Patent ID: 8650906

Claim:
A system for recovering and liquefying a natural gas boil-off stream, the system comprising: a refrigeration vessel including a first heat exchange path for cooling a stream of mixed refrigerant, the first heat exchange path having a refrigerant inlet and a cooled refrigerant outlet, a second heat exchange path for warming a cooled refrigerant stream, the second heat exchange path having a reduced pressure refrigerant inlet and a reduced pressure refrigerant outlet positioned such that the refrigerant in the second heat exchange path flows countercurrent to the refrigerant flowing through the first heat exchange path, and a third heat exchange path for liquefying a stream of boil-off gas, the third heat exchange path having a boil-off gas inlet and a liquefied boil-off gas outlet positioned such that the boil-off gas in the third heat exchange path flows countercurrent to the refrigerant flowing through the second heat exchange path; and a closed-loop refrigeration cycle comprising— a screw compressor having an inlet in fluid communication with the reduced pressure refrigerant outlet of the second heat exchange path and a high pressure refrigerant outlet for discharging a compressed refrigerant from the screw compressor; a cooler for cooling the compressed refrigerant, the cooler having a compressed refrigerant inlet in fluid communication with the high pressure refrigerant outlet of the screw compressor and a cooled refrigerant outlet; a refrigerant separator having a separator inlet in fluid communication with the cooled refrigerant outlet of the cooler, a separator liquid refrigerant outlet for discharging a stream of liquid refrigerant and a separator gaseous refrigerant outlet for discharging a stream of gaseous refrigerant; a refrigerant vapor line in fluid communication with the separator gaseous refrigerant outlet, the refrigerant vapor line including a pressure controller disposed therein; a refrigerant liquid line in fluid communication with the separator liquid refrigerant outlet, the refrigerant liquid line including a flow controller disposed therein, wherein the pressure controller disposed in the refrigerant vapor line is configured to adjust the flow rate of liquid refrigerant passing through the refrigerant liquid line; a reconstituted refrigerant line for receiving and combining the vapor and liquid refrigerant streams from each of the refrigerant vapor and liquid lines, respectively, wherein the reconstituted refrigerant line is configured to discharge a combined stream of vapor and liquid refrigerant into the refrigerant inlet of the first heat exchange path of the refrigeration vessel; and an expansion valve having an inlet in fluid communication with the cooled refrigerant outlet of the first heat exchange path and an outlet in fluid communication with the reduced pressure refrigerant inlet of the second heat exchange path.