Power and Propulsion

Promoting LNG and other gases

Paul Gunton
Paul Gunton

05 December 2018

Promoting LNG and other gases

In July 2016, a new impetus was given to promoting LNG with the formation of a coalition of partners known as SEA\LNG. The aim of the group is to accelerate the widespread adoption of LNG as a marine fuel and to break down the barriers hindering the global development of LNG in marine applications. The main areas of focus for the coalition include supporting the development of LNG bunkering in major ports, educating stakeholders as to the risks and opportunities in the use of LNG fuel, and developing globally consistent regulations for cleaner shipping fuels.

Recently two other fuels have been added to the list of alternatives to oil with successful use of both ethane and methanol. Both fuels have been on the horizon for some time and, although their use may be limited to certain vessel types, ensuring the engines run correctly is a vital precursor to their wider adoption.

In May 2015, Wärtsilä announced that its four-stroke 50DF engine has been certified to run on liquid ethane gas fuel after a successful testing programme in collaboration with petrochemical and gas shipping company Evergas. The engines can switch between LNG, ethane, liquid fuel oil and heavy fuel oil with uninterrupted operation.

Just as with LNG carriers, the ability for ethane carriers to burn ethane boil-off gas as engine fuel significantly reduces the need for gas re-liquefaction during the voyage, meaning that less power is needed for the cargo handling.

MAN Energy Solutions has secured an order for engines for eight ethane carriers belonging to German shipowner Hartmann Reederei. Their G50ME-C9 engines will run on boil-off gas when running in gas mode and can also operate on the full range of fuel oils from HFO to MGO.

Methanol is a fuel that avoids some of the problems associated with LNG and ethane because it is liquid at ambient temperature and so does not need such specialised fuel storage systems. The issues with methanol are not related to its environmental impact as it is considered as a clean fuel on a par with LNG and unlike fuel oil requires no exhaust treatment to meet MARPOL requirements.

Converting to gas

The advent of dual-fuel engines has raised the possibility of converting some existing Diesel engines to the new configuration. The modular aspect of engines aids in this regard allowing newer versions the potential although converting older versions may present more difficulties. At SMM in 2012, MAN Diesel exhibited an engine showing how a conversion could be achieved.

The L35/44 engine on view was specifically developed for the retrofit of 32/44CR-T2 engines where it can avail of a high level of component synergies and the same crankcase, which could be re-machined on board.

Subsequent engine operation would mainly be intended for gas mode with a separate pilot ignition system that is independent of the primary, common rail injection system. However, the common rail system is retained and remains fully functional as a back-up system in the event of any problem while operating in gas mode. Similarly, Caterpillar’s MaK M46DF is a development of the M43 C engine, which has become a popular choice for cruise ships.

Having shown the possibility of conversion, MAN Energy Solutions has followed through and contracted with German shipowner Wessels Reederei to convert the 8L48/60B main engine of the 1,000-teu feeder container ship Wes Amelie to dual-fuel operation as an 8L51/60DF. This first conversion was completed in 2017 and others are now in progress.

Among the few major components of the original engine that were re-used were the main casing and the crankshaft. The increased bore obviously signifies that cylinder jackets, liners pistons and piston rings must all be different and gas injection and fuel lines needed to be added. The combustion chambers and cylinder heads were replaced because of the additional fuel feed and the pilot oil system necessary for gas operation was completely rebuilt. To allow for the changed ignition timing with a 51/60DF engine, new valve cams and a new turbocharger rotor assembly were required.

Controlling the multi-fuel engine is more complex than the original running on HFO making conversion of the engine sensors and new instrumentation necessary. This allows switching between fuels automatically if the supply of fuel is interrupted without any interruption in the engine loading.

A C-type gas tank was located in the forward part of the vessel under deck allowing containers still to be loaded on deck above. The reduction in overall power when converted and running in LNG mode is an almost 14% loss of power but this has no effect on the operation of the vessel which rarely needed all of the initial installed power.

After the successful conversion project was initiated, Germany’s Federal Ministry for Transport and Digital Infrastructure (BMVI) began promoting the upgrading and conversion of seagoing vessels to LNG. The support is are made available from the mobility and fuel strategy (MKS) fund.

Other conversions that have been announced are a containership belonging to Hapag Lloyd and two ro-pax ferries owned by Spanish operator Baleària Eurolineas Maritimas. In the latter project, the sister ships Nápoles and Sicilia – each currently powered by two MAN 9L48/60A main engines – will have the engines converted to 9L51/60DF units.

A twist on the theme of converting existing engines was made by the new Wärtsilä 31 engine which was unveiled in June 2015. It comes in three alternative versions: diesel, dual-fuel and spark-ignited gas. The multi-fuel capabilities extend the possibilities for operators to burn different qualities of fuels, from very light to very heavy diesel, and a range of different qualities of gas. Its fuel consumption efficiency in its diesel version is as low as 165g/kWh.

The first engines have been ordered but these are as yet only the diesel- burning version. Four of them will be used in fishing vessels, two in a ro-pax ferry being built for Mols Linien and three for Russian icebreakers.