Patent ID: 6192705
Filing Date: 2001-02-27
Classification: F17C,F25J

Abstract:
A process for reliquefying pressurized boil-off gas produced by pressurized liquid natural gas, comprising the steps of:(a) providing refrigeration duty to a heat exchanger by means of a refrigeration cycle;(b) passing pressurized natural gas through the heat exchanger to cool the natural gas, said pressurized natural gas being warmer than the pressurized boil-off gas;(c) expanding the cooled natural gas to a lower pressure, thereby liquefying at least part of the cooled natural gas, the liquefied gas having a temperature above about -112.degree. C. (-170.degree. F.) and a pressure sufficient for the liquefied gas to be at or below its bubble point;(d) separating in a first phase separator any vapor phase, if a vapor phase exists after the expansion of step (c), from the liquefied gas;(e) warming in the heat exchanger the boil-off gas to be reliquefied, thereby providing refrigeration duty to the heat exchanger;(f) compressing and cooling the warmed boil-off gas;(g) returning the compressed boil-off gas to the heat exchanger to further cool the compressed boil-off gas;(h) expanding the compressed boil-off gas to a lower pressure to produce a gas phase and a liquid phase;(i) phase separating in a second phase separator the gas phase and the liquid phase of step (h);(j) passing the liquid phase of step (i) to the first phase separator;(k) recovering vapors from the second phase separator; and(l) withdrawing liquid from the first phase separator as pressurized liquid natural gas having a temperature above about -112.degree. C. (-170.degree. F.) and a pressure sufficient for the liquid to be at or below its bubble point.