Corn to Ethanol Process
Transcript of Corn to Ethanol Process
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The Dry Grind Corn to Ethanol Process
TM
National Corn-to-Ethanol Research Center
Southern Illinois University
Education and Workforce Development
400 University Park Drive
Edwardsville, Illinois 62025-3604
Office: (618) 659-6737 ext. 239Fax: (618) 659-8762
www.ethanolresearch.com
A copyright statement is as follows:
----------------------------
Copyright 2007, Board of Trustees of Southern Illinois University, National Corn to Ethanol Research Center,
Edwardsville, Illinois 62026
All rights reserved.
These materials are protected by copyright and may not be reproduced, copied, displayed, or disseminated
in any media without the express consent of the National Corn to Ethanol Research Center
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12
9
13
Yeast
7
Hammer Mill Slurry
Tank JetCooker
CO2
Enzyme
4
Enzyme
4
Fermentation
Denatured
Ethanol Molecular
Sieve
10
Distillation
System
CentrifugeEvaporator(Syrup)Drum Dryer
5Liquefaction
8
9
911
12
3
Dried Distillers
Grain with Solubles
The Corn to Ethanol ProcessNational Corn-to-Ethanol Research Center, SIUE
5%
Gasoline
Added
(200 Proof )
(190 Proof )
(Whole
Stillage)
Start HereAmmonia
Steam
(Recycled Water)
Urea
(Cooling)
( Wet Cake)
(Thin
Stillage)
Water
(Heating)
Enzyme
6
TM
2007 All Rights Reserved
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Midwest Corn typically contains: 70-72% starch, 9% protein, 4% oils, and
9% fiber on a dry basis, plus approximately 15% water.
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Hopper
Most corn grown for ethanol production is #2 yellow dent corn, so named
because of the indentation that occurs on top after the kernel is allowed
to dry.
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The corn kernels are milled to a coarse flour and passed through a fine
mesh screen.
2
Hammer Mill
The corn particle sizing is a compromise between:
(B) leaving large enough particles for drying the Distillers Grain
at the end for animal feed.
(A) grinding fine enough to provide increased surface area to makestarch granules available for reaction with water and enzymes and
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Slurry
Tank
3AmmoniaorSulfuric Acid
(Recycled Water)
Water
Corn flour from the hammer mill is mixed first in the slurry mixer
with hot water and alpha-amylase enzyme.
The resulting slurry is adjusted to a pH of 5.6 to 6.0 with acid or base.
Hammer Mill
Slurry Mixer
(Corn flour)
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SlurryTank
alpha-
amylase
3
Only one third of the total alpha-amylase is added in the slurry
Tank.
The remaining alpha-amylase will be added later in the
liquefaction tank.
Temperature = 185oF
pH = 5.6 to 6.0% Solids = 32%
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Jet Cooker
Steam
Slurry Mash
The slurry mash is heated to above 220F in a jet cooker using direct
steam.
holding column
Upon exiting the jet cooker, the corn slurry enters a holding column
where the mixture is held for 5 to 10 minutes.
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LiquefactionTank
alpha-amylase
5
From the holding column, the slurry enters a Liquefaction Tank (5).
The jet cooking and liquefaction steps break apart the long starch
granules. The shorter molecules are called dextrin.
holding column
Temperature = 185oF
pH = 5.6 to 6.0% Solids = 30%
Additional alpha-amylase is added and the mash is allowed to react
(liquefy) for approximately 30 minutes.
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Glucose is converted by yeast (7) through a series of multi-step reactions
to ethanol and carbon dioxide in the fermentation tanks (8).
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CO2
Fermentation
Tanks
SSF
Yeast
7
8
Liquefaction Tank
A second enzyme, gluco-amylase (6), is added to complete the dextrin
breakdown to glucose.
gluco-amylase
6
Temperature = 90oFpH = 3.5 to 4.0
Over the past 10 years, many ethanol plants have started adding the
saccharifying enzyme (gluco-amylase) directly to the fermentation tank.
This faster process is know as Simultaneous Saccharification and
Fermentation (SSF).
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CO2
Carbon dioxide is a major co-product in the fermentation process.
9
Fermentation
Tanks
Every bushel of corn (approximately 56 pounds) will produce
approximately 18 pounds of carbon dioxide gas.
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Yeast can withstand extreme environmental stresses including highethanol concentrations (final concentrations of 12-18% by volume), as
well as organic acids produced by contaminating bacteria. Fortunately,
most bacterial contaminants do not grow below pH 4.
