First DUAL FUEL Electric-driven LNG Carrier
Picture electric drive with four-stroke dual fuel enginesCouplings 100% by VULKAN
“The dual-fuel-electric machinery concept is far ahead of the competition in terms of evironmental friendliness, reliability, redundancy, maintainability, fuel flexibility, as well as economy and safety,” said Mikael Mäkinen, group vice president, Wärtsilä Ship Power. “The recent introduction of heavy fuel oil (HFO) as fuel for the engines´s diesel-mode further enhances fuel flexibility and provides ship operators the highest degree if control over operating costs under fluctuating gas and liquid prices.”
‘Gaz de France’ dared the first step and ordered three LNG carriers in 2004 at the formerly named Chantiers de l’Atlantique shipyard, which became AKER Yards Saint Nazaire and recently member of the STX group.
Series of the three LNG carriers have three novelties:
The use of boil-off gases to feed dual-fuel medium-speed engines;
A Dual-Fuel-electric propulsion system;
A newly-patented design of the cargo holds and its heat insulations.
Liquid Natural Gas is kept at –163°C at atmospheric pressure in cargo holds. A certain amount of the liquid evaporates, as the heat insulation of the cargo holds is not a 100 percent isotherm. In general 0,15 percent of the volume boils off every day. Passing from liquid into vapour is known as the boiling process. In case of M T “PROVALYS” five tonnes LNG boil off every hour. The WÄRTSILA 50 DF type engine is a dual fuel version with Diesel oil pilot injection.
Three WÄRTSILÄ diesel engines gen-sets on board of “PROVALYS” and “GASELYS” (two times 12V50 DF and one 6L50 DF) guarantee flexibility in power supply.
VULKAN supplied two RATO-S type couplings of 562W size and one RATO-R G392TR for the gensets. The diesel engines and the alternators are seated on resin. The electric energy is transferred via bus rails towards two electric drive motors, which are connected to a marine reduction gear of twin input and single output.
The marine reduction gear is of an impressive size and reduces the high revolutions of two electric drive motors to economic speed for the single fixed pitch propeller measuring eight meters of diameter. Two VULKAN METAFLEX type couplings of 2800 size compensate radial and axial movements between the electric motors and the reduction gear under various conditions of the ship.
‘Gaz de France’ used a completely new design for the cargo holds. The principle consists of a double layer of membranes and nitrogen circulating in between membranes. The nitrogen gas it is constantly analysed in order to detect leaks immediately. This design has the ultimate advantage not to require the typical ball shape design of the holds anymore, as used for classic LNG carriers.
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