AN ANALYSIS OF MODERN CORN ETHANOL TECHNOLOGIES

Prepared for:

Illinois Corn Marketing Board 

Prepared by:

Steffen Mueller 

Ken Copenhaver 

Technical Review Provided by:

Martha Schlicher, GTL Resources USA, Inc. 

February 16, 2009 

Energy Resources Center, 1309 South Halsted Street, Chicago, IL 60607 

http://www.erc.uic.edu 
LEGAL NOTICE 

This report was prepared by the Energy Resources Center of the University of Illinois at Chicago 

(UIC) under an agreement with the Illinois Corn Marketing Board. The content of this report is 

solely the responsibility of the authors and does not necessarily represent the official views of 

the UIC, officers, trustees, or staff nor any person acting on their behalf. 
Energy Resources Center 

University of Illinois at Chicago

ii 

Executive Summary 

This study conducted by the University of Illinois at Chicago assesses emerging technologies 

that reduce the energy consumption and the Global Warming Impact (GWI) of corn ethanol 

production. These new technologies have emerged for corn production as well as for ethanol 

processing at the biorefinery. The study documents that many ethanol plants have already 

adopted energy/environmental footprint reducing technologies such as corn oil extraction, 

fractionation, cold cook processes, advanced motors, combined heat and power systems, 

anaerobic digesters, biomass combustion/gasification systems, and other renewable energy 

systems. In summary, a total of 25 out of the 160 operating ethanol plants in the US, or 16%, 

have adopted one or the other of the described technologies. Furthermore, the study documents 

that advanced technologies in corn agriculture such as GPS and Auto-Steer systems in farm 

equipment, slow release fertilizers, nitrification inhibitors, N-application based on soil testing 

and remotely sensed imagery, and N-side dressing reduce the energy/environmental footprint of 

corn ethanol. 

In addition to reducing the energy and environmental footprint these technologies greatly expand 

the diversity of products from a corn ethanol plant. The traditional dry mill process produces 

ethanol and a co-product called distillers grain with solubles, which is sold either wet (as 

WDGS) or dried (as DDGS) to the feed market. Depending on the configuration, modern ethanol 

plants can produce many more co-products including high protein DDG, bran cake, corn oil, 

corn gluten feed, bran energy feedstock, zein protein for bio-plastics, and fertilizer products. 

Integrated combinations of emerging technologies can substantially eliminate the natural gas 

energy consumption at an ethanol plant. One example includes combining fractionation with 

anaerobic digesters and advanced motor systems. Energy assessments performed as part of this 

study indicate that the base energy needs for such a system would drop from 30,000 Btu/gal to 

22,010 Btu/gal of 

which 21,000 Btu/gal 

would be offset by 

biogas produced in the 

anaerobic digester. An 

additional 3,500 Btu 

would be offset by 

combusting bran (in an 

added solid fuel boiler) 

leaving a net surplus 

energy production of 

the plant of 2,490 

Btu/gal. The figure 

provides a flow 

diagram of such a 

system. Besides corn 

ethanol, the plant 

would also co-produce 

2.6 lbs of high protein 

Ethanol 

Storage

Cooking

Fermentation

Distillation

Ethanol

Centrifuge

Evaporator

Dryer

Fractionation Unit

Stillage

Whole

Thin

Stillage

HPDDG

Syrup/Solubles

Corn 

Corn Oil

Thermal 

Energy

Electric 

Energy

Dry Mill Fractionation with

Anaerobic Digestion, Bran 

Combustion and Advanced 

Motors

Farm Energy

Chemicals

Corn Traits

We

Ca

t

ke

Bran Energy

Feedstock

Molecular Sieve

Digester
Energy Resources Center 

University of Illinois at Chicago

iii 

distillers grain (HPDDG) with a highly desirable protein content of 37-44% and 0.25 lbs/gal of 

NPK fertilizer for every gallon of ethanol (while only slightly reducing ethanol yield from 2.73 

gallons per bushel to 2.64 gallons per bushel). 

