Method for the integration of a nitrogen liquefier and liquefaction of natural gas for the production of liquefied natural gas and liquid nitrogen

Abstract

A method for the integration of a nitrogen liquefier and liquefaction of natural gas for the production of liquefied natural gas and liquid nitrogen is provided. The method may include providing a nitrogen liquefaction unit and providing a natural gas liquefaction unit. Liquefaction of the nitrogen can be achieved via a nitrogen refrigeration cycle within the nitrogen liquefaction unit. Liquefaction of the natural gas can be achieved through the use of natural gas letdown and a second nitrogen refrigeration cycle. The two liquefaction units can be integrated via a common nitrogen recycle compressor, thereby providing significant capital savings.

We claim: 
     
         1 . A method for the integration of a nitrogen liquefier and natural gas liquefier for the production of liquefied natural gas (“LNG”) and liquid nitrogen (“LIN”), the method comprising the steps of:
 a) providing a nitrogen liquefier having a first nitrogen refrigeration cycle, wherein the nitrogen liquefier comprises a turbine, a booster and a plurality of coolers, wherein the first nitrogen refrigeration cycle is configured to provide refrigeration within a first heat exchanger; 
 b) providing a second nitrogen refrigeration cycle, wherein the second nitrogen refrigeration cycle comprises a second turbine, a second booster and a plurality of second coolers, wherein the second nitrogen refrigeration cycle is configured to provide refrigeration within a second heat exchanger; 
 c) purifying a first natural gas stream in a first purification unit to remove a first set of impurities to produce a purified first natural gas stream; 
 d) cooling and liquefying the first natural gas stream in the second heat exchanger using the refrigeration from the nitrogen refrigeration cycle to produce an LNG stream, wherein the first natural gas stream has an LNG refrigeration requirement, wherein the LNG stream is liquefied at a first pressure P H ; 
 e) purifying a second natural gas stream in a second purification unit to remove a second set of impurities to produce a purified second natural gas stream; 
 f) partially cooling the second natural gas stream in the second heat exchanger; 
 g) withdrawing the partially cooled natural gas stream from an intermediate section of the second heat exchanger; 
 h) expanding the partially cooled natural gas stream to a medium pressure P M  in a natural gas expansion turbine to form a cold natural gas stream, wherein the medium pressure P M  is at a pressure lower than the first pressure P H ; and 
 i) warming the cold natural gas stream in the second heat exchanger by heat exchange against the first natural gas stream to produce a warm natural gas stream at the warm end of the second heat exchanger, 
 wherein the natural gas expansion turbine drives a first booster, 
 wherein the LNG refrigeration requirement is supplied by a combination of refrigeration from the second nitrogen refrigeration cycle and step i), 
 wherein a portion of the liquid nitrogen within the first nitrogen refrigeration cycle is withdrawn as product liquid nitrogen, wherein at least an equal portion of gaseous nitrogen is introduced to the first nitrogen refrigeration cycle as is withdrawn as product liquid nitrogen, and 
 wherein the first nitrogen refrigeration cycle and the second nitrogen refrigeration cycle share a common nitrogen recycle compressor. 
 
     
     
         2 . The method as claimed in  claim 1 , wherein the first booster is configured to compress the second natural gas stream or a stream derived from the second natural gas stream. 
     
     
         3 . The method as claimed in  claim 1 , wherein the first booster is configured to compress a stream selected from the group consisting of the first natural gas stream, the purified first natural gas stream, the second natural gas stream, the purified second natural gas stream, the partially cooled natural gas stream, the warm natural gas stream, and a nitrogen fluid within the nitrogen refrigeration cycle. 
     
     
         4 . The method as claimed in  claim 1 , wherein the first set of impurities has a freezing point at or above the liquefaction temperature of methane at the first pressure P H . 
     
     
         5 . The method as claimed in  claim 1 , wherein the second set of impurities comprises water. 
     
     
         6 . The method as claimed in  claim 1 , wherein the first nitrogen refrigeration cycle further comprises a nitrogen feed compressor. 
     
     
         7 . The method as claimed in  claim 1 , wherein the first nitrogen refrigeration cycle is a closed refrigeration cycle. 
     
     
         8 . The method as claimed in  claim 1 , wherein the first natural gas stream and the second natural gas stream come from the same natural gas source. 
     
     
         9 . The method as claimed in  claim 8 , wherein the natural gas source is a natural gas pipeline having a pressure between 15 and 100 bara. 
     
     
         10 . The method as claimed in  claim 1 , wherein the first natural gas stream comes from a first natural gas source, and the second natural gas stream comes from a second natural gas source, wherein the first and second natural gas sources are different sources. 
     
     
         11 . The method as claimed in  claim 10 , wherein the first natural gas source comprises a natural gas pipeline. 
     
     
         12 . The method as claimed in  claim 11 , wherein the natural gas pipeline has a pressure between 15 and 100 bara. 
     
     
         13 . The method as claimed in  claim 1 , wherein the first purification unit and the second purification unit are the same unit. 
     
     
         14 . The method as claimed in  claim 1 , wherein the first purification unit and the second purification unit are separate units, wherein the first purification unit is configured to remove at least water and carbon dioxide, and wherein the second purification unit is configured to remove at least water. 
     
