Integrated process for ngl (natural gas liquids recovery) and lng (liquefaction of natural gas)

Abstract

The invention relates to an integrated process and apparatus for liquefaction of natural gas and recovery of natural gas liquids. In particular, the improved process and apparatus reduces the energy consumption of a Liquefied Natural Gas (LNG) unit by using a portion of the already cooled overhead vapor from a fractionation column from an NGL (natural gas liquefaction) unit to, depending upon composition, provide, for example, reflux for fractionation in the NGL unit and/or a cold feed for the LNG unit, or by cooling, within the NGL unit, a residue gas originating from a fractionation column of the NGL unit and using the resultant cooled residue gas to, depending upon composition, provide, for example, reflux/feed for fractionation in the NGL and/or a cold feed for the LNG unit, thereby reducing the energy consumption of the LNG unit and rendering the process more energy-efficient.

1 . A process for integrated liquefaction of natural gas and recovery of natural gas liquids, said process comprising:
 cooling a feed stream containing light hydrocarbons in one or more heat exchangers, wherein said feed stream is cooled and partially condensed by indirect heat exchange;   introducing the partially condensed feed stream into a gas/liquid cold separator producing an overhead gaseous stream and bottoms liquid stream which are to be introduced into a fractionation system, said fractionation system comprising a demethanizer column;   expanding at least a portion of the overhead gaseous stream from the gas/liquid cold separator and introducing the expanded portion of said overhead gaseous stream into an upper region of said demethanizer column;   introducing at least a portion of the bottoms liquid stream from said gas/liquid cold separator into said demethanizer column at an intermediate point thereof;   removing a liquid product stream from the bottom of said demethanizer column; and   removing a overhead gaseous stream from the top of said demethanizer column,   said process further comprising:   
       (A)
 removing a portion of the overhead gaseous stream from the demethanizer column as a side stream, and partially liquefying said side stream by heat exchange; 
 introducing the partially liquefied side stream into a further separation means, recovering liquid product from said further separation means and introducing the recovered liquid product into said demethanizer column as a liquid reflux stream; and 
 recovering an overhead vapor stream from said further separation means, subjecting said overhead vapor stream from said further separation means to indirect heat exchange for additional cooling and partial condensation, and removing the resultant condensate from said partial condensation as liquefied natural gas product; 
  or 
 
       (B)
 subjecting at least a portion of said overhead gaseous from the demethanizer column to heat exchange wherein said overhead gaseous from the demethanizer column is used to cool at least one other process stream, and then compressing the least a portion of said overhead gaseous from the demethanizer column from the heat exchange to form a residue gas; 
 cooling at least portion of said residue gas to obtain a cooled residue gas; 
 introducing a part of the cooled residue gas into said demethanizer column as a reflux stream; and 
 introducing another part of the cooled residue gas into a further separation means, and recovering liquefied natural gas product from said further separation means. 
 
     
     
         2 . (canceled) 
     
     
         3 . (canceled) 
     
     
         4 . (canceled) 
     
     
         5 . The process according to  claim 1 , wherein:
 said feed stream containing light hydrocarbons is split into at least a first partial stream and a second partial stream;   introducing said first partial stream of the feed stream into a main heat exchanger wherein said first partial stream of the feed stream is cooled and partially condensed by indirect heat exchange with process streams removed from said demethanizer column;   introducing said second partial stream of the feed stream into another heat exchanger wherein said second partial stream of the feed stream is cooled and partially condensed by indirect heat exchange at least a portion of the overhead gaseous stream from said demethanizer column;   recombining said first and second partial streams of the feed stream, and optionally subjecting the resultant recombined feed stream to heat exchange with a refrigerant; and   introducing the recombined feed stream into said gas/liquid cold separator to produce said overhead gaseous stream and said bottoms liquid stream.   
     
