Wärtsilä prepares to retrofit marine engines to LPG

Wärtsilä’s has completed full scale testing with a 2-stroke marine engine burning liquid petroleum gas (LPG) as fuel. This was the world’s first such testing protocol. Eight of BW LPG’s ships will be retrofitted to sail on LPG.

It was initially decided to retrofit the LPG Fuel Supply System (LFSS) to four very large gas carrier (VLGC) vessels owned by Oslo-listed BW LPG. However, following the tests, in which performance exceeded expectations, BW LPG decided to exercise their option to retrofit an additional four vessels.

LPG as a marine fuel

In 2019, classification society DNV GL developed new class rules for LPG as a ship fuel. According to Torill Grimstad Osberg, Head of Section LNG, Cargo Handling & Piping Systems at DNV GL, LPG is ‘at least as attractive an energy source as LNG, with shorter payback periods, lower investment costs and lower sensitivity to fuel price scenarios. Furthermore, there is considerable LPG infrastructure available around the world.’

‘The use of LPG virtually eliminates sulphur emissions and can help comply with local and global sulphur restrictions,’ says Osberg. ‘The reduction of NOx emissions depends on the engine technology used. In the case of a two-stroke diesel engine, the NOx emissions can be expected to be reduced by ten to twenty per cent compared to heavy fuel oil (HFO), whereas the expected reduction for a four-stroke Otto cycle engine is larger and may actually meet Tier III NOx standards.’

He also adds that particulate matter and black carbon emissions will largely be avoided. ‘What is more, the combination of low production and combustion-related emissions results in an overall greenhouse gas emissions reduction of seventeen per cent compared to HFO or marine gas oil (MGO).’

When compared to LNG, LPG has a lower flammability range, with a lower explosion limit of two per cent. On the other hand, LPG is less challenging with regard to temperatures since it has a higher boiling point and, unlike LNG, it is not stored at cryogenic temperatures.

VLGC retrofit

Wärtsilä has been designated as the system integrator for the retrofittings for BW LPG. This involves not only the installation of the LPG fuel system, but also the required ship design modifications, integration of the LFSS control system into the ships’ integrated automation system (IAS), and acting as the coordinator between the yard, the engine manufacturer, and the owner.

Retrofitting of the LFSS to the first of the vessels will take place in April 2020. The system is available as a stand-alone solution, or as an integrated element within the LPG cargo handling system.

Author: Mariska Buitendijk

Mariska Buitendijk is one of SWZ|Maritime's journalists as well as the magazine's copy editor.