Converting LNG tankers into floating storage and liquefaction plants, or FLNG units offers security to critical infrastructure at pace, with the flexibility to alter policy course rapidly.

 

As with all vessels, the market drives demand. For Golar LNG, the Bermuda-based FLNG company, its innovative, speculative conversion of a Moss-type LNG tanker into a floating storage and liquefaction unit was a risk that looks to be paying off.

 

The Golar Hilli began operations in 2018 and has completed its first eight-year contract, just as Golar has announced an order of its fourth FLNG unit, which will be built at Yantai CIMC Raffles.

 

Golar CEO Karl Fredrik Staubo commented on the company’s second Mk II FLNG, which has a liquefaction capacity of 3.5mtpa: “We believe this FLNG order combines the world’s earliest available FLNG delivery [and] is well positioned to provide clients with an attractive gas monetisation solution, whilst driving value for Golar.”

 

Conversion of the new unit will be similar to that of the FLNG Esperanza, currently under construction at CIMC Raffles, with the fourth unit scheduled for a late-2029 delivery.

 

CIMC Raffles and Golar have built on their experience of developing the Mk I conversions to offer the more sophisticated Mk II conversions which differ significantly from their predecessors.

 

Maran Gas Maritime engineer Dr Oleksandr Pliesnoi explained that the Mk I conversions, Hilli and Gimi, were Moss tankers, with the original vessels also remaining as the basis for the LNG processing plant.

 

“The engineering philosophy was therefore relatively conservative,” explained Pliesnoi, “it was to retain as much of the proven LNG carrier as possible and build the FLNG around it.”

 

Using a Moss tanker as a base unit meant: “The developer did not have to design and construct an entirely new hull and LNG containment system. An existing LNG carrier already represented a significant amount of marine infrastructure,” said Pliesnoi.

 

The design, however, exposed new engineering challenges, as the weight of equipment placed on the hull affected displacement, longitudinal strength, stability, centre of gravity, structural foundations, fatigue behaviour, piping and cable routing, fire and gas zoning, and maintenance access.

 

Another constraint was the lack of deck area which led to the addition of sponsons, widening the vessel and allowing equipment such as the LNG processing plant to be added. However, this is not a scalable solution.

 

Enter the Mk II conversion, which sees a tanker cut in half and a new midship section welded into place.

 

Both Hilli and Gimi had capacities of 2.45mtpa, the Mk II designs surpass that by 1.05mtpa, with larger liquefaction trains when compared to the Mk I.

 

“More importantly, the modularised conversion approach is intended to reduce construction, delivery and commissioning time while increasing the number of shipyards and fabrication facilities capable of executing the project,” commented Pliesnoi.

 

According to Pliesnoi LNG conversions are essentially the convergence of two design concepts that must be combined when designing a FLNG unit.

 

Ship designers focus on, structure, marine systems, stability, class and outfitting. Whereas an LNG conversion design must account for feed gas, separation, acid gas removal, dehydration, mercury removal, refrigeration, liquefaction and LNG storage.

 

LNG conversions offer a rapid response in a world where the availability of floating storage and processing plants is constrained, mainly by geopolitical disruption in critical regions.

 

Since the first LNG conversion others have followed Golar’s lead. Companies such as offshore solutions provider MODEC are now offering conversions of bulk carriers and oil tankers, with class approval in principle and early deliveries.

 

MODEC is offering conversion projects of up to 20mtpa LNG production capacity, with storage capacity of 160,000m³ and 20,000m³ condensate capacity on vessels 300m in length with a 50m beam.

 

Nevertheless, Golar believes that none of its competitors “has successfully emulated Golar's execution model”.

 

The company added: “Although the approach with FLNG is similar to an FSRU [floating storage and regasification unit] conversion, the cost and scale of FLNG represent a significant step up. We therefore believe that it will be some time before we face serious competition in the FLNG business.”

 

The Mk II concept, like the Mk I before it, has its limitations with even small changes to its processing equipment requiring major adaptations, for weight, an increased electrical load, or a change in safety requirements, and that often means more space is needed.

 

To overcome these limitations, Pliesnoi points to the 5.4mtpa Mk III newbuild units that will be necessary as conversions will no longer offer the optimum solution.