A study on design optimization of lng power system onboard a dual fueled platform supply vessel

LNG is an environmentally friendly fuel, using LNG as marine fuel has the potential to reduce air pollutants emissions such as NOx, SOx and PM by 85-90%, 90-95% and 20-25% respectively, and to cut GHG emissions by up to 21% along the entire gas chain (Well-to-Wake) compared with conventional fuel oil. Therefore, LNG is of great significance for achieving the target of green and sustainable shipping. In the context of China’s extended emission control areas and low carbon economy vision, the owners of platform supply vessels (PSVs) are seeking LNG as a fuel solution. In 2018, China Oilfield Services Limited (COSL) decided to build 12 LNG fueled PSVs (5,000HP⨯4 and 4,000HP⨯8) being operated in China’s coastal waters. The power system of each vessel mainly includes a set of 170 m³ vacuum insulated IMO type-C LNG fuel tank, low-pressure LNG fuel gas supply system (FGSS), LNG-diesel dual-fuel generators and rotary FPP rudder propellers. The challenges for the safety of LNG system onboard are brought about by bad sea conditions, frequent variation of power load and compact ship layout. Taking a 4,000HP LNG fueled PSV as an example, the study investigates the layout scheme of LNG power system onboard based on its configurational characteristics. Considering the risks of cryogenic damage, flammable vapor dispersion and fire, the optimization design principles for several key issues, including the arrangement of LNG fuel tank, air lock design for tank connection space (TCS) and the arrangement of drip tray in the LNG bunkering station, are analyzed. Suggestions on optimizing design LNG power system onboard a PSV are given.