Method and apparatus for storing liquefied natural gas

Abstract

Systems and methods for storing liquid natural gas is provided. In one embodiment, the natural gas vapor in the storage tank containing the liquefied natural gas may be directed a heat exchange unit attached to the storage tank, cooled by a refrigerant in the heat exchange unit, and then returned to the storage tank.

1 . A method of storing liquefied natural gas in a storage tank, comprising:
 introducing vaporized natural gas in the storage tank into a heat exchange unit;   introducing a refrigerant into the heat exchange unit;   liquefying the natural gas by exchanging heat with the refrigerant;   vaporizing the refrigerant; and   returning the liquefied natural gas to the storage tank.   
     
     
         2 . The method of  claim 1 , further comprising providing a first fluid path for flowing the vaporized natural gas from the storage tank and introducing the vaporized natural gas into the heat exchange unit. 
     
     
         3 . The method of  claim 2 , wherein the liquefied natural gas is returned to the storage tank through a second fluid path in fluid communication with the first fluid path. 
     
     
         4 . The method of  claim 2 , wherein the liquefied natural gas is returned to the storage tank through a second fluid path not in fluid communication with the first fluid path. 
     
     
         5 . The method of  claim 2 , further comprising providing a gas compressor in the first fluid path. 
     
     
         6 . The method of  claim 1 , wherein the vaporized natural gas is introduced into the heat exchange unit through the same port as the liquefied natural gas leaving the heat exchange unit. 
     
     
         7 . The method of  claim 1 , wherein the returning liquefied natural gas reduces a temperature in the storage tank. 
     
     
         8 . The method of  claim 1 , wherein heat exchange unit is at least partially disposed in the storage tank. 
     
     
         9 . The method of  claim 8 , wherein the vaporized natural gas is introduced into the heat exchange unit through an inlet opening of the heat exchange unit that is located inside the storage tank. 
     
     
         10 . The method of the  claim 9 , wherein the liquefied natural gas leaves the heat exchange unit through an outlet opening that is located inside the storage tank. 
     
     
         11 . The method of  claim 1 , wherein the refrigerant comprises liquid nitrogen. 
     
     
         12 . The method of  claim 11 , further comprising venting the vaporized nitrogen to atmosphere. 
     
     
         13 . The method of  claim 1 , further comprising venting the vaporized refrigerant to atmosphere. 
     
     
         14 . A system for storing liquefied natural gas, comprising:
 a storage tank containing the liquefied natural gas;   heat exchange unit having:
 a container; 
 a heat exchanger; and 
 an opening in fluid communication with the storage tank, wherein the heat exchange unit is configured to condense a vaporized natural gas from the storage tank and to return the condensed natural gas to the storage tank; and 
   a refrigerant source in fluid communication with the heat exchanger.   
     
     
         15 . The system of  claim 14 , wherein the opening allows inflow of the vaporized natural gas and outflow of the liquefied natural has. 
     
     
         16 . The system of  claim 14 , wherein the storage tank includes a port for outflow of the vaporized natural gas and inflow of liquefied natural gas. 
     
     
         17 . The system of  claim 14 , further comprising a gas compressor connected between the storage tank and the heat exchange unit. 
     
     
         18 . The system of  claim 14 , wherein the heat exchange unit is at least partially disposed in the storage tank. 
     
     
         19 . The system of  claim 18 , wherein the opening is positioned inside the storage tank. 
     
     
         20 . The system of  claim 14 , wherein the refrigerant is liquid nitrogen.