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Benefits of LNG

LNG reduces air-polluting emissions to best-in-class levels

LNG as a ship fuel can help significantly reduce the environmental impacts of shipping operations, most likely without increasing costs.  Several gas solutions are available:

  • spark-ignited lean-burn gas engine
  • low-pressure dual-fuel engine
  • gas-diesel

Available studies point to a significant reduction of pollutant emissions in the gas mode.

 

Reduction potential of LNG per pollutant
Air pollutant emission (in gas mode)Reduction potential
NOx85-90%
SOx~100%
PM~100%

 

The exact air pollutant emission reduction potential depends on the type of engine used. More detailed technical information on these issues can be found in the Technology section.

GHG emissions can be ultimately 20% lower

LNG’s contribution to GHG emission reduction is due to its lower carbon content. The well-to-propeller GHG reduction potential depends on the fuel taken as a reference. Use of LNG fuel results in 20% lower GHG emissions compared with Heavy Fuel Oil (HFO). If Marine Gas Oil (MGO) is used, the reduction of GHG emissions is more limited.

Bio-LNG

LNG can be gradually replaced by biomethane produced by anaerobic digestion and perhaps, in the future, by gasification of biomass. Bio-LNG is no different from fossil LNG, but has the potential to drastically reduce GHG emissions. The infrastructure now under development allows for a change from fossil LNG to its biological counterpart; only the “upstream route” is different.

Biomethane is currently used for power production, heating purposes and to a limited extent in transport applications, with public transport as one example. Despite its limited availability, interest from different sectors is great. This may lead to discussions about future availability of biomass sources for LNG production.

Methane slip

Loss of unburned methane is called “methane slip.” Methane slip from gas engines can be divided into two categories:

  • operational emissions

  • engine emissions

 

Operational emissions

Under certain operating conditions, methane may have to be vented into the atmosphere. During refuelling operations as well as during storage on land, there may also be minor methane releases.

 

Engine emissions

One drawback of gas engines is their proneness to methane slip due to incomplete combustion of the methane in the engine. The global warming potential of methane is a 25 times higher than that of CO2. As a result, a few grams of methane emitted per kWh add 10-15% to an LNG-fuelled vessel’s GHG emissions. Methane emissions of 4-8 g/kWh for spark-ignited and low-pressure dual-fuel engines are reported.

 

Methane slip does not occur in diesel-cycle mode, but only in Otto-cycle mode (dual-fuel as well as spark-ignited) and is generally higher at lower engine loads. Engine manufacturers are currently working on prevention of methane slip in order to guarantee the GHG reduction potential of LNG.

Further reading

85-100% less pollutants

LNG as a shipping fuel can help significantly reduce the environmental impacts of maritime transport, most likely without increasing costs. With this fuel, NOx, SOx and particulate emissions can be reduced by 85-100% in comparison with HFO.