32
LNG
INDUSTRY
MARCH
2016
Ophir’s responsibility will be to drill, complete and tie-back
the wells to the FLNG vessel.
Gas will be produced from the subsea wells via gathering
flowlines, manifolds and flexible risers to the external turret
of the FLNG vessel. All upstream production control will be
operated from the FLNG vessel. As the operator of the
upstream development, it is Ophir’s responsibility to manage
the performance of the reservoirs.
Midstream development
The Golar FLNG concept is based on the conversion of
Moss LNG carriers. Given the certified condition of the hull
structure and LNG tanks, the allocated vessels are excellent
candidates to have second lives as FLNG vessels. The
Gandria
, the third vessel that Golar is converting and which
will be leased to Ophir, has been trading in benign waters
and has been maintained to the highest standards. In order
to prepare it for a 20-year placement in Equatorial Guinea,
it will undergo an extensive refit and life extension scope of
work at Keppel’s shipyard in Singapore. The hull structure will
receive class renewal at CAP1 rating. Existing marine, utility
and cargo systems are removed, completely overhauled or
fully renewed.
In order to provide deck area and space for the topsides
and utility systems, sponson steel structures are constructed
and welded to the sides of the vessel over the full length of
the cargo tank area. These sponsons are integral parts of the
hull structure, contributing to strength, displacement and
stability.
The bow of the
Gandria
will be removed and replaced by
an enlarged new bow section. The sponsons on the ship sides
will be flush integrated into this new bow section. The specific
inlet facilities for the Fortuna project will be installed on the
deck of the new bow section. An external turret mooring
system is mounted at the very front of the bow, which
provides the mooring, riser hang-off and swivel systems for
fluid transfer to and from the subsea production system.
Golar has contracted Keppel to convert three of its carriers
to FLNG vessels. Keppel has simultaneously entered into
sub-contracts with global engineering, procurement and
construction (EPC) company, Black & Veatch, to provide its
licensed PRICO
®
technology, perform detailed engineering
and process design, specify and procure topside equipment,
and provide commissioning support for the FLNG vessel
topsides and liquefaction process. Golar selected
Black & Veatch’s technology for the liquefaction process
because of its long-established record of reliable performance
in global LNG operations over the last 50 years.
The vessel will be turret moored with facilities for
side-by-side offloading. Golar will own, operate and maintain
the vessel throughout the life of the project.
Gas handling
Block R gas will arrive at the FLNG facility at a pressure of
70 bara and at a temperature of between -3°C and +6°C.
The lean biogenic nature of the gas lends itself towards
a comparatively simple FLNG facility with standard gas
pretreatment and minimal natural gas liquid (NGL) handling.
Following pretreatment, gas will be liquefied to form LNG.
The FLNG facility will be permanently moored in a water
depth of approximately 1780 m.
Liquefaction technology
PRICO liquefaction technology has been selected for all
of the Golar FLNG vessels. Black & Veatch has undertaken
extensive work over the past decade to develop and certify
the technology for marine application and will be providing
performance guarantees.
PRICO uses a single refrigeration series and a simple,
downward flowing main heat exchanger (cold box). This
results in a reduced equipment count, compact layout and
simplified operation. Black & Veatch approved the PRICO
LNG technology for floating application in February 2010.
Owing to the widespread application of floating
production, storage and offloading (FPSO) vessels in the
offshore oil and gas industry over the past 30+ years, all of
the PRICO components have been engineered and are
available for marine application, except for the cold box.
The cold box used in each liquefaction train will be a
brazed aluminium heat exchanger supplied, on licence, by
Chart Industries. It is a pressure fed system with no weirs or
levelling devices, therefore avoiding any operational issues
relating to misdistribution of refrigerant. Furthermore, it is
completely welded. All connections are external with no
moving parts, valves or vessels inside, leaving the process
performance unaffected by motion.
The cold box is a gravity-based system with the
refrigerant and feed gas condensing flowing downward. The
unit operates ‘cold end down’, which ensures cold liquids stay
in the cryogenic area of the core on shutdown. No cold liquid
flows into the warm part of the system and no special
precautions are required in case of shutdown. Such a design
results in significant operational flexibility with superior
turndown and start-up performance vs the spiral wound heat
exchangers found in other liquefaction systems.
Each of the four liquefaction trains installed on the vessel
will utilise one cold box with six cores in each.
Storage and offloading
Produced LNG will be stored onboard the FLNG vessel
in five Moss type tanks with maximum total capacity of
126 000 m
3
. The LNG will be offloaded from the tanks through
common pipework and loading arms onto the LNG carrier in a
side-by-side formation. The maximum offloading loading rate
is 10 000 m
3
/hr, which implies that a full offloading would
be completed in approximately 12 hr (excluding approach,
berthing and departure time).
LNG carriers of up to 180 000 m
3
can be moored
side-by-side to the FLNG vessel. For LNG carriers with larger
storage capacity than the FLNG vessel, a full loading will
typically be conducted in two operations.
Conclusion
FLNG is coming of age with Ophir on track to take FID in
mid-2016 and deliver first gas in 2019. It is a tough climate for
the hydrocarbon sector, but this project is going faster and
smarter thanks to industry leading partners and innovative
commercial strategies to minimise CAPEX.
