|The converted Bit Viking. The twin LNG tanks are mounted on the deck. Click to enlarge.|
Wärtsilä Corporation has completed the conversion of the 25,000 dwt product tanker Bit Viking from heavy fuel oil to liquefied natural gas (LNG) operation. The conversion enables the Bit Viking to qualify for lower nitrogen oxides (NOx) emission taxes under the Norwegian NOx fund scheme.
In August 2010, Wärtsilä signed a turnkey project with Tarbit Shipping to convert the Bit Viking to LNG operation. The Bit Viking has twin screw propulsion, with each screw originally powered by a 6-cylinder in-line Wärtsilä 46 engine running on heavy fuel oil (HFO). The conversion involved changing these to 6-cylinder in-line Wärtsilä 50DF dual-fuel engines that operate on LNG.
Wärtsilä dual-fuel engines in gas mode produce roughly 80% less NOx compared to IMO Tier I levels and practically zero SOx and particulates. When gas is used in a dual-fuel engine, CO2 emissions are reduced by about 20% compared to liquid fuels.
The scope of the conversion package from Wärtsilä included deck-mounted gas fuel systems, piping, two two six-cylinder Wärtsilä 46 engines converted to Wärtsilä 50DF units with related control systems and all adjustments to the ship’s systems necessitated by the conversion. The vessel’s classification certificate was also updated.
The engines are connected directly to the propeller shafts through a reduction gearbox, thus avoiding the electrical losses that are an unavoidable feature of diesel-electric configurations. This enables a significant improvement in propulsion efficiency, reduced fuel consumption, and corresponding reductions in emissions. This is the first LNG fueled vessel to be classified by Germanischer Lloyd.
The Bit Viking utilizes Wärtsilä’s new LNGPac system, which enables the safe and convenient onboard storage of LNG. The two 500 cubic meter LNG storage tanks are mounted on the deck to facilitate bunkering operations and permit the bunkering of LNG at a rate of 430 cubic meters per hour.
The LNGPac tanks are insulated with perlite/vacuum and consist of a stainless steel inner vessel, which is designed for an internal pressure, and an outer vessel that acts as a secondary barrier. The outer vessel can be made of either stainless steel or carbon steel.The storage tanks provide the vessel with 12 days of autonomous operation at 80% load, with the option to switch to marine gas oil if an extended range is required. When visiting EU ports, which have a 0.1% limit on sulfur emissions, the vessel operates on gas.
This is the first marine installation to involve converting Wärtsilä 46 engines to Wärtsilä 50DF engines, and the first 50DF marine installation with mechanical propulsion.
The vessel was handed over to the customer, Tarbit Shipping, in October. The re-commissioned vessel is operated by Statoil along the Norwegian coastline.
The Norwegian NOx fund is a cooperative effort whereby participating companies may apply for financial support in return for introducing NOx reducing measures.
This is a major step for Wärtsilä in consolidating its market leading position in LNG solutions for the shipping industry. The successful sea trials with this vessel provide yet further validation of the viability of LNG as the marine fuel of the future. We anticipate that this development will rapidly accelerate during the coming few years.—Sören Karlsson, General Manager, Gas Applications, Ship Power Technology
Sören Karlsson, and Leonardo Sonzio (2010)￼Enabling the safe storage of gas onboard ships with the Wärtsilä LNGPac. Wärtsilä Technical Journal 01.2010