Subsea -to-Amidships LNG Transfer (SALT) System
Publication Date: 2011-Oct-07
The IP.com Prior Art Database
The current invention describes systems and methods of transferring cryogenic fluids to or from a floating vessel. More particularly, the invention involves the transfer of LNG from (or to) an LNG carrier at a terminal location via a cryogenic disconnectable subsea riser to (or from) a subsea cryogenic pipeline while stationkeeping for the LNG carrier is provided by a "dumb" turret, i.e., a turret without fluid transfer capability. The primary embodiment has two functional attributes, which are: (1) the mooring turret and (2) the subsea riser system that connects and disconnects to the LNG carrier amidships manifold. The invention is most applicable in a location where the wind, waves and current environment is "directional", i.e., where most of the time, the wind, waves, and current are aligned so that the limitation on weathervaning imposed by the attachemnt of the riser at the amidship manifold does not necessarily impose a restriction on operability as environmental conditions worsen.
A. Area of Technology
The Subsea-to-Amidships LNG Terminal (SALT) System is an invention intended for application as an element in the delivery of liquefied natural gas (LNG) via ships. A typical LNG delivery chain consists of:
· gas production from underground reservoirs,
· gas processing/treating to remove heavier hydrocarbons and undesirable components, such as hydrogen sulfide and carbon dioxide,
· a liquefaction plant to refrigerate the natural gas to a liquid state for storage and transport,
· an export terminal facility, typically a harbor with berths for LNG carriers,
· LNG carrier ships for marine transportation of the LNG from the export terminal to the market location, and
· an import terminal at the market location to receive the LNG from the LNG carrier ships and vaporize the LNG into natural gas to be transmitted to the market by pipeline.
The invention is associated primarily with the import terminal component of the delivery chain, but also has application to the export terminal facility.
The invention involves the transfer of LNG from (or to) an LNG carrier at a terminal location via a cryogenic disconnectable subsea riser to (or from) a subsea cryogenic pipeline while stationkeeping for the LNG carrier is provided by a "dumb" turret, i.e., a turret without fluid transfer capability.
This disclosure references US Patent 7836840, Subsea Cryogenic Fluid Transfer System (SCFTS), and this disclosure is written assuming the reader will be familiar with this patent.
SALT is an alternative LNG carrier turret-mooring and cryogenic riser configuration to the internal turret fluid path and swivel arrangement shown in SCFTS. SALT is compatible with all other features of SCFTS and can be integrated with the primary SCFTS embodiment and most alternative SCFTS embodiments, subject to the differences outlined in the following paragraphs.
SALT, in its primary embodiment has two functional differences from the SCFTS turret-mooring and cryogenic riser system, which are: (1) the weathervaning capability of the LNG carrier is limited for the SALT system, unlike the fully weathervaning SCFTS system; and (2) the LNG transfer for SALT occurs not through the disconnectable turret and swivel system (as for SCFTS), but through a subsea riser system that connects and disconnects to the LNG carrier amidships manifold. For SALT, the limitation on weathervaning is necessary to enable the subsea-to-amidships riser component to be used. However, it is the loading/offloading of LNG at the LNG carrier's amidships manifold that eliminates the need for a cryogenic swivel system in each ship (a potentially significant cost reduction over the "fleet" of ships needed for a delivery chain).
Thus, the two key features of SALT are the "dumb" turret mooring for stationkeeping of the LNG carrier and the subsea-to-amidships LNG riser/transfer concept and capability. Fig...