Imans,
Use this proven approach (assumed 1 feed, 2 product tower below) with any simulator to find overall column efficiency (theoretical stages / actual stages):
1) Specify a distillate and bottoms stream (flow and composition)
2) Mix the two streams in a mixer to use as tower feed
3) bring feed to plant conditions with a heater
4) send feed to a distillation column specifying plant values for tower pressure, reflux flow and temperature, and distillate flow (note that this is same flow as in #1 above)
5) Run sensitivity on number of theoretical stages- you can either keep feed location in proportion, or (if you believe section efficiencies can vary) you can run a 2 dimensional sensitivity on total stages and feed stage.
6) Pick the sensitivity result that gives the closest match to your distillate composition (bottoms will also be close due to material balance constraint). This is your number of theoretical stages.
Once you have used this approach, you will see how it works and can make various refinements to my method to suit your needs (including sensitivity on murphree tray or vaporization efficiencies if you are a fan of those).
The biggest stumbling blocks for new simulation users are: to try and use feed data as simulation input and expect product data to match plant (it may not be consistent)- steps#1 and #2 completely eliminates this problem; and to fail to recognize that we should use the actual plant values for reflux and distillate flow as simulation inputs- step#4 addresses this.
best wishes,
sshep