Environmental Engineering Reference
In-Depth Information
produce a mixture containing 28 vol % yeast that are fed to the reactor for another batch of fermen-
tation. Sulfuric acid is added to the yeast medium to avoid bacterial contamination.
Gases released during fermentation are collected and washed to recover ethanol in an absorption
column. The alcoholic solution obtained is mixed with the centrifuged wine and fed to the distilla-
tion columns.
21.9.3 d
iStillation
and
d
Ehydration
Product purification takes place in double-effect and extractive distillation systems. A series of dis-
tillation and rectification columns are used for hydrous bioethanol production (93 wt % ethanol).
Hydrous ethanol in vapor phase is dehydrated to produce anhydrous ethanol (AE, 99.5 wt % ethanol)
in the extractive distillation process with monoethyleneglycol. In the double effect distillation, column
reboilers and condensers are integrated, thus diminishing energy consumption on the distillation.
21.9.4 S
imulationS
for
i
incrEaSing
E
fficiEncy
of
h
ydratEd
B
ioEthanol
p
roduction
Product purification is a critical step during ethanol production because it is an energy intensive
operation. Ordinary distillation is used to produce hydrous bioethanol (approximately 93 wt %
ethanol), which is used as fuel in ethanol-based or flex-fuel engines. The conventional configuration
of the distillation process used in Brazilian refineries consists of a series of distillation columns
(A, A1, and D) and rectification (B and B1) columns. This configuration is depicted in Figure 21.2.
In conventional bioethanol production (first generation), wine obtained from fermentation of
sugars containing between 7 and 12 wt % ethanol is the feedstock to obtain ethanol. However, wine
produced in the fermentation process with an extractive vacuum flash chamber can achieve 50 °GL
(Atala and Maugeri 2006), what may lead to a significant reduction in the separation costs.
21.9.4.1 ordinary distillation
Because distillation operations require significant amounts of energy and have a great importance
in bioethanol production, the simulation of an operation unit has to be as representative as possible.
2
nd
grade
ethanol
R
E
D
Hydrous ethanol
93% ethanol
Liquid phlegm
Wine
A1
B
Fusel oil
Vapor phlegm
A
B1
Vinasse
K
Phlegmasse
L
FIGure 21.2
Configuration of conventional distillation process.
