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For the considered operating conditions the refri-
geration compressor will be of centrifugal type. For
the base case, the external power grid has been
considered capable to supply the required po-
wer to drive the refrigerant compressor. Common
motor driver and dedicated motor driver solutions
have been considered, with different electrical sy-
stem design and hence different substation buil-
ding arrangement.

An alternative solution based on an aero-derivative
gas turbine is also available, considering the nitro-
gen and the gas refrigerant compressors mounted
on the same shaft.

The heating system is ensured by a hot water cir-
cuit that supplies heat mainly to the amine regene-
ration reboiler and to the molecular sieve regenera-
tion first heater (the trim heating of regeneration gas
is performed by an electrical heater). genic bullets, the estimated project duration Small scale LNG plant 3D
Instrument air and nitrogen are produced within the is 23 months from effective date to Ready for model
LNG plant. Potable, service and demineralized wa- Start-Up.
ter is supplied from external sources, but could be It is based on an existing typical FEED that needs
produced on site, should the necessity arise. little consolidation to cope with the actual project
requirements, i.e. small adjustments to cope with
The design approach based on the proposed li- actual gas characteristics and site conditions.
quefaction concept leads to a compact layout of This FEED consolidation period is estimated at
approximately 1,500 m . two months and is performed during project ne-
2
gotiation and before project effective date so that
Two alternatives have been evaluated for storage: purchase orders for Long Lead Items (LLIs) can be
• Vacuum insulated cryogenic bullets done within the two initial months of the project.
• Atmospheric Full containment Tank LLIs are the equipment having a delivery time
longer than 12 months and are typically:
For the first storage option a limited LNG storage - the compression train
capacity is considered. The produced LNG from - the boil off gas compression
liquefaction unit is stored in 8 horizontal cryogenic - the turbo expanders
bullets (800 m each) and then exported through - the cold box
3
LNG trucks or LNG barge. The selection of the - the vacuum insulated cryogenic bullets
cryogenic bullets simplifies the BOG management,
but it is applicable to smaller overall storage ca- The construction strategy is based on maximizing
pacity. the portion of the plant to be delivered in modules.
Equipment and systems having a shorter delivery
For the second option, the produced LNG is sto- time will hence be assembled in modules, and
red in a 30,000 m storage tank. The boil-off gas they will typically include:
3
produced in the tank is compressed, used for mo- - pressure vessels (separators, scrubbers…)
lecular sieve regeneration and then recycled to the - air coolers
pre-treatment. A part of the boil-off gas is used to - pumps
supply fuel users. - and associated bulk items (piping, structure,
The stored LNG can be exported to LNG trucks or cables)
to small scale LNG carrier. The fabrication of the modules will start after 8
months of the project effective date and will be
Execution strategy performed in a high efficiency yard.
The execution strategy is based on a standard and LLIs will be built at vendors workshops and be
pre-engineered gas treatment and liquefaction sy- delivered directly at site, assembled in skids for
stem. The presence of this standardized design the rotating equipment and loose for the static
package is essential as it leads to significant savin- equipment (cold box and bullets).
gs in terms of engineering documents preparation, During modules and LLIs fabrication and manufac-
purchasing activities and modules construction turing, the site is prepared to be ready to accom-
and installation. modate them (foundations, buildings, some piping
For the option based on vacuum insulated cryo- and structures) and some stick-built installation

Impiantistica Italiana - Gennaio-Febbraio 2020 31 31