Intermediate pressure lng refluxed ngl recovery process

Abstract

Liquefied natural gas (LNG) facility employing an intermediate pressure distillation column for recovery of ethane and heavier components from the processed natural gas stream in a way that increases operational stability and minimizes capital and operating costs.

1 . A process for liquefying a natural gas stream, said process comprising:
 (a) cooling at least a portion of said natural gas stream;   (b) expanding a vapor portion of the cooled natural gas stream in a turboexpander;   (c) introducing a liquid portion of the cooled natural gas stream into a distillation column; and   (d) using work produced by said turboexpander to compress at least a portion of said natural gas stream upstream of said distillation column.   
     
     
         2 . The process of  claim 1 , further comprising separating the cooled natural gas stream into said vapor and liquid portions upstream of said distillation column. 
     
     
         3 . The process of  claim 1 , further comprising introducing at least a portion of the expanded stream from said turboexpander into said distillation column at a location above the location where said liquid portion is introduced into said distillation column. 
     
     
         4 . The process of  claim 1 , further comprising introducing a reflux stream into said distillation column. 
     
     
         5 . The process of  claim 4 , wherein said reflux stream originates from an overhead stream produced from said distillation column. 
     
     
         6 . The process of  claim 5 , further comprising compressing and cooling at least a portion of said reflux stream prior to introduction into said distillation column. 
     
     
         7 . The process of  claim 6 , wherein at least a portion of said cooling of said reflux stream is provided by indirect heat exchange with a predominately methane stream. 
     
     
         8 . The process of  claim 1 , wherein said distillation column is the only distillation column employed in said process. 
     
     
         9 . The process of  claim 1 , wherein said process employs a first refrigeration cycle utilizing a predominately propane and/or propylene refrigerant, a second refrigeration cycle utilizing a predominately ethane and/or ethylene refrigerant, an open methane refrigeration cycle. 
     
     
         10 . A process comprising: vaporizing LNG produced by the process of  claim 1 . 
     
     
         11 . A process comprising: using a computer to simulate the process of  claim 1 . 
     
     
         12 . A process for liquefying a natural gas stream, said process comprising:
 (a) using a distillation column to separate at least a portion of said natural gas stream into an overhead stream and a bottom stream;   (b) cooling at least a portion of said overhead stream via indirect heat exchange with a predominately methane refrigerant stream; and   (c) using at least a portion of the cooled overhead stream as a reflux stream in said distillation column.   
     
     
         13 . The process of  claim 12 , further comprising compressing at least a portion of said overhead stream in a methane compressor, wherein at least a portion of said reflux stream is derived from the compressed overhead stream. 
     
     
         14 . The process of  claim 13 , wherein at least a portion of said cooling of said overhead stream with said predominately methane stream takes place after said compressing of said overhead stream. 
     
     
         15 . The process of  claim 12 , wherein at least a portion of said predominately methane refrigerant stream is derived from said overhead stream. 
     
     
         16 . The process of  claim 12 , further comprising cooling at least a portion of said overhead stream via indirect heat exchange with a second refrigerant stream having a higher boiling point than said predominately methane refrigerant stream. 
     
     
         17 . The process of  claim 16 , wherein said second refrigerant stream comprises predominately propane and/or propylene. 
     
     
         18 . The process of  claim 16 , further comprising cooling at least a portion of said overhead stream via indirect heat exchange with a third refrigerant stream having a boiling point lower than second refrigerant and higher than said predominately methane refrigerant stream. 
     
     
         19 . The process of  claim 18 , wherein said second refrigerant stream comprises predominately propane and/or propylene and said third refrigerant stream comprises predominately ethane and/or ethylene. 
     
     
         20 . The process of  claim 12 , further comprising using at least a portion of said overhead stream to cool at least a portion of said natural gas stream. 
     
     
         21 . The process of  claim 12 , further comprising separating at least a portion of said natural gas stream into a predominately vapor fraction and a predominately liquid fraction, introducing at least a portion of said predominately liquid fraction into said distillation column, expanding at least a portion of said predominately vapor fraction in a turboexpander, and introducing at least a portion of the resulting expanded stream into said distillation column. 
     
