DESIGN OF AN ETHANOL FERMENTATION PLANT. John Schrilla

Transcription

1 DESIGN OF AN ETHANOL FERMENTATION PLANT By John Schrilla Approved: Dean Kashiwagi Director Jacob Kashiwagi Second Committee Member Accepted: Dean, Barrett, the Honors College

2 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.

3 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

4 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) liquid 1. 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 bonding 2. In Figure 1 on the following page, the hydroxyl group is visible as a part of the overall ethanol chemical structure. 1

5 Figure 1: Ethanol Chemical Structure Drawing 2 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 acetaldehyde 2. 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 explosive 2. 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 g can be fatal 2. 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 polymers 3. Currently, 2

6 the US ethanol market is dominated by fuel ethanol, with 92% of ethanol used in fuel, 4% in beverages, and 4% in other industrial applications 4. 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 ethanol 5. 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 combustion 6. Additionally, ethanol is overwhelmingly produced in the US from domestically grown corn as opposed to gasoline which is chiefly derived from imported petroleum 7. 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 E10 5. 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 vehicles 5. 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 3

7 compressible than gasoline, which allows for more fuel to be combusted and therefore more power to be delivered by the engine 6. 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 gasoline 5. 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 emissions 6. 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 fuels 8. 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 health 8. 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 4

8 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 all 8. 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, oil 8. 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 5

9 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 Sources 9 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 US 7. 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. 6

10 Percent GHG Emissions of Petroleum Counterpart John Schrilla 100% 80% 60% 40% 20% 0% -20% Petroleum Gasoline Corn Ethanol Sugarcane Ethanol Switchgrass Ethanol Figure 3: Lifecycle GHG Emissions from Biofuels, Compared to their Petroleum Substitutes 10 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 crop 10. 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 worldwide 4. As the primary feedstock for all ethanol fuel, corn benefits from the 7

11 Corn Production (Billions of Bushels) John Schrilla 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. 16,000 14,000 12,000 10,000 8,000 6,000 Total Production Used for Ethanol 4,000 2, Figure 4: US Corn Production and Use for Fuel 11 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 industry 12,13. The growth of US ethanol production is presented in Figure 5 on the following page. 8

12 Production (billion gal) John Schrilla Capacity Production Figure 5: US Ethanol Capacity and Production 12 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

13 Vehicles Sold John Schrilla 3,000,000 2,500,000 2,000,000 1,500,000 1,000, ,000 0 Figure 6: E85 Fuel Vehicles in Use in the US 14 It is obvious that the number of flexible-fuel vehicles being sold is increasing, especially in the years since 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 fuels 14. 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 E 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. 10

14 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 below 16. C 6 H 12 O 6 2C 2 H 5 OH + 2CO 2 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 Processes 17 11

15 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 byproducts 17. 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 components 18. 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 viable 17. 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 processes 17,19. 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 hour 17. 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 MT per year 4. 12

16 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 screen 17. 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 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 hours to allow the yeast to fully metabolize the sugars and convert as much as possible into ethanol 17. Due to the long processing times required, fermentation is typically implemented as a batch process. Upon completion, the fermentor outputs 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. 13

17 The third and final major section of the ethanol plant consists of the separation and John Schrilla purification stages. This section has been modeled in Aspen HYSYS software to allow for a more detailed look, presented in Figure 8 below 20. 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. 14

18 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 15

19 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 used 21. When substituted for gasoline, the ethanol produced has the capability to reduce annual US carbon emissions by 13.7 thousand metric tons 22. 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. Yearly Prod / Price per Unit Yearly Resources Consumption Revenue / Cost Products Ethanol 7,347,546 gallons $ 1.50 $ 11,021,319 DDGS 20,235 MT $ $ 3,844,650 Fusel Oil 1,904 MT $ $ 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 16

20 operating ethanol plants 23. 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 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, DDGS $ 923,750 $ 1,884,913 $ 2,846, Fusel Oil $ 1,475,552 $ 1,884,913 $ 2,294, Corn $ 4,509,035 $ 1,884,913 $ (739,210.28) Water $ 1,893,723 $ 1,884,913 $ 1,876, Natural Gas $ 2,325,012 $ 1,884,913 $ 1,444, Table 2: Plant Profit Sensitivity to Resource Price Fluctuation 17

