The ethanol rich product stream from the fermenter is sent to a
concentration (Conc) tower. An absorber with a side vapour draw can
be used to represent this tower. This vapour draw is taken from Stage 2
so as to have an azeotropic ethanol product with less methanol
contamination. The top vapour is fed to a light purification tower
(Lights) where most of the remaining CO2 and some methanol is
vented.