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DESIGN OF AN ETHANOL FERMENTATION PLANT
By
John Schrilla
Approved:
Dean Kashiwagi Director
Jacob Kashiwagi Second Committee Member
Accepted:
_____________________________________
Dean, Barrett, the Honors College
Abstract
Ethanol is a widely used biofuel in the United States that is typically produced
through the fermentation of biomass feedstocks. Demand for ethanol has grown
significantly from 2000 to 2015 chiefly due to a desire to increase energy independence
and reduce the emissions of greenhouse gases associated with transportation. As demand
grows, new ethanol plants must be developed in order for supply to meet demand. This
report covers some of the major considerations in developing these new plants such as the
type of biomass used, feed treatment process, and product separation and investigates
their effect on the economic viability and environmental benefits of the ethanol produced.
The dry grind process for producing ethanol from corn, the most common method of
production, is examined in greater detail. Analysis indicates that this process currently
has the highest capacity for production and profitability but limited effect on greenhouse
gas emissions compared to less common alternatives.
John Schrilla
3/31/2015
Design of an Ethanol Fermentation Plant
Table of Contents
Executive Summary .........................................................................................................................1
Background ......................................................................................................................................1
Properties ....................................................................................................................................1
Uses .............................................................................................................................................2
Environmental Impacts ...............................................................................................................4
Market .........................................................................................................................................7
Design ............................................................................................................................................11
Process ......................................................................................................................................11
Plant ..........................................................................................................................................12
Analysis.....................................................................................................................................16
Conclusions ....................................................................................................................................20
References ......................................................................................................................................21
Appendix ........................................................................................................................................22
John Schrilla
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1
Executive Summary
This report covers the design of a plant for producing ethanol from the fermentation of
biomass and investigates its potential for profitability and environmental benefit. Ethanol is a
common fuel additive and $33 billion industry in the United States with the potential to
simultaneously reduce foreign energy dependence and domestic carbon emissions. The proposed
plant converts corn into ethanol and several valuable byproducts through dry grind processing
and fermentation. It yields 7.3 million gallons of ethanol each year at an estimated annual profit
of $1.8 million, with the potential to reduce annual carbon emissions by 13.7 thousand metric
tons when substituted for pure gasoline. This process is the most common because it is the most
economically viable, but there are alternatives with greater environmental benefits.
Background
Properties
Ethanol (C2H5OH), also known as ethyl alcohol or simply alcohol, is an organic chemical
most known for its use as a fuel additive and beverage. At ambient temperatures and pressures,
it is a clear, colorless liquid. It is relatively volatile and can typically be identified by its
noticeable, characteristic alcoholic odor. Compared to water, it is a relatively low freezing point
(-114°C), low boiling point (78°C), and low density (0.789g/mL) liquid1. Despite these
differences in properties, ethanol and water are commonly mixed and are very miscible due to
their similar intermolecular forces. Both molecules contain hydroxyl (-OH) groups which
increase polarity and allow for hydrogen bonding2. In Figure 1 on the following page, the
hydroxyl group is visible as a part of the overall ethanol chemical structure.
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Figure 1: Ethanol Chemical Structure Drawing2
The hydroxyl group is also an important factor in most chemical reactions involving ethanol. It
serves as a reactive site in organic reactions such as dehydration, dehydrogenation and
esterification. Through these reactions, ethanol can be used to form common industrial chemical
feedstocks such as ethylene and acetaldehyde2. For these reasons, pure ethanol should be stored
and transported separately from other reactive organic compounds and metals in order to avoid
side reactions that produce undesirable byproducts.
The chief risks associated with ethanol production and use are its high flammability and
its potential to cause intoxication or even poisoning when consumed. Its flash point is 14°C and
vapor concentrations as low as 3.3% by volume are potentially explosive2. To avoid risk of
explosion, it should be stored at lower temperatures and kept away from any source of ignition.
Although ethanol vapors are typically not toxic, liquid doses as low as 75–80g can cause
intoxication and 250–500g can be fatal2. It should therefore be consumed sparingly and in low
doses.
Uses
Ethanol produced in the United States has three major applications: fuel ethanol,
beverage ethanol, and industrial ethanol. Fuel ethanol is blended with gasoline for use as motor
fuel. Beverage ethanol is used to produce beer, wine, and other spirits. Industrial ethanol is a
chemical feedstock typically used to produce pharmaceutical products and polymers3. Currently,
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the US ethanol market is dominated by fuel ethanol, with 92% of ethanol used in fuel, 4% in
beverages, and 4% in other industrial applications4.
Fuel ethanol can be found in nearly every gas station in the country – in fact, over 95% of
gasoline currently sold in the US is blended with ethanol5. For the most part, gasoline blended
with ethanol is the norm and is not even noticeable aside from a small sign located at the pump.
Ethanol fuel blends have grown in popularity over the last 15 years due to their ability to
simultaneously reduce air pollution associated with fuel combustion and lower dependence on
foreign oil. Ethanol functions as an oxygenating agent when mixed with gasoline, which means
that the fuel burns more cleanly and more completely. This limits the production of carbon
monoxide, a harmful byproduct of incomplete combustion6. Additionally, ethanol is
overwhelmingly produced in the US from domestically grown corn – as opposed to gasoline
which is chiefly derived from imported petroleum7. In this way, ethanol blends diversify the
energy sources relied upon by the US and shift them from unreliable foreign sources to more
easily controlled domestic sources.
