Total Methane and CO2 Emissions from Liquefied Natural Gas Carrier Ships: The First Primary Measurements

Environ Sci Technol. 2022 Jul 5;56(13):9632-9640. doi: 10.1021/acs.est.2c01383. Epub 2022 Jun 14.

Abstract

Mitigating methane emissions is vital in meeting global climate targets, but there is a lack of understanding of emissions and abatement opportunities to enable this. The natural gas supply chain is a key emission source, where methane emissions from liquefied natural gas (LNG) shipping have until now not been directly measured. This study provides the first measurement and modeling of total methane and CO2 emissions from an LNG carrier on a round trip voyage from the USA to Belgium and back, including loading, laden voyage, unloading, and ballast voyage, measuring emissions from exhaust stacks, vents, and fugitives. Venting and fugitive emissions were extremely low, contributing less than 0.1% of total greenhouse gas emissions. CO2 emissions from fuel usage were also lower than previous estimates due to improved efficiencies in modern engines and ship design. However, methane slip through the engines were higher than those in prior studies, averaging 3.8% across all engines: equating to 0.1% of delivered LNG. Generator engines are not typically included in emissions analyses but were the key cause of methane emissions. Engines exhibited higher methane slip rates at low loads, and optimized operation could reduce slip rates by half. More measurement studies are now needed to better understand fleet emissions and enable cost-effective mitigation strategies.

Keywords: FTIR and OGI measurement; LNG carrier ships; bottom-up measurement; engine slip; greenhouse gas emissions; methane emissions; natural gas supply chain.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Air Pollutants* / analysis
  • Carbon Dioxide
  • Methane / analysis
  • Natural Gas* / analysis
  • Ships

Substances

  • Air Pollutants
  • Natural Gas
  • Carbon Dioxide
  • Methane