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Classification society Bureau Veritas has granted approval in principle (AIP) to a 4,000-cubic-metre bunkering ship concept [pictured] developed by French liquefied natural gas (LNG) containment manufacturer Gaztransport & Technigaz (GTT).

The concept is for a bunker tanker which could deliver LNG as a ship's fuel using tanks with a GTT Mark III Flex cargo containment system operating up to a pressure of 2 Bar Gauge (BarG). Combining the membrane containment system with the ability to store LNG at pressure up to 2 BarG would allow the bunker vessel to have a higher capacity and increased operational flexibility, Bureau Veritas says.

In a statement, Philippe Donche-Gay, Executive Vice President and head of Bureau Veritas's Marine and Offshore Division, commented: "Practical LNG bunker tankers are the key to building a viable LNG supply chain on which to develop LNG as a ship's fuel. This pressurised membrane tank concept from GTT means LNG bunker tankers can manage boil-off gas (BOG) better and increase loading and delivery flow rates. Our studies show it is both safe and practical. We look forward to seeing the concept taken forward to a new construction."

Bureau Veritas claims that, under GTT's system, the BOG management during loading and bunkering operations is more flexible because of the wide vapour pressure operating range. Vapour can be buffered and condensed in the tanks to help the fuelled ship or feeding facility handle the vapour. Condensation may be performed by spraying LNG into the vapour phase. The higher pressure also means that during voyage and stand-by mode, the duration before gas pressure in the bunker tanker's tanks reaches the upper limit is longer. This improves the holding time when BOG is not being consumed and reduces the use of reliquefaction plant, thus diminishing costs.