Measurement Automation Strategy: Key to Bio-Ethanol ... - Krohne

Fermentation
KROHNE White Paper Measurement Automation Strategy Key to Bio-Ethanol Refinery Efficiency
By Hemant Narayan
Fermentation employs yeast to
convert the glucose into ethanol.
Fermentation can be done in
batches or continuously when
combined with saccharification.
Depending on yeast strain,
fermentation can take one to five
days. Yeast dosage is dependant
on the sugar content and the
desired percent of alcohol at the
end of the fermentation process.
Fermentation severely slows
after reaching 14% alcohol,
because alcohol denatures the
process. However, some types of
yeast can ferment up to 21%.
Tightly controlling temperature
is critical to maximizing
efficiency, because fermentation
will usually cease above 85°F.
The fermentation process
produces “beer” containing
diluted alcohol and solids. Two
downstream processes,
distillation and dehydration,
extract the liquid and purify it in
steps to achieve 100% alcohol
content (200 proof) as required
for E100 fuel ethanol
specification.
Carbon dioxide (CO2)
Carbon dioxide (CO2), a second
co-product of the ethanol
production process, is given off
in large quantities during
fermentation. As a gas, CO2 is
colorless, odorless, and
incombustible. In its liquid form,
CO2 reaches an extreme -17°F,
which makes it an excellent
source for cooling and freezing
applications. CO2 vapors released from
fermentation are usually scrubbed to
recover any alcohol vapors and cleaned.
If sold to commercial users, the CO2 is
liquefied. Otherwise, it is typically
released back into atmosphere.
Distillation
Distillation is the process by which
alcohol is separated from the mash and
water. It exploits the difference in
boiling points between alcohol and
water. Distillation can only purify the
ethanol to about 94% alcohol (6%
water), because water and alcohol form
an azeotrope at atmospheric pressure.
Dehydration
Dehydration A molecular sieve is the
simplest method and most common
method of purifying ethanol from 190 to
200 proof.
Evaporation and Drying
Evaporation and Drying The solids
waste at the bottom of (a?) beer well is
processed separately in a
centrifuge/evaporation/drying process
to produce distillers dried grains with
solubles (DDGS). Distillers grains are
rich in cereal proteins, fat, minerals,
and vitamins, and they serve as an
excellent source of digestible protein
and energy.
Each area of the plant described briefly
above – milling, slurry preparation,
liquefaction, fermentation, distillation,
dehydration, evaporation and drying —
requires a measurement solution that
provides an optimal relationship
between performance and purchase
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