ethanol process fundamentals[1]
TRANSCRIPT
By: Josh Kaurich
OverviewFacilities started with farm-led projects
Wanted to increase profits margins on cornFarmer knew that availability was not an
optionLow transportation costVariable corn prices, who cares?
What about other price increases? [fuel, pesticides, herbicides, nutrient values]
Outcomes of ethanol cooperativesHigh profits [drew in corporations]Reduce foreign oilImprove air qualityCreate rural jobsBoost local economies
Ethanol Production3 billion gallons in 20046 billion gallons in 2007
Expectations of 12 billion gallons in 2009
Questions:Why are some of the benefits/drawbacks of
increased ethanol production?
Uses of EthanolE10, a blend of 10% ethanolReplace MTBE [EPA on MTBE]For use in FFV [E85]Increase octane levelsDecrease engine emissions
History of EthanolAlcohol was brewed in Mesopotamia and
Egypt as early as 4000 b.c. Here mass production of home brews were born.
Used to be produced from fruit, now in USA from corn.
Ethanol that is now used as a fuel is denatured
History cont.
Model T Video
Ethanol TodayEthanol is contained in over 11% of all
gasoline today in the USA.Marketed by the largest oil companies.Since 1978, Americans have driven 2 trillion
miles on ethanol1990’s was the start of FFVs [E85 fuel] [Flex Fuel Vehicles]
Question:What is the key component in FFVs?
Why EthanolClean air Amendment of 1990
Metropolitan areas in US that suffer from air quality problems must use reformulated gasoline [octane enhancing] additives.
MTBEIn ground waterPossible carcinogen
EthanolBiodegradableEnhances performanceRegional energy sourceReduces carbon monoxide [emission facts]
General Production MethodsChemical synthesis
Hydrolysis of ethylene obtained from coal gasification
Biological fermentationUse of enzymes and fermentation tanks to form
ethanol
Question:What is the problem with using chemical
synthesis for ethanol?
FeedstockIn most cases
Corn (15% mc) 56 lb. test weight 67% fermentable starch content
DiscussionWhat are some benefits of utilizing ethanol
for transportation fuels?What are some of the draw backs to using
ethanol for transportation fuels?What is of utmost importance to understand
all of the environmental aspects of ethanol?[Al Gore]
OverviewYou must understand the LCA of ethanol to
fully grasp its benefits and draw backs.
GREET Model
Ethanol ProductionCurrently produced
from starches and sugarsCorn in the US and
sugarcane in BrazilUses enzymes to
break down starches to simple sugars which are then fermented into ethanol
Mature industry - cost not likely to decrease substantially
Source: USDA Amber Waves
Grain ethanol is centered in the upper Midwest
U.S. Ethanol Volume Trajectory
0
2,000
4,000
6,000
8,000
10,000
12,000
14,000
16,00019
99/0
0
2000
/01
2001
/02
2002
/03
2003
/04
2004
/05
2005
/06
2006
/07
2007
/08
2008
/09
2009
/10
2010
/11
2011
/12
2012
/13
Sep.-Aug. Crop Year
Mill
ion
Gal
lon
s
Renewable Fuels Standard (Crop Yr. Equivalent)Ethanol Prodn., Slow Growth After 2007/08 (No Cellulosic)Ethanol Prodn., High Growth After 2007/08 (No Cellulosic)
ForecastHistory
U.S. Corn Use
John C. FelmyChief EconomistAmerican Petroleum Institute
Department of Energy announced biorefinery awards on Feb. 28:
DOE will invest up to $385 million for six DOE will invest up to $385 million for six biorefinery projects over the next four yearsbiorefinery projects over the next four years
• Abengoa Bioenergy $76 million • ALICO $33 million• BlueFire Ethanol $40
million• Broin Companies $80 million• Iogen Biorefinery $80 million.• Range Fuels $76 million
Combined with the industry cost share, more than $1.2 billion will be invested in these six biorefineries
Wisconsin Ethanol Plants7 Operating Ethanol Plants
2007 Production: 300 million gallons
• Badger Ethanol: Monroe
• Ace Ethanol: Stanley
• Utica Energy: Utica
• United WI Grain Producers: Freisland
• Western WI: Wheeler
• United: Milton
• Renew: Jefferson6 Proposed Ethanol Plants
1. Necedah 2. Belmont 3. Arena
4. WI Rapids 5. Cambria 6. Sharon
AceWWRE
Utica
Renew
1
2
UWGP
3
United Badger
4
5
6
70 Wisconsin E85 Stations!= 1 E85 Station Dispensing or Coming Soon
Worldwide UseBrazil and Sweden are using large volumes of
ethanolCanada offers ethanol subsidies up to 45 cents
per gallon for ethanolIndia beginning stages of mass productionFrance, ethanol from grapesSweden has used ethanol for chemical
production for many yearsIn 2006 Brazil proclaimed energy independence
Now they make so much they export ethanol!
