LNG bunkering by means of ship-to-ship (STS) transfers is set to proliferate. Today, this method of fuelling ships is utilised only in Stockholm, where the small, converted bunker vessel Seagas transfers about 70 tonnes of LNG daily to the passenger cruise ferry Viking Grace using flexible cryogenic hoses.
But two other STS transfer technologies have been developed for LNG bunkering and both are set for their first applications in tandem with the first dedicated fuelling vessels under construction. Although the new concepts both feature vessel-mounted, articulated arms, there are important differences between the two.
FMC Technologies’ new bunkering loading arm (BOA) for ship-to-ship LNG refuelling is a natural progression from its established shore-based and offshore loading arm concepts. Like the arms for the other two applications, the new BOA is made of rigid, articulated piping and equipped with Chiksan swivel joints as well as FMC’s proven quick connect/disconnect coupler (QC/DC) and emergency-release system (ERS) technologies.
The engineering company’s marine loading arm division at Sens in France initially developed a set of BOA designs covering several possible bunkering configurations but in 2014, when Shell chose the arm for mounting on its 6,500m3 LNG bunker vessel building at STX Offshore & Shipbuilding in Korea, FMC progressed the project to an actual LNG-transfer system.
Close co-operation between FMC and Shell engineers since the contract signing has brought the development work full circle. The counterbalanced BOA is essentially a scaled down version of FMC’s jetty-mounted loading arms. Because it is mounted on a vessel subject to dynamic motions during transfer operations, the BOA also incorporates motion-compensating features from the company’s offshore arms.
“Development of the BOA system did not pose any direct design obstacles per se,” says FMC business development manager Eric Morilhat. “Rather, it was the lack of applicable standards for LNG bunker transfers and the need to accommodate operational constraints such as variable manifold arrangements that posed greater challenges.
“As the relevant standards are still under development, for our pioneering BOA system we had to make use of other norms not fully adapted to this application.”
The BOA for the Shell vessel incorporates an 8in liquid line and a 6in vapour return line, both of which can accommodate a maximum operating pressure of 19 barg (2,000 kPa). The liquid line can handle LNG flow rates of up to 1,100 m3/hour.
The inboard arm for the liquid line is 8.5m long and the outboard arm is 10m.
The vapour line is piggybacked on the liquid line and the BOA, articulated in both the vertical and horizontal planes, can rotate a full 270˚.
The remote-operated arm’s ERS uses a single hydraulic actuator to operate the two double ball valve assemblies fitted on each line. The arrangement is geared to providing perfectly synchronised disconnections and a level of integrity equivalent to that in conventional LNGC cargo-transfer operations.
Shell is set to take delivery of its bunker vessel from STX early next year. FMC points out that the BOA will not require periodic inspection and replacement as is the case for systems based on flexible hoses.
“FMC is supporting the LNG-fuelled vessel concept by developing LNG bunkering transfer designs, including BOA, for specific project applications,” Mr Morilhat says. “The three main design drivers are the range of LNG-fuelled vessels to be handled, the bunkering operation frequency and the maximum bunkering time accepted. Once these main parameters are identified and specified, FMC is able to provide the transfer system that is the optimum, in terms of cost, safety and reliability, for the given application.”
Gaz Transport & Technigaz (GTT) is another French engineering company whose generic vessel-mounted transfer system design has been specified for an LNG bunker vessel newbuilding.
GTT’s Reach4 bunker mast system for STS bunkering operations is being fitted on the non-propelled, 2,200m3 LNG tank barge that the Conrad shipyard at Orange in the US state of Texas is building for a consortium comprising WesPac and Clean Marine Energy (CME). It is the first application of this GTT technology.
The unmanned barge will be utilised in Jacksonville, Florida to bunker the two LNG-powered container ships that TOTE operates on its route to Puerto Rico.
The deck-mounted Reach4 mast comprises a 20m lattice boom structure supporting a liquid line and a vapour return line, each linking to the manifold of the receiving ship via a flexible cryogenic hose. These hoses are also utilised at the mast pedestal to link the arm’s lines with the bunker vessel’s LNG systems.
A passive, drybreak QC/DC system and emergency shutdown (ESD) valves are fitted on the lines at the connection point with the outboard hoses. Any excessive stress on the flexible hose triggers an emergency disconnect and a hose brake is in place to control the fall.
The Reach4 system has been designed for a flow rate of up to 900 m3/hour but GTT points out that it is easy to upgrade the concept to handle greater flows.
“We have established a partnership with the French yard CNIM covering the construction of Reach4,” says Gillaume Gelin, head of product development with GTT’s LNG as Fuel division. “The arrangement provides shipbuilders with the options of either building the Reach4 mast to GTT plans themselves or ordering it from CNIM.
“Conrad is manufacturing the Reach4 arm for the WesPac/CME barge. Although custody transfer is not a direct part of our Reach4 package, GTT also works closely with MECI, the French metering equipment supplier, to cover this function should the customer require it. Under this collaboration MECI is able to provide a skid-mounted custody transfer unit for measuring the volumes of LNG transferred via the Reach4 mast.
“WesPac and CME have specified such an MECI skid for their barge.”
To be named Clean Jacksonville, the WesPac/CME vessel is set to go into operation in the first quarter of 2017 when the small-scale JAX LNG liquefaction plant is commissioned. The barge, which features a GTT Mark III Flex membrane tank containment system and reliquefaction facilities to handle boil-off gas, will then be used in the Florida port to shuttle LNG bunker fuel the short distance from the plant to the TOTE containership berths.
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