Liquefaction of Natural Gas

Abstract

A method and apparatus for liquefying natural gas vapour is provided. Firstly, liquid natural gas is sub-cooled at a first heat exchanger using a liquid coolant such as liquid nitrogen. The sub-cooled liquid natural gas is then used to condense the natural gas vapour at a second heat exchanger.

1 . A method for condensing natural gas vapour to generate liquefied natural gas (LNG), comprising:
 providing a liquid coolant, wherein the liquid coolant has a boiling point less than that of natural gas;   cooling LNG at a first heat exchanger using the liquid coolant to generate sub-cooled LNG; and   condensing natural gas vapour at a second heat exchanger using the sub-cooled LNG to liquefy the natural gas vapour and thereby generate further LNG.   
     
     
         2 . A method according to  claim 1 , further comprising:
 obtaining the LNG for cooling at the first heat exchanger from at least one LNG storage tank; and   returning the sub-cooled LNG to the at least one LNG storage tank after it is used at the second heat exchanger.   
     
     
         3 . A method according to  claim 2 , further comprising delivering the further LNG to the at least one LNG storage tank. 
     
     
         4 . A method according to  claim 1 , wherein the natural gas vapour is boil-off gas. 
     
     
         5 . A method according to  claim 1 , wherein the liquid coolant is liquid nitrogen. 
     
     
         6 . A method according to  claim 1 , further comprising compressing the natural gas vapour. 
     
     
         7 . A method according to  claim 1 , further comprising:
 delivering LNG from a first vessel to a second vessel; and   receiving the natural gas vapour from the second vessel.   
     
     
         8 . A system for condensing natural gas vapour to generate liquefied natural gas (LNG); comprising:
 a first heat exchanger arranged to cool LNG using a liquid coolant to generate sub-cooled LNG, wherein the liquid coolant has a boiling point less than that of natural gas; and   a second heat exchanger arranged to condense natural gas vapour using the sub-cooled LNG to liquefy the natural gas vapour and thereby generate further LNG.   
     
     
         9 . A system according to  claim 8 , further comprising at least one LNG storage tank, wherein the first heat exchanger is arranged to receive the LNG for cooling at the first heat exchanger from the at least one LNG storage tank, and wherein the system is arranged to return the sub-cooled LNG to the LNG storage tank after it is used at the second heat exchanger. 
     
     
         10 . A system according to  claim 9 , wherein the system is arranged to deliver the further LNG to the at least one LNG storage tank. 
     
     
         11 . A system according to  claim 8 , wherein the natural gas vapour is boil-off gas. 
     
     
         12 . A system according to  claim 8 , wherein the liquid coolant is liquid nitrogen. 
     
     
         13 . A system according to  claim 8 , further comprising a compressor for compressing the natural gas vapour. 
     
     
         14 . A vessel having a system for condensing natural gas vapour to generate liquefied natural gas, the vessel comprising:
 a first heat exchange exchanger arranged to cool LNG using a liquid coolant to generate sub-cooled LNG, wherein the liquid coolant has a boiling point less than that of natural gas;   a second heat exchanger arranged to condense natural gas vapour using the sub-cooled LNG to liquefy the natural gas vapour and thereby generate further LNG; and   a transfer boom arranged to transfer LNG to a second vessel and to receive natural gas vapour from the second vessel.   
     
     
         15 . A vessel according to  claim 14 , wherein the vessel is a bunker vessel.