Rmin By Underwood

Hej,

I have the task to simulate a distillation column for the removal of SO2 and NOx (some 1000 ppm)from a stream of more than 90% CO2 (from a Carbon Capture ans Storage (CCS) power plant). I am working with Aspen Plus for the simulation, and every thing seems to be ok.
My problem ist now, that I would like to optimes the Energy input into the destillation. But as I have just smal changes in the mol fractions of the light key (CO2), I get negative values for the minimal reflux ration (Rmin).
Does this mean, that I did something wrong , or does it just meen that I could do it even without reflux (just a stripping section) ?

Thanks a lot!

uwsdan