21 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. 18

22 CO2 Emissions Reduction (MT) Corn Ethanol Switchgrass Ethanol Full E10 Adoption 2.55*10 7 (2.1%) 1.34*10 8 (11.0%) Full E85 Adoption 2.17*10 8 (17.8%) 1.14*10 9 (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 ethanol 10. 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 stations 14. 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 corn 10. This path has its own difficulties, including a more complicated production process and lower theoretical yields of ethanol 24. 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 gasolinerelated 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. 19

23 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. 20

24 References [1] Ethanol. NIST: ETHANOL [2] Ethanol. Kirk-Othmer Encyclopedia of Chemical Technology [Online]; Wiley & Sons, Posted 18 June 2004 [3] Ethanol. Coskata, Inc: EE3777CF-954D FDA-CAA6F [4] Clark, B. Ethanol. ICIS Chemical Business [Online] (Apr 8 Apr ): 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: [7] Ethanol Production. Alternative Fuels Data Center: [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: [10] Alternative Fuels Data Center. [11] Alternative Fuels Data Center. [12] Alternative Fuels Data Center. [13] AEO2014 Table [14] Alternative Fuels Data Center. [15] E85Prices. [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: [18] How Ethanol Is Made. Renewable Fuels Association. [19] Ethanol Production. Alternative Fuels Data Center. [20] AspenHYSYS Tutorials and Applications. University of Minnesota. [21] Iowa Corn Growers Association. [22] Calculations and References. [23] Hofstrad, D. Ag Decision Maker. Iowa State University [24] Ethanol Feedstocks. AFDC. 21

25 Appendix A: Raw Data Figure 4: Figure 5: Year Production For Ethanol , , , ,087 1, ,806 1, ,112 1, ,531 2, ,038 3, ,092 3, ,092 4, ,447 5, ,360 5, ,780 4, ,925 5,050 Year Capacity Production ,840 1, ,007 1, ,738 2, ,190 2, ,699 3, ,398 3, ,317 4, ,623 6, ,424 9, ,541 10, ,460 13, ,631 13, ,047 13, ,887 13,312 Figure 6: Year FFV Sold , , , , , , ,011, ,115, ,175, , ,484, ,116, ,466,743

26 Appendix B: Equipment Schematics Fermentation Vessel Distillation Column

27 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 E+07 Ferm_Out E+08 Steam_In E+08 Vent_To_Wash E+07 Beer E+08 CO2_Out E+07 Ferm_Recycle E+07 Conc_To_Light E+06 Stillage_A E+08 Conc_To_Rect E+07 Light_Vent E+05 Prod E+05 Light_To_Rect E+06 Rect_Vap E+04 Rect_Dist E+04 Stillage_B E+07 Prod E+07 Fusel E+04 Energy Streams Stream Light_CondQ Rect_RebQ Rect_CondQ Heat Flow kj/h 3.58E E E+07

28 Stream Compositions Stream Ethanol H2O CO2 Methanol Acetic Acid 1- Propanol 2- Propanol 1- Butanol 3-M-1- C4ol 2- Pentanol Glycerol H2O_In Ferm_Out Steam_In Vent_To_Wash Beer CO2_Out Ferm_Recycle Conc_To_Light Stillage_A Conc_To_Rect Light_Vent Prod Light_To_Rect Rect_Vap Rect_Dist Stillage_B Prod Fusel

29 Appendix D: Calculations Corn land use Emissions per gallon E10/E85 from corn bu corn 1 acre = acres 171 bu kg kg = 8.70kg CO gal gas gal eth 2 gal E kg kg = 7.30kg CO gal gas gal eth 2 gal E10 Total US CO2 emissions from gasoline gal gas MT gal gas Emissions reduction from full corn E10 adoption gal eth MT gal eth = MT CO 2 emitted = MT CO 2 reduction