Methods for separating hydrocarbon gases

In a process for separating a hydrocarbon gas containing at least ethane and C3 and heavier 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 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;
• the improvement 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 further comprising:
• (5) recovering a recycle gas stream from an expander-compressor or residue gas compressor;
• (6) cooling and partially condensing the recycle stream in said one or more heat exchangers;
• (7) expanding the recycle stream thereby further condensing a portion of and cooling the recycle stream;
• (8) feeding the expanded recycle stream to a subcooler, whereby the expanded recycle stream is heat exchanged in the subcooler with gases from top of a light-ends fractionation column;
• thereby providing colder temperatures to the vapors from the heavy ends fractionation column.