Studies that assess the energy and environmental differences between corn ethanol and cellulose 

ethanol should be based on a comparative technology stage, which means advanced cellulose 

systems must be compared against advanced corn ethanol systems like the zero energy and 

multiple co-product plants described here. 
Energy Resources Center 

University of Illinois at Chicago

iv 

TABLE OF CONTENT 

1) Introduction ...............................................................................................................................................1

2) Ethanol Processing Technologies ............................................................................................................4

2.1) Corn Oil Extraction ............................................................................................................................................4

2.2) Dry Mill Corn Fractionation...............................................................................................................................6

2.3) Cold Cook Process (aka raw starch hydrolysis) .................................................................................................9

2.4) New Boilers and Motors...................................................................................................................................10

2.5) Combined Heat and Power...............................................................................................................................12

2.6) Anaerobic Digesters .........................................................................................................................................14

2.7) Biomass Combustion/Gasification ...................................................................................................................16

2.8) Other Renewable Energy..................................................................................................................................17

3) Corn Production Technologies ...............................................................................................................18

3.1) Farm Energy.....................................................................................................................................................18

3.2) Corn Traits........................................................................................................................................................21

3.3) Chemicals.........................................................................................................................................................22

4) Energy Summary ....................................................................................................................................26

List of Figures 

Figure 1: Block Diagram of the Ethanol Base Process..................................................................................................2

Figure 2: GWI of Corn Ethanol Produced at Illinois River ...........................................................................................3

Figure 3: Corn Oil Extraction and the Ethanol Process.................................................................................................4

Figure 4: Dry Mill Fractionation and the Ethanol Process ............................................................................................6

Figure 5: Raw Starch Hydrolysis and the Ethanol Process............................................................................................9

Figure 6: New Boilers and Motors and the Ethanol Process .......................................................................................10

Figure 7: Combined Heat and Power and the Ethanol Process....................................................................................12

Figure 8: Anaerobic Digestion and the Ethanol Process..............................................................................................14

Figure 9: Biomass Combustion and Gasification and the Ethanol Process .................................................................16

Figure 10: Other Renewable Energy and the Ethanol Process ....................................................................................17

Figure 11: Farm Energy and the Ethanol Process........................................................................................................18

Figure 12: Corn Traits and the Ethanol Process ..........................................................................................................21

Figure 13: Corn Trait Selection of Farmers Supplying to IRE ....................................................................................21

Figure 14: Chemicals and the Ethanol Process............................................................................................................22

Figure 15: Determining N-Requirements Using Remote Sensing...............................................................................23

Figure 16: Relationship Between Global Warming Impact and Fertilizer Application...............................................25

List of Tables 

Table 1: Efficiency Improvements of New Motors and Boilers..................................................................................11

Table 2: Tractor Trips and Tillage Practices................................................................................................................19

Table 3: Thermal and Electric Energy Consumption by Technology..........................................................................26
1) Introduction 

Over the last three years modern ethanol plants have started to adopt technologies that 

transform the industry into integrated biorefineries producing multiple fuel, feed, and 

bioplastic products. These technologies also alter the energy, environmental impact, and 

co-product balance from corn ethanol production. The Illinois Corn Marketing Board 

retained the University of Illinois at Chicago Energy Resources Center to assess 

emerging technologies that have the potential to reduce the energy consumption and the 

Global Warming Impact (GWI) of corn ethanol production. 

The study looks at both corn production as well as ethanol processing technologies. As 

illustrated in Figure 1 corn is produced by combining the corn hybrid appropriate for the 

soil and climate conditions, with the corn transgenic traits desired for herbicide tolerance 

or pest control and the corresponding agro-economic practice (including fertilizer, 

pesticide, herbicide, tillage, irrigation, and other practices). The harvested corn is stored 

on farm or shipped from the farm directly to the ethanol plant or to a grain elevator first 

and then to the ethanol plant for processing. 

Once arrived at the ethanol plant the traditional dry mill process consists of the following 

steps: Corn is cleaned, ground and slurried with water and enzymes (alpha amylase), 

followed by cooking of the slurry to gelatinize and liquefy the starch (liquefaction). After 

liquefaction, the mash is cooled, and another enzyme is added (gluco amylase) to convert 

the liquefied starch into fermentable sugars. The yeast is added to ferment the sugars to 

ethanol and carbon dioxide, followed by distillation and dehydration.1

 Besides ethanol a 

typical plant also processes the non-fermentable nutrients (protein, fat, and fiber) left over 

after the distillation and dehydration process. If dried these compounds are called 

distillers dried grain with solubles (DDGS), otherwise wet distillers grains with solubles 

(WDGS). DDGS and WDGS are generally used as animal feed. DDGS has a longer shelf 

life than WDGS and can be shipped more economically. The ratio of WDGS and DDGS 

production from a dry mill ethanol plant depends on local market conditions. Large 

lifestock operations in an area will often provide a high demand for WDGS. 

The ethanol dry mill process is energy intensive and requires both thermal energy 

(mainly for cooking, distillation, and drying) as well as electricity (to operate motors, 

fans, and pumps). The natural gas fired dry mill base plant energy system consists of a 

boiler, a direct fired or steam tube drying system, and a regenerative thermal oxidizer 

(RTO). 

