Patent ID: 7921656

Claim:
A process for reliquefaction of boiloff gas from a liquefied natural gas storage container, said process comprising the steps of: drawing boiloff gas; warming the drawn boiloff gas by passing it through a first flow path of a first heat exchanger for recovering the refrigerative value therefrom; passing the warmed boiloff gas from the first flow path of said first heat exchanger as an intact volume through a boiloff compressor; cooling the compressed boiloff gas from the boiloff compressor through a boiloff aftercooler; passing the cooled compressed boiloff gas from the boiloff aftercooler through a second flow path of said first heat exchanger in a direction countercurrent to the boiloff gas flowing through the first flow path for imparting thereto the refrigerative value recovered from the boiloff gas passing through the first flow path; refrigerating said further cooled boiloff gas at a substantially constant pressure after compression through a refrigerant distinct and separate from the cooled boiloff gas to a temperature sufficient to achieve liquefaction thereof; wherein the refrigerating step further comprises the steps of: passing the refrigerant within a closed system through only one single stage main compressor to yield a compressed refrigerant; passing the compressed refrigerant from the only one single stage main compressor through a first aftercooler for cooling to a first temperature; passing the cooled refrigerant from the first aftercooler through a first flow path of a second heat exchanger for further cooling to a second temperature lower than said first temperature; withdrawing a portion of said refrigerant at said second temperature from the first flow path of said second heat exchanger; passing the portion of said refrigerant through a first turboexpander for cooling to a third temperature lower than said second temperature; passing the refrigerant from said first turboexpander through a second flow path of the second heat exchanger; returning the refrigerant from the second flow path of the second heat exchanger back to the single stage main compressor; and passing the further cooled boiloff gas from said first heat exchanger through a third flow path of said second heat exchanger in a direction countercurrent to the refrigerant flowing through the second flow path of the second heat exchanger for refrigerating to a temperature sufficient to achieve liquefaction thereof.