4. Liquefied Natural Gas (LNG)

This chapter explores the role of liquefied natural gas (LNG) in global energy systems, its environmental impact, transportation issues, and potential as a marine fuel. LNG is a fossil fuel consisting primarily of methane, with smaller amounts of ethane, propane, butane, nitrogen, and carbon dioxide. A large LNG carrier is typically used because LNG's high density compared to NG makes it economical for long-distance transport, but it has the operational issues of boil-off gas (BOG) generation due to the very low storage temperature of LNG. With stricter GHG emission regulations, advanced dual-fuel gas injection engines with reliquefaction are now being used. While LNG emits less CO₂ than conventional heavy fuel oil (HFO), its GHG emissions intensity may close to that of HFO when considering engine type and methane slip. Demand for LNG as a fuel will gradually decline in the distant future because it is essentially a fossil fuel, but the use of LNG as a feedstock for alternative fuels such as hydrogen is expected to continue for a considerable period of time. In addition, alternative sources of LNG, such as biogas, can offer a more sustainable future by reducing net GHG emissions.