Reliquefaction of boil-off from liquefied natural gas

A method of converting a boil-off stream comprising methane to a liquid having a preselected bubble point temperature, comprising the steps of:

• (a) pressurizing the boil-off stream;
• (b) cooling the pressurized boil-off stream of step (a);
• (c) expanding the cooled, pressurized boil-off stream of step (b), thereby producing pressurized liquid;
• and
• (d) obtaining the preselected bubble point temperature of the pressurized liquid by performing at least one of the following steps:
• i. before, during, or after one or more of steps (a) to (c), removing from the boil-off stream a first predetermined amount of nitrogen, and
• ii. before, during, or after one or more of steps (a) to (c), adding to the boil-off stream a second predetermined amount of one or more C2+ hydrocarbons,
• wherein the first predetermined amount of the nitrogen removed and the second predetermined amount of the one or more C2+ hydrocarbons added are controlled to obtain the preselected bubble point temperature of the pressurized liquid.

A method of converting a boil-off stream comprising methane to a liquid having a preselected bubble point temperature, comprising the steps of:

• (a) pressurizing the boil-off stream;
• (b) cooling the pressurized boil-off stream of step (a);
• (c) expanding the cooled, pressurized boil-off stream of step (b), thereby producing pressurized liquid;
• and
• (d) obtaining the preselected bubble point temperature of the pressurized liquid by performing at least one of the following steps:
• i. before, during, or after one or more of steps (a) to (c), removing from the boil-off stream a first predetermined amount of nitrogen, and
• ii. before, during, or after one or more of steps (a) to (c), adding to the boil-off stream a second predetermined amount of one or more C2+ hydrocarbons,
• wherein the first predetermined amount of the nitrogen removed and the second predetermined amount of the one or more C2+ hydrocarbons added are controlled to obtain the preselected bubble point temperature of the pressurized liquid, and further comprising before step (d), determining the first predetermined amount of the nitrogen to be removed from the boil-off stream, and determining the second predetermined amount of the one or more C2+ hydrocarbons to be added to the boil-off stream, both of said determinations being performed by determining the composition of the boil-off stream and performing an equation of state analysis to determine a pressurized liquid composition needed to obtain the preselected bubble point temperature in said pressurized liquid at a preselected pressure.