Boil-off gas reliquefaction system and method of discharging lubricant oil from boil-off gas reliquefaction system

A method of discharging lubricant oil from a BOG reliquefaction system configured to reliquefy BOG, the method comprising

• compressing, by a compressor, the BOG,
• cooling, by a heat exchanger, the compressed BOG through heat exchange with non-compressed BOG,
• reducing, by a pressure reducer, a pressure of the compressed BOG cooled through the heat exchange,
• detecting, by a detection unit, whether the heat exchanger is clogged by the lubricant oil,
• determining whether the heat exchanger is clogged by the lubricant oil based on a result of the detection unit, wherein the BOG reliquefaction system comprises a bypass line through which BOG is supplied to the compressor after bypassing the heat exchanger, and a bypass valve disposed on the bypass line,
• responsive to determining, by a determination unit, that the heat exchanger is clogged by the lubricant oil, controlling, by the determination unit, a bypass valve to be opened, thereby supplying the BOG from a storage tank to the compressor through the bypass line without supplying the BOG from the storage tank to a cold fluid channel of the heat exchanger while the BOG compressed by the compressor is supplied to a hot fluid channel of the heat exchanger, which allows a temperature of the hot fluid channel of the heat exchanger to rise to discharge impurities accumulated inside the heat exchanger,
• wherein a time point for discharging condensed or solidified lubricant oil is determined based on at least one of a temperature difference and a pressure difference of equipment, and an alarm is generated to indicate the time point for discharging the condensed or solidified lubricant oil.