Split feed addition to iso-pressure open refrigeration lpg recovery

Abstract

A process is disclosed herein for recovery of natural gas liquids from a feed gas stream, comprising forming a first portion of the feed gas stream and a second portion of the feed gas stream, wherein the mass ratio of the first portion to the second portion is in the range of 95:5 to 5:95, cooling the first portion in a heat exchanger and at least partially condensing the first portion, and feeding the second portion and the cooled and at least partially condensed first portion to a distillation column wherein lighter components are removed from the distillation column as an overhead vapor stream and heavier components are removed from the distillation column in the bottoms as a product stream, and wherein the second portion is fed into the distillation column at a point one or more vapor-liquid equilibrium stages below the first portion, thereby allowing mass transfer exchange between liquids of the cooled second portion and vapors of the second portion within the column. A corresponding apparatus is also disclosed.

What is claimed is: 
     
         1 . A process for recovery of natural gas liquids from a feed gas stream, comprising:
 (a) forming a first portion of the feed gas stream and a second portion of the feed gas stream, wherein the mass ratio of the first portion to the second portion is in the range of 95:5 to 5:95;   (b) cooling the first portion in a heat exchanger and at least partially condensing the first portion;   (c) feeding the second portion and the cooled and at least partially condensed first portion to a distillation column wherein lighter components are removed from the distillation column as an overhead vapor stream and heavier components are removed from the distillation column in the bottoms as a product stream, and wherein the second portion is fed into the distillation column at a point one or more vapor-liquid equilibrium stages below the first portion, thereby allowing mass transfer exchange between liquids of the cooled first portion and vapors of the second portion within the column;   (d) feeding the distillation column overhead stream to the heat exchanger and cooling the distillation column overhead stream to at least partially liquefy the distillation column overhead stream;   (e) feeding the at least partially liquefied distillation column overhead stream to a first separator;   (f) separating the vapor and liquid in the first separator to produce an overhead vapor stream comprising sales gas and a bottoms stream comprising a mixed refrigerant;   (g) feeding the mixed refrigerant stream to the heat exchanger to provide cooling, wherein the mixed refrigerant stream vaporizes as it passes through the heat exchanger;   (h) compressing the vaporized mixed refrigerant stream and passing the compressed mixed refrigerant stream through the heat exchanger; and   (i) feeding at least a portion of the compressed mixed refrigerant stream to the distillation column as a reflux stream.   
     
     
         2 . The process of  claim 1 , further comprising, before (i), feeding the compressed mixed refrigerant stream to a second separator, and feeding the bottoms from the second separator to the distillation column as the reflux stream. 
     
     
         3 . The process of  claim 1 , further comprising reducing the temperature of the mixed refrigerant stream before the mixed refrigerant stream enters the heat exchanger by reducing the pressure of the mixed refrigerant using a control valve. 
     
     
         4 . The process of  claim 1 , further comprising combining the overhead stream from the second separator with the overhead stream from the distillation column and feeding the combined stream to the first separator. 
     
     
         5 . The process of  claim 1 , further comprising cooling the compressed mixed refrigerant in a cooler before passing the compressed mixed refrigerant stream through the heat exchanger. 
     
     
         6 . The process of  claim 1 , wherein the first separator is an absorber. 
     
     
         7 . The process of  claim 1 , wherein the feed gas stream is one of natural gas or refinery gas. 
     
     
         8 . The process of  claim 1 , wherein the distillation column operates at a pressure of between about 100 psia and 450 psia. 
     
     
         9 . The process of  claim 1 , wherein the first and second portions of the feed gas stream have the same composition. 
     
     
         10 . The process of  claim 1 , wherein the first portion and second portion of the feed gas streams have a mass ratio in the range of 95:5 to 65:35. 
     
     
         11 . The process of  claim 1 , wherein the first portion and second portion of the feed gas streams have a mass ratio in the range of 95:5 to 70:30. 
     
     
         12 . The process of  claim 1 , wherein a portion of compressed mixed refrigerant stream is removed as a supplemental product stream. 
     
