The absorber-stripper configuration is common for gas plants. If we are to apply advanced process control (APC) systems on a gas plant, it better to address the control problemmaximizing recovery of propane or propylene (C3) while minimizing C2 at propane contamination limits. Absorber/strippers work like the rectifying and stripping sections of any distillation column, but the presence of lean-oil makes it more complex. The absorber preferentially absorbs and returns C3 to the stripper, whereas the stripper preferentially evaporates C2 in the absorber. However, it is impossible to absorb C3 without some C2, and likewise, it is impossible to boil C2 without evaporating some C3. That creates a large recycle of C2 and C3 between the two columns. Separation gets better with increased recycle as long as the columns do not flood.