Ted Moon, Technology Editor
Independent LNG shipowner Golar LNG has signed a contract with Singapore-based Keppel Shipyard Ltd. for the conversion of an existing LNG carrier into an LNG floating storage and regasification unit (FSRU), the world’s first. The total contract value is approximately Singapore $90 million (about US $55 million), and calls for the converted vessel to be delivered in 2Q 2007.
Golar LNG sees this development as a way to diversify its offering into other parts of the LNG value chain. Golar market surveys have identified several specific opportunities for the FSRU, but as of now no fixed employment contract has been signed.
Golar LNG will work in partnership with Keppel Shipyard in the engineering, procurement and construction of the FSRU. The scope of work calls for installation of a new forward turret, side-by-side mooring system, LNG loading arms, aft thruster with compartment and a regasification plant, and replacement of cargo pumps. In addition, the existing steam power electrical and marine systems need to be upgraded.
Moss Maritime AS has been selected to prepare the conceptual basis for the FSRU and will carry out the design and engineering for the conversion.
3D representation of Golar LNG's FSRU.
The proposed LNG terminal is a steel mono hull fitted with six Moss LNG tanks in the middle, regasification plant in the forward end, and crew facilities, control room, and utility machinery in the aft end. Built in 1981, the retrofitted vessel will have a LNG storage capacity of 129,000 cu m at -163° C.
The vessel is designed to be permanently moored to the seabed with a turret mooring arrangement, with the gas send-out line arranged through the turret down to the seabed and to shore via a pipeline on the seafloor. The operational life is scheduled for 20 years in water depths of between 50 and 150 m, and they are aiming to locate the vessel in an area with benign environmental conditions.
There is a significant engineering and construction effort at work to successfully complete the conversion.
Mooring systems
The FSRU will include two mooring systems, one for the turret that that will moor the vessel to the seabed, and one that will allow for safe side-by-side mooring of standard LNG carriers during offloading.
The turret will be connected to the forward part of ship, resulting in the need for modification of the bow area. The turret shall be configured to provide a non-rotating platform for supporting the anchor lines, as well as flexible risers and any associated control and service lines. In order to allow 360º continuous rotation of the FSRU, the turret shall be equipped with a turntable.
LNG carriers offloading to the FSRU will be moored in a side-by-side fashion. The approach and berthing operation will take place in a very similar manner to that used for onshore terminals. During berthing, the LNG carrier will need assistance from two tug boats with minimum 50 metric ton bollard pull.
The mooring system will consist of various components:
•Primary and secondary fenders.
•Nylon mooring lines that will be connected to the wire part of the LNG carrier line with specially-designed mooring shackles.
•Roller fairleads, which will guide the nylon lines as required.
•Hydraulic quick release hooks with built-in capstan and adjustable release load.
The side-by-side mooring system will also allow for ease of hook up and detachment, so that the entire process of berthing, loading and unberthing will take approximately 24 hours.
Loading arms
Standard loading arms will be included on the FSRU to allow side-by-side transfer of LNG and vapor return. There will be a total of three 16-in. loading arms, two for LNG and one for vapor return. The two LNG arms will ensure a loading time of 16 hr.
While the loading arms will be very similar to those used for onshore terminals, they will be modified to account for the relative motions between the FSRU and the carrier.
A regasification skid will be situated forward on the FSRU, and will consist of booster pumps and steam heated vaporizers. The booster pumps will increase the pressure of the LNG coming from the tanks to about 90 bar, prior to the LNG being vaporized. The gas is then passed through a fiscal metering unit and sent to the subsea pipeline via gas swivel and flexible risers.
The system will send gas out at a maximum pressure of 85 bar, at a rate of 240 metric tons/hr and a minimum temperature of 0º C.
The maximum boil-off gas (BOG) from the storage tanks is expected to be 0.25%, as per the original design requirements of the LNG carrier. The FSRU tanks will be operated at higher pressure than the offloading LNG carriers, which avoids the need for BOG handling equipment.
The existing power generation equipment on the LNG carrier will be used once it has been converted to the FSRU. This equipment consists of two steam-driven turbo generators, which will be boosted by the addition of a larger steam-driven turbo generator of 6 MW. There are two additional diesel-driven generators on board as well.
The boilers will run on natural gas, supplied by the BOG collected in the vapor header and partly by additional fuel supplied by the LNG vaporizers.
Graeme McDonald, group technical director of Golar LNG, is optimistic that this type of vessel will be of great benefit to both Golar LNG and their customers. “The Golar terminal can be available approximately three years ahead of a conventional land-based terminal, and annual savings in overall energy production costs can be more than $50 million,” he said.
In addition, Golar LNG’s commitment to build a FSRU “has the dual advantages of locking in a start-up date for a project and thus allowing potential end users to make firm preparations and commitments.”•
