Methods for providing refrigeration in natural gas liquids recovery plants

Abstract

A process and plant for natural gas liquids (NGL) recovery includes a main heat exchanger, a cold gas/liquid separator, a separation or distillation column, and an overhead gas heat exchanger. A pressurized residue gas generated from an overhead gas stream removed the top of the separation or distillation column is expanded and used as a cooling medium in the overhead gas heat exchanger and the main heat exchanger. The expanded residue gas, used as a cooling medium, is then compressed up to a pressure to be combined with the overhead stream from the separation or distillation column.

1 . A process for natural gas liquids (NGL) recovery comprising:
 introducing a natural gas feed stream into a main heat exchanger wherein the feed stream is cooled and partially condensed,   introducing the partially condensed feed stream into a cold gas/liquid separator wherein the partially condensed feed stream is separated into a liquid fraction and a gaseous fraction,   introducing the liquid fraction into a separation or distillation column,   separating the gaseous fraction into a first portion and a second portion,   cooling the first portion of the gaseous fraction in an overhead heat exchanger by indirect heat exchange with an overhead gaseous stream removed from the top of the separation or distillation column, and introducing the cooled and partially condensed first portion of the gaseous fraction into the separation or distillation column at a point above the introduction point of the liquid fraction into the separation or distillation column,   expanding the second portion of the gaseous fraction and introducing the expanded second portion of the gaseous fraction into the separation or distillation column at a point above the introduction point of the liquid fraction into the separation or distillation column,   removing a C2+ or C3+ liquid product stream (NGL) from the bottom of the separation or distillation column,   removing the overhead gaseous stream from the top of the separation or distillation column, the overhead gaseous stream being enriched with methane,   using the overhead gaseous stream as a cooling medium in the overhead heat exchanger and then in the main heat exchanger,   compressing the overhead gaseous stream in a residue gas compression unit to obtain a pressurized residue gas stream,   expanding a portion of the pressurized residue gas stream and using the expanded residue gas as a cooling medium in the overhead heat exchanger and in the main heat exchanger, and   compressing the expanded residue gas used as a cooling medium to form a compressed residue gas stream and then combining the compressed residue gas stream with the overhead gaseous stream upstream of the residue gas compression unit.   
     
     
         2 . The process according to  claim 1 , wherein the separation or distillation column is a demethanizer. 
     
     
         3 . The process according to  claim 1 , wherein the separation or distillation column is a deethanizer. 
     
     
         4 . The process according to  claim 1 , wherein the gas feed stream is compressed by a feed compressor prior to being introduced into said main heat exchanger. 
     
     
         5 . The process according to  claim 4 , wherein expansion of the second portion of the gaseous fraction is performed in a turbo-expanded which is coupled to said feed compressor. 
     
     
         6 . The process according to  claim 1 , wherein cooled first portion of the gas fraction is expanded via an expansion valve before being introduced into the separation or distillation column. 
     
     
         7 . The process according to  claim 1 , wherein the liquid fraction from the cold gas/liquid separator is expanded via an expansion valve before being introduced into a lower region of the separation or distillation column. 
     
     
         8 . The process according to  claim 1 , wherein the liquid fraction from the cold gas/liquid separator is split into a first liquid substream and a second liquid substream, the first liquid substream is expanded via an expansion valve and then introduced into a lower region of the separation or distillation column, and the second liquid substream is combined with the first portion of the gaseous fraction from the cold gas/liquid separator and the resultant combined stream is cooled in the overhead heat exchanger by heat exchange with the overhead gaseous stream removed from the top of the separation or distillation column. 
     
     
         9 . The process according to  claim 8 , wherein said combined stream is expanded via an expansion valve and before being introduced into an upper region of the separation or distillation column. 
     
     
         10 . The process according to  claim 1 , wherein said portion of the compressed residue gas that is to be expanded is sent directly to a turbo-expander for expansion and the resultant expanded residue gas portion is then used as a cooling medium in the overhead heat exchanger and in the main heat exchanger. 
     
     
         11 . The process according to  claim 1 , wherein said portion of the compressed residue gas that is to be expanded is first cooled in the main heat exchanger and then is sent to a turbo-expander for expansion. 
     
     
         12 . The process according to  claim 1 , wherein a further portion of the compressed residue gas is cooled in the main heat exchanger and the overhead heat exchanger, expanded in an expansion valve, and introduced into the upper region of the separation or distillation column as a reflux stream. 
     