     
         6 - 16 . (canceled) 
     
     
         17 . An apparatus for integration of liquefaction of natural gas and recovery of natural gas liquids, said apparatus comprising:
 one or more heat exchangers for cooling and partially condensing by indirect heat exchange a feed stream containing light hydrocarbons;   a gas/liquid cold separator and means for introducing a partially condensed feed stream from the one or more heat exchangers into the gas/liquid cold separator, the gas/liquid cold separator having upper outlet means for removing an overhead gaseous stream and lower outlet means for removing a bottoms liquid stream;   means for introducing overhead gaseous stream and bottoms liquid stream from the gas/liquid cold separator into a fractionation system comprising a demethanizer column, the means comprising an expansion device for expanding at least a portion of overhead gaseous stream from the gas/liquid cold separator and means for introducing expanded overhead gaseous stream into an upper region of a demethanizer column, and means for introducing at least a portion of bottoms liquid stream from the gas/liquid cold separator into a demethanizer column at an intermediate point thereof;   means for removing a liquid product stream from the bottom of the demethanizer column;   means for removing a overhead gaseous stream from the top of the demethanizer column, and   
       said apparatus further comprising: 
       (A)
 (i) a heat exchanger for subjecting a first portion of the overhead gaseous stream from the demethanizer column to indirect heat exchange with a stream obtained by combining a portion of the overhead gaseous stream from the gas/liquid cold separator and a portion of the bottoms liquid stream from gas/liquid cold separator to obtain a residue gas; 
 (ii) means for removing a second portion of the overhead gaseous from the demethanizer column as a side stream, and a further heat exchanger for partially liquefying the side stream by heat exchange; 
 (iii) means for introducing the partially liquefied side stream into a further separation means, means for recovering liquid product from the further separation means and introducing the recovered liquid product into the demethanizer column as a liquid reflux stream, and 
 (iv) means for recovering an overhead vapor stream from the further separation means, a further heat exchange means for subjecting this overhead vapor stream to indirect heat exchange for additional cooling and partial condensation, and means for removing the resultant condensate as a final LNG liquid product; or 
 
       (B)
 (i) a heat exchanger for subjecting the demethanizer column overhead gaseous stream to indirect heat exchange with a stream obtained by combining a portion of the overhead gaseous stream from the gas/liquid cold separator and a portion of the bottoms liquid stream from gas/liquid cold separator; 
 (ii) means for subjecting the overhead gaseous stream from the demethanizer column to further heating and a compressor for compressing the overhead gaseous stream from the demethanizer column to produce a residue gas; 
 (iii) a further heat exchanger for cooling at least a portion of the residue gas whereby the portion of the residue gas is partially liquefied; 
 (iv) means for introducing this partially liquefied residue gas into a further separation means; 
 (v) means for recovering liquid product from the further separation means and introducing the recovered liquid product as reflux to the demethanizer column; 
 (vi) means for recovering an overhead vapor stream from the further separation means, means for subjecting this overhead vapor stream to heat exchange whereby the overhead vapor stream is partially liquefied; 
 (vii) means for introducing this partially liquefied overhead vapor stream into another further separation means; and 
 (viii) means for recovering LNG liquid product from the another further separation means. 
 
     
     
         18 . (canceled) 
     
     
         19 . The process according to  claim 1 , wherein said process comprises:
 removing a portion of the overhead gaseous from the demethanizer column as a side stream, and partially liquefying said side stream by heat exchange;   introducing the partially liquefied side stream into a further separation means, recovering liquid product from said further separation means and introducing the recovered liquid product into said demethanizer column as a liquid reflux stream; and   recovering an overhead vapor stream from said further separation means, subjecting said overhead vapor stream from said further separation means to indirect heat exchange for additional cooling and partial condensation, and removing the resultant condensate from said partial condensation as liquefied natural gas product.   
     
     
         20 . The process according to  claim 1 , wherein said process comprises:
 subjecting at least a portion of said overhead gaseous from the demethanizer column to heat exchange wherein said overhead gaseous from the demethanizer column is used to cool at least one other process stream, and then compressing the least a portion of said overhead gaseous from the demethanizer column from the heat exchange to form a residue gas;   cooling at least portion of said residue gas to obtain a cooled residue gas;   introducing a part of the cooled residue gas into said demethanizer column as a reflux stream; and   introducing another part of the cooled residue gas into a further separation means, and recovering liquefied natural gas product from said further separation means.   
     
