
assembly mounted at the top of the tube
bundles should be provided.
Support structures. Tube bundles for
ambient air heaters are generally installed
at an elevation of 10 m-13 m. Since water
condensation routinely takes place, a supporting
structure of concrete can be used
for the AAH, instead of conventional hotdip
galvanized steel. In this case, the shop
run-in test at the AAH supplier's factory
should be carried out with a dummy supporting
structure.
Tube length. A longer tube length,
a higher number of tube passes and the
maximum utilization of allowable pressure
drop are the key factors to achieving
an optimized thermal design for an
AAH. However, the selection of tube
length must be aligned with market
availability, the available plot area, the
feasibility of finning and transportation
limitations (if any).
Takeaway. LNG regasification technology,
encompassing an intermediate fluid
and ambient air as a primary source of
heat, has witnessed several environmental,
CAPEX and OPEX benefits compared
to other technologies, especially for
humid and warm locations. The design
and configuration features of AAHs described
in this article have already been
implemented at various LNG regasification
terminals, resulting in economical
and optimized selection and trouble-free
operation of the AAHs.
Selection of an intermediate fluid, operating
cases, design ambient temperature,
design relative humidity and dewpoint
temperature are critical parameters
for the sizing of AAHs. A CFD analysis
that considers all consequential site meteorological
data (e.g., prevailing wind
direction, wind velocity and surrounding
tall structures like LNG tanks, buildings)
provides an accurate prediction of
cold air recirculation. This prediction
can be used to determine the necessary
correction for design air temperature or
adequate overdesign margins,
suitable
elevation and the most effective layout.
An effective layout and suitable elevation
also minimize the generation of fog due to
condensed water vapor. GP
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. At present, he works with Graham India Pvt.
Ltd. as an Application Engineer. Previously, he worked
at L&T Chiyoda and Fluor Daniel India Pvt. Ltd.
EWA provides decision-makers the data necessary to:
* Enable superior business development strategy and
execution.
* Facilitate strategic planning and asset optimization.
* Streamline global research and macro-trend analysis
Gas Processing & LNG | SEPTEMBER/OCTOBER 2021 23
Hydrocarbon Processing - October 2021

Table of Contents for the Digital Edition of Hydrocarbon Processing - October 2021