     
         13 . The process of  claim 1 , wherein separating the vapors and liquids in the separator further includes producing a side draw fraction. 
     
     
         14 . The process of  claim 13 , wherein the overhead vapor stream is enriched in nitrogen and depleted in propane, the bottoms fraction is depleted in nitrogen and enriched in propane, and the side draw fraction has intermediate propane and nitrogen content. 
     
     
         15 . The process of  claim 1  further comprising reboiling a portion of the distillation column bottoms in a distillation column reboiler, wherein the energy input to the distillation column reboiler is at least 5% lower than the energy input for a process with the same volumes and compositions of the feed gas stream, product stream and sales gas stream, and in which no second portion is formed from the feed gas stream. 
     
     
         16 . The process of  claim 1  further comprising reboiling a portion of the distillation column bottoms in a distillation column reboiler, wherein the energy input to the distillation column reboiler is at least 10% lower than the energy input for a process with the same volumes and compositions of the feed gas stream, product stream and sales gas stream, and in which no second portion is formed from the feed gas stream. 
     
     
         17 . The process of  claim 1 , wherein the total compressor duty of the process is at least 5% lower than the compressor duty for a process with the same volumes and compositions of the feed gas stream, product stream and sales gas stream, but in which no second portion is formed from the feed gas stream. 
     
     
         18 . The process of  claim 1 , wherein the total compressor duty of the process is at least 10% lower than the compressor duty for a process with the same volumes and compositions of the feed gas stream, product stream and sales gas stream, but in which no second portion is formed from the feed gas stream. 
     
     
         19 . An apparatus for separating natural gas liquids from a feed gas stream, the apparatus comprising:
 (a) a primary feed gas line configured to deliver a feed gas stream;   (b) a heat exchanger operable to provide the heating and cooling necessary for separation of natural gas liquids from a feed gas stream by heat exchange contact between the feed gas stream and one or more process streams thus forming a cooled feed gas stream;   (c) a distillation column configured to receive the feed gas stream and to separate the feed gas stream into a column overhead stream comprising a substantial amount of the lighter hydrocarbon components of the feed gas stream and a column bottoms stream comprising a substantial amount of the heavier hydrocarbon components;   (d) a first separator configured to receive the distillation column overhead stream and to separate the column overhead stream into an overhead sales gas stream and a bottoms stream comprising a mixed refrigerant configured to provide process cooling in the heat exchanger;   (e) a compressor configured to compress the mixed refrigerant stream after the mixed refrigerant stream has provided process cooling in the heat exchanger; and   (f) a feed gas bypass line configured to remove a portion of the feed gas stream prior to it being sent to the heat exchanger, wherein the feed gas bypass line is fluidly connected to the distillation column at a point one or more vapor-liquid equilibrium stages below the point at which the cooled feed gas stream from the heat exchanger is fluidly connected, thereby allowing mass transfer exchange between the liquids of the cooled feed gas stream from the heat exchanger and the vapors of the bypass feed gas stream within the column.   
     
     
         20 . The apparatus of  claim 19 , further including a second separator configured to receive the compressed mixed refrigerant stream and separate the compressed mixed refrigerant into an overhead stream and a bottoms stream that is fed to the distillation column as a reflux stream. 
     
     
         21 . The apparatus of  claim 19 , further including a splitter configured to provide that the stream entering the feed gas bypass line has the same composition as the portion of the feed gas stream sent to the heat exchanger. 
     
     
         22 . The apparatus of  claim 19 , wherein the splitter is configured to provide that the bypass line receives about 5 to 35 weight % of the feed gas from the primary feed gas line. 
     
     
         23 . The apparatus of  claim 19 , further including a splitter configured to remove a portion of the compressed mixed refrigerant as a product stream. 
     
     
         24 . The apparatus of  claim 19 , wherein the first separator is an absorber. 
     
     
         25 . The apparatus of  claim 24 , wherein the absorber has a side draw line configured to remove a side draw stream.