Methods for separating hydrocarbon gases

Abstract

A process for separating a hydrocarbon gas into a fraction containing a predominant portion of the methane or ethane and lighter components and a fraction containing a predominant portion of the C2 or C3 and heavier components in which the feed gas is treated in one or more heat exchange and expansion steps; partly condensed feed gas is directed into a separator wherein a first residue vapor is separated from a C2 or C3-containing liquid; and C2 or C3-containing liquids at substantially the pressure of separation are directed into a distillation column wherein the liquid is separated into a second residue to recover a C2 or C3-containing product. A portion of the vapor and/or a portion of the liquid from the first hydrocarbon vapor/liquid separation is further cooled and introduced into a fractionation column to increase the C2 or C3 and heavier hydrocarbons recovery from the natural gas stream.

Having thus described the invention, what we claim is: 
     
         1 . A process for separating a hydrocarbon gas containing at least methane, ethane and C3 components into a fraction containing a predominant portion of the ethane and lighter components and a fraction containing a predominant portion of the C3 and heavier components or a predominant portion of the methane and lighter components and a fraction containing a predominant portion of the C2 and heavier components, in which process
 (a) the feed gas is treated in one or more heat exchangers, and expansion steps to provide at least one partly condensed hydrocarbon gas, providing thereby at least one first residue vapor and at least one C2 or C3-containing liquid which liquid also contains lighter hydrocarbons; and   (b) at least one of the C2 or C3-containing liquids is directed into a distillation column wherein said liquid is separated into a second residue containing lighter hydrocarbons and a C2 or C3-containing product; comprising:   (1) cooling said second residue to partially condense it;   (2) intimately contacting at least part of one of said first residue vapors with at least part of the liquid portion of the partially condensed second residue in at least one contacting stage and thereafter separating the vapors and liquids from said contacting stage;   (3) supplying the liquids thereby recovered to the distillation column as a liquid feed thereto; and   (4) directing the vapors thereby recovered into heat exchange relation with said second residue from the distillation column, thereby to supply the cooling of step (1), and thereafter discharging said residue gases; the improvement comprising:   (5) withdrawing a portion of the first residue vapor;   (6) cooling said portion of the first residue vapor to partially condense it;   (7) intimately contacting at least part of one of said first residue vapors with at least part of the liquid portion of the partially condensed portion of the first residue in at least one contacting stage and thereafter separating the vapors and liquids from said contacting stage;   (8) supplying the liquids thereby recovered to the distillation column as a liquid feed thereto; and   (9) directing the vapors thereby recovered into heat exchange relation with said portion of the first residue from the separator, thereby to supply the cooling of step (6), and thereafter discharging said residue gases;   the improvement further comprising:   (10) withdrawing a portion of the C2 or C3 containing liquid from the separator;   (11) directing said portion of the C2 or C3 containing liquid from the separator into a heat exchange relationship with the liquid product from the contacting device;   (12) cooling said portion of the C2 or C3 containing liquid from the separator;   (13) intimately contacting at least part of one of said first residue vapors with at least part of the C2 or C3 containing liquid from the separator in at least one contacting stage and thereafter separating the vapors and liquids from said contacting stage;   (14) supplying the liquids thereby recovered to the distillation column as a liquid feed thereto;   (15) directing the vapors thereby recovered into heat exchange relation with said portion of the first residue from the separator, thereby to supply the cooling of step (6), and thereafter discharging said residue gases; and   (16) directing the liquids thereby recovered into heat exchange relation with said portion of the C2 or C3 containing liquid from the separator, thereby to supply the cooling of step (11), and thereafter discharging said liquids to a heavy ends fractionation column.   
     
     
         2 . The process according to  claim 1  wherein said contacting step (2) is carried out in a feed separator/absorber which includes fractionation means for vapor/liquid counter-current contact and
 (i) wherein said partly condensed second residue is introduced into said separator/absorber above or at an intermediate point in said fractionation means, whereby the liquid portion of it passes downwardly through said fractionation means; and 
 (ii) wherein said partly condensed portion of the first residue is introduced into said separator/absorber above or at an intermediate point in said fractionation means, whereby the liquid portion of it passes downwardly through said fractionation means; and wherein said portion of the cooled C2 or C3 containing liquid from the separator is introduced into said separator/absorber above or at an intermediate point in said fractionation means, whereby the liquid portion of it passes downwardly through said fractionation means; and 
 (iii) said at least part of one of said first residue vapors is supplied to said separator/absorber below said fractionation means, whereby the first residue vapor rises through said fractionation means in counter-current contact with the liquid portion of the partly condensed second residue. 
 
