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
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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 o
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.
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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
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. 2. The method according to claim 1, further comprising the step of retaining in the LNG storage tank an amount of surplus boil-off gas that is in excess of the treatment capacity of the boil-off gas treating means of the LNG carrier. 3. The method according to claim 2, further comprising the steps of: retaining the surplus boil-off gas at the beginning of the loaded voyage of the LNG carrier; anddischarging boil-off gas during the voyage to maintain a constant pressure in the LNG storage tank. 4. The method according to claim 3, wherein the treatment capacity of the reliquefaction plant corresponds to the amount of boil-off gas generated in the LNG storage tank when the pressure in the LNG storage tank is maintained at a constant level. 5. The method according to claim 1, further comprising the steps of: compressing the boil-off gas discharged from the LNG storage tank in a boil-off gas compression unit;condensing the compressed boil-off gas in a condenser by exchanging heat with a refrigerant; andreturning the condensed boil-off gas to the LNG storage tank. 6. The method according to claim 5, further comprising the step of precooling the boil-off gas discharged from the LNG storage tank in a precooler so as to stably reliquefy the boil-off gas, before the step of compressing the boil-off gas. 7. The method according to claim 5, further comprising the step of temporarily storing the condensed boil-off gas in a gas-liquid separator so as to stably return to the LNG storage tank the boil-off gas which has been condensed while passing through the condenser, after the step of condensing the boil-off gas. 8. 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 a step of setting a set pressure of the LNG storage tank at a pressure greater than 0.25 bar to 2 bar according to the volume of the LNG in the LNG storage tank while discharging a constant amount of boil-off gas from the LNG storage tank, wherein a uniform temperature distribution is maintained in the LNG storage tank by spraying the LNG from a lower portion of the 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. 9. The method according to claim 8, wherein the amount of boil-off gas discharged corresponds to a treatment capacity of the reliquefaction plant. 10. The method according to claim 1, further comprising the step of measuring the composition of the boil-off gas by gas chromatography. 11. The method according to claim 1, further comprising the step of selecting measurement values according to the flow rate of the fuel gas. 12. The method according to claim 1, further comprising the step of compressing boil-off gas within the fuel gas supply line. 13. The method according to claim 12, further comprising the step of storing boil-off gas compressed within the fuel gas supply line. 14. The method according to claim 1, further comprising the step of gasifying LNG from the LNG storage tank and delivering the gasified LNG as a fuel gas to the fuel gas propulsion means. 15. The method according to claim 5, further comprising the step of exchanging heat of the boil off gas in the boil-off gas compression unit with the LNG of the fuel gas supply line. 16. The method according to claim 1, further comprising the step of extracting LNG from the LNG storage tank and compressing the extracted LNG to meet the flow rate and pressure demands of the fuel gas propulsion means. 17. The method according to claim 1, further comprising the step of exchanging heat between the boil-off gas from the LNG storage tank with LNG in the fuel gas supply line. 18. The method according to claim 17, further comprising the step of pumping LNG in the fuel gas supply line to the fuel gas propulsion means. 19. The method according to claim 17, further comprising the step of heating LNG in the fuel gas supply line to supply the fuel gas propulsion means.
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이 특허에 인용된 특허 (5)
Pozivil, Josef, Apparatus for reliquefying compressed vapour.
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