Over the last 8 years, the natural gas consumption at dry mill ethanol plants has been 

steadily decreasing. The 2001 Ethanol Plant Development Handbook quotes a natural gas 

use of 40,000 Btu per denatured gallon (Higher Heating Value or HHV) and 1.4 kWh/gal 

of electricity (assumes 100% DDGS drying).2

 In 2006, ICM, Inc. a major ethanol plant 

process developer provided process guarantees for new natural gas fired ethanol plants in 

 

1

 Ethanol Producer Magazine. “Break it Down”; January 2006. 2

 Ethanol Plant Development Handbook, Third Edition; Published by BBI International; January 2001. 
Energy Resources Center 

University of Illinois at Chicago

 

2

the range of 32,000-34,000 Btu per denatured gallon (thermal energy) and 0.75 kWh/gal 

(electricity) with 100% DDGS drying and 22,000 to 24,000 Btu per denatured gallon 

without DDGS drying. Today, the natural gas energy consumption of a modern ethanol 

plant is even lower. A recent energy balance conducted at the Illinois River Energy 

Center (IRE) documented a natural gas consumption of 29,000 Btu per denatured gallon 

(30,000 Btu per anhydrous gallon) and 0.69 kWh per denatured gallon (0.71 per 

anhydrous gallon) of electricity.3,4 It should be noted that IRE is a modern ethanol plant, 

but with a standard layout consisting of a natural gas fired boiler and a direct fired dryer 

system for DDGS production. Corn ethanol plants that utilize biomass sourced in the 

vicinity of the plant or biomass co-produced with ethanol as an energy source can further 

reduce their natural gas/fossil fuel consumption. 

Ethanol 

Storage

Cooking

Fermentation

Distillation

Ethanol

Centrifuge

Evaporator

Dryer

Grinding

Stillage

Whole

Thin

Stillage

DDGS

WDGS

We

Ca

t

ke

Syrup/Solubles

Corn 

Thermal 

Energy

Electric 

Energy

Farm Energy

Chemicals

Corn Traits

Ethanol Base Process

Corn 

Production

Ethanol 

Processing

Molecular Sieve

Figure 1: Block Diagram of the Ethanol Base Process

In addition to energy reductions at the ethanol plant level, farm-energy use has also been 

steadily decreasing. This is largely due to modern farming equipment (including GPS 

guided equipment with auto-steer) and the use of genetically enhanced corn, which 

increases yield and thus reduces the energy requirements per acre. As a result of these 

developments, the on farm energy consumption per bushel of corn in Argonne’s GREET 

model was revised in 2008 down from 22,500 Btu/bu to 12,600 Btu/bu.5

 A recent case 

 

3

 The Illinois River Energy Center is located in Rochelle, Illinois. The plant recently expanded production 

from 58 million gallons per year to 100 million gallons per year. 

4

 Mueller Steffen and Ken Copenhaver, Michelle Wander; “The Global Warming and Land Use Impact of 

Corn Ethanol Produced at the Illinois River Energy Center”; Revised 10/22/08. 

5

 The Greenhouse gases, Regulated Emissions, and Energy use in Transportation (GREET) model was 

developed by Argonne National Laboratory. It allows researchers and analysts to evaluate various vehicle 

and fuel combinations on a full fuel-cycle/vehicle-cycle basis. 
Energy Resources Center 

University of Illinois at Chicago

 

3

study of farm energy use around the Illinois River Energy Center showed even lower onfarm energy use of 7,800 Btu/bu.6

 

Reduced ethanol plant and on-farm energy consumption result also in lower greenhouse 

gas emissions. Figure 2 shows the life cycle greenhouse gas reduction of the Illinois 

River Energy Center relative to gasoline. At 28.7 gCOe/MJ the ethanol plant energy 

system is the biggest contributor to the overall GWI of 54.8 gCOe/MJ. 

Nitrous oxide emissions from nitrogen fertilizer inputs to corn production are the second 

largest contributor to the GWI of corn ethanol (14.2 gCO2e/MJ). The remainder includes 

on-farm energy use, corn and ethanol distribution, and denaturant (11.6 gCO2e/MJ 

combined). With the main contributors to GWI identified, the present study focuses on 

technology improvements to plant energy systems, improvements to on-farm energy, as 

well as nitrogen fertilizer inputs. 