     
         21 . The process according to  claim 1 , wherein said process further comprises:
 dividing said bottoms liquid stream from said gas/liquid cold separator into at least a first portion and a second portion;   dividing said overhead gaseous stream from said gas/liquid cold separator into at least a first portion and a second portion;   expanding said first portion of said bottoms liquid stream from said gas/liquid cold separator and introducing the expanded first portion of said bottoms liquid stream from said gas/liquid cold separator into said demethanizer column at said intermediate point;   expanding said first portion of said overhead gaseous stream from said gas/liquid cold separator and introducing the expanded first portion of said overhead gaseous stream from said gas/liquid cold separator into said upper region of said demethanizer column;   combining said second portion of said bottoms liquid stream from said gas/liquid cold separator with said second portion of said overhead gaseous stream from said gas/liquid cold separator;   cooling the resultant combined cold separator stream by indirect heat exchange with at least a portion of said overhead vapor from said demethanizer column, whereby the combined cold separator stream is cooled and partially condensed and the overhead gaseous stream from the top of said demethanizer column is heated; and   expanding the cooled resultant combined cold separator stream, and then introducing the expanded cooled combined cold separator stream into the top of said demethanizer column.   
     
     
         22 . The process according to  claim 5 , wherein said process further comprises introducing said liquid product stream removed from the bottom of said demethanizer column into said main heat exchanger for indirect heat exchange with said first partial stream of the feed stream. 
     
     
         23 . The process according to  claim 5 , wherein said process further comprises:
 dividing said bottoms liquid stream from said gas/liquid cold separator into at least a first portion and a second portion;   dividing said overhead gaseous stream from said gas/liquid cold separator into at least a first portion and a second portion;   expanding said first portion of said bottoms liquid stream from said gas/liquid cold separator and introducing the expanded first portion of said bottoms liquid stream from said gas/liquid cold separator into said demethanizer column at said intermediate point;   expanding said first portion of said overhead gaseous stream from said gas/liquid cold separator and introducing the expanded first portion of said overhead gaseous stream from said gas/liquid cold separator into said upper region of said demethanizer column;   combining said second portion of said bottoms liquid stream from said gas/liquid cold separator with said second portion of said overhead gaseous stream from said gas/liquid cold separator;   cooling the resultant combined cold separator stream by indirect heat exchange with at least a portion of said overhead vapor from said demethanizer column, whereby the combined cold separator stream is cooled and partially condensed and the overhead gaseous stream from the top of said demethanizer is heated; and   expanding the cooled resultant combined cold separator stream, and then introducing the expanded cooled combined cold separator stream into the top of said demethanizer column.   
     
     
         24 . The process according to  claim 23 , wherein said process further comprises:
 after said overhead gaseous stream from the top of said demethanizer column is subjected to indirect heat exchange with the combined cold separator stream, further heating said overhead gaseous stream from the top of said demethanizer by indirect heat exchange with said second partial feed stream in said another heat exchanger, and then compressing and removing at least a portion of the overhead gaseous stream from said demethanizer as said residue gas;   introducing at least a portion of said residue gas stream from the overhead gaseous stream of said demethanizer into said another heat exchanger wherein the residue gas stream is cooled by indirect heat exchange, and then subjecting the cooled residue gas stream to further indirect heat exchange with said overhead gaseous stream from the top of said demethanizer whereby the residue gas stream is further cooled and partially liquefied;   expanding a first portion of the further cooled residue gas stream and introducing the resultant partially liquefied first portion of the residue gas stream into the upper region of said demethanizer as said reflux stream; and   introducing a second portion of the further cooled residue gas stream into said further separation means, recovering an overhead residue gas stream from said further separation means, recovering a liquid stream from said further separation means as said liquefied natural gas.   
     
     
         25 . The process according to  claim 21 , wherein said process further comprises:
 dividing said overhead vapor from said demethanizer column into at least a first portion and a second portion, wherein said second portion of said overhead vapor from said demethanizer column forms said side stream; and   using the first portion of said overhead vapor from said demethanizer column to cool said resultant combined cold separator stream by said indirect heat exchange, whereby the combined cold separator stream is cooled and partially condensed and the o first portion of overhead gaseous stream from the top of said demethanizer column is heated.   
     
     
         26 . The process according to  claim 21 , wherein said process further comprises:
 after said overhead gaseous stream from the top of said demethanizer column is subjected to indirect heat exchange with the combined cold separator stream, further heating said overhead gaseous stream from the top of said demethanizer by indirect heat exchange with said second partial feed stream in said another heat exchanger, and then compressing and removing at least a portion of the overhead gaseous stream from said demethanizer as residue gas.   
     
     
         27 . The process according to  claim 25 , wherein said process further comprises:
 after said overhead gaseous stream from the top of said demethanizer column is subjected to indirect heat exchange with the combined cold separator stream, further heating said overhead gaseous stream from the top of said demethanizer by indirect heat exchange with said second partial feed stream in said another heat exchanger, and then compressing and removing at least a portion of the overhead gaseous stream from said demethanizer as residue gas.   
     