Yeast
7Fermentation
Tanks
Contaminating microorganisms can lower the yield by converting glucoseto some undesirable fermentation products like fusel oils (undesired
alcohols), acetic acid, and lactic acid. Antibiotics maybe added to the
fermentation process to minimize bacterial contamination.
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Distillation System
At the end of fermentation, the product is called beerand contains 12%
or higher concentration of ethanol. The beer is typically stored in a tank
referred to as the beer well.
Beer Well
The distillation system typically consists of three columns.
(beer)
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(gases) M l l Si
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First, the beer is passed through a degassing column (gray) to removecarbon dioxide and other gases.
Distillation SystemBeer Well
Centrifuge
(gases) Molecular Sieve
(whole stillage)
Separation of ethanol/water from the non-converted solids mixture occurs
on the beer column (blue). These non-converted solids (whole stillage)
fall to the bottom and are sent to the centrifuge for separation.
Further separation of the ethanol/water mixture is accomplished using a
rectifier column (red). The 190 proof ethanol is sent through a
molecular sieve column to convert it to 200 proof.
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from Rectifier Column190 Proof
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Conventional distillation methods yield 190 proof (95% pure ethanol)
because ethanol and water form an azeotrope. An azeotropeis simply a
mixture of two substances that form a constant boiling point mixture.
Molecular
Sieve
10
Denatured
Ethanol Tank
from Rectifier Column
200 Proof
190 Proof
Temperature > 280oF
Pressure = 6 psig
The remaining 5% water is removed by molecular sieves, which rely on
pore sizes to separate the smaller water molecules from ethanol.
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Finally, anhydrous (100% or 200 proof) ethanol is denatured, typically
with 5% gasoline to exempt the ethanol from beverage alcohol taxes.
5%
GasolineAdded
Denatured Ethanol
11
Molecular Sieve
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Centrifuge whole stillage
wet cake
thin stillage
The solids materials remaining after distillation of ethanol from the beercolumn is called whole stillage. Whole stillage contains 13-17% solids
and is composed primarily of small particles of corn that did not get
converted to ethanol. This whole stillage is separated in the centrifuge
into wet cake and thin stillage.
Wet cake is a more concentrated form of the whole stillage and
contains approximately 35% solids after leaving the centrifuge. Since it
contains mostly solids, it must be augured or conveyed to the drum
dryer.
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backset
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Evaporator
(syrup)
12Centrifuge
Drum Dryer
backset
(wet cake)
(thin
stillage)
The thin stillage is primarily water with between 4 and 5% solids. The thinstillage is evaporated down to a concentrated syrup in the evaporator.
The condensed water is recycled to the Slurry tank. This condensed
water is called backset and helps to conserve total water usage.
The remaining liquid is concentrated (called syrup) by evaporation and
mixed with the wet cake before entering the dryer. Syrup is
approximately 28-30% solids and contains mostly protein and oils from
the corn. The addition of syrup increases the nutritional value of the
DDG.
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Evaporator
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Rotary Drum DryerDDGS Centrifuge
(wet cake)
Evaporator(syrup)
The mixture of syrup and wet cake is dried to generate Dried Distillers
Dried Grain with Syrup or Solubles (DDGS). DDGS is typically dried to a
10% moisture level.
The moisture content and correspondingly short shelf-life of wet distillers
grains limit use of this feed product to the immediate vicinity of ethanol
plants.
The shelf life of the DDGS can be lengthened by adding organic acids as
preservatives and removing almost all the moisture content.
Inlet Air Temperature = 600-1200oF
DDGS Residence time = approximately 30 minutes
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Distillers Dried
Grain with Solubles
In the dry grind process, corn is ground whole and fermented to ethanol.
The only major by-products are ethanol, carbon dioxide, and Distillers
Dried Grain with Solubles.
DDGS is sold primarily as cattle feed.
NCERC
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Hammer Mill
Slurry
Tank JetCooker
Fermentation
Ethanol
StorageMolecular
Sieve
Distillation
System
Evaporator(Syrup)Drum Dryer
Liquefaction
9
9
Centrifuge
DDGS
(200 Proof )
(190 Proof )
Whole
Stillage
(Recycled Water)
(Cooling)
( Wet Cake)
(Thin
Stillage)
(Heating)
TM
Centrifuge
DE
TS %
pH
DE
pH pHHPLC
H2O %
Proximate
Analysis
TS%
Proximates
Amino Acids
Total P
Ash
etc.
HPLC
Particle SizeGrain
Qual