     
         15 . The method as claimed in  claim 1 , wherein the nitrogen liquefier further comprises a subcooler. 
     
     
         16 . A method for the integration of a first liquefier and a second liquefier for the production of a first liquefied gas and a second liquefied gas, the method comprising the steps of:
 a) providing a first liquefier having a first refrigeration cycle, wherein the first liquefier comprises a recycle compressor, a first heat exchanger, and a turbine booster;   b) providing a second refrigeration cycle, wherein the second refrigeration cycle is configured to provide refrigeration within a second heat exchanger,   c) cooling and liquefying a first gas stream in the second heat exchanger by heat exchange with the second refrigeration cycle to produce a liquefied first gas stream, wherein the liquefied first gas stream is at a first pressure;   d) expanding a second gas stream to a second pressure to produce an expanded second gas stream; and   e) warming the expanded second gas stream in the second heat exchanger to produce a warmed gas stream,   wherein a portion of a first refrigeration gas within the first refrigeration cycle is withdrawn and liquefied yielding a liquid first refrigeration gas product, wherein at least an equal portion of gaseous first refrigeration gas is introduced to the first refrigeration cycle as is withdrawn as liquid first refrigeration gas product,   wherein step e), in addition to the refrigeration provided by the second refrigeration cycle, provides the refrigeration used to cool and liquefy the first gas stream, and   wherein the first refrigeration cycle and the second refrigeration cycle share a common recycle compressor.   
     
     
         17 . The method as claimed in  claim 16 , wherein the first refrigeration cycle is selected from the group consisting of a nitrogen refrigeration cycle and a hydrogen refrigeration cycle. 
     
     
         18 . The method as claimed in  claim 16 , wherein the first gas stream liquefied in step c) is derived from the expanded second gas stream, wherein the first pressure and the second pressure are about the same. 
     
     
         19 . The method as claimed in  claim 16 , wherein the second refrigeration cycle is selected from the group consisting of a nitrogen refrigeration cycle and a hydrogen refrigeration cycle. 
     
     
         20 . The method as claimed in  claim 16 , wherein the first gas stream cooled and liquefied in step c) comprises natural gas. 
     
     
         21 . The method as claimed in  claim 16 , wherein the second gas stream expanded in step d) comprises natural gas. 
     
     
         22 . The method as claimed in  claim 16 , wherein the liquid first refrigeration gas product is liquid nitrogen. 
     
     
         23 . A method for the integration of a first liquefier and a second liquefier for the production of a first liquefied gas and a second liquefied gas, the method comprising the steps of:
 a) providing a first liquefier having a first refrigeration cycle using a first refrigerant, wherein the first refrigeration cycle is configured to provide refrigeration within a first heat exchanger;   b) providing a second liquefier having a second refrigeration cycle using a second refrigerant, wherein the second refrigeration cycle is configured to provide refrigeration within a second heat exchanger;   c) cooling a first gas stream in the first heat exchanger by heat exchange with the first refrigeration cycle to produce a cooled first gas stream;   d) cooling a second gas stream in the second heat exchanger by heat exchange with the second refrigeration cycle to produce a cooled second gas stream;   e) expanding a third gas stream to produce an expanded third gas stream; and   f) warming the expanded third gas stream in a heat exchanger selected from the group consisting of the first heat exchanger, the second heat exchanger, and combinations thereof, to produce a warmed gas stream,   wherein step f), in addition to the refrigeration provided by the second refrigeration cycle, provides the refrigeration used to cool the second gas stream,   wherein step f), in addition to the refrigeration provided by the first refrigeration cycle, provides the refrigeration used to cool the first gas stream, and   wherein the first refrigeration cycle and the second refrigeration cycle share a common recycle compressor.   
     
     
         24 . The method as claimed in  claim 23 , wherein the first and second refrigeration cycles are nitrogen refrigeration cycles. 
     
     
         25 . The method as claimed in  claim 23 , wherein the first refrigerant and the second refrigerant have the same composition. 
     
     
         26 . The method as claimed in  claim 23 , wherein the first gas stream is selected from the group consisting of natural gas, ethane, ethylene, acetylene, other C 3 -C 6  alkanes, alkenes, and alkynes, and nitrogen, and wherein the first gas stream is liquefied during cooling step c). 
     
     
         27 . The method as claimed in  claim 23 , wherein the first gas stream is selected from the group consisting of hydrogen and helium, wherein the first gas stream is not liquefied during cooling step c). 
     
     
         28 . The method as claimed in  claim 23 , wherein the third gas stream expanded in step e) comprises natural gas. 
     
     
         29 . The method as claimed in  claim 23 , wherein a portion of the first refrigerant within the first refrigeration cycle is withdrawn and liquefied yielding a liquid first refrigerant product, wherein at least an equal portion of gaseous first refrigerant is introduced to the first refrigeration cycle as is withdrawn as liquid first refrigerant, 
     
     
         30 . The method as claimed in  claim 23 , wherein a portion of the second refrigerant within the second refrigeration cycle is withdrawn and liquefied yielding a liquid second refrigerant, wherein at least an equal portion of the second refrigerant is introduced to the second refrigeration cycle as is withdrawn as liquid second refrigerant.