Simulating the Variability of Methane and CO2 Emissions from Liquefied Natural Gas Shipping: A Time-in-Mode and Carrier Technology Approach

Greenhouse gas emissions from liquefied natural gas (LNG) shipping are not currently well understood, but depend on individual carrier characteristics, distance traveled, and the number of days spent maneuvering and docked. A tool was developed that estimates greenhouse gas emissions from LNG carriers, accounting for changes in containment and engine technology, types of propulsion systems, and differences in the containment size. Emissions of methane and CO2 are based on boil-off generation, the amount of slip during combustion, and combustion stoichiometry. The tool estimates emissions for individual LNG carriers based on carrier and journey characteristics. Estimated methane emissions per volume of LNG delivered for a case study round-trip voyage from North America to Europe varied by a factor of 9 over the range of LNG carriers in the current fleet. CO2 emission estimates varied by a factor of 3. When a 20-year global warming potential of 82.5 for methane is applied, the emissions for carriers making this journey ranged from 43-170 kg of CO(2)eq/m(3) LNG delivered across carrier technologies. A spreadsheet tool for estimating carbon dioxide and methane emissions for specific carriers in the current fleet undergoing specific LNG delivery journeys is provided.