     
     
         3 . The process according to  claim 2  wherein the fractionation means in said separator/absorber provide the equivalent of at least one theoretical distillation stage arranged to contact at least part of one of said first residue vapors with the liquid portion of the partly condensed second residue. 
     
     
         4 . The process according to  claim 1  wherein at least part of one of said first residue vapors are co-mingled with the liquid portion of the partially condensed second residue, liquid portion of the partially condensed portion of the first residue and portion of the cooled C2 or C3 containing liquid from the separator. 
     
     
         5 . The process according to  claim 1  wherein at least part of one of said first residue vapors are comingled with both the liquid portions and vapor portions of said partially condensed second residue, partially condensed portion of the first residue vapor and portion of the cooled C2 or C3 containing liquid from the separator. 
     
     
         6 . An apparatus for separating a hydrocarbon gas containing at least methane, ethane and C3 components into a fraction containing a predominant portion of methane or ethane and lighter components and a fraction containing a predominant portion of the C2 or C3 and heavier components in which apparatus
 (a) one or more heat exchange means and one or more expansion means are provided which are cooperatively connected to provide at least one partly condensed hydrocarbon gas, providing thereby at least one first residue vapor and at least one C2 or C3-containing liquid which liquid also contains lighter hydrocarbons; and   (b) a distillation column connected to receive at least one of said C2 or C3-containing liquids which is adapted to separate the C2 or C3-containing liquids into a second residue containing lighter hydrocarbons and a C2 or C3-containing product;   the improvement comprising:   (1) heat exchange means connected to said distillation column to receive said second residue and to partially condense it;   (2) heat exchange means connected to said distillation column to receive said a portion of the first residue and to partially condense it;   (3) contacting and separating means connected to receive at least part of one of the first residue vapors and at least part of the liquid portion of the partially condensed second residue and partially condensed first residue vapor and to comingle said vapor and liquid in at least one contacting stage, which means include separation means for separating the vapor and liquid after contact in said stage;   (4) said means (2) and (3) being further connected to supply the liquids separated therein to the distillation column as a liquid feed thereto;   (5) said means (2) and (3) also being connected to direct the vapors separated therein into heat exchange relation with said second residue and portion of the first residue from the distillation column in said heat exchange means (1); and   (6) heat exchange means connected to said distillation column to receive said liquids and to cool the portion of the C2 or C3 containing liquid from the separator.   
     
     
         7 . The apparatus according to  claim 6  wherein said contacting and separating means includes fractionation means for countercurrent vapor/liquid contact and wherein said means is connected to receive the portion of one of first residue vapors to be treated therein below said fractionation means and to receive the portion of said liquids from the partially condensed second residue, portion of the partially condensed first residue and portion of the cooled C2 or C3 containing liquid from the separator to be treated therein above or at an intermediate point in said fractionation means said fractionation means thereby being adapted so that the first residue vapors rise there-through in countercurrent contact with partially condensed second residue and portion of the partially condensed first residue and being further adapted so that the portion of the C2 or C3 containing liquid from the separator is cooled by the liquids exiting the fractionation means. 
     
     
         8 . The apparatus according to  claim 7  wherein said fractionation means includes vapor/liquid contacting means which are the equivalent of at least one theoretical distillation stage. 
     
     
         9 . The apparatus according to  claim 6  wherein said contacting and separating means (2) comprise means for comingling at least part of one of said first residue vapors with the liquid portion of the partially condensed second residue, liquid portion of the partially condensed portion of the first residue and portion of the cooled C2 or C3 containing liquid from the separator. 
     
     
         10 . The apparatus according to  claim 6  wherein said contacting and separating means (2) comprise means for comingling at least part of one of said first residue vapors with both the liquid and vapor portion of said partially condensed second residue, said partially condensed portion of the first residue and portion of the cooled C2 or C3 containing liquid from the separator.