Refrigerant cycle pressure control system for reliquefaction system for ship

A refrigerant cycle pressure control system for a reliquefaction system for a ship, comprising:

• a heat exchanger provided to the reliquefaction system and configured to cool boil-off gas received from a storage tank;
• a refrigerant cycle comprising a refrigerant circulation line through which a refrigerant is circulated to cool the boil-off gas in the heat exchanger, a refrigerant compressor disposed on the refrigerant circulation line and configured to compress the refrigerant discharged from the heat exchanger after cooling the boil-off gas in the heat exchanger, and an expander configured to expand and cool the refrigerant compressed by the refrigerant compressor and having been cooled through the heat exchanger and supply the expanded and cooled refrigerant to the heat exchanger;
• an inventory tank configured to store the refrigerant to be charged to the refrigerant cycle;
• a refrigerant supply line connecting the inventory tank to an upstream side of the refrigerant compressor to replenish the refrigerant cycle with the refrigerant;
• a refrigerant discharge line connecting a downstream side of the refrigerant compressor to the inventory tank to discharge the refrigerant from the refrigerant cycle to the inventory tank;
• and
• a pressure regulation line branched off of the refrigerant discharge line,
• wherein the refrigerant cycle pressure control system is configured to discharge the refrigerant from the refrigerant cycle through the refrigerant discharge line or the pressure regulation line to depressurize the refrigerant cycle,
• wherein, to depressurize the refrigerant cycle, the refrigerant cycle pressure control system is configured to discharge the refrigerant first to the inventory tank through the refrigerant discharge line, and then discharge the refrigerant to the pressure regulation line in response to pressure reversal between the inventory tank and the refrigerant cycle, and
• wherein the refrigerant cycle pressure control system further comprises a device connected to the pressure regulation line and configured to receive the discharged refrigerant through the pressure regulation line to reuse the discharged refrigerant for onboard utility, or for blanketing, instead of discharging the refrigerant overboard.