Corn ethanol can’t satisfy the transportation demandThe US produced 11.1
B bushels of corn in 2005
Each bushel of corn produces 2.6 - 2.8 gal of ethanol
Therefore, 29 B gal of ethanol could be produced if we used 100% of the corn produced
140 B gal of gasoline currently used by the transportation sector
Would be enough to make all fuel used E15
To replace 140 B gal with E85 would require 120 B gal of ethanol, 50 B bushels of corn, and 300 M acres of landAbout 90 M acres corn
were grown in 2007Tom Jeffries, US Forest Products Lab, 2007
Reference: Journey to Forever
Ethanol production from grain has a positive energy efficiencyEthanol from grain yields 1.34 units of
energy for each unit consumed in its production
Biodiesel yields 3.2 units of fuel for every unit of fossil energy consumed in its life cycle
Gasoline has an energy ratio of 0.805. For every unit of energy dedicated to the
production of gasoline there is a 19.5 percent energy loss.
The ethanol processEthanol Process Overview
The US produces large amounts of biomass annuallyThis country could produce
enough renewable fuels from biomass to provide 40% of our automotive needs
More funding for basic bioconversion research is desperately required
Tom Jeffries, US Forest Products Lab, 2007
Carbon Dioxide Cycle
Ethanol ProcessesDry milling or wet milling
Most ethanol is produced using the dry milling method
Wet MillingWet Mill Process
Basic Dry-Mill Etoh Production1. Corn kernels are cleaned & conditioned2. Kernels pass through roller mill to separate
germ, endosperm, hull by gravity
Image from www.cerealprocess.com/ html/fractionation.html
Corn CompositionEndosperm: houses the starch. 65-70% of the
kernel weight is endosperm.Germ: houses the corn oil. 5% of the kernel
is the germ.Pericarp: commonly called the hull or outer
layer. Comprises about 5% of the kernelOther: Moisture [15%], salts, other solubles.
Corn ReceivingHigh starch and high protein (gluten: type of
protein) corn is desired by ethanol facility. Protein is unfermentable in the process but makes for a high value by-product.Transportation of product
Combine, Truck or Rail, Elevator, Storage bin
Corn ReceivingCorn entering the facility is checked for m.c.,
weight, it is passed over a magnet and a screen to remove larger, undesired matter.
Number 2 Yellow Corn Specifications:Bushel weighs 56 lbs.Limit of 0.2% heat damaged kernels5% total damaged kernels3% total broken kernel/foreign material
presenceMoisture level of 15% or lower
Corn Receiving cont.All corn is checked for aflatoxin, a major
mold found in corn. A black light is used to look for rodent urine and aflatoxin. Aflatoxin and rodent urine can lead to bacteria
infection in the fermentation tank.
Milling/GrindingIncoming feedstock is screened for large
particles and ground to a consistency of coarse flour in either a hammer mill or roller mill. After this step the feedstock is called meal.
Question:What is the significance of proper milling of
corn?
Milling/Grinding Cont.Hammer mill can operate at around 2000
bushels per hour or 110,000 pounds per hour.The hammer mill creates a flour like
substance.The hull or protective layer is destroyed
Question:What is another option besides milling your
product at the facility?
Milling/Grinding Cont.Sieve Analysis
Conducted each twelve hour shift to ensure the hammer mill is operating correctly and the proper sized particles are being produced.
The conflict of particle sizeSmaller is better…in regards to surface area
and ethanol production, however; smaller particles means more suspended particles in the centrifuges (used to separate solids from liquids in the final by-products)
Water addition before cookingNot all the meal can be broken down fine
enough to be attacked by the enzymes. The meal is cooked using condensate, backset (50%: comes from centrifuged byproduct line), and new water which is taken form the CO2 scrubber. The final meal is referred to as gelatinization. At the end of cooking the meal becomes known as mash.
CookingThesis: to chemically prepare starch for
fermentationCooking is conducted in a slurry tank.
Anhydrous ammonia is added in the slurry tank for pH balance and to create free nitrogen (why?). The meal will sit in the slurry tank for 25-30 minutes.pH near 5.5-6.5 pending on enzyme and bacteria
used.28-32% solids contentTemperature kept near 185 degrees
Cooking Cont.The meal is mixed with water and
steam and passed through a jet cooker. The starch in the corn is liquified in this step (230 degrees +).This is done to sterilize the mealReduce bacteria levels in the mashHelps unravel long chain starch
molecules
What is the common theme so far?large energy inputs!
