APPARATUS AND METHOD FOR RELIQUEFYING BOIL-OFF GAS CAPABLE OF REFRIGERATION LOAD VARIABLE OPERATION

摘要

An apparatus for reliquefying boil-off gas is provided to minimize amount of nitrogen gas during reliquefying load operation, and to reduce power consumption during idling by allowing refrigeration load of a refrigeration system to be varied during variation of reliquefying load. An apparatus for reliquefying boil-off gas comprises a refrigeration system. The refrigeration system for compressing and expanding refrigerant is connected to an ultra low temperature heat exchanger(11). The refrigeration system includes a multi-step compressor(53), an expander(23) and a motor(M). An inverter(60) is connected to the motor. The refrigeration system uses nitrogen as refrigerant. A refrigerant circuit of the multi-step compressor is connected to one end of a nitrogen gas supply line(L4) for supplying nitrogen gas inside the refrigeration system.