Reliquefaction
Reliquefaction is the process of turning the boil-off gas from a liquefied-gas cargo back into liquid and returning it to the cargo tanks. A reliquefaction plant compresses and cools the vapour until it condenses, so the cargo that evaporated is recovered rather than burned or vented.
Reliquefaction is standard on LPG carriers and is increasingly fitted on LNG carriers as an alternative to burning boil-off as fuel — keeping the full cargo intact for delivery, which matters as cargo values and efficiency rules rise. It controls tank pressure while preserving cargo quantity.
Reliquefaction means the boil-off is kept as cargo rather than lost, so the ship delivers more of what it loaded — a direct commercial gain as cargo values rise. It also decouples cargo management from the ship fuel choice, which matters as ships move to other fuels for efficiency and emissions reasons.
Why reliquefy boil-off gas instead of burning it?
Burning boil-off consumes cargo; reliquefying it recovers the vapour back into the tanks, so more of the loaded cargo is delivered. This is standard on LPG carriers and increasingly used on LNG carriers as cargo values rise.