Methods and apparatus for liquefaction of natural gas

Abstract

A liquefaction unit that may include a first treating unit, a second treating unit, a liquefaction heat exchanger, a changeover unit, a liquid nitrogen tank, an LNG product storage tank, and a pressure build unit. During a first operating phase, the associated piping defines a first operating phase flow path for natural gas from the natural gas inlet stream to the first treating unit to the liquefaction unit to the LNG product stream, and a first operating phase flow path for nitrogen from the liquid nitrogen stream to the liquefaction unit to the second treating unit. During a second operating phase, the associated piping defines a second operating phase flow path for natural gas from the natural gas inlet stream to the second treating unit to the liquefaction unit to the LNG product stream, and a first operating phase flow path for nitrogen from the liquid nitrogen stream to the liquefaction unit to the first treating unit. During a changeover operating phase, the associated piping defines a changeover flow path for the natural gas from the natural gas inlet stream to the changeover treating unit to the liquefaction unit to the LNG product stream.

1 . A natural gas liquefaction apparatus comprising:
 associated piping and valves that interconnect the following:
 a natural gas inlet stream; 
 a liquid nitrogen stream; 
 a first treating unit; 
 a second treating unit; 
 a changeover treating unit; 
 a liquefaction unit; and, 
 a LNG product stream; 
   wherein during a first operating phase, the associated piping defines a first operating phase flow path for natural gas from the natural gas inlet stream to the first treating unit to the liquefaction unit to the LNG product stream, and a first operating phase flow path for nitrogen from the liquid nitrogen stream to the liquefaction unit to the second treating unit;   wherein during a second operating phase, the associated piping defines a second operating phase flow path for natural gas from the natural gas inlet stream to the second treating unit to the liquefaction unit to the LNG product stream, and a first operating phase flow path for nitrogen from the liquid nitrogen stream to the liquefaction unit to the first treating unit; and,   wherein during a changeover operating phase, the associated piping defines a changeover flow path for the natural gas from the natural gas inlet stream to the changeover treating unit to the liquefaction unit to the LNG product stream.   
     
     
         2 . A method of liquefying natural gas comprising the steps of:
 During a first operating stage, flowing the natural gas to a first treating unit to form treated natural gas, flowing the treated natural gas to the liquefaction unit to form LNG, and flowing liquid nitrogen to the liquefaction unit and then to a second treating unit;   During a second operating stage, flowing the natural gas to the second treating unit to form treated natural gas, flowing the treated natural gas to the liquefaction unit to form LNG, and flowing liquid nitrogen to the liquefaction unit and then to the first treating unit; and,   During a changeover operating stage, flowing the natural gas a changeover treating unit to form treated natural gas, flowing the treated natural gas to the liquefaction unit to form LNG.