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Bioethanol: Market and Production Processes 99

(e) vapor recompression, (f) multieffect distillation, and (g) six-column
reagent alcohol system [9, 47]. These methods are reviewed by Kosaric
[9]. The following parameters should be considered for selection of the
industrial distillation systems:
Energy consumption (e.g., steam consumption or cooling water con-
sumption per kilogram of ethanol produced).
Quality of ethanol (complete separation of fusel oil and light compo-
nents).
How to deal with the problem associated with clogging of the first dis-
tillation column and its reboiler because of precipitation or formation
of solids. Special design and use of a vacuum may be applied for over-
coming the problem in the column. Using open steam instead of appli-
cation of a reboiler can prevent clogging of the reboiler, in spite of the
increase in amount of wastewater.
Simplicity in controlling the system.
Simplicity in opening column parts and cleaning the columns.
Of course, lower capital investment is also one of the main parameters
in the selection of distillation systems.
Ethanol is present in the market with different degrees of purity. The
majority of ethanol is 190 proof (95% or 92.4%, minimum) used for sol-
vent, pharmaceutical, cosmetic, and chemical applications. Technical-
grade ethanol, containing up to 5% volatile organic aldehyde, ester, and
sometimes methanol, is used for industrial solvents and chemical syn-
theses. High-purity 200 proof (99.85%) anhydrous ethanol is produced
for special chemical applications. For fuel use in mixture with gasoline
(gasohol), nearly anhydrous (99.2%) ethanol, but with higher available
levels of organic impurities, is used [47].
A simple two-column system is described here, while other systems
are presented in the literature (e.g., [9, 47]). Simple one- or two-
column systems with only a stripping and rectification section are
usually used to produce lower-quality industrial alcohol and azeotrope
alcohol for further dehydration to fuel grade. The simplest continu-
ous ethanol distillation system consists of stripping and rectification
sections, either together in one column or separated into two columns
(see Fig. 3.10).
The mash produced is pumped into a continuous distillation process,
where steam is used to heat the mash to its boiling point in the stripper
column. The ethanol-enriched vapors pass through a rectifying column
and are condensed and removed from the top of the rectifier at around
95% ethanol. The ethanol-stripped stillage falls to the bottom of the
stripper column and is pumped to a stillage tank. Aldehydes are drawn