New Study Finds GHG Benefit for LNG as a Marine Fuel

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Published Apr 12, 2019 7:51 PM by The Maritime Executive

SEA\LNG and the Society for Gas as a Marine Fuel have sponsored a new study by consultancy Thinkstep on LNG's total greenhouse gas emissions profile, from well to wake. The analysis determined that compared with HFO, LNG delivers lifecycle greenhouse gas emission reductions of between 14 and 21 percent for two-stroke engines.

Burning LNG can reduce on-board CO2 emissions by as much as 30 percent. The full "well-to-wake" lifecycle of gas production, liquefaction, transport and utilization of LNG as a marine fuel involves additional emissions sources which reduce LNG's net climate benefit - including fugitive emissions of methane, the main component of LNG. When burned, methane produces water and carbon dioxide; when released unburned, it is a greenhouse gas with 30 times the potency of CO2. 

According to Thinkstep, the lifecycle emissions of LNG-fueled two-stroke engines offer a 14-21 percent reduction in net GHG emissions relative to HFO in two-stroke engines. The reduction is even more favorable when considering post-2020 sulfur requirements: exhaust scrubbers increase the GHG emissions of HFO fuel operation, and the study estimates that LNG's GHG advantage widens by an additional percentage point when compared with a scrubber-equipped ship. 

Not all studies have reached similar results. In a recent review by Imperial College London, researchers found a relatively limited GHG reduction benefit for using LNG as a marine fuel. The studies examined in the review indicated that LNG's GHG profile is "six percent lower on average [than HFO] and ten percent lower when comparing lowest estimates." In addition, the metastudy found that "at worst, natural gas fueled [ships] may have lifecycle emissions exceeding" HFO-fueled ships - especially for low pressure dual fuel (LPDF) engines, which tend to release more uncombusted methane. 

The authors acknowledged that the results of any study of this nature are contingent on input variables. "GHG emissions are highly dependent on the application and hence engine technology," Thinkpoint wrote. "General statements on the GHG of LNG as marine fuel can therefore be rather misleading and special care has to be taken when comparing the results."