40 Offshore January 2018 • www.offshore-mag.com
ENGINEERING, CONSTRUCTION, & INSTALLATION
ruptions, and eliminated port congestion and
Onshore LNG terminals are predominantly
developed for baseload (large-scale) capacities
that exceed 6 MTPA, while near-shore FLNG
and FLNG are typically ranging between 1-4
MTPA capacities, with a few special cases (i.e.
lean gas feedstocks) reported beyond this range.
A PLNG terminal can be designed in incremen-
tal intervals for total LNG production capacities
to meet small, mid-, and large-scale demands,
as required. The PLNG concept is considered
favorable for the small and mid-scale LNG seg-
ment as a viable alternative to either onshore or
floating LNG. The capacity of near-shore FLNG,
or FSRU, could be widely constrained if rigor-
ous feedstock gas processing requirements are
needed as limited by the available deck space
for a given hull size. Whereas the modularized
PLNG has no such constraint due to the construction of stackable levels and/or additional
platform(s) to meet such requirements.
Another parameter regarding terminal ca-
pacity is the size and type of LNG storage. For
an onshore terminal, storage is essentially
unrestricted as long as land accessibility, ter-
rain, siting and other requirements do not
prevent construction of additional LNG storage
tanks. Depending on the type of hull used for
near-shore FLNG, storage is directly linked
to hull size. In some instances, storage can
be increased via additional floating storage
units (FSUs) moored alongside the near-shore
FLNG vessel but adds complexity to the moor-
ing and LNG transfer systems. Similarly for
FLNG facilities, storage is hull-size dependent.
Of the offshore alternatives, the PLNG solution
is the most flexible. Storage platforms can be
added and tailored for project volume require-
ments using the FSP tank design.
Near-shore FLNG and FSRU terminals
mostly rely on conventional LNG contain-
ment systems including self-supportive types,
prismatic, spherical and membrane type used
commonly in LNG carriers. The enhanced
Braemar-TankTek FSP tank design incorporates several elements that differentiate it
from its competition. These include a lower
construction cost than for equivalent tanks for
most size ranges, and the ability to be fabricated in parallel with the platform in order to
shorten the critical path. The FSP volumetric
efficiency is flexible to meet specific requirements, and the FSP is more robust with less
construction tolerance than other tank types.
Water depth is very relevant to all offshore
solutions. The deepwater FLNG solution is de-
signed with full navigation autonomy offshore
for water depths beyond 60 m. Near-shore FLNG
developments can either be ship-shaped or
barge-shaped, and can either process (pre-treat)
and convert natural gas into LNG or simply
convert it directly into LNG. Near-shore FLNG
shares, to some degree, several interface aspects
with onshore components. Therefore, water
depths are dictated by design draft requirements
of the LNG carrier fleet visiting the near-shore
FLNG unit for loading. Some near-shore FLNGs
are not necessarily designed for full naviga-
tion capabilities so site weather conditions (i.e.
storms, hurricanes) can play a decisive role in
the configuration and even the applicability of
FLNG to certain sites prone to extreme weather
conditions. The FLNG solution in shallower
waters may involve significantly higher loads
on mooring systems than deepwater locations,
making the mooring system more complicated.
The PLNG solution overcomes limitations of
near-shore and deepwater FLNGs for the 60
m or less of water depths and site conditions.
The PLNG’s structural construction, with deep
support piles penetrating into the seabed, allows
for greater stability and simpler mooring, and
increased terminal utilization rates.
Onshore LNG terminals, especially greenfield projects in remote locations and difficult
terrains, can involve extremely high costs,
long schedules and complex execution plans,
making them cost prohibitive, particularly for
small and mid-scale LNG projects. FLNG solutions requiring sophisticated, high-technology
designs of offshore components tend to involve
similar drawbacks. Both the near-shore FLNG
and PLNG terminals are being developed as al-
Typical LNG terminal solutions (upper left–onshore; lower left–near-shore FLNG; upper right–PLNG; lower right–FLNG).