A low-pressure olefins recovery process and plant are described. The feed
gas is compressed and distilled at a primary distillation pressure. The
overhead stream is chilled at a pressure less than 30 kg/cm2 (430 psia)
to partially condense the overheads. The primary distillation tower is
refluxed with at least a portion of the condensate. The overhead vapor is
further chilled and partially condensed and the condensate is fed to a
demethanizer. The remaining vapor is cooled in a cold section and the
resultant liquid is phase-separated and expanded to provide refrigeration
for the cold section. The expanded vapor from the cold section is
recycled to the process gas compressor. The bottoms streams from the
primary distillation zone and the demethanizer are fractionated into
respective streams consisting essentially of ethylene, ethane, propylene,
propane, C4's, and C5+.