Global Warming Impact of IRE Produced Corn Ethanol

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

Gasoline IRE

gCO 2/MJ

IRE Biorefinery

Other Ag and

Distribution

N Fertilizer

Figure 2: GWI of Corn Ethanol Produced at Illinois River

 

6

 These values are stated in Lower Heating Value as used in GREET. Otherwise, unless noted, all values 

are stated in Higher Heating Value (HHV). 
Energy Resources Center 

University of Illinois at Chicago

 

4

2) Ethanol Processing Technologies 

2.1) Corn Oil Extraction

Ethanol 

Storage

Cooking

Fermentation

Distillation

Ethanol

Centrifuge

Evaporator

Dryer

Grinding

Stillage

Whole

Thin

Stillage

DDGS

WDGS

Syrup/Solubles

Corn 

Corn

Oil

Extraction

Corn Oil Thermal 

Energy

Electric 

Energy

Farm Energy Corn Oil Extraction

Chemicals

Corn Traits

We

Ca

t

ke

Corn

Oil

Extraction

COPE

Zein/Oil

Extraction

Bio Plastics

Molecular Sieve

Figure 3: Corn Oil Extraction and the Ethanol Process

In addition to removing corn oil during a fractionation process (discussed later) it can 

also be removed from the ground kernel using centrifuges. As shown in Figure 3 this type 

of extraction is possible before or after the ethanol distillation process. Corn oil removed 

before distillation results in a food grade product, whereas corn oil removed after 

distillation often enters the fuel product market where it is refined to a diesel (substitute) 

product. 

Corn oil removed after distillation can be extracted either from the whole stillage, thin 

stillage, or the wet distillers grains with solubles. Since the corn oil is removed after the 

distillation process, the extraction process has no impact on the ethanol yield. 

Manufacturers quote an extraction rate of about 3-4% by volume, which means a 100 

million gallon per year ethanol plant can produce an additional 3-4 million gallons of 

corn oil. Depending on the fat content the resulting deoiled/debranned DDGS may be of 

equal or lower value to the feed industry. Thermal energy requirements remain 

unchanged from the base process. However, VOC emissions during the drying process 

are reduced. Electricity needs will increase by about 10% to operate the centrifuges for 

oil extraction. 
Energy Resources Center 

University of Illinois at Chicago

 

5

The COPE process developed by Prairie Gold Inc. uses a different approach and extracts 

the corn oil prior to the fermentation by percolating ethanol back through the ground corn 

meal. This extraction process produces food grade corn oil as well as the protein “zein” 

that can be used for biodegradable products and plastics.7

Key Technology Providers: 

Greenshift Corporation 

Primafuel Solutions 

Prairie Gold, Inc. 

Installations:

Little Sioux Corn Processors, Marcus, Iowa (Greenshift system) 

Utica Energy, LLC, Oshkosh, WI (Greenshift system, corn oil extracted an converted into 

biodiesel) 

Western NY Energy, LLC, Medina, New York (Greenshift system, corn oil extracted and 

converted into biodiesel) 

Amaizing Energy LLC, Denison, Iowa (Primafuel system) 

 

7

 Personal conversation with Phil Shane, Prairie Gold 
Energy Resources Center 

University of Illinois at Chicago

 

6

2.2) Dry Mill Corn Fractionation

Ethanol 

Storage

Cooking

Fermentation

Distillation

Ethanol

Centrifuge

Evaporator

Dryer

Fractionation Unit

Stillage

Whole

Thin

Stillage

HPDDG

Bran Cake

Syrup/Solubles

Corn 

Corn Oil

Thermal 

Energy

Electric 

Energy

Dry Mill Fractionation

Bran Feed 

Products

Farm Energy

Chemicals

Corn Traits

We

Ca

t

ke

Bran Energy

Feedstock

Corn Gluten 

Feed

Molecular Sieve

Figure 4: Dry Mill Fractionation and the Ethanol Process

Fractionation separates the corn kernel into its main building blocks: the pericarp, the 

endosperm, the germ, and the tip cap. The endosperm contains 92 to 96% of the starch, 

the germ contains close to half of the oil, and the pericarp and the tip cap (collectively 

called bran) consist primarily of cellulose/fiber. By separating these parts, multiple 

products are possible: The endosperm is processed into ethanol and a higher protein, 

higher value animal feed, the germ into food grade corn oil. The bran can be converted 

into cellulose ethanol, it can be sold as a feed product, or it can be used as a biomass 

energy feedstock. 

Feed Products from Corn Kernel: 

The low oil and bran/fiber content in the stillage produces higher protein DDG (HPDDG) 

that provides greater flexibility in ruminant rations and opens markets in monogastric 

animals (particularly hogs and poultry). By removing non fermentable components at the 

front end, the percentage of starch in the slurry is higher, requiring less enzymes. While 

additional electricity is required for the fractionation system, this is partially offset by the 

elimination of the requirement for hammermills in the base plant. Also, the removal of 

non-fermentable compounds reduces the drying load and thus the thermal energy 

requirements. 

