LNG in shipping

The burning of natural gas in internal 

combustion engines is not a new concept. 

Neither is its use associated with diesel-

electric propulsion or mechanical drive 

systems for ships. A significant step in 

the adoption of natural gas as a fuel 

has been the Dual Fuel Diesel-Electric 

systems on LNG carriers that are either 

being built or already in service. However, 

ship operating philosophies have varied 

between companies. Some operators 

prefer to use conventional heavy fuel oil 

when its cost is lower than the commercial 

value of boil-off gas from the LNG tanks; or 

when the ship is running with limited LNG 

on board in the ballast condition or during 

lay-up. In this case the need for a shipboard 

re-liquefaction is limited. However, it can 

be installed so that on the occasions when 

the boil-off cargo exceeds the ship’s fuel 

requirements the additional boil-off fluid 

can be returned to the cargo tanks. By 

way of contrast, a large fleet of ships has 

been built using the opposite philosophical 

viewpoint. These ships operate on heavy 

fuel oil and use a large liquefaction plant 

to reliquefy all of the boil-off LNG: this 

auxiliary plant also runs on heavy fuel oil. 

Consequently, these latter ships deliver all 

the cargo loaded and use heavy fuel oil for 

the ships’ operational energy needs.