Boil-Off Gas Reliquefaction

• The BOG reliquefaction unit is a technology that relies on proven reverse nitrogen Brayton cycle to reliquefy BOG. Depending on the available pressure of the BOG, process schemes with one or two expanders may be used. The use of a nitrogen cycle allows a broad flexibility of operation, which is very well suited since BOG flow can highly variate over time.
• The second technology provided by Air Liquide Engineering & Construction, so-called “LIN to LNG box”, uses liquid nitrogen (LIN) as a cooling agent to recover BOG generated in LNG storages. Compared with a BOG reliquefaction unit, the technology offers the benefit of reduced initial investment cost, and is more suitable for moderate LNG storage capacity. It is typically the most adapted solution all along the small scale LNG chain.

Advantages of BOG Reliquefaction

• Recovers BOG all along the LNG transport chain, from well to end user, therefore ensuring “zero flaring” logistics
• Maintains LNG fuel specification
• Helps debottleneck LNG export terminals

Key figures

• Capacity: 30 to 500 tons per day
• BOG unit consumption: 500 to 800 kilowatts per hour / ton
• LIN consumption: 2 tons of LIN per ton of reliquefied BOG

See also Air Liquide Advanced Business & Technologies' Turbo-Brayton cryogenic systems for the reliquefaction of Boil-Off Gas.