Cooking Cont. (Flash Tank)Pressure is kept high in the cooking process
which keeps the mash in a liquid form. The mash is allowed to vapor off by reduction of pressure within the vessel. This process removes heat to a point where the mash will be near 185 degrees F. The vapor is condensed and reused.
LiquifactionLiquifaction: the conversion of a solid substance
into a liquid state.This process takes place during a holding period.
Mash is heated to 180-190 degrees for roughly 2 hours. Alpha amylase (an enzyme) chemically breaks down the
starch polymers. AA also decreases the viscosity of the mash so it can be
transported by pipe. Completion of solubilization of starch.
Starch Structure
Liquifaction Cont.A second enzyme is also added in this step.
But first the liquifaction must be cooled before gluco amylase is introduced.Gluco amylase added to break down short
starch polymers into glucose molecules. GA releases individual glucose molecules from the liquified mixture. This is known as saccharification.
GA can some time be added in the cooking phase. This is called simultaneous saccharification
http://academic.brooklyn.cuny.edu/biology/bio4fv/page/1-6branch2.JPG
What is an enzyme?Made from bacteria, yeast, fungi
A complex proteinSafe to handle but can cause allergensEach enzyme has only one jobEnzymes do not get used up in a processWhen an enzymes job is done it will be broken
down naturally Cellulosic ethanol [hexane and pentane research]
Testing An iodine test is conducted after liquifaction
to determine the levels of starch in the mash. If starch is detected, retention time in the liquifaction tanks can be increased.
QuestionsWhy is meal ground fine?What is the acceptable m.c. for ethanol corn?What are the two enzymes added to break
down starch?The liquifaction process takes how long?
Fermentation“Beer is proof that God loves us and wants
us to be happy.” Ben Franklin
The mash from the liquifaction process is pumped into fermentation tanks along with large amounts of yeast.
Yeast is added to ferment sugar to ethanol and CO2. Heat is also a by-product of the reaction.
What is Yeast
Fermentation Cont.Yeast attacks maltose and glucose to produce
ethanolIMPORTANT: fermentation time can vary
considerably due to: various yeast strands used rate of enzyme addition temperature of fermentation (90-95 degrees F) type of enzyme used final target ethanol concentration.
Why not just let it ferment to completion?
Yeast Stress FactorsSugar concentrationEthanol concentrationTemperatureBacteria infectionMycotoxinsNutrient levels (N)
Fermentation Process OptionContinuous Fermentation
The mash migrates through several fermentation vessels until fully fermented and then it leaves the final tank
Batch FermentationThe mash stays in one fermenter for about 48
hours before it is transferred to the beerwell prior to distillation.
Question:What are the pros and cons to each process?
Beerwellbeer flows from the fermentation tank to the
beerwell. The beerwell seperates the fermentation tank from the distillation process.
The beerwell does not have a heat exchanger present.
The beerwell is usually never emptied and cannot be CIP’d without shutting down the process.
Beer leaving the beerwell is heated by mash leaving the liquifaction tank.
Beerwell Image
Beerwell continuedFermentation continues in the beerwell
resulting in 1-2% more ethanol. It takes about 2.5 hours to transfer a batch from the fermenter to the beerwell. The beerwell is in continuous operation.
Question:What is the problem with having a process step
in continuous operation?Genesis Plastics Example
DistillationThe fermented mash, now called beer,
contains about 10% alcohol, water, as well as the non-fermentable solids from the corn and yeast cells.
Beer is feed into the continuous flow, multi-column distillation system where heat is applied to boil off the ethanol.
Alcohol leaves the distillation column at about 96% strength.
Fraction distillation
How Refining Works
Ethanol distillationWill generally have three columns
1. Beer Column2. Side Stripper3. Rectifier
Of these, only the beer column and side stripper have an external heat source. The rectifier uses vapor heat from the other two columns as a heat source.
Home Brew Ethanol
Beer ColumnBeer from the beerwell enters the beer column
near the top. In a 50 MGY facility, 700-900 gallon per minute of beer is pumped in the column.
The column is maintained at negative pressure which allowing liquids to boil below standard conditions.
Side StripperWater and non-fermentables that enter the
beer stripper will cascade down the column. All the alcohol and some water will be vaporized and exit the top of the column as low proof vapor. This low proof alcohol vapor enters the rectifier.
The side stripper received low proof bottoms from the rectifier and beer column.
