New niche LNG FPSO concept gets AIP

ABS continues to be at the forefront of technical standards for gas production at sea and transport technologies with its approval in principle (AIP) of a novel concept from ABB Lummus Global (ABB) for a liquefied natural gas and liquefied petroleum gas, floating production storage and offloading unit (Niche LNG FPSO). The concept is the offshore application and marinization of the NicheLNG process, a proprietary dual turbo-expander based LNG liquefaction scheme developed by ABB Lummus Global.

The equipment layout is similar to a typical FPSO, however, the concept for this new purpose-built FPSO allows for processing facilities onboard which incorporate both the gas feed pre-treatment (removal of CO2, Mercury etc., dehydration of the gas and LPG extraction) and LNG liquefaction.

LNG and LPG have different compositions thus requiring storage at different temperatures. LNG must be stored at extremely low temperatures (-162 degrees C) while LPG can be stored at a much higher or warmer temperature (-40 degrees C).

Described by ABB as primarily a floating liquefaction facility for LNG production, storage and export, its process facilities are compact enough to fit onto the deck of a 312-metre long Niche LNG FPSO, yet is capable of delivering 1.5 million tonnes per year combined output from its three LNG production trains. The design storage capacity is in the 200,000m3 range, with six tanks total, four for LNG storage and two for LPG storage. The design features a flat deck making it easier to arrange and accommodate the topside process modules.

The vessel will utilize a storage concept such as IHI?s self-supporting, Prismatic-Shape, IMO Type-B tank system or SPB. ABS has previously classed the only LNG carriers to use this containment system and also classed the first LPG FSO newbuild, the Escravos, and the first LPG FPSO newbuild, the Sanha, both operating offshore Angola.

“Industry has successfully dealt with oil and gas processing facilities on Floating Production Storage Units for a number of years. However, the liquefaction and cryogenic storage of LNG and LPG offshore is a whole new arena,” comments ABS Vice President of Energy Development William J. Sember. “This transition requires a comprehensive approach toward the integration of marine and typically shore-based gas processing facilities in the design of a floating concept,” he adds. “A key issue for a floating concept like this is designing for the relative motions likely to occur during loading/offloading operations.”

Transfer of LNG at subzero temperatures through a loading hose or arm presents industry with a technological challenge. ABS is working with industry to evaluate appropriate technologies to optimize reliability and flexibility for the LNG transfer in an offshore environment.

The ABB Niche LNG FPSO design has incorporated a number of measures to minimize the effects of the motions experienced on a floating platform. The vessel will be held on station via an external turret mooring system at the bow and offloading will most likely be conducted tandem-style from the stern although side-by-side offloading is a possibility and is being explored.

The power generation demands for this concept call for an onboard power plant with the capability of providing 40MWs of generation. Three main gas turbines will drive the main compressors. Together the three trains can liquefy 225 million cubic feet per day of gas.