The SRV is an LNG vessel with onboard LNG vaporisers. The SRV system has been designed and developed by Höegh LNG, and normally encompasses a twin mooring and unlading buoy system and at least three SRVs to allow for continuous delivery of regasified LNG. Höegh LNG has two SRVs on order from Samsung Heavy Industries for delivery in 2009 and 2010 for the Neptune LNG deepwater port terminal project offshore Boston in the USA.

The concept

The SRV is a modified standard LNG vessel. The main additions to a standard LNG vessel will be:

• A cylindrical trunk forward of tank no.1 to accommodate the submerged turret mooring buoy and swivel system
• Skid mounted regasification units on deck
  
• Bow and stern thrusters
  
• Supplementary electrical power supply
  
• Supplementary steam production for regasification
  
• The SRV can be a converted LNG carrier or a newbuilding, and will also be capable of traditional delivery of LNG. Conversion studies of our own vessels have been performed and no showstoppers have been identified.

LNG is pumped from the tanks and sent to regasification units mounted on the vessel’s deck. Pressure is boosted by large cryogenic LNG pumps. Steam generated by auxillary boilers in the vessel main engine room produces the heat necessary to regasify the LNG in the regasification unit’s heat exchanger. The regasification units design has been developed by Hamworthy Gas Systems in Norway.

Regasified LNG is discharged via a turret and swivel through a mooring and unloading buoy connected to a riser and subsea pipeline, designed by Advanced Production Loading (APL) and based on their North Sea proven STL technology. Two separate buoys will ensure continuous send-out by overlap between arriving and departing SRVs.

The containment system can be either reinforced membrane type, Moss spherical tank type or SPB type. The important issue is to ensure that the containment system is designed to allow for maximum operational flexibility with regards to filling levels to ensure that sloshing does not occur during operation in exposed offshore locations with partially filled cargo tanks.

Unloading Buoy


Unloading Buoy in Moon-pool

The benefits

By discharging the LNG through an SRV the need for a land based receiving and regasification terminal will be redundant. This offers many obvious benefits, some of which are:

• No land or port requirements for the receiving terminal
• No physical encroachment to the local land based environment
• No visual impact from shore
• Shorter overall time to market
• Enhanced safety
• Higher delivery regularity, even in harsh weather conditions

Normally one additional SRV is required to deliver the same volume as a traditional solution due to the regasifiaction time of each vessel on the buoy. In spite of this, the economics of the SRV system compares very favourably to traditional LNG receiving terminals for small to medium regasification volumes and short to medium shipping distances (up to 4000 nmiles/6480 km). The SRV system may be used in harsh (and benign) environment worldwide.