[emilio]

I am modeling a cryogenic air separation system with double Linde columns in Aspen. Are included a Crude Argon column (CrArC) and an Argon column (ArC) as last step. Inlet air feed is 16 kg/s approx.

From lower pressure column at 1,2 bar (LPC) there is a withdrawn to the CrArC in vapour form (Flow A) in stage 75 with 3 kg/s and from the  CrArC at bottom a return in liquid form to LPC (flow B) 2,9 kg/s.

I am expecting to obtain in Flow A the compositions that adjunct in the diagram that are 92% O2 and 8% Ar approx. But what I obtain is that the vapor compositions shift all to the right and appear N2 in above 80%. What happened? Thanks a lot for your help