Ethanol can be blended into fuel at a variety of specifications depending on the needs of
the consumer. The blend most likely seen by consumers contains 10% ethanol with 90%
gasoline and is commonly known as E105. This blend is popular chiefly because it is able to
offset large amounts of gasoline use without having a significant effect on engine performance.
Other high-level ethanol blends, such as E15 and E85, are growing in popularity but they are
only intended for use in specialty vehicles known as flexible-fuel vehicles5.
The high ethanol content has significant effects on the properties of the fuel which can
have unforeseen results in the engines of traditional vehicles. The differences can mostly be
traced back to the differing vapor properties between ethanol and gasoline. Ethanol is more
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compressible than gasoline, which allows for more fuel to be combusted and therefore more
power to be delivered by the engine6. This is reflected in the high octane rating of ethanol,
which is actually higher than gasoline itself. Ethanol is blended with gasoline to increase its
octane rating, making it more suitable for use in high performance engines. This benefit is offset
by the relatively low energy density of ethanol. On a per volume basis, ethanol contains about
30% less energy than gasoline5. This means that combustion of fuel blends releases less energy
than pure gasoline and in practice results in more frequent refueling. In the E10 blend that is
common today these effects are minimal, but as higher level blends become more widely used
they will be an important consideration for vehicle manufacturers and consumers.
Environmental Impacts
Ethanol fuel owes most of its success to its low environmental footprint in comparison to
pure gasoline. The earliest environmental benefit observed in ethanol fuel was its ability to
function as an oxygenating agent, improving the combustion performance of the fuel and
reducing carbon monoxide emissions6. Emissions of carbon monoxide associated with
transportation rose throughout the 1980s until the US Environmental Protection Agency stepped
in to regulate them. Amendments to the Clean Air Act passed in 1992 mandated lower carbon
monoxide emissions and were an important first step in the development of cleaner-burning
fuels8. However, it would take another 10 years before ethanol was utilized as a fuel additive on
a large scale. In the meantime, methyl-tertiary butyl ether (MTBE) was used. However, in the
early 2000s it was found that MTBE was contaminating groundwater and could have harmful
effects on public health8. It was at this time that ethanol came to the forefront as a safe,
environmentally friendly fuel additive able to reduce carbon monoxide emissions without
poisoning local water supplies. There are drawbacks, however. Ethanol fuel has notably higher
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emissions of acetaldehyde, a pollutant and potential carcinogen, than traditional gasoline. The
emission of other air pollutants, such as nitrogen oxides (NOx) and volatile organic compounds
(VOCs) is not significantly reduced and may not be affected at all8. Ethanol offers
improvements in some respects, but it is far from a perfect fuel and comes with problems of its
own.
Increased awareness regarding fossil fuel use and its effect on global climate change has
also brought ethanol to the forefront as a potentially carbon-neutral transportation fuel.
Increased concentrations of carbon dioxide in the environment have been linked to climate
change in numerous studies by research groups across the world, and carbon dioxide emissions
can be easily traced back to the widespread combustion of fossil fuels such as coal, methane, and
most relevantly, oil8. Extracting and burning these fossil fuels releases carbon that has long been
trapped underground and leaves it in the atmosphere with no pathway for it to be removed.
Ethanol and other fuels derived from biological sources are very attractive as an alternative to
fossil fuels because they are theoretically carbon-neutral – any carbon emitted by their
combustion is then quickly converted back into organic form when the feedstock is regrown. In
the case of ethanol, carbon cycles between the atmosphere and the corn crop but the overall
carbon concentration never changes.
In reality, biofuels do not live up to the promise of carbon-neutrality. There are carbon
emissions associated with growing corn and transporting ethanol that are not offset, not to
mention the remaining 90% of the fuel blend that consists of gasoline. These factors have been
heavily investigated in recent years due to the widespread deployment of ethanol fuel blends and
so they are fairly well understood and quantified. The results of a study carried out by the Center
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for Transportation Research at Argonne National Laboratory to determine the actual emissions
balance are presented in Figure 2 below.
Figure 2: Emissions Balance of Ethanol from Various Sources9
These results show that a large amount of energy derived from fossil fuels is actually consumed
in order to provide ethanol fuel to consumers. In every case, ethanol fuel requires more energy
to produce than gasoline. However, when accounting for only energy derived from fossil fuels
the requirements for ethanol are substantially lower. This is because a large portion of the
energy required is derived from renewable sources, a substantial benefit over gasoline. This
section also introduces the differences between corn ethanol and cellulosic ethanol. Corn is by
far the most common source of ethanol due to its availability and ease of production in the US7.
However, ethanol produced from cellulosic sources such as switchgrass are significantly more
effective at reducing carbon emissions. This is reflected in the results of an EPA study presented
in Figure 3 on the following page.
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Figure 3: Lifecycle GHG Emissions from Biofuels, Compared to their Petroleum Substitutes10
It can be seen here that corn ethanol, despite its popularity, only reduces carbon
emissions by 21%. Switchgrass ethanol is a very effective alternative, reducing carbon
emissions by an incredible 110% due to its ability to trap carbon within the soil and its biomass.