     
         13 . The process according to  claim 1 , wherein the separation or distillation column is a deethanizer and said liquid fraction from said cold gas/liquid separator is first expanded via an expansion valve then introduced into said main heat exchanger as a cooling medium, and then and introduced into a lower region of the separation or distillation column. 
     
     
         14 . A plant for natural gas liquids (NGL) recovery comprising:
 a main heat exchanger for cooling and partially condensed a natural gas feed stream,   a separation or distillation column for separating the natural gas feed stream into a C2+ or C3+ liquid product stream and an overhead gaseous stream enriched in methane,   a cold gas/liquid separator wherein the partially condensed feed stream is separated into a liquid fraction and a gaseous fraction,   a pipeline for removing the liquid fraction from the bottom of the cold gas/liquid separator and introducing the liquid fraction into the separation or distillation column,   means for separating the gaseous fraction into a first portion and a second portion,   an overhead heat exchanger for cooling the first portion of the gaseous fraction by indirect heat exchange with an overhead gaseous stream removed from the top of the separation or distillation column,   a pipeline for removing the cooled first portion of the gaseous fraction from the overhead heat exchanger and introducing the cooled first portion into the separation or distillation column at a point above the introduction point of the liquid fraction into the separation or distillation column,   means for expanding the second portion of the gaseous fraction,   a pipeline for removing the expanded first portion of the gaseous fraction from the means for expanding and introducing the expanded second portion of the gaseous fraction into the separation or distillation column at a point above the introduction point of the liquid fraction into the separation or distillation column,   a bottom outlet for removing the C2+ or C3+ liquid product stream the bottom of the separation or distillation column,   a top outlet for removing the overhead gaseous stream from the top of the separation or distillation column,   a residue gas compression unit for compressing the overhead gaseous stream to obtain a pressurized residue gas stream,   means for expanding a portion of the pressurized residue gas stream to form an expanded residue gas stream,   a pipeline for removing the expanded residue gas stream from the means for expanding and introducing the expanded residue gas stream into overhead heat exchanger as a cooling medium,   a pipeline for removing the expanded residue gas stream from the overhead heat exchanger and introducing the expanded residue gas stream into the main heat exchanger as a cooling medium, and   means for compressing the expanded residue gas to form a compressed residue gas stream and means for combining the compressed residue gas stream with the overhead gaseous stream upstream of the residue gas compression unit.   
     
     
         15 . The plant according to  claim 14 , wherein the separation or distillation column is a demethanizer. 
     
     
         16 . The plant according to  claim 14 , wherein the separation or distillation column is a deethanizer. 
     
     
         17 . The plant according to  claim 14 , further comprising feed compressor for compressing the gas feed stream prior to being introduced into said main heat exchanger. 
     
     
         18 . The plant according to  claim 17 , wherein the means for expansion of the second portion of the gaseous fraction is a turbo-expanded which is coupled to said feed compressor. 
     
     
         19 . The plant according to  claim 14 , further comprising means for dividing the liquid fraction from the cold gas/liquid separator into a first liquid substream and a second liquid substream, an expansion valve for expanding the first liquid substream before the first liquid substream is introduced into a lower region of the separation or distillation column, and means for combining the second liquid substream with the first portion of the gaseous fraction from the cold gas/liquid separator. 
     
     
         20 . The plant according to  claim 19 , further comprising an expansion valve for expanding the combined stream before the combined stream is introduced into an upper region of the separation or distillation column, 
     
     
         21 . The plant according to  claim 14 , further comprising means for introducing the portion of the compressed residue gas, before being expanded, into the main heat exchanger where it is cooled and wherein the means for expanding the portion of the compressed residue gas is a turbo-expander for expansion. 
     
     
         22 . The plant according to  claim 14 , further comprising means for removing a further portion of the compressed residue gas, means for introducing the further portion of the compressed residue gas into the main heat exchanger and then into the overhead heat exchanger, an expansion valve for expanding the further portion of the compressed residue gas, and means for introducing the further portion into the upper region of the separation or distillation column as a reflux stream. 
     
     
         23 . The plant according to  claim 14 , further wherein the separation or distillation column is a deethanizer and said plant further comprising an expansion valve for expanding the liquid fraction from said cold gas/liquid separator, means for introducing the expanded liquid fraction into said main heat exchanger as a cooling medium, and means for introducing expanded liquid portion into a lower region of the separation or distillation column. 
     
