Sevan’s FLNG Concept Approved-in-Principle by ABS

A Sevan designed FLNG facility and HiLoadLNG offshore transfer system, image: Sevan

“By awarding Sevan AIP, we have acknowledged that the company’s innovative approach to designing and constructing a first-of-its-kind FLNG production unit is based on sound engineering practices and ABS classification standards,” said Tor-Ivar Guttulsrød, Director of FLNG, Global Gas Solutions, at ABS. “ABS continues to support new FLNG concepts that, when fully developed and implemented, will strengthen the emerging FLNG market.”

Sevan’s cylindrical designs have been proven within the drilling and offshore oil and gas production sectors, but never for liquefied natural gas.  In fact, nobody has yet produced, liquefied and offloaded LNG from a floating vessel before, although that will likely change in 2015 when Petronas’ ship-shaped FLNG facility comes on line.

This design will be capable of operating in more than 3,000 m (10,000 ft) water depth and in harsh environments, such as extreme North Atlantic and cyclonic conditions.  The unit design is based on environmental load calculations for a 100-year return storm in the Barents Sea. Similar to the Sevan FPSOs, the FLNG unit’s axio-symetric hull shape enables high capacity for LNG storage and deck loads and tolerance for weather spreading and eliminates the need to weathervane in rough seas.   Because there’s no need for weathervaning, there is no need for a turret and high pressure swivel system.

Sevan notes the unit can be designed to have gas processing and liquefaction up to 4 MTPA and store up to 240,000 m³ of LNG and 36,000 m³ of condensate.

With major natural gas disoveries being made planet-wide, dozens of these FLNG facilities will likely be constructed over the next 10 years, but it’s a new technology and not all the issues have been fully resolved, particularly when it comes to getting the ultra-cold liquid off the vessel.

The two options are either doing a side-by-side transfer with an LNG carrier pulling up alongside the FLNG facility and then completing the transfer there, or via a tandem offload, where the LNG carrier “parks” behind the FLNG facility and the transfer is completed via spooled hoses off the stern.

The former option is perhaps easiest in calm seas, however as sea state increases, the only real feasible option from a risk standpoint is the tandem option.  And, considering Sevan’s design is a cylinder, pulling up alongside is never an option.

Enter HiLoad LNG

To transfer LNG in tandem mode, a system called HiLoad LNG has been developed to eliminate the need for LNG carriers to be outfitted with special LNG transfer systems on their foc’s’le, like a DP shuttle tanker, but rather, a small dynamically-positioned vessel is deployed from the FLNG facility with the cryogenic hose in tow and mates with the LNG carrier a bit like a giant pallet truck.  The combined unit is then able to be positioned dynamically and safety while the transfer occurs.

The following video shows how this works from a Sevan FLNG facility:

And from a ship-shaped facility: