Class societies approve of innovation

An increasing share of class society LNG shipping expertise is being applied to the expanding LNG bunkering sector, explains Craig Jallal

There are activities that take place in LNG shipping these days that were unheard of 10 years ago. With the arrival of LNG bunkering, other shipping sectors are being drawn into the LNG safety envelope. In this article, we look at some of the recent LNG bunker vessel (LNGBV) and fuelling innovations that class has assisted with, and others that may never leave the CAD screen.

LNG as a ship fuel

2017 may go down in history as the year LNG propulsion went mainstream, with the order of nine 22,000 TEU vessels by CMA CGM. Bureau Veritas (BV) is classing not only these, but also some of the most prestigious LNG-powered ship newbuildings set to be delivered over the next five years. Notable among these are a number of gas-fuelled cruise ships, including the new electric-hybrid and LNG-fuelled icebreaking cruise ship ordered by Ponant.

Currently, LNG fuel is primarily delivered to the ship on the jetty side by means of truck-to-ship (TTS) transfers. This is a slow process but not necessarily a hindrance for ships on fixed schedule services, like ferries. For LNG fuelling to gain ground in the wider world of shipping, especially for larger ships requiring significant volumes of fuel, ship-to-ship (STS) bunkering will have to become an established practice.

The first newbuilding LNG bunkering vessels entered service in April 2017 in Northern Europe. BV classed the first-ever purpose-built LNG bunker vessel, the 5,800 m³ Zeebrugge-based ENGIE Zeebrugge, as well as the 5,800 m³ Coralius, the second LNG bunker vessel to enter service. Along with a small, converted barge in Spain, there are now three BV-classed dedicated LNG bunkering vessels in operation.

Bureau Veritas is a key partner in new bunkering projects worldwide, sharing its understanding of LNG bunkering technology and safety methodologies with those industry players making a commitment to the use of LNG as marine fuel.

One of the most demanding commercial operations will be the bunkering of ultra large containerships (ULCSs). To minimise operational disruption, large containerships need to be able to take on board bunkers while alongside and handling boxes.

Taking on board 15,000 m³ of LNG could take 12 to 15 hours in an operation which includes connection, inerting, testing, LNG transfer, purging, inerting again and disconnection. The responsible parties also need to complete a bunker delivery note and meet all the requirements of the International Code of Safety for Ships using Gases or other Low-Flashpoint Fuels (IGF Code) throughout.

Prior to port arrival, providing a marine fuel supplier with perhaps 40 hours’ notification is more than adequate for bunkering operations. The main challenges to be addressed for the STS transfer of LNG include the provision of an appropriate safety zone and the creation of a procedure to minimise the impact on simultaneous vessel operations.

Sloshing – critical factor for membrane tanks

For ships using large volumes of LNG as fuel, membrane tanks are an attractive option. A membrane bunker tank has been chosen for the CMA CGM ULCSs. However, the membrane containment systems in LNG-fuelled ships must be robust enough to handle all filling levels, as the consumption of bunkers gradually empties the tanks.

Accordingly, membrane LNG fuel tanks have to be designed to withstand sloshing impacts in all partially filled conditions. Sloshing is a critical safety issue to be addressed. For broad-beam ULCSs, a tank spanning the breadth of the ship is potentially subject to heavy sloshing impacts in beam seas when in a partially filled condition.

Proper assessment, calculation and, if required, adjustments to the design of the tank can address the risks of sloshing. BV has developed a methodology to assess loads and verify the appropriate design responses.

For a large containership with a single, full-width membrane LNG bunker tank, the solution may involve a strengthened containment system and modifications to the tank shape, including chamfered upper sections to better deflect sloshing loads. The combination of a seakeeping and sloshing analysis, followed by application of the sloshing loads, enables a strength assessment under BV rules to be made for the entire membrane containment system, including inner hull and pump tower.

The purpose-built, BV-classed LNGBVs is one approach. The other option is to convert an existing vessel into a gas bunkering vessel. At ABS global gas solutions, Tor-Ivar Guttulsrød highlighted the attraction of converting offshore platform supply vessels (PSVs) into LNGBVs.

First, there are a large number of almost new PSVs available due to the collapse of the offshore oil and gas sector. Some PSVs have gone straight from launch into lay-up.

In the case of the ABS bunker delivery concept, the PSV could use either a large single LNG tank as the main storage unit or, alternatively, a bank of cryogenic tank containers stacked on deck to hold the LNG fuel. Tor-Ivar Guttulsrød’s proposal envisages the LNG bunkering PSV loading at an LNG terminal or fuelling station jetty and then proceeding to the LNG-powered vessel, where STS bunkering operations would be carried out.

ABS has also extended the PSV conversion concept to include floating modular LNG power station and regasification vessel versions.

The latter version of the concept lies behind Dreifa Energy’s proposed floating regasification PSV conversion project. The design has been granted approval in principle by DNV GL.

The Dreifa floating regasification unit (FRU) consists of a regasification plant and associated utility systems located on the deck of a PSV acquired by the company. The FRU would operate in combination with an LNG carrier acting as a floating storage unit.

DNV GL’s approval in principle was awarded following an examination of the basic engineering package developed by Dreifa Energy. In addition to confirming compliance with the rules of the society at the current stage of engineering, approval in principle provides clarity on the regulatory framework and classification procedure towards final approval. This is an important step forward in Dreifa Energy’s efforts to finalise contracts for the necessary equipment and conversion work.

ABS to partner probunkers on LNGBVs

An exciting announcement at the Posidonia event in June 2018 was made by probunkers, a start-up company that aims to build a fleet of LNGBVs for positioning at seven key bunkering ports around the world. ABS has been appointed to provide the regulatory compliance guidance for the fleet and to define applicable rules and standards.

Headquartered in Athens, probunkers is seeking participation from companies active in the shipping and energy sectors, as well as investments to the tune of US$343M based on a 10-year plan. A shipping division will be established to design, build, own and operate the LNGBVs, while a commercial division will have a presence in the seven bunkering ports and be responsible for securing LNG supplies and negotiating bunker contracts.

The seven LNGBVs will all be single vessel entities 100% owned by probunkers. The company aims to be operational by 2022, following a year of planning and two years of LNGBV construction and finalising LNG supply logistics.