     
         22 . A process comprising: vaporizing LNG produced by the process of  claim 12 . 
     
     
         23 . A process comprising: using a computer to simulate the process of  claim 12 . 
     
     
         24 . A process for liquefying a natural gas stream, said process comprising:
 (a) using a distillation column to separate at least a portion of said natural gas stream into an overhead stream and a bottom stream;   (b) withdrawing a side stream from said distillation column; and   (c) heating at least a portion of said side stream via indirect heat exchange with at least a portion of said natural gas stream upstream of said distillation column to thereby produce a heated side stream.   
     
     
         25 . The process of  claim 24 , further comprising introducing at least a portion of said heated side stream into said distillation column at a location below the location where said side stream is withdrawn. 
     
     
         26 . The process of  claim 24 , wherein said heating of step (c) causes cooling of said natural gas stream. 
     
     
         27 . The process of  claim 24 , further comprising, separating at least a portion of said natural gas stream into a predominately vapor fraction and a predominately liquid fraction, introducing at least a portion of said predominately liquid fraction into said distillation column, expanding at least a portion of said predominately vapor fraction in a turboexpander, and introducing at least a portion of the resulting expanded stream into said distillation column. 
     
     
         28 . The process of  claim 27 , wherein said turboexpander produces useful work that is employed elsewhere in said process. 
     
     
         29 . The process of  claim 28 , wherein at least a portion of said useful work is used to compress a process stream. 
     
     
         30 . The process of  claim 29 , wherein said process stream comprises predominately methane. 
     
     
         31 . The process of  claim 24 , wherein said distillation column is equipped with a bottoms reboiler. 
     
     
         32 . The process of  claim 24 , wherein the overhead pressure of said distillation column is less than about 550 psia. 
     
     
         33 . The process of  claim 24 , wherein said distillation column is the only distillation column employed in said process. 
     
     
         34 . The process of  claim 24 , wherein said process is a cascade-type LNG process. 
     
     
         35 . A process comprising: vaporizing LNG produced by the process of  claim 24 . 
     
     
         36 . A process comprising: using a computer to simulate the process of  claim 24 . 
     
     
         37 . A process for liquefying a natural gas stream, said process comprising:
 (a) using a distillation column to separate at least a portion of said natural gas stream into an overhead stream and a bottom stream;   (b) introducing at least a portion of said overhead stream into a vapor/liquid separator;   (c) compressing at least a portion of a predominately vapor stream produced from said phase separator to thereby provide a high-pressure stream;   (d) introducing a first fraction of said high-pressure stream into said distillation column; and   (e) introducing a second fraction of said high-pressure stream into said vapor/liquid separator.   
     
     
         38 . The process of  claim 37 , wherein said first fraction of said high-pressure stream is provided as a reflux stream to said distillation column. 
     
     
         39 . The process of  claim 37 , further comprising expanding said second fraction prior to step (e). 
     
     
         40 . The process of  claim 37 , further comprising cooling and at least partially condensing at least a portion of said high-pressure stream prior to steps (d) and (e). 
     
     
         41 . The process of  claim 40 , wherein said at least a portion of said cooling of said high-pressure stream is provided by indirect heat exchange with a predominately methane refrigerant stream. 
     
     
         42 . The process of  claim 37 , wherein said at least a portion of said cooling of said high-pressure stream is provided by indirect heat exchange with a predominately propane and/or propylene refrigerant stream. 
     
     
         43 . The process of  claim 37 , wherein said at least a portion of said cooling of said high-pressure stream is provided by indirect heat exchange with a predominately ethane and/or ethylene refrigerant stream. 
     
     
         44 . The process of  claim 37 , further comprising, separating at least a portion of said natural gas stream into a predominately vapor fraction and a predominately liquid fraction, introducing at least a portion of said predominately liquid fraction into said distillation column, expanding at least a portion of said predominately vapor fraction in a turboexpander, and introducing at least a portion of the resulting expanded stream into said distillation column. 
     
     
         45 . A process comprising: vaporizing LNG produced by the process of  claim 37 . 
     
     
         46 . A process comprising: using a computer to simulate the process of  claim 37 .