The LNG Greenstream Tanker is an electrically powered ship due to its LNG (Liquid Natural Gas) powered generators. By using LNG, the emissions of CO2 and nitrogen oxides (NOx) are reduced by more than 25% and 80% respectively. Moreover, no sulphur oxide (SO2) or particulate matter are released. The installation of two LNG packs with a total of four engines reduces energy consumption and increases navigation safety. If an engine fails, then there are three left to sail.
Installation and integration
In early 2013, Alewijnse worked on its first LNG powered ship, the LNG Greenstream Tanker that was built by Peters Shipyards. As the systems integrator, Alewijnse is responsible for the installation and integration of four Sandfirden LNG engine generators, each generating 285 kW that will power two drive motors, and the corresponding electrical infrastructure. The core of the system is formed by a special DC bus developed by Alewijnse. The DC bus is powered by two generators via an AC/DC converter. Due to this configuration, no synchronisation of the generators is needed, and they will feed the bus immediately after start-up, even before they reach their rated speed.
The use of LNG as an energy source does offer some challenges, such as the important fact that LNG powered engines respond more slowly to sudden increases in load than conventional diesel engines. The DC system will compensate for this effect. Alewijnse, Peters Shipyards, EPC and LRoS have gone to great lengths to satisfy competence and category requirements.
Pure LNG systems offer advantages with respect to bi-fuel alternatives. Not only are they less complex and cheaper than bi-fuel systems, but they are also much cleaner than when combined with conventional diesel fuel, since the carbon content is much lower. LNG contains no polluting sulphur or additives. The owner of the ship is also aware that LNG is more cost-efficient at lower loads. The disadvantages of LNG include a relatively low energy content per volume and the need for specialised refuelling facilities that can handle high pressures and very low temperatures. However, this is compensated by the lower gaseous emissions and particulate emissions, the fact that any discharges dissipate in the atmosphere almost immediately, its quiet operation and stable prices.