LNG Breakthrough For Wärtsilä

Wärtsilä Corporation received an order to supply four Wärtsilä 6L50DF dual-fuel engines to power a 75,000 cu. m. LNG carrier contracted by the French gas holding company Gaz de France at the French shipyard Chantiers de l'Atlantique. Due for delivery in 2004, this newbuilding is breaking away from traditional practices in the propulsion of LNG (liquefied natural gas) carriers. It will be the first LNG carrier to be powered by electric propulsion, and one of few to have internal-combustion engines instead of the more usual steam turbine plant. The four dual-fuel engined generating sets will meet all the ship's propulsion and shipboard electrical requirements. The Wärtsilä 6L50DF engines each develop 5,700 kW at 514 rpm. This membrane-type vessel (GTT-CS1) will be employed transporting LNG from Skikda in Algeria to Fos near Marseilles. This round voyage will take about one week at a service speed of 16 knots, which can be achieved with three of the four generating sets. The ship is also designed for spot market trading, such as voyages to the U.S. For such times, the service speed can be 18.5 knots using all four generating sets. Compared with the alternative power plants, the Wärtsilä 50DF engines have distinctive benefits in LNG carriers. While making maximum use of the gas fuel (boil-off from the cargo of liquefied natural gas) to develop useful power, the high efficiency of these engines calls for a much lower fuel consumption overall and thus lower operating costs than the conventional steam turbine plant. The Wärtsilä 50DF engines also have much lower stack emissions than a steam plant. Their low NOx emissions are about one-tenth those of the equivalent diesel engines. The combination of the engines' low fuel consumption and their maximum use of natural gas means the 50DF engines also have low CO2 emissions. The Wärtsilä 50DF engines have cylinder dimensions of 500 mm bore by 580 mm piston stroke. Available in configurations with six, eight and nine cylinders in line, and 12, 16 and 18 cylinders Vee-form, the 50DF engines develop 950 kW per cylinder MCR at 500 or 514 rpm for 50Hz and 60Hz electricity generation, respectively.