A fractionation system can produce the following feed products: 
Energy Resources Center 

University of Illinois at Chicago

 

7

a) High Protein Distillers Dried Grains 

The low oil and bran content in the now degermed and debraned corn stream allows 

production of a high protein animal feed (HPDDG) that is commercially sold as 37-44% 

protein. 

b) Corn Gluten Feed 

Mixing the deoiled germ, bran, and syrup results in an animal feed product that is 

commercially sold as 20% protein. 

c) Bran Cake: 

Mixing the bran and the syrup results in an animal feed product that is commercially sold 

as bran cake. 

In many instances lifestock markets buy corn gluten feed and bran cake wet. However, if 

all products are dried to a low moisture content (10%) to increase shelf life, the total 

thermal energy savings from either producing HPDDG combined with Corn Gluten Feed 

or from producing HPDDG combined with Bran Cake is 17.6%. 

On the electric side, the hammer mills in traditional dry mill processes are replaced by 

roller mills. Two manufacturers report that their dry mill fractionation process requires 

about 1 kWh/gal electricity.8

 

Biomass Fuel from Corn Kernel: 

Finally, the bran can be used as a biomass fuel via combustion in a solid fuel boiler 

system. The fractionation process produces approximately 0.5 lbs (between 0.42 to 0.61) 

of bran for every gallon of ethanol.9 At an assumed energy content of 7,000 Btu/lb and a 

bran fractionation yield of 0.5 lbs/gallon combusting the bran in a solid fuel boiler could 

result in additional energy savings of 3,500 Btu/gallon. Using the bran as a biomass fuel 

obviously reduces corn gluten feed and bran cake production from fractionation 

proporationally. 

Cellulose Ethanol from Corn Kernel: 

Bran conversion to cellulose ethanol utilizes specific enzymes which can convert corn 

kernel fibers into fermentable sugars. The technology can increase the ethanol yield from 

a bushel of corn by between 4 to 10 percent.10 The challenges are to develop affordable 

enzymes, and create process streams which are concentrated enough for ethanol 

recovery.11 According to the National Corn to Ethanol Research Center this technology 

will likely be adopted with corn fractionation. While the technology increases yield, the 

energy conversion efficiency is expected to remain constant. 

 

8

 Email exchanges with CPT technologies and ICM Inc. 9

 Review by Martha Schlicher, GTL Resources USA, Inc. 

10 Per Martha Schlicher, GTL Resources USA, Inc. 

11 Critics argue that fractionation results in a loss of starch and reduced ethanol yields. Source: Ethanol 

Producer Magazine. “Corn Fractionation for the Ethanol Industry”; November 2005 Issue. 
Energy Resources Center 

University of Illinois at Chicago

 

8

Key Technology Providers:

Buhler Inc. 

Ocrim/Delta-T 

Cereal Process Technologies 

MOR Technologies 

Satake USA 

Crown Iron Works 

Renessen LLC (joint venture between Cargill and Monsanto; process name: Extrax) 

ICM via Applied Milling (“Total Kernel Optimization”) 

FCStone Carbon LLC with Maize Processing Innovators Inc licensing University of 

Illinois’ Quick Germ Quick Fiber technology. 

Current Plants Employing Technology:

Illinois River Energy, Rochelle, Illinois 

Renew Energy, Jefferson, Wisconsin (using the CPT Process) 

Pilot Plant in Eddyville, Iowa (using the Extrax Process) 

Didion Milling, Johnson Creek, Wisconsin 

Badger State Ethanol, Monroe, Wisconsin 
Energy Resources Center 

University of Illinois at Chicago

 

9

2.3) Cold Cook Process (aka raw starch hydrolysis)

Ethanol 

Storage

Cooking

Fermentation

Distillation

Ethanol

Centrifuge

Evaporator

Dryer

Grinding

Stillage

Whole

Thin

Stillage

DDGS

WDGS

Syrup/Solubles

Corn 

Thermal 

Energy

Electric 

Energy

Farm Energy

Chemicals

Corn Traits

Cold Cook Process

We

Ca

t

ke Molecular Sieve

Figure 5: Raw Starch Hydrolysis and the Ethanol Process 

Cold cook/raw starch hydrolysis allows producers to eliminate the cooking step. The cold 

cook process (which occurs at 86 to 104 degrees F) skips the liquefaction and 

saccharification steps. The ground corn is slurried with water and both gluco amylase and 

alpha amylase are added, followed directly by fermentation. Skipping the cooking 

process reduces both water and energy consumption. In an February 2008 Press Release 

Poet quoted that the cold cook process is “utilized in 20 of POET’s 22 ethanol production 

facilities.”12 Critics argue that the process needs significantly more enzymes (20% 

more), reduces yield in fermentation, and increases antibiotic use.13 In a personal 

conversation with an industry insider, the energy savings from cold cooking were 

estimated to be about 5,000 btu/gal (5,000/30,000 Btu/gal) or 16.6%. Electricity 

consumption is likely similar to current dry mill ethanol plants; no increase or decrease in 

electricity consumption was assumed. 

