LNG BOG RELIQUEFACTION APPARATUS AND METHOD

摘要

An LNG BOG(Liquefied Natural Gas Boil-Off Gas) reliquefaction apparatus and a method are provided to reduce the mass flow of nitrogen in a nitrogen cycle for reliquefying BOG by supplying cold energy to a condenser and to compress nitrogen by low pressure. An LNG BOG reliquefaction apparatus includes a BOG cycle for compressing the BOG generated from an LNG storage tank, by a BOG compression unit(110) and then condensing the compressed BOG by a condensing unit(120) and a nitrogen cycle for supplying cold energy to the condensing unit. The nitrogen cycle comprises a nitrogen gas compression unit(130) compressing nitrogen gas and an expansion unit changing the nitrogen gas into a cryogenic state by expanding the compressed nitrogen gas and then supplying cryogenic nitrogen gas to the condensing unit. The expansion unit comprises an expansion valve branching off and supplying the compressed nitrogen gas and an expansion turbine(134). A cold energy recovery unit(114) is installed at a BOG line between the storage tank and the BOG compression unit, to recover the cold energy of the BOG flowing from the storage tank by heat-exchanging the BOG flowing from the storage tank and high-temperature fluid. The cold energy recovery unit recovers the cold energy of the BOG into the BOG cycle by heat-exchanging the BOG ejected from the storage tank, with the BOG compressed at high pressure by the BOG compression unit.