Ah, we called it "bottoms" product as it was then sent off to the cracker: oil distillation!
You probably want two phases. Liquid phase, which will be a mixture of ethanol and water (I assume stillage is mostly water). Similarly a gas phase with ethanol-vapour and water-vapour. Phase change is handled in the Phase panel.
For the initial condition you will want Standard initialisation and then patch the phase/species for which ever phase wasn't in the initial condition. Use a cell zone or register for the patch. You may need to think a bit about species & phase as the species fraction is on the phase, it's a little confusing so I'd patch and post process to understand what's going on.
Multiphase models are often quite long runs. Think about 2d or 3d sectors depending on the geometry. Also look at parallel processing. There are cheats to get around some of the time issues, but you then need to understand (and defend) those assumptions.