     
         24 . A process for natural gas liquids (NGL) recovery comprising:
 introducing a natural gas feed stream into a main heat exchanger(s) wherein the feed stream is cooled and partially condensed,   introducing the partially condensed feed stream into a cold gas/liquid separator wherein the partially condensed feed stream is separated into a liquid fraction and a gaseous fraction,   introducing the liquid fraction into a separation or distillation column system,   separating the gaseous fraction into a first portion and a second portion,   cooling the first portion of the gaseous fraction in an overhead heat exchanger by indirect heat exchange with an overhead gaseous stream removed from the top of the separation or distillation column system, and introducing the cooled and partially condensed first portion of the gaseous fraction into the separation or distillation column system,   expanding the second portion of the gaseous fraction and introducing the expanded second portion of the gaseous fraction into the separation or distillation column at,   removing a C2+ or C3+ liquid product stream (NGL) from the bottom of the separation or distillation column system,   removing the overhead gaseous stream from the top of the separation or distillation column system, the overhead gaseous stream being enriched with methane,   using the overhead gaseous stream as a cooling medium in the overhead heat exchanger and in the main heat exchanger(s),   compressing the overhead gaseous stream in a residue gas compression unit to obtain a pressurized residue gas stream,   expanding a portion of the pressurized residue gas stream and using the expanded residue gas as a cooling medium in the overhead heat exchanger and in the main heat exchanger(s), and   compressing the expanded residue gas used as a cooling medium to form a compressed residue gas stream and then combining the compressed residue gas stream with the overhead gaseous stream upstream of the residue gas compression unit.   
     
     
         25 . The process according to  claim 24 , wherein the separation or distillation column system contains one column that acts as a demethanizer column or a deethanizer column. 
     
     
         26 . The process according to  claim 24 , wherein the separation or distillation column system contains two columns that together act as a demethanizer column or a deethanizer column. 
     
     
         27 . A plant for natural gas liquids (NGL) recovery comprising:
 a main heat exchanger(s) for cooling and partially condensing a natural gas feed stream,   a separation or distillation column system for separating the natural gas feed stream into a C2+ or C3+ liquid product stream and an overhead gaseous stream enriched in methane,   a cold gas/liquid separator wherein the partially condensed feed stream is separated into a liquid fraction and a gaseous fraction,   a pipeline for removing the liquid fraction from the bottom of the cold gas/liquid separator and introducing the liquid fraction into the separation or distillation column system,   means for separating the gaseous fraction into a first portion and a second portion,   an overhead heat exchanger for cooling the first portion of the gaseous fraction by indirect heat exchange with an overhead gaseous stream removed from the top of the separation or distillation column system,   a pipeline for removing the cooled first portion of the gaseous fraction from the overhead heat exchanger and introducing the cooled first portion into the separation or distillation column system,   means for expanding the second portion of the gaseous fraction,   a pipeline for removing the expanded first portion of the gaseous fraction from the means for expanding and introducing the expanded second portion of the gaseous fraction into the separation or distillation column system,   a bottom outlet for removing the C2+ or C3+ liquid product stream (NGL) from the bottom of the separation or distillation column system,   a top outlet for removing the overhead gaseous stream from the top of the separation or distillation column,   a residue gas compression unit for compressing the overhead gaseous stream to obtain a pressurized residue gas stream,   means for expanding a portion of the pressurized residue gas stream to form an expanded residue gas stream,   a pipeline for removing the expanded residue gas stream from the means for expanding and introducing the expanded residue gas stream into the overhead heat exchanger as a cooling medium,   a pipeline for removing the expanded residue gas stream from the overhead heat exchanger and introducing the expanded residue gas stream into the main heat exchanger as a cooling medium, and   means for compressing (e.g., a single or multistage compressor) the expanded residue gas to form a compressed residue gas stream and means for combining the compressed residue gas stream with the overhead gaseous stream upstream of the residue gas compression unit.   
     
     
         28 . The plant according to  claim 27 , wherein the separation or distillation column system contains one column that acts as a demethanizer column or a deethanizer column. 
     
     
         29 . The plant according to  claim 27 , wherein the separation or distillation column system contains two columns that together act as a demethanizer column or a deethanizer column.