BOG RELIQUEFACTION APPARATUS AND METHOD

摘要

A BOG(Boil-Off Gas) reliquefying device and a reliquefying method thereof are provided to keep the temperature of BOG constant within a set range, at an inlet of a heat exchanger although the generation amount of BOG or the temperature is changed, by precooling the BOG with low-temperature nitrogen. A BOG reliquefying device for compressing BOG generated from an LNG(Liquefied Natural Gas) storage tank(3), reliquefying the compressed BOG, and returning the reliquefied BOG to the tank is composed of a nitrogen pressurizing and cooling unit for pressurizing and cooling nitrogen by a nitrogen circulation unit supplying cold heat for reliquefying BOG; a third nitrogen heat exchanger(46) cooling down high-temperature nitrogen gas passing through the nitrogen pressurizing and cooling unit; a second nitrogen heat exchanger(44) additionally cooling down the high-temperature nitrogen gas passing through the third nitrogen heat exchanger; and a nitrogen expander(39) generating the cryogenic and low-pressure nitrogen gas by expanding the high-temperature nitrogen gas passing through the second nitrogen heat exchanger. The cold heat of the cryogenic and low-pressure nitrogen gas expanded in the nitrogen expander is deprived in the first nitrogen heat exchanger and then additionally taken away in exchanging heat with the high-temperature nitrogen gas passing through the nitrogen pressurizing and cooling unit, with passing through the second and third nitrogen heat exchangers. And then, the cryogenic and low-pressure nitrogen gas is returned to the nitrogen pressurizing and cooling unit. The BOG compressed in the BOG compressor is heat-exchanged in the second nitrogen heat exchanger and precooled before the BOG is reliquefied in the first nitrogen heat exchanger.