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In this module, you will simulate an Ethanol Plant. You will get more
practice with the Column unit operation of HYSYS by:
• modeling columns with side draws
• adding a column with real trays.
Typically an ethanol fermentation process produces mainly ethanol
plus several by-products in small quantities: methanol, 1-propanol, 2-
propanol, 1-butanol, 3-methyl-1-butanol, 2-pentanol, acetic acid, and
The CO2 produced in the fermentation vessel carries some ethanol.
This CO2 stream is washed with water in a vessel (CO2 Wash) to recover
the ethanol, which is recycled to the fermenter.
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
The feed to the Rectifier (Rect) is the bottoms product of the Lights
purification tower and the vapour draw from the concentration tower.
The Rectifier is operated as a conventional distillation tower.
Methanol concentrates towards the top stages, so a small distillate
draw is provided at the condenser. Also, a small vent for CO2 is provided
at the condenser.
Another interesting point is the concentration of heavy alcohols in the
interior of the Rectifier. These alcohols are normally referred to as Fusel
oils. Fusel oils are a mixture of propanols, butanols and pentanols, with
a potential value superior to that of ethanol. Accumulation of fusel oils
in the Rectification Tower can cause the formation of a second liquid
phase and subsequent deterioration of performance for these trays, so
small side liquid draws of fusel oils are installed on the rectifier to avoid