 

12Dr. Mark Stowers, Vice President of Research & Development at POET ; “POET funds starch to ethanol 

research collaboration with Iowa State University”, 

http://www.poetenergy.com/news/showRelease.asp?id=108 13 Ethanol Producer Magazine. “Break it Down”, January 2006. 
Energy Resources Center 

University of Illinois at Chicago

 

10

2.4) New Boilers and Motors

Ethanol 

Storage

Cooking

Fermentation

Distillation

Ethanol

Centrifuge

Evaporator

Dryer

Grinding

Stillage

Whole

Thin

Stillage

DDGS

WDGS

Syrup/Solubles

Corn 

Thermal 

Energy

Electric 

Energy

Farm Energy New Boilers and Motors

Chemicals

Corn Traits

We

Ca

t

ke Molecular Sieve

Figure 6: New Boilers and Motors and the Ethanol Process 

Technologies that are currently in various stages of the commercialization process will 

increase the efficiency of currently utilized energy generating and conversion equipment 

such as natural gas boilers, motors, fans, and pumps. 

GTI and Cleaver Brooks are developing the SuperBoiler with DOE funding. The 

development is on schedule and the efficiency of this technology reportedly reaches 94%. 

Two units are installed at Specification Rubber in Alabama and at Clement Pappas 

Company in Ontario. 

NEMA Premium efficient motors and the installation of extra inverters decrease both 

energy consumption and peak demand. Efficiency improvements from premium efficient 

motors are reportedly in the 5% range.14

Additional improvements include the development of advanced process control and 

automation systems for ethanol plants. Siemens partners with National Corn to Ethanol 

Research Center for 10 years to develop distributed control and instrumentation systems. 

Table 1 provides an efficiency comparison between traditional and advanced boiler and 

motor technologies. 

 

14 Personal conversation with the US DOE Industrial Assessment Center at University of Illinois at 

Chicago. 
Energy Resources Center 

University of Illinois at Chicago

 

11

Table 1: Efficiency Improvements of New Motors and Boilers

 From To 

Motors 90% 95%

 Efficiency Improvement 5.3%

Boilers 80% 94%

 Efficiency Improvement 14.9%

Key Technology Providers:

Various 

Current Plants Employing Technology:

Pacific Ethanol, Sacramento, California 

ADM, Decatur, Illinois 
Energy Resources Center 

University of Illinois at Chicago

 

12

2.5) Combined Heat and Power

Ethanol 

Storage

Cooking

Fermentation

Distillation

Ethanol

Centrifuge

Evaporator

Dryer

Grinding

Stillage

Whole

Thin

Stillage

DDGS

WDGS

Syrup/Solubles

Corn 

Combined 

Heat and 

Power 

(CHP)

Farm Energy Combined Heat and Power

Chemicals

Corn Traits

Electric 

Energy

Thermal 

Energy

We

Ca

t

ke Molecular Sieve

Electricity Export

Figure 7: Combined Heat and Power and the Ethanol Process 

Combined heat and power systems (CHP, also known as cogeneration) generate 

electricity and useful thermal energy from the same fuel source in a single integrated 

system. The primary fuel feed stocks for CHP systems at ethanol plants include natural 

gas, coal, and biomass. The general equipment configuration for a natural gas fired CHP 

system consists either of a) a combustion turbine (for electricity production) with a heat 

recovery steam generator (for thermal energy production), or b) a natural gas fired boiler 

(for thermal energy production) with a steam turbine (for electricity production). The 

general equipment configuration for a coal or biomass fired CHP system consists of a 

solid fuel boiler with a steam turbine.15 The thermal energy generated from a CHP system 

can be utilized to meet the cooking, distillation, and the drying needs of the plant. The 

electricity can be utilized to meet all or a portion of the electric load of the plant with 

supplemental electricity purchased from the incumbent utility company. Moreover, 

several ethanol plant CHP systems are sized to meet the thermal energy requirements of 

the plant, but generate electricity in excess of the ethanol plant load. These systems sell 

excess electricity back to the grid as a co-product. 

