ABSTRACT

A proprietary floating LNG concept was developed to address project execution and operational concerns arising from large, complex, integrated FLNG concepts.  These concerns included versatility and reusability, the use of large, purpose built hull designs and the cost/reliability of side by side and tandem LNG offloading in open sea conditions. 

Several Floating LNG concepts have been advanced in recent years.  Much of the design discussion to date addresses the choice of liquefaction technology, LNG cargo storage and offloading arrangement.  From the perspective of an independent oil & gas operator focused on deepwater and floating platform operations, the author contends that the key concept drivers are use of conventional hull designs, providing a generic design with residual value and ensuring reliable open water offloading operations, even in moderate to severe sea states. 

A FLNG concept is presented based on separation of functions into:

     1.  Spread moored FPSO for primary production/gas treatment, condensate handling
     2.  3 x Liquefaction vessels based on standard Moss type LNG carriers
     3.  Optimization of N2 dual expansion liquefaction process
     4.  A storage/transfer jetty in sheltered water for loading conventional LNG tankers

The concept offers shorter design/build time due to use of conventional hull forms, high residual value due to maximum use of generic processing and elimination of open water LNG cargo transfer.  The optimized N2 Dual Expansion liquefaction process offers several advantages on size, weight, safety and operability, but now has fuel efficiency comparable to mixed refrigerant processes.   The offshore transfer of LNG is avoided altogether and cargo transfer is conducted in sheltered water.  Unit capital cost is typically $700 – 1000/TPA and project execution risk is reduced.  The system is scalable from 1 – 6 MTA capacity.