     
         28 . The process according to  claim 20 , wherein said process further comprises:
 introducing the cooled residue gas into a separation means and recovering a residue liquid stream from said separation means as said part of the cooled residue gas and recovering an overhead gas stream from said separation means as said another part of the cooled residue gas;   introducing said part of the cooled residue gas into the top region of said demethanizer as said reflux stream; and   cooling said another part of the cooled residue gas by indirect heat exchange to produce a further cooled residue gas, expanding said further cooled residue gas and introducing the expanded further cooled residue gas into a said further separation means, recovering an overhead stream from said further separation means as a further residue gas, and recovering a liquid stream from said further separation means as said liquefied natural gas product.   
     
     
         29 . The process according to  claim 20 , wherein
 said at least a portion of said residue gas is cooled by indirect heat exchange with at least a portion of the overhead gaseous stream of the demethanizer column to form said cooled residue;   expanding a portion of the cooled residue gas stream to form said part of the cooled residue gas and introducing said part of the cooled residue gas into an upper region of said demethanizer column as said reflux stream, and   expanding another portion of the residue gas stream and introducing the resultant expanded another portion as said another part of the cooled residue gas into said further separation means.   
     
     
         30 . The process according to  claim 20 , wherein
 said at least a portion of said residue gas is cooled by indirect heat exchange with at least a portion of the overhead gaseous stream of the demethanizer column to form said cooled residue;   dividing said cooled residue gas stream into at least a first portion and a second portion   expanding the first portion of the cooled residue gas stream and introducing the resultant expanded first portion of the cooled residue gas stream into an upper region of said demethanizer,   further cooling and partially condensing the second portion of the cooled residue gas stream by indirect heat exchange, and then introducing the cooled and partially condensed second portion of the residue gas stream into a separation means, recovering a residue liquid stream from said separation means and introducing the residue liquid stream into the top region of said demethanizer as said reflux stream; and   recovering an overhead gas stream from said separation means, cooling said overhead gas stream from said separation means by indirect heat exchange, expanding the further cooled overhead gas stream from said separation means and introducing this expanded further cooled overhead gas stream from said separation means into said further separation means.   
     
     
         31 . The process for integrated liquefaction of natural gas and recovery of natural gas liquids, said process comprising:
 cooling a feed stream containing light hydrocarbons by indirect heat exchange in a feed heat exchanger;   introducing the cooled feed stream into a gas/liquid cold separator, removing from said gas/liquid cold separator an overhead gaseous stream and bottoms liquid stream, and introducing said overhead gaseous stream and bottoms liquid stream into a fractionation system, said fractionation system comprising a demethanizer column;   removing a liquid product stream from said fractionation system;   removing an overhead gaseous stream from said fractionation system;   generating a residue gas stream from said overhead gaseous stream from said fractionation system;   introducing said residue gas stream into a further separation means, and recovering from said further separation means a liquid product stream and an overhead vapor stream;   introducing either said liquid product stream or said overhead vapor stream to an LNG exchanger/separator;   subjecting either said liquid product stream or said overhead vapor stream to liquefaction in said LNG exchanger/separator; and   removing LNG liquid product from said LNG exchanger/separator.   
     
     
         32 . The process according to  claim 31 , said process further comprising:
 splitting said overhead gaseous stream from said gas/liquid cold separator into a first cold separator overhead gaseous stream and a second cold separator overhead gaseous stream;   splitting said bottoms liquid stream from said gas/liquid cold separator into a first cold separator bottoms liquid stream and a second cold separator bottoms liquid stream;   introducing said first cold separator overhead gaseous stream and said cold separator first bottoms liquid stream into said demethanizer;   combining said second cold separator overhead gaseous stream and said second cold separator bottoms liquid stream;   splitting an overhead gaseous stream from said demethanizer into a first demethanizer overhead gaseous stream and a second demethanizer overhead gaseous stream;   heating said first demethanizer overhead gaseous stream by indirect heat exchange with the combined second cold separator overhead gaseous stream and second cold separator bottoms liquid stream;   cooling said second demethanizer overhead gaseous stream by heat exchange;   introducing the cooled second demethanizer overhead gaseous stream into said further separation means as said residue gas;   introducing said liquid product stream from said further separation means into said demethanizer as said liquid reflux stream; and   introducing said gaseous vapor stream from said further separation means into said LNG exchanger/separator.   
     