 

15 “Research Investigation for the Potential Use of Illinois Coal in Dry Mill Ethanol Plants”; Report to the 

Illinois Clean Coal Institute, Mueller and Cuttica, October 2006. 
Energy Resources Center 

University of Illinois at Chicago

 

13

Natural Gas CHP systems at ethanol plants16 

• Adkins Energy, Lena, Illinois (5 MW combustion turbine with heat recovery, 

sized to meet the electric needs of the plant, supplemental thermal energy 

provided by additional natural gas fired boilers) 

• Northeast Missouri Grain LLC, Macon, Missouri (10 MW natural gas fired 

combustion turbine, provides excess electricity to the municipal electricity system 

of the City of Macon) 

• US Energy Partners, Russell, KS (15 MW natural gas fired combustion turbine, 

provides excess electricity to the City of Russel, Kansas) 

• East Kansas Agri Ethanol (EKAE) ethanol plant in Garnett, Kansas (1.6 MW 

natural gas boiler with steam turbine plant) 

• POET Biorefining Ashton, Iowa (7 MW natural gas fired combustion turbine 

system with heat recovery) 

• Andersons Albion Ethanol LLC Albion, Michigan (2 MW steam turbine system) 

• Little Falls Plant Little Fall, Minnesota (2 MW steam turbine system) 

• POET Biorefining Laddonia, Missouri (10.7 MW steam turbine system) 

• Prairie Horizon Ethanol Phillipsburg, Kansas (4 MW steam turbine system) 

Coal fired CHP Systems

• Heron Lake, MN (Coal-fired fluidized bed boiler) 

• Corn LP in Goldfield, IA (Coal-fired fluidized bed boiler) 

• Lincolnway Energy, Nevada, IA (Coal-fired fluidized bed boiler) 

• Blue Flint Ethanol Plant Underwood, ND (6.5 MW steam turbine co-located next 

to coal fired power plant) 

Biomass Fired CHP Systems

Corn Plus, MN (combusting syrup supplemented by natural gas) 

Technology Providers

Various, including: 

Solar Combustion Turbines 

Dresser Rand Steam Turbines 

Energy Products of Idaho (Fluidized Bed Boilers) 

 

16 Source: Midwest CHP Application Center. www.chpcentermw.org
Energy Resources Center 

University of Illinois at Chicago

 

14

2.6) Anaerobic Digesters

Ethanol 

Storage

Cooking

Fermentation

Distillation

Ethanol

Centrifuge

Evaporator

Dryer

Grinding

Stillage

Whole

Thin

Stillage DDG

WDGS

Syrup/Solubles

Corn 

Digester

Thermal 

Energy

Electric 

Energy

Anaerobic Digestion

Fertilizer

Farm Energy

Chemicals

Corn Traits

Boiler/CHP

We

Ca

t

ke Molecular Sieve

Electricity Export

Figure 8: Anaerobic Digestion and the Ethanol Process 

A modern ethanol plant produces approximately 5 gallon of thin stillage for each gallon 

of ethanol. An anaerobic digester can convert the thin stillage into biogas that consists 

approximately 60% of methane. An energy balance available for this study showed that 

an efficient anaerobic digester system sized to convert 100% of the thin stillage into 

biogas would produce approximately 21,000 Btu/gal (HHV) of energy. This approach 

leaves the wet cake for conversion into DDG (without the solubles). The plant’s total 

energy demand is further reduced by 2,710 Btu/gal from the base plant consumption 

(from 30,000 Btu/gal to 27,290 Btu/gal) because the solubles are not dried. Therefore the 

digester will provide approximately 77% of the plant’s thermal energy requirements.17 

Furthermore, for every gallon of stillage one gallon of effluent water is produced 

containing suspended solids, including nitrogen, phosphorus and potassium which can be 

recovered and reformed into a fertilizer product. An engineering study showed that an 

anaerobic digester sized to digest 100% thin stillage would recover approximately 0.25 

lbs/gal of NPK product. 

 

17 Engineering and Design Proposal provided by NewBio e-Systems for the “Bioconversion of Thin 

Stillage to Methane” at the Illinois River Energy Center, April 2008. 
Energy Resources Center 

University of Illinois at Chicago

 

15

The electricity requirements of an ethanol plant with an anaerobic digester system would 

be about 3% higher (0.73 kWh/gal) to operate pumps and motors for thin stillage/effluent 

movement. 

Alternatively, a digester could be sized to convert whole stillage and thereby produce 

even more energy. However, this approach is less likely from a financial point of view 

since it would reduce DDG output, a valuable co-product. However, integration of 

anaerobic digesters from thin stillage with corn-fractionation may provide synergistic 

benefits. 

