With the rise to prominence of floating storage and regasification units (FSRUs) and LNG bunker vessels (LNGBVs), hose-based solutions are joining the traditional marine loading arm (MLA) as a key cargo transfer technology. As LNG cargo transfer technology advances Hoses become an inevitable part of it, says a report published in LNG World Shipping.
Hoses can be utilised for not only ship-to-ship and ship-to-shore transfers of LNG but also for the ship-to-jetty discharge of high-pressure natural gas from FSRUs.
LNGBV’s Hoses Dependence
The nascent LNGBV fleet depends on hoses for quick transfers of fuel to a wide and growing variety of gas-powered ships. Hoses can accommodate the myriad locations that are being encountered in the expanding fleet of LNG-fuelled ships with relative ease. While MLAs might be utilised to load an LNGBV at its dedicated jetty, their use is impractical for the majority of fuel transfer operations.
High-pressure gas hoses
Speaking at the Asian LNG Ship/Shore Interface conference organised by LNG World Shipping in Singapore in early June 2018, MIB International head of sales and business development, Luca Chiodetto described how his company has responded to the innovative ideas, technologies and applications that have characterised the LNG shipping industry over the past decade.
MIB International has been developing and supplying specialist LNG cargo transfer equipment since 1969. The company put the world’s first LNG quick connect/disconnect coupler into service at Shell’s Brunei stern-loading jetty in 1976 and brought the world’s first LNG-powered emergency release system (ERS) coupling into operation at the Montoir terminal in France in 1982. The latter equipment is still in operation, some 36 years later.
The ERS couplings introduced by the industry 36 years ago are critical to safe operations at the ship/shore interface, and have been called into play on over 2,000 occasions. The equipment performed as required and enabled rapid, co-ordinated halts to cargo transfer operations without safety being compromised.
The design of ERS couplings for transfers of high-pressure natural gas from FSRUs has posed challenges for equipment manufacturers. In such applications the transfer system is subject to high loads due to the connection between the high-pressure jumpers. Also, the stresses induced by relative ship-jetty excursions are significant, as are the dynamics following ERS activation.
The ERS device is required to be of compact assembly and must minimise not only the volume of high-pressure gas entrapped between valves but also venting times. In the MIB solution the sequence valve and pressure transducer in the ERS are interlocked via hydraulic lines to ensure the coupling releases only when the pressure of the high-pressure natural gas between the valves has reached the pre-set safety level.
Spurious releases can thus be avoided and the arrangement also allows the gas trapped in the ERS to be depressurised and to blowdown back to the FSRU piping. A typical timing sequence for a high-pressure gas ERS activation would be 7 seconds, comprising 5 seconds to close the valves and the 2 seconds taken in the coupler release. The blowdown part of the sequence is instantaneous. The activation of a 10-inch ERS in such circumstances would leave 3.2 m3 of gas trapped between the closed valves.
In summing up the advantages of hose-based solutions over MLAs in certain LNG transfer applications, Mr Chiodetto pointed out that hoses require substantially lower capital expenditure and less lead time to provide a complete system. The time factor can be critical in FSRU projects which are often on fast-track construction schedules.
The relatively low weight of hoses and hose-handling arrangements enables lighter jetty structures while hoses offer fewer potential leak paths than rigid MLAs. Loading arm maintenance typically requires equipment shutdowns and, occasionally, removal from the jetty for servicing. Hoses in need of attention can simply be replaced by new or refurbished lengths.
In fact, hoses and associated platforms and structures are maintenance-free during normal operations. This is due, not least, to the fact that no moving parts, such as swivels, bearings and motors, are involved.
The advantages offered by hoses do not end there. Because most of the equipment can be containerised, onsite delivery of hoses and hose-handling arrangements entails lower shipping costs. Also, installation of the ERS coupling and the relevant power control system can be carried out at the yard, obviating the need for any fitting out of the required equipment at the final terminal site.
The use of hoses involves a minimum requirement for hydraulic power, as it is only needed for the activation of the ERS in case of an emergency.
Combined, these advantages add up to reduced operating costs, as there is limited need for spare parts and interventions.
The North and Baltic Seas, the originally designated IMO emission control areas, have been the birthplace of LNG bunkering. Most of the early fuelling operations involved jettyside transfers of LNG from road tankers and shoreside pressure tanks to relatively small ships such as cross-fjord ferries and offshore support vessels.
The use of LNG as marine fuel has entered new realms in more recent years. Larger LNG-powered ships have entered service and orders in the past few years have included the world’s largest cruise and container ships. LNGBVs have a key role to play in servicing larger vessels.
One company active in supplying hoses for LNG bunkering is MannTek of Sweden. Customers include LNGBV and terminal operators as well as bunker suppliers. Another notable user is Florida East Coast Railway in the US which recently chose MannTek hoses for its fleet of LNG-powered locomotives.
Use of Transfer Hoses
An example of the use of transfer hoses on a tight bunkering timetable is given by the 49,000 gt roro passenger ferry Megastar. Running daily between Helsinki and Tallinn at the eastern end of the Baltic Sea, the vessel is bunkered with LNG each night in Tallinn by Eesti Gaas. A fleet of eight road tankers has been provided to fuel the Tallink-operated, gas-powered vessel.
Built by Gofa Gocher Fahrzeugbau GmbH of Germany, the road tankers are each able to carry 18-19 tonnes of LNG, depending on the fuel density, and the tank operating pressure is set at a maximum of 7 bar. Each bunkering operation involves the hose transfer of four road tanker-loads of LNG to the Megastar’s bunker tanks, with the fuelling procedure involving two road tankers at a time.
Megastar makes three Tallinn-Helsinki roundtrips per day and the four road tanker-loads, or 72 tonnes, of LNG taken on board each night are sufficient for one full day of ferry operations on the two-hour crossing.
Because the bunkering has to be completed within a four-hour time window, the road tankers are provided with high-performance pumps and special piping. MannTek’s truck-to-ship transfer equipment is a key element in the safe, efficient and timely fuelling operations. Besides the company’s hoses and self-closing dry cryogenic couplings, MannTek also supplied the cable-released breakaway couplings that were prescribed as an additional safety feature.
In an emergency situation, such as a driftaway of the ferry from the berth, the CBCs ensure a controlled valve closure and separation of the pipework links. When MannTek equipment on board Megastar went into operation in January 2017, the company’s products had already been involved with 14,000 cryogenic bunkering operations.
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Source: LNG World Shipping