Boil-off gas (BOG)

Boil-off gas is the vapor continuously generated as heat leaks into a cryogenic LNG cargo or fuel tank held near -162 C. On LNG carriers natural BOG (historically around 0.10 to 0.15 percent of cargo per day) is burned in the engines, reliquefied, or in excess sent to a gas combustion unit. On LNG-fueled ships BOG is managed to feed the engine or a small reliquefaction plant, and tank pressure is controlled to keep it within the engine’s supply window.