Method and apparatus for treating boil-off gas in an LNG carrier having a reliquefaction plant, and LNG carrier having said apparatus for treating boil-off gas

摘要

Disclosed are a method and an apparatus for treating boil-off gas generated in an LNG storage tank of an LNG carrier for transporting LNG in a cryogenic liquid state, the LNG carrier having a boil-off gas reliquefaction plant, wherein an amount of boil-off gas corresponding to a treatment capacity of the reliquefaction plant among the total amount of boil-off gas generated during the voyage of the LNG carrier is discharged from the LNG storage tank and reliquefied by the reliquefaction plant. The boil-off gas treating method and apparatus can maintain an amount of boil-off gas discharged from an LNG storage tank at a constant level by storing in the LNG storage tank, instead of discharging and burning, surplus boil-off gas which has not been returned to the LNG storage tank through the reliquefaction plant among the total amount of boil-off gas generated in the LNG storage tank, and can prevent waste of boil-off gas and save energy by allowing an internal pressure of the LNG storage tank to be increased.

主权项

1. A method for treating boil-off gas generated in an LNG storage tank of an LNG carrier for transporting LNG in a cryogenic liquid state, comprising the steps of discharging boil-off gas from the LNG storage tank at a pressure greater than 0.25 bar to 2 bar, and reliquefying said boil-off gas in a reliquefaction plant, wherein a uniform temperature distribution is maintained in the LNG storage tank by spraying the LNG from a lower portion of the LNG storage tank toward boil-off gas at an upper portion of the LNG storage tank and injecting the boil off gas into the LNG at the lower portion of the LNG storage tank, and wherein the amount of boil-off gas that is discharged is regulated as a function of the level of LNG in the LNG storage tank, wherein the level of LNG in the LNG storage tank is calculated by measuring the flow rate of fuel gas supplied from the LNG storage tank to a fuel gas supply line to a fuel gas propulsion means, and wherein the flow rate of fuel gas is measured by a flow rate measurer within the fuel gas supply line.