LNG's role in decarbonisation

  • Apr 23, 2019
  • LNG World Shipping

Burning LNG as a fuel is not a silver-bullet solution, but it does cut greenhouse gas emissions significantly, says John Snyder

A well-to-wake (WtW) study has confirmed the environmental benefits of burning LNG as a marine fuel, reporting emissions reductions of up to 21% as compared with current and post-2020 oil-based marine fuels. Operating on LNG as a marine fuel reduces emissions of sulphur oxides (SOx) to almost zero, nitrogen oxides (NOx) by 95% and particulate matter by 99% as compared to conventional marine fuels.

Reducing greenhouse gas (GHG) emissions such as NOx, SOx, CO2 and cutting particular matter is critical to human health and mitigating the climate change threat. Burning fossil fuel accounts for about three-quarters of the CO2 emissions produced by anthropogenic GHG emissions.

To address climate change, last year IMO adopted ambitious goals of reducing GHG emissions and cutting CO2 emissions by 50% in the shipping sector by 2050 as compared with 2008 levels. Shipping is also implementing Energy Efficiency Design Index (EEDI) measures to improve energy efficiency and fuel consumption through ship design.

SEA/LNG, an association that promotes LNG as a marine fuel, and its partner, non-governmental organisation the Society for Gas as a Marine Fuel commissioned the study to assess LNG’s environmental benefits as a marine fuel based on hard data. German sustainability consultancy thinkstep AG performed the study, which was reviewed by academics in Japan, France, Germany and the US. Data for the study was provided by eight marine engine manufacturers and oil majors ExxonMobil, Shell and Total.

On an engine technology basis, the study reports absolute WtW emissions reduction benefits for gas-fuelled engines compared with heavy fuel oil-fuelled ships are between 14-21% for two-stroke, slow-speed engines – which power about 75% of the oceangoing fleet – and between 7-15% for four-stroke, medium-speed engines.

One of the issues that still needs to be addressed is methane slip, unburned gas released during the combustion process, according to the study. Methane is a powerful GHG, some 20 times more potent than CO2. Methane emissions from the supply chain and engine slip need to be reduced further to maximise the positive impact on both air quality and GHG emissions.

While high-pressure, two-stroke diesel-cycle, dual-fuel engines incur methane slip of less than 1% of the overall WtW GHG emissions, Otto-cycle dual-fuel engines did not fare as well, said the study. Low-pressure, two-stroke and four-stroke Otto-cycle, dual-fuel engines are sensitive to methane slip with 10-17% of WtW GHG emissions resulting from unburned methane in the combustion process.

Among the other key findings in the study:

As shipping moves towards decarbonisation by 2050, LNG as a marine fuel, while not the silver-bullet solution, will have a critical role to play along with renewable energy in cutting CO2 and GHG emissions in the years ahead. Wider adoption now will start shipping on a path towards decarbonisation. With 250,000 additional deaths per year between 2030 and 2050 expected to be caused by climate change, waiting around is not an option.