Cellulosic ethanol as a whole is a very promising alternative to corn ethanol, and can even be
produced from corn stover, or the leaves and stalks of the corn crop10. This has the added benefit
of leaving the corn kernel for use as food when compared to typical corn ethanol which uses the
entire plant. Although cellulosic ethanol is not commonly used due to a more complex and
expensive fermentation process, but it should not be ignored as a potential source for ethanol in
the future.
Market
The market for ethanol has experienced tremendous growth over the past 15 years,
chiefly due to government mandates and incentives regarding vehicle emissions. The driving
force behind these regulations is the corn industry. The ready availability of corn is a large part
of why the US has pushed corn ethanol so heavily and why it is the number one producer of
ethanol fuel worldwide4. As the primary feedstock for all ethanol fuel, corn benefits from the
-20%
0%
20%
40%
60%
80%
100%
PetroleumGasoline
Corn Ethanol SugarcaneEthanol
SwitchgrassEthanol
Pe
rce
nt
GH
G E
mis
sio
ns
of
Pe
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m C
ou
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John Schrilla
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8
growth of the ethanol industry more than any other. Figure 4 below shows corn production over
the last 15 years since corn ethanol became widespread.
Figure 4: US Corn Production and Use for Fuel11
Although total corn production has risen steadily over this time period, the more significant trend
is the growth in the fraction of corn that is used for producing ethanol. Since 2000, this fraction
has risen from less than 10% to greater than 40% of the total corn crop, making corn producers
very reliant on the ethanol market. Based on this data, it is safe to assume that the corn industry
will lobby heavily in favor of corn ethanol for the predictable future and any efforts to phase it
out will be difficult and slow.
Thanks to the ready availability of corn as a feedstock and assistance from government
mandates, the growth of the ethanol industry has been remarkable. Over 13.3 billion gallons
were sold in 2013 at an average value of approximately $2.50 per gallon, making ethanol a $33
billion industry12,13. The growth of US ethanol production is presented in Figure 5 on the
following page.
0
2,000
4,000
6,000
8,000
10,000
12,000
14,000
16,000
2000 2002 2004 2006 2008 2010 2012 2014
Co
rn P
rod
uct
ion
(B
illio
ns
of
Bu
she
ls)
Total Production
Used for Ethanol
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Figure 5: US Ethanol Capacity and Production12
It can be seen that US ethanol production has increased from less than 2 billion gallons per year
to over 13 billion gallons per year, an increase of over seven times. This is an incredible rate of
growth over a very short time. However, production has actually leveled off over the last few
years. The industry grew so quickly due to the introduction of the E10 fuel blend, but now that it
has been so widely distributed the potential for growth is limited. The market has reached a
saturation point and in order for growth to increase, a new market must be found.
Enter flexible-fuel vehicles. These vehicles are specially designed to run on high-level
ethanol fuel blends in addition to pure gasoline or E10 blends. These vehicles represent a market
for E85, which contains over eight times the ethanol content of E10 and has the potential to bring
about another significant increase in ethanol demand. Although they are currently niche and not
very well understood by the general public, they are becoming increasingly common (thanks
again to government mandates of the automotive industry). It is estimated that there are more
than 15 million flexible-fuel vehicles on the road in the US currently, and this number will likely
continue to grow. Figure 6 on the following page shows how flexible-fuel vehicle availability
has grown in the US since 2000.
-
2
4
6
8
10
12
14
16
2000 2005 2010 2015
Pro
du
ctio
n (
bill
ion
gal
)
Capacity
Production
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Figure 6: E85 Fuel Vehicles in Use in the US14
It is obvious that the number of flexible-fuel vehicles being sold is increasing, especially in the
years since 2010. This is likely a response to the plateau in ethanol demand and a need to
expand the market for E85 fuel. Although this market looks promising, its potential is currently
untapped. The majority of Americans who own flexible-fuel vehicles are not even aware of it
and continue to use standard fuels14. Additionally, E85 is not yet widely available so even those
who understand their vehicle cannot always make use of it.
Although the ethanol market has reached a plateau in recent years, it is poised to undergo
another period of rapid growth when E85 fuel becomes more well-known. It is already priced
competitively with gasoline with a current cost of $1.85 per gallon for E85 and $2.30 per gallon
for E1015. Factoring in the lower energy density of ethanol, these two fuels cost approximately
the same amount per unit of energy delivered. Currently the only limiting factor is consumer
awareness and demand. Increasing this awareness will drive more gas stations to carry E85 and
further increase demand. Advertising of these high-level ethanol blends should therefore be a
priority for the ethanol industry moving forward, and if properly executed it could have huge
impacts on ethanol demand across the country.
0
500,000
1,000,000
1,500,000
2,000,000
2,500,000
3,000,000
Ve
hic
les
Sold
John Schrilla
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Design
Process
Ethanol intended for use in fuel is typically produced through the fermentation of corn.
In a fermentation process, microorganisms called yeast are used to metabolically convert sugars
into ethanol and carbon dioxide via the simplified chemical reaction below16.