RectifierCollects the low proof alcohol vapor (80-100
proof) from the top of the other two columns. Some vapors condense upon entering the rectifier though there is no external heat source. A vacuum in the rectifier column creates a vapor state in the column. Vapors from other columns enter at the lower level Reagent grade alcohol from the molecular sieve bed
enters in the middle of the rectifier 190 proof alcohol exit the top.
Rectifier Column Cont.Three draw streams leave the rectifier column
High proof alcohol vapors This high proof alcohol vapor is condensed, 2/3rd of
it returns to the rectifier to maintain temp. and purity. 1/3rd of it goes to storage
Rectifier bottoms Still contains some alcohol, is pumped to the side
stripper for further upgrading. Fusel oils (German for higher alcohols)
By-products of fermentation, congregate at certain temps and must be removed or else they can form fusel plugs.
Distillation ContinuedResidue water and non-fermentable
components [called whole stillage], collect at the base of the distillation columns. This stillage is transferred from the base of the column to the co-product processing area.
Note: The energy required for distillation decreases with increased alcohol concentration in the beer. Over 15% conc. This relationship fails.
DehydrationThere is still water in the ethanol which was
distilled from the top of the distillation column. A dehydration system is further used to remove the remaining water.Azeotropic distillation
An azeotrope is a mixture of two or more pure compounds (chemicals) in such a ratio that its composition cannot be changed by simple distillation. Other compounds must be added so separate can occur.
Molecular Sieves The azeotrope is run over a molecular membrane which
grabs at the water molecules and removes them.
A molecular sieve compound
Molecular Sieve cont.Three important aspects of the molecular
sieveHeat PressureVacuum
In most ethanol facilities there will be two or three sieves. One will be on-line while other is purging water by vacuum and re-pressurizing.
Sieve Chemistry
The molecular sieve is a crystalline zeolite bead bed with 3 anstrom size holes. Ethanol is 4.4 angstroms in size while water is 2.8 angstroms in size.
DenaturingEthanol is denatured using standard
gasoline, leaving it unfit for human consumption. This is done by blending 200 proof alcohol with 2-5% gasoline. Blindness and death can result from its
consumption. Other additives might be added to give the final product a bitter taste in-case one tries to consume it!
Co-productsTwo main co-products [distillers grain and
CO2]Distillers Grain
Generally goes through centrifugation to separate the majority of the water from the solids. 10-15% to 25-40% solids. This can then be further
dried to increase the solids content to over 88%. This product is called Dried Distillers Grain (DDG)
CO2 Collected off the fermentation vessels, compressed,
and sold to various industries.
CO2 gas ScrubbersCO2 leaving the top of the fermenters and
beerwell is piped into a CO2 scrubber system. CO2 gas is fan driven to the bottom of the scrubber. Once here:1. CO2 gas raises through the packing to the top2. Fresh water is sprayed into the top and filter
through the packing, grabbing ethanol and other compounds.
The liquid residual is recycled in the slurry blender, the CO2 can be released or sold for industrial purposes.
Co-products cont.Whole Stillage = waste solution from the
ethanol process is pumped to the centrifuges. Two process streams result:Wet cake at 35% solidsThin stillage at 4-5% solids.
Wet CakeThis material leaves the centrifuge at about 20
tons/hr. It can be sold as is or can be dried further and sold as dried distiller grain (DDG).
Thin StillageSolid particles that stay in
the thin stillage after centrifugation end up in the backset. The water in the backset is recycled back into the fermentation tanks. The solids invariably travel back to the tanks as well. These can build up in the bottom of the tanks reducing the contact surface area and slow production.
Thin Stillage Cont.This watery solution can be pushed through
evaporator to remove water from the syrupy solid. Once this is complete, the syrupy by-product can be mixed with the wet cake to form wet distillers grain with solubles (WDGS) or added to the wet cake, dried and called dried distillers grain with solubles (DDGS). The syrup in thin stillage has a high fat content
making it very attractive as a feed supplement.
Rotary Drum DryerA direct fired RDD can be used to produce
the needed dry products. A 50 MGY facility can produce 7.5 tons/hr of
DDGS FEECO
Pollution ControlCyclones
Handle particulatesThermal Oxidizer
Destroy CO, VOCs, NOx
Final PathwaysWet cake for feedSyrup for feedDDGDDGSWDGSA 50% m.c. product known as modified wet
distillers grain with solubles (MWDGS)
Question What is the order of operation in an ethanol
facility?Milling/GrindingCookingLiquifactionFermentationDistillationDehydrationDenaturing
QuestionWhat is the main difference between
continuous flow and batch fermentation?What are a few ways to vary the fermentation
time?