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LNG MAY NOT RESULT IN OVERALL DECARBONISATION, SAYS STUDY

Tuesday, February 4, 2020 

A paper released by the International Council on Clean Transportation (ICCT) suggests that LNG as a marine fuel may not, after all, provide a complete solution to decarbonisation of shipping.

The conclusion of the study suggests that, although LNG contains less CO2 per unit of energy than conventional fuels, its use is not likely to significantly reduce greenhouse gas (GHG) emissions on a life-cycle basis.

Looking at upstream emissions, combustion emissions and methane slip (unburned methane), the study says that over a 100-year time frame, the best case suggests a 15% improvement in GHG emissions for LNG over MGO, but only for vessels using a high pressure gas injection system – only about 12% of current dual-fuel tonnage employs such a system. Additionally, this improvement assumes upstream emissions can be well controlled; something the authors consider will become difficult as LNG production moves to shale gas.

In a 20-year time frame, more relevant to the maritime industry and the IMO decarbonisation targets, the study finds no climate change benefits from using LNG, regardless of engine technology. This, it says, reflects the higher upstream emissions as well as the crankcase emissions, particularly from engines with low pressure gas systems.

In fact, says the study, high pressure dual fuel engines are likely to emit an extra 4% life-cycle GHG emissions over MGO, while the most popular dual fuel low pressure four-stroke option – as employed in the type of cruise ship pictured - could result in 70% to 82% more GHG emissions than from burning distillate fuel in a medium-speed diesel engine.

The study is said to employ standard methodologies for estimating upstream emissions, i.e. datasets relating to production of both LNG and conventional diesel fuels, as well as user data for a fuel’s well-to-hull and well-to-wake carbon emissions, described as ‘downstream’ emissions. Although downstream emissions are consistent regardless of the source of the LNG, upstream emissions can vary widely according to LNG source. The study therefore concentrated on US models, which were considered to give a representative mid-range figure.

The study suggests additional investigations are needed into methane emissions as a function of engine load, as well as black carbon emissions associated with the various fuel options. It also sounds a note of caution regarding bio-methane, even from waste, which is likely to incur high costs for little, if any, saving in overall GHG emissions.

Finally, the study considers that current investment in LNG infrastructure is likely to make it harder to transition to the renewable energy, batteries, fuel cells and zero-carbon fuels that ICCT favours.

The complete paper can be downloaded from here.

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