𝐶6𝐻12𝑂6 → 2𝐶2𝐻5OH + 2𝐶𝑂2
The process is considerably more complex than a single reaction, however, and requires a good
deal of preparation before exposing the corn feed to the yeast. Additionally, there are several
valuable products and byproducts that must be purified and separated after fermentation has
taken place. Ethanol plants typically carry this preparation and purification out through one of
two major processes: dry grind and wet mill. The steps involved in each of these processes are
outlined in Figure 7 below.
Figure 7: Comparison of Ethanol Fermentation Processes17
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In the dry grind process, the whole corn kernel is milled into a floury mash then mixed
with water to form a liquid mash. Enzymes are added to convert the starch within the mash into
sugars, and then yeast is added to ferment these sugars into ethanol. The resulting mixture is
separated into three major groups of byproducts: carbon dioxide, distiller’s dry grains (DDGS),
and purified ethanol. This process is favored for its lower capital costs and energy requirements,
but this simplicity results in some loss of value in unrecovered byproducts17.
In the wet mill process, the corn kernel is first steeped in a sulfurous acid solution to
separate it into its germ, fiber, gluten, and starch components18. This allows for oil and gluten to
be recovered before the remaining starch is liquefied, converted into sugars and fermented. The
oil and corn gluten feed products represent added value in addition to the ethanol and carbon
dioxide products also found in the dry grind process. This comes at the cost of greater capital
investment in equipment and higher energy use so it is not always economically viable17.
Due in large part to the greater simplicity of the dry grind process, it is significantly more
common and is utilized in approximately 75% of all ethanol production processes17,19. This
project will therefore examine the dry grind process in greater depth in the following sections.
Plant
The plant proposed in this project will produce approximately 900 gallons (2700 kg) of
ethanol per hour. Based on typical industrial yields of 2.8 gal ethanol per bushel of corn, this
will require a feed of just over 320 bushels of corn per hour17. Assuming that the plant operates
8150 hours per year, this corresponds to 22,000 metric tons of ethanol produced every year. This
is relatively small scale for an industrial ethanol plant – the largest plant in the US produces
1,250,000 MT of ethanol yearly, with many more in the range of 325,000–350,000 MT per year4.
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The first major section of ethanol plant operation involves the preparation of the corn
feedstock for fermentation. This section includes the milling, liquefying, and starch converting
steps. In the dry grind process, this section is very simple. Whole corn kernels are fed into a
hammer mill and ground until they can be fed through a 30 mesh screen17. The resulting meal is
then slurried with water to form mash. At this stage, the plant must accommodate approximately
8050 gal mash per hour (based on industrial records of 22 gal mash per bushel of corn)17. It must
be adjusted to pH 6.0 before being exposed to alpha-amylase, the enzyme that begins the
conversion of starch to glucose. The mash is then heated to 100°C and held for 30–40 minutes
before being cooled slightly, adjusted to pH 4.5 and exposed to the second enzyme glucoamylase.
This second enzyme completes the conversion of starch into glucose and the resulting mixture is
ready for fermentation.
The second major section of the ethanol plant consists of the fermentation reaction itself.
At this point, yeast is added and the mixture is fed into a fermentor. A fermentor is a specialized
vessel with a motorized impeller for stirring and outlets for regular testing of the contents. This
allows for mixture to be uniformly exposed to the yeast and for the progress of the reaction to be
monitored over time. The fermentor is held at 32°C and left for 48–72 hours to allow the yeast
to fully metabolize the sugars and convert as much as possible into ethanol17. Due to the long
processing times required, fermentation is typically implemented as a batch process. Upon
completion, the fermentor outputs 12680 gal per hour of a mixture that consists of mostly water,
carbon dioxide, and ethanol with small amounts of other alcohols, glycerol, and acetic acid. This
mixture must then be separated so the various valuable byproducts can be recovered.
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The third and final major section of the ethanol plant consists of the separation and
purification stages. This section has been modeled in Aspen HYSYS® software to allow for a
more detailed look, presented in Figure 8 below20.
Figure 8: Ethanol Separation Process Flow Diagram
This model shows that the separation process consists of five major pieces of equipment: the
CO2 Vent Separator, CO2 Wash Tower, Concentrator, Lights Tower, and Rectifier.
The fermentor output first flows into the CO2 Vent Separator for the simplest separation.
Here the gas and liquid phases of the reaction mixture are allowed to separate naturally by
density, with the gas flowing up into the CO2 Wash Tower and the liquid flowing down into the
Concentrator.
The gaseous component of the reaction mixture consists of mostly carbon dioxide, but
also trace amounts of ethanol that must be recovered. In the CO2 Wash Tower, the gas stream is
washed with water over 10 stages in order to condense the remaining ethanol. This separates the
stream into purified carbon dioxide, which can be captured and sold or vented, and a water and
ethanol mixture that can be recycled back into the fermentor feed.
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The ethanol rich liquid that exits the fermentor is typically called beer, and it contains
ethanol as well as most of the valuable byproducts. It undergoes a multi-stage purification
process beginning in the Concentrator, where it is mixed with steam. This separates the mixture
by boiling point through a 17 stage distillation, with light components being sent to the Lights
Tower, middle components sent to the Rectifier through a side draw, and heavy components
removed as stillage. The stillage consists of mostly water, with trace amounts of glycerol and
acetic acid.