     
         33 . The process according to  claim 31 , said process further comprising:
 splitting said overhead gaseous stream from said gas/liquid cold separator into a first cold separator overhead gaseous stream and a second cold separator overhead gaseous stream;   splitting said bottoms liquid stream from said gas/liquid cold separator into a first cold separator bottoms liquid stream and a second cold separator bottoms liquid stream;   introducing said first cold separator overhead gaseous stream and said cold separator first bottoms liquid stream into said demethanizer;   combining said second cold separator overhead gaseous stream and said second cold separator bottoms liquid stream;   heating an overhead gaseous stream said demethanizer by indirect heat exchange with the combined second cold separator overhead gaseous stream and second cold separator bottoms liquid stream;   heating and compressing the heated overhead gaseous stream from said demethanizer column to produce said residue gas;   cooling said residue gas and introducing the cooled residue gas into said further separation means;   introducing said liquid product stream from said further separation means into said demethanizer as said liquid reflux stream; and   introducing said gaseous vapor stream from said further separation means into said LNG exchanger/separator.   
     
     
         34 . The process according to  claim 31 , wherein said fractionation system comprises a demethanizer column, and said process further comprises:
 splitting said feed stream containing light hydrocarbons into a first partial feed stream and a second partial feed stream;   cooling said first partial feed stream in said feed heat exchanger by indirect heat exchange;   cooling said second partial feed stream in another heat exchanger by indirect heat exchange;   recombining said first and second partial feed streams, and optionally cooling the resultant recombined feed stream by heat exchange with a refrigerant; and   introducing the recombined feed stream into said gas/liquid cold separator.   
     
     
         35 . The process according to  claim 34 , wherein said fractionation system comprises a demethanizer column, and said process further comprises splitting said overhead gaseous stream from said gas/liquid cold separator into a first cold separator overhead gaseous stream and a second cold separator overhead gaseous stream;
 splitting said bottoms liquid stream from said gas/liquid cold separator into a first cold separator bottoms liquid stream and a second cold separator bottoms liquid stream;   expanding said first cold separator overhead gaseous stream and introducing the expanded first cold separator overhead gaseous stream into an upper region of said demethanizer column;   expanding said cold separator first bottoms liquid stream and introducing the expanded cold separator first bottoms liquid stream into an intermediate region of said demethanizer; and   combining said second cold separator overhead gaseous stream and said second cold separator bottoms liquid stream.   
     
     
         36 . The process for integrated liquefaction of natural gas and recovery of natural gas liquids, said process comprising:
 cooling a feed stream ( 1 ) containing light hydrocarbons by indirect heat exchange in a feed heat exchanger ( 2 );introducing the cooled feed stream into a gas/liquid cold separator ( 3 ), removing from said gas/liquid cold separator ( 3 ) an overhead gaseous stream ( 4 ) and bottoms liquid stream ( 8 ), and introducing said overhead gaseous stream ( 4 ) and bottoms liquid stream ( 8 ) into a fractionation system, said fractionation system comprising a demethanizer column;   removing a liquid product stream ( 15 ) of natural gas liquids from said fractionation system;   removing an overhead gaseous stream ( 12 ) from said fractionation system;   generating a residue gas stream ( 23 ,  59 ) from said overhead gaseous stream from said fractionation system;   cooling ( 48 ) said residue gas stream, introducing the cooled residue gas stream into a further gas/liquid separator or further distillation column ( 26 ), and removing from said further gas/liquid separator or further distillation column ( 26 ) a liquid stream ( 27 ) and an overhead vapor stream ( 28 );   introducing said liquid stream ( 27 ) from said further gas/liquid separator or further distillation column ( 26 ) into said light ends fractionation column ( 7 ), said heavy ends fractionation column ( 9 ) or said demethanizer ( 62 ) of said fractionation system as a liquid reflux stream;   introducing said overhead vapor stream ( 28 ) from said further gas/liquid separator or further distillation column ( 26 ) to a heat exchanger ( 48 ) wherein said overhead vapor stream is cooled;   introducing the cooled overhead vapor stream ( 29 ) into a separator ( 50 ); and   removing a liquid product of liquefied natural gas from said separator.