LNG carriers have used LNG as fuel for decades. Other ship types have used LNG as fuel since 2000. The technical main systems used in LNG as fuel technology are the containment systems, used to store the LNG on board, the process systems for conditioning the LNG and the engines to generate propulsion power and electrical energy.
Piston Engine Room Free Efficient Containership (PERFECt)
In late 2015 GTT, CMA CGM (and its subsidiary CMA Ships) and DNV GL released a technical and feasibility study for a new mega box ship – the Piston Engine Room Free Efficient Containership PERFECt. The concept vessel is LNG-fuelled, powered by a combined gas and steam turbine, and is electrically driven. The feasibility study established that technically and economically, a COGES-powered electric ship was worth a more detailed study. In 2016, ABB as expert in electric propulsion, OMT as naval architect, and Caterpillar’s Solar Turbines as the COGES supplier joined the consortium. Exploring this novel configuration resulted in the partners identifying and analyzing a propulsion concept that has the potential to offer a more efficient, more flexible and greener box ship design than current 20,000 TEU two-stroke diesel engine driven ultra large container vessels.
The containment systems which store LNG on board ships follow the design principles known from gas carriers. Nevertheless, LNG as a ship fuel has initiated new design concepts for containment systems. To drive forward these innovations, DNV GL is working with a number of LNG containment system suppliers to gain approval of their new systems.
To use LNG as fuel it is necessary to extract it from the tank with pumps or pressure, to condition it by vaporisation, pressurisation and warming. Finally, the natural gas has to be routed to the engine’s gas valve unit and into the engine itself. All these process technology steps must be accomplished without any gas leakage into the ship.
Engines for gas-fuelled ships
The switch to natural gas as a ship fuel is possible today. In light of the sulphur limits in Emission Control Areas and the upcoming global sulphur cap, LNG-fuelled ships are a viable option to achieve compliance. However, many ship owners and operators are asking themselves which engines are the best for changing over to a gas-fuelled ship. The two key engines on the market today are dual-fuel and gas-only types. To support the decision-making process, we take a closer look at the differences and benefits of these two engine types, as well as their positive effects on emissions to air.