The light components sent to the Lights Tower contain ethanol mixed with residual water,
carbon dioxide and other alcohols. These components are separated by 5 stage distillation, with
most of the carbon dioxide and methanol vented through the condenser at the top, some ethanol
recovered after being condensed, and the remaining mixture of ethanol and other byproducts
collected at the bottom and sent to the Rectifier.
The final and most important separation takes place in the Rectifier. The side draw from
the Concentrator and the bottoms product of the Lights Tower are fed into the Rectifier where
they are again separated through distillation, this time over 29 stages. The lightest components
are collected as vapor and contain chiefly ethanol that is contaminated by methanol. The ethanol
product is collected at a higher purity through a side draw. Fusel oil, consisting of most of the
remaining propanol, butanol, and pentanol, is removed through a lower side draw. The bottoms
product consists of mostly water and is also removed as stillage.
Overall, this separation process utilizes the fermentor reaction mixture as well as 11,000
kg per hour of steam at 140°C and 2340 kg per hour of water at 25°C. Several valuable
byproducts are separated and collected. Stillage can be repurposed and sold as wet or dry
distiller’s grains and fusel oil can also be sold for industrial use. There are three ethanol-rich
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streams, with 21 kg per hour being recycled to the fermentor and 3060 kg per hour recovered as
valuable product. The product is collected at 88% purity with balance water, the highest allowed
by azeotropic conditions. If necessary, further processing is possible to obtain 100% purity.
Analysis
The proposed plant is on a very small scale compared to the overall US ethanol market –
its output of over 7.3 million gallons per year represents less than 0.1% of annual US ethanol
production capacity, and less than 0.01% of annual US gasoline consumption. This is more
representative of the sheer size of the US ethanol market than the actual size of the plant,
however. The proposed plant consumes over 2.6 million bushels of corn each year, a number
that corresponds over 15 thousand acres of land used21. When substituted for gasoline, the
ethanol produced has the capability to reduce annual US carbon emissions by 13.7 thousand
metric tons22. While these numbers are small compared to the US as a whole, they are certainly
significant for a single plant. A look at the total resource use and associated economics of this
plant are presented in Table 1 below.
Resources
Yearly Prod /
Consumption
Price per Unit Yearly
Revenue / Cost
Products Ethanol 7,347,546 gallons $ 1.50 $ 11,021,319
DDGS 20,235 MT $ 190.00 $ 3,844,650
Fusel Oil 1,904 MT $ 860.00 $ 1,637,440
Raw Corn 2,624,123 bushels $ (4.00) $ (10,496,492)
Materials Water 3,524,428 gallons $ (0.01) $ (35,244)
Operating Natural Gas - - $ (1,760,400)
Costs Yeast, Enzymes - - $ (850,860)
Maint & Electric - - $ (725,500)
Labor - - $ (750,000)
Yearly Profit $ 1,884,913
Table 1: Plant Profitability Analysis
This table shows annual revenue for each valuable product and byproduct, annual costs
for each raw material, and estimates for the major operating costs based on records for actual
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operating ethanol plants23. The most obvious takeaway from this table is the relative importance
of ethanol and corn to the profitability of the plant. Ethanol sales represent 67% of the total
revenue while corn purchases represent 72% of the total costs, making these two resources the
most important factors in determining the economic viability of the plant. That does not mean
that the other resources can be ignored. The byproducts of ethanol production (DDGS and fusel
oil) are not often considered by the public but they represent 33% of the total revenue of the
plant and can be the difference between making and losing money. This underscores the
importance of the multi-stage separation process in purifying and recovering these byproducts.
All of this analysis is based on current resource prices, but ethanol plants typically
operate for a period of 15–20 years. Conditions can change significantly over that much time
and so plants must plan for this fluctuation and maintain profitability. These changing
conditions can involve governmental regulation, resource availability, or resource prices, among
others. The government has been supportive of the ethanol industry in recent years and that
shows no signs of changing. Resource availability has been similarly positive due to the high
capacity of the US agricultural industry. The most likely change will come in resource prices.
As ethanol production has skyrocketed and demand has leveled off, prices have already begun to
fall. The effects of price fluctuations of up to 25% in each individual resource are examined in
Table 2 below.
Yearly Profit
Price -25% Base Price Price +25%
Ethanol $ (870,417) $ 1,884,913 $ 4,640,242.47
DDGS $ 923,750 $ 1,884,913 $ 2,846,075.22
Fusel Oil $ 1,475,552 $ 1,884,913 $ 2,294,272.72
Corn $ 4,509,035 $ 1,884,913 $ (739,210.28)
Water $ 1,893,723 $ 1,884,913 $ 1,876,101.65
Natural Gas $ 2,325,012 $ 1,884,913 $ 1,444,812.72
Table 2: Plant Profit Sensitivity to Resource Price Fluctuation
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These results reinforce the conclusions that have already been drawn – ethanol and corn prices
have the most significant effect on plant profitability. The prices of other resources are less
impactful, with even 25% fluctuations remaining profitable. The most concerning scenarios
involve a 25% decrease in ethanol prices (to $1.13 per gallon) or a 25% increase in corn prices
(to $5.00 per bushel), both of which result in the plant operating at a loss. With all other prices
remaining constant, the plant will break even if ethanol prices drop below $1.24 per gallon or
corn prices rise above $4.72 per bushel. Both of these scenarios are unlikely in the near future
but important to be aware of when considering a possible lifetime of 20 years. Conditions can
change greatly over that much time and so extensive research into future prices is necessary
when deciding to invest in developing a new plant.
