Leakages from Routine LNG Bunkering "Can Have a Disproportionate Impact on Overall GHG Emissions"

Thursday March 3, 2016

Methane emissions from liquefied natural gas (LNG) bunkering operations in some cases negate the environmental advantages the fuel is supposed to provide: that's a key finding of a new study released by the United States Maritime Administration.

"Methane Emissions from Natural Gas Bunkering Operations in the Marine Sector: A Total Fuel Cycle Approach", by the University of Delaware and the Rochester Institute of Technology, focuses on how methane emissions from LNG use in the maritime sector impact overall greenhouse gas (GHG) emissions; it derives its data from a total fuel cycle analysis methodology of evaluating "well- to-hull" vessel operations emissions.

Of the many findings contained in the study, one shows that LNG fuels used in diesel cycle natural gas engines offer GHG emissions benefits compared to conventional fuels in most cases, "although methane leakage and slip can diminish those benefits considerably."

In sharp contrast, "LNG fuels used in lean-burning, Otto cycle (spark ignition) natural gas engines offer little to no benefits compared to conventional fuels."

That's because the "methane slip is more significant, and can actually negate the advantages of the LNG system; in the spark ignited cases, emissions from the LNG system were higher even in cases where no bunkering leakages were assumed."

Another key finding is that routine LNG bunkering leakages "can have a disproportionate impact on overall GHG emissions due to the high volume of natural gas throughput and the high global warming potential of methane."

The study's authors discovered that even a methane leakage as small as 1 percent causes a 10 percent increase in net GHG emissions: "In the compression ignition engine, this 1 percent bunkering leakage cut the net GHG emissions advantages of LNG from a 14.9 percent benefit down to a 6.7 percent benefit compared to low-sulfur diesel fuel."

The authors stress that several opportunities in the bunkering process exist where leakage can be reduced, "and these require additional research and/or testing to improve upon the available literature."

The study did not cover non-routine or chronic leakage, and the authors say this merits future research because "on an annual basis, a few of these incidents could increase the net GHG impact of natural gas as a marine fuel."

Boston Consulting Group (BCG) last year predicted that LNG is likely to become the marine fuel of the future, commanding up to 27 percent of the bunker market by 2025.