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LNG fuel system layout

LNG fuel system layout

Retrofitting an existing diesel engine with an LNG pack can be feasible, as several cited examples have shown. However, existing ships have limited design flexibility and limited available space on board. Furthermore, the ship’s stability needs to be maintained. Whether retrofitting is possible needs to be evaluated on a case-by-case basis. 


Key LNG-related components of an LNG-fuelled vessel

Bunkering station The ship’s connection with the LNG terminal, bunkering barge or truck
LNG vacuum-insulated pipes LNG piping from the ship’s connection to the fuel tank
Process skid and tank room Type A, B or C tank
Process skid and tank room Consists of a pressure build-up unit and the product evaporator
LNG engineEither a single-fuel or bi-fuel engine


The equipment required depends on the engine type chosen. Below, the process flow diagram of a high-pressure gas-diesel engine is shown as an example. The exact equipment specifications will depend on the need for high gas pressure and the pressure available in the LNG tank.

When purchasing an LNG-fuelled ship or retrofitting an existing ship’s engine, decisions essentially have to be made on two points:

 Process flow diagram (MAN/Cryostar)                      



Because gas/air mixtures are highly flammable and potentially explosive, significant attention needs to be paid to safety as part of the design process, too. Ventilation is very important. Fuel tanks just below the main deck and in front of the machine room or on the open deck will facilitate ready ventilation.


An important aspect currently under discussion is the location of the LNG storage tank directly underneath the crew and passenger accommodation, which would be interesting from a business perspective, but the latest IMO IGF code draft proposal does not allow it. Short LNG piping is also important, to minimise the potential for LNG leakage.


More information on standardisation can be found here.


Further reading


LNG tanks

All LNG ships in the current fleet (2015) are fitted with a type C tank, a cylindrical pressure vessel requiring 2-4 times more space than a conventional fuel storage tank.