Profitability is not the sole driving factor in the development of the ethanol industry – it
and other biofuels have also been promoted due to their environmental benefits over traditional
fossil fuels. This has led to many of the tax credits and subsidies that are relied upon by ethanol
manufacturers and consumers. When considering whether an ethanol plant is worth constructing,
it is therefore important to consider the actual environmental benefits it will bring about. The
fermentation process varies based on the biomass used as a feedstock, and any change in
feedstock would require expensive alterations to the plant. The proposed plant uses starch from
corn kernels, the most common source of biomass, but there are several alternatives. One
alternative that shows promise but has not been widely implemented is cellulosic ethanol. This
utilizes feedstocks such as corn stover and switchgrass and has been proven to bring about a
greater reduction in carbon dioxide emissions than ethanol from corn kernels. The potential
benefits of each of these sources and multiple fuel blends being utilized on a national scale are
presented in Table 3 on the following page.
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CO2 Emissions Reduction (MT)
Corn Ethanol Switchgrass Ethanol
Full E10 Adoption 2.55*107 (2.1%) 1.34*108 (11.0%)
Full E85 Adoption 2.17*108 (17.8%) 1.14*109 (93.5%)
Table 3: Potential US Carbon Emissions Reductions
This table shows the potential reduction in carbon dioxide emissions that could be accomplished
by replacing all gasoline with E10 or E85 fuel blends using ethanol produced from corn kernels
or switchgrass. The emissions reduction is shown in metric tons of carbon dioxide and as a
percentage of current carbon dioxide emissions due to gasoline. The current situation is most
similar to full E10 adoption of corn ethanol, which reduces gasoline-related emissions by only
2.1% over pure gasoline. The low effect is due to both the low ethanol content of the fuel and
the limited emissions reductions associated with corn ethanol10.
There are two possible avenues for further reducing carbon emissions – increasing the
ethanol content of the fuel or using a different type of biomass. The recent push for more
flexible-fuel vehicles is a sign that the US is moving towards further E85 adoption, but this path
comes with some difficulty. It will require even greater land use to supply the necessary corn
and an overhaul of the ethanol fuel blending and distribution system, which at this time does not
even supply E85 to most gas stations14. Similar emissions reductions could be accomplished by
moving to ethanol produced from switchgrass, which fixes carbon more effectively and reduces
carbon emissions by nearly 5 times as much as ethanol produced from corn10. This path has its
own difficulties, including a more complicated production process and lower theoretical yields of
ethanol24. In the long run, however, switchgrass ethanol has a far greater potential for reducing
carbon emissions. Full adoption of E85 fuel with switchgrass ethanol could reduce gasoline-
related carbon emissions by an impressive 93.5%. Whether that scenario is economically
feasible remains to be seen, but the environmental benefits certainly warrant further investigation.
John Schrilla
3/31/2015
20
Conclusions
Ethanol is currently a valuable resource in the US, but its future is uncertain. Demand
has experienced limited growth since E10 fuel blends are already prevalent and higher level
ethanol blends have not yet been widely adopted. As such, investment in an ethanol plant is
risky and should be carefully considered. Corn and ethanol prices are a key factor in
determining plant success, but the added value of distiller’s dry grains and fusel oil byproducts
cannot be ignored. At current prices and with current tax credits and subsidies, corn ethanol
production is profitable. It is also the most well developed and well understood production
process. Although prices may change, regulations will typically favor corn ethanol and help it
maintain viability due to its importance to the agricultural industry and perceived environmental
benefits as a biofuel. This support may be misplaced, however, as the actual impact of corn
ethanol on carbon emissions is fairly low. Alternative biomass feedstocks like switchgrass show
much greater environmental benefits at the cost of much lower economic viability. If carbon
emissions reduction is the priority, governmental incentives would be better spent on research
and development for some of these promising alternatives. If increased domestic energy
independence is the priority, corn ethanol is a proven commodity that can deliver immediately.
It is likely that the future will involve a combination of both. The alternatives have a long way to
go before they can compete with corn, though, and for the immediate future corn ethanol is the
safest option for ethanol plant development.
John Schrilla
3/31/2015
21
References
[1] Ethanol. NIST: 2011. http://webbook.nist.gov/cgi/cbook.cgi?Units=SI&Name=
ETHANOL
[2] Ethanol. Kirk-Othmer Encyclopedia of Chemical Technology [Online]; Wiley & Sons,
Posted 18 June 2004
[3] Ethanol. Coskata, Inc: 2011. http://www.coskata.com/ethanol/index.asp?source=
EE3777CF-954D-4610-9FDA-CAA6F5166155
[4] Clark, B. Ethanol. ICIS Chemical Business [Online] 283.12 (Apr 8 – Apr 14 2013): 34
[5] Alcohol Fuels. Kirk-Othmer Encyclopedia of Chemical Technology [Online]; Wiley &
Sons, Posted 4 December 2000
[6] Ethanol Fuel Basics. Alternative Fuels Data Center:
http://www.afdc.energy.gov/fuels/ethanol_fuel_basics.html
[7] Ethanol Production. Alternative Fuels Data Center:
http://www.afdc.energy.gov/fuels/ethanol_production.html
[8] Air Quality Impacts of Increased Use of Ethanol Under the United States’ Energy
Independence and Security Act. EPA Office of Transportation and Air Quality, 2010
[9] Updated Energy and Greenhouse Gas Emission Results for Fuel Ethanol: Center for
Transportation Research: 2005.
www.eri.ucr.edu/ISAFXVCD/ISAFXVAF/UGEEERF.pdf
[10] Alternative Fuels Data Center. http://www.afdc.energy.gov/data/10328
[11] Alternative Fuels Data Center. http://www.afdc.energy.gov/data/10339
[12] Alternative Fuels Data Center. http://www.afdc.energy.gov/data/10342
[13] AEO2014 Table 12. http://www.eia.gov/forecasts/aeo/er/tables_ref.cfm
[14] Alternative Fuels Data Center. http://www.afdc.energy.gov/data/10299
[15] E85Prices. http://www.e85prices.com
[16] Fermentation. Kirk-Othmer Encyclopedia of Chemical Technology [Online]; Wiley &
Sons, Posted 16 January 2004
[17] Bothast, R. Schlicher, M. Biotechnological Process for Conversion of Corn into Ethanol:
2004. http://www.tamu.edu/faculty/tpd8/BICH407/fulltext.pdf
[18] How Ethanol Is Made. Renewable Fuels Association.
http://www.ethanolrfa.org/pages/how-ethanol-is-made
[19] Ethanol Production. Alternative Fuels Data Center.
http://www.afdc.energy.gov/fuels/ethanol_production.html
[20] AspenHYSYS Tutorials and Applications. University of Minnesota.
https://wiki.umn.edu/pub/Nieber/IntroductionToEngineeringDesign/TutApps.pdf
[21] Iowa Corn Growers Association. http://www.iowacorn.org/en/corn_use_education/faq/
[22] Calculations and References. http://www.epa.gov/cleanenergy/energy-resources/refs.html
[23] Hofstrad, D. Ag Decision Maker. Iowa State University
[24] Ethanol Feedstocks. AFDC. http://www.afdc.energy.gov/fuels/ethanol_feedstocks.html
John Schrilla
3/31/2015
Appendix A: Raw Data
Figure 4: Figure 5:
Year Production For Ethanol
2000 9,915 630
2001 9,503 707
2002 8,967 996
2003 10,087 1,168
2004 11,806 1,323
2005 11,112 1,603
2006 10,531 2,119
2007 13,038 3,049
2008 12,092 3,709
2009 13,092 4,591
2010 12,447 5,019
2011 12,360 5,000
2012 10,780 4,648
2013 13,925 5,050
Figure 6:
Year Capacity Production
2000 1,840 1,622
2001 2,007 1,765
2002 2,738 2,140
2003 3,190 2,810
2004 3,699 3,404
2005 4,398 3,904
2006 6,317 4,884
2007 11,623 6,521
2008 13,424 9,309
2009 14,541 10,938
2010 14,460 13,298
2011 14,631 13,929
2012 15,047 13,218
2013 14,887 13,312
Year FFV Sold
2000 600,832
2001 581,774
2002 834,976
2003 859,261
2004 674,678
2005 743,948
2006 1,011,399
2007 1,115,069
2008 1,175,345
2009 805,777
2010 1,484,945
2011 2,116,273
2012 2,466,743
John Schrilla
3/31/2015
Appendix B: Equipment Schematics
Fermentation Vessel
Distillation Column
John Schrilla
3/31/2015
Appendix C: HYSYS Data
Material Streams
Stream
Vapour
Fraction Temperature Pressure
Molar
Flow Mass Flow
Volume
Flow
(liq) Heat Flow
°C kPa kgmole/h kg/h m3/h kJ/h
H2O_In 0.000 25.0 101.325 130.00 2341.96 2.347 -3.70E+07
Ferm_Out 0.028 30.0 101.325 2400.00 46716.67 48.159 -6.89E+08
Steam_In 1.000 140.0 101.325 610.60 11000.00 11.022 -1.45E+08
Vent_To_Wash 1.000 30.0 101.325 66.47 2857.17 3.454 -2.56E+07
Beer 0.000 30.0 101.325 2333.53 43859.50 44.705 -6.64E+08
CO2_Out 1.000 26.1 101.325 64.72 2792.20 3.375 -2.52E+07
Ferm_Recycle 0.000 33.3 101.325 131.75 2406.93 2.426 -3.75E+07
Conc_To_Light 1.000 85.9 101.325 10.03 301.94 0.351 -2.56E+06
Stillage_A 0.000 100.0 101.325 2616.11 47130.97 47.226 -7.30E+08
Conc_To_Rect 1.000 94.8 101.325 317.99 7426.58 8.150 -7.54E+07
Light_Vent 1.000 46.4 101.325 1.60 68.89 0.084 -5.68E+05
Prod2 0.000 46.4 101.325 2.69 104.78 0.129 -7.44E+05
Light_To_Rect 0.000 80.9 101.325 5.74 128.27 0.139 -1.60E+06
Rect_Vap 1.000 78.0 101.325 0.10 4.31 0.005 -2.32E+04
Rect_Dist 0.000 78.0 101.325 0.05 2.00 0.002 -1.26E+04
Stillage_B 0.000 99.7 101.325 254.47 4590.85 4.602 -7.11E+07
Prod1 0.000 78.1 101.325 69.03 2954.69 3.675 -1.87E+07
Fusel 0.000 83.4 101.325 0.09 3.00 0.004 -2.44E+04
Energy Streams
Stream Heat Flow
kJ/h
Light_CondQ 3.58E+05
Rect_RebQ -2.76E+07
Rect_CondQ 4.04E+07
John Schrilla
3/31/2015
Stream Compositions
Stream Ethanol H2O CO2 Methanol
Acetic
Acid
1-
Propanol
2-
Propanol
1-
Butanol
3-M-1-
C4ol
2-
Pentanol Glycerol
H2O_In - 1.000000 - - - - - - - - -
Ferm_Out 0.026900 0.946411 0.026600 0.000027 0.000003 0.000009 0.000009 0.000007 0.000021 0.000005 0.000007
Steam_In - 1.000000 - - - - - - - - -
Vent_To_Wash 0.016962 0.040865 0.942121 0.000013 - 0.000010 0.000009 0.000006 0.000008 0.000006 -
Beer 0.027183 0.972206 0.000521 0.000027 0.000003 0.000009 0.000009 0.000007 0.000022 0.000005 0.000007
CO2_Out 0.000001 0.033292 0.966703 - - 0.000001 - 0.000001 - 0.000002 -
Ferm_Recycle 0.008557 0.990951 0.000468 0.000006 - 0.000004 0.000004 0.000002 0.000004 0.000002 -
Conc_To_Light 0.316207 0.561185 0.121283 0.000164 0.000002 0.000318 0.000310 0.000148 0.000127 0.000256 -
Stillage_A - 0.999991 - - 0.000003 - - - - - 0.000006
Conc_To_Rect 0.189508 0.809949 - 0.000195 0.000003 0.000056 0.000057 0.000044 0.000156 0.000032 -
Light_Vent 0.188961 0.051717 0.758931 0.000147 - 0.000068 0.000172 0.000001 - 0.000003 -
Prod2 0.745019 0.252440 0.000728 0.000354 - 0.000578 0.000803 0.000016 - 0.000063 -
Light_To_Rect 0.151088 0.847512 0.000042 0.000080 0.000004 0.000267 0.000118 0.000251 0.000222 0.000417 -
Rect_Vap 0.888367 0.105665 0.002439 0.003351 - 0.000002 0.000175 - - - -
Rect_Dist 0.888674 0.108953 0.000002 0.002163 - 0.000005 0.000203 - - - -
Stillage_B 0.000172 0.999501 - - 0.000004 0.000026 - 0.000059 0.000200 0.000037 -
Prod1 0.882618 0.116193 - 0.000899 - 0.000018 0.000272 - - - -
Fusel 0.296676 0.530766 - 0.000080 - 0.133726 0.000335 0.003558 0.000017 0.034842 -
John Schrilla
3/31/2015
Appendix D: Calculations
Corn land use
2624123 𝑏𝑢 𝑐𝑜𝑟𝑛 ∗1 𝑎𝑐𝑟𝑒
171 𝑏𝑢= 15346 𝑎𝑐𝑟𝑒𝑠
Emissions per gallon E10/E85 from corn
0.9 ∗8.887𝑘𝑔
𝑔𝑎𝑙 𝑔𝑎𝑠+ 0.1 ∗
0.79 ∗ 8.887𝑘𝑔
𝑔𝑎𝑙 𝑒𝑡ℎ= 8.70𝑘𝑔 𝐶𝑂2 𝑔𝑎𝑙⁄ 𝐸10
0.15 ∗8.887𝑘𝑔
𝑔𝑎𝑙 𝑔𝑎𝑠+ 0.85 ∗
0.79 ∗ 8.887𝑘𝑔
𝑔𝑎𝑙 𝑒𝑡ℎ= 7.30𝑘𝑔 𝐶𝑂2 𝑔𝑎𝑙⁄ 𝐸10
Total US CO2 emissions from gasoline
1.37 ∗ 1011𝑔𝑎𝑙 𝑔𝑎𝑠 ∗8.887 ∗ 10−3𝑀𝑇
𝑔𝑎𝑙 𝑔𝑎𝑠= 1.22 ∗ 109𝑀𝑇 𝐶𝑂2 𝑒𝑚𝑖𝑡𝑡𝑒𝑑
Emissions reduction from full corn E10 adoption
0.1 ∗ 1.37 ∗ 1011𝑔𝑎𝑙 𝑒𝑡ℎ ∗0.21 ∗ 8.887 ∗ 10−3𝑀𝑇
𝑔𝑎𝑙 𝑒𝑡ℎ= 2.55 ∗ 107𝑀𝑇 𝐶𝑂2 𝑟𝑒𝑑𝑢𝑐𝑡𝑖𝑜𝑛