An ethanol plant integrating anaerobic digestion (from thin stillage) with fractionation 

would still produce HPDDG. Since the thin stillage would not be dried, the energy 

requirements of this plant type are reduced from the fractionation base plant requirements 

of 24,720 Btu/gal to 22,010 Btu/gal (by 2,710 Btu/gal). Digesting the thin stillage would 

offset 21,000 Btu/gal and thus result in plant energy requirements of 1,010 Btu/gal. Since 

the plant would also be able to produce 0.5 lbs of bran per gallon produced, this product 

could be combusted in a small solid fuel boiler system and further offset energy 

consumption at the plant. In fact, at an energy content of 7,000 Btu per lb and 0.5 lbs per 

gallon produced, combusting the bran would result in additional energy production of 

3,500 Btu/gal producing a net energy surplus of 2,490 Btu/gal for the plant, which could 

be used to supplement seasonal variations from the digester’s biogas production. 

Technology Providers:

New BioE 

Biothane 

 

Current Plants Employing Technology:

E3 Nebraska18 (co-digestion of both manure and thin stillage) 

Otter Tail Ag Enterprises, Fergus Falls, Minnesota (55-million-gallon corn dry mill 

interested in stillage digestion) 

 

18 The N3 plant is currently in bankruptcy proceedings. However, prior to the bankruptcy filing, the 

digester system was fully operational (personal conversation with Richard Mattocks, Biothane 

Corporation). 
Energy Resources Center 

University of Illinois at Chicago

 

16

2.7) Biomass Combustion/Gasification

Several ethanol plants are utilizing biomass as an energy feedstock. Biomass energy 

feedstocks have the potential to reduce a plant’s reliance on fossil fuel and to reduce the 

emissions and greenhouse gas profile of the operation. 

The Chippewa Valley Ethanol Plant in Benson, Minnesota is an example of a biomass 

gasification retrofit system. An 80% efficient gasifier generates producer gas that is fed to 

a boiler, dryer, and regenerative thermal oxidizer system (RTO). The boiler, dryer, and 

RTO are identical to the natural gas fired plant equipment. Due to the efficiency loss in 

he gasifier, the biomass requirements are derived by dividing the natural gas fired boiler 

plant requirements by the gasifier efficiency. Therefore, at an assumed natural gas base 

plant energy consumption of 30,000 Btu/gal a gasification retrofit configuration would 

require approximately 37,500 Btu/gal. 

The Corn Plus ethanol plant in Winnebago, Minnesota is an example of a plant 

combusting biomass, in this case syrup. Supplemental energy needs are met by a natural 

gas fired boiler system. 

Ethanol 

Storage

Cooking

Fermentation

Distillation

Ethanol

Centrifuge

Evaporator

Dryer

Grinding

Stillage

Whole

Thin

Stillage

DDGS

WDGS

Corn 

Thermal 

Energy

Electric 

Energy

Farm Energy

Chemicals

Corn Traits

Biomass Combustion/Gasification

Biomass

Biomass

Syrup/Solubles

Boiler/

Gasifier/

CHP

We

Ca

t

ke Molecular Sieve

Electricity Export

Figure 9: Biomass Combustion and Gasification and the Ethanol Process 

Current Plants Employing Technologies:

Corn Plus Ethanol in Winnebago, Minnesota (combusting syrup) 

Central Minnesota Ethanol in Little Falls (combusting wood) 

Chippewa Valley Ethanol in Benson, Minnesota (gasifying wood waste) 
Energy Resources Center 

University of Illinois at Chicago

 

17

2.8) Other Renewable Energy

Ethanol 

Storage

Cooking

Fermentation

Distillation

Ethanol

Centrifuge

Evaporator

Dryer

Grinding

Stillage

Whole

Thin

Stillage

DDGS

WDGS

Syrup/Solubles

Corn 

Thermal 

Energy

Electric 

Energy

Farm Energy

Chemicals

Corn Traits

Other Renewable Energy

Other 

Renewables

(Wind, 

Landfill, 

etc.)

We

Ca

t

ke Molecular Sieve

Electricity Export

Figure 10: Other Renewable Energy and the Ethanol Process

In order to reduce fossil fuel consumption at the plant, several plants are starting to 

integrate other renewable technologies. 

Key Technology Providers

Abengoa Solar is developing solar thermal systems for integration with ethanol plants.19

John Deere (providing wind turbines for Corn Plus) 

Current Plants Employing Technology

Siouxland Ethanol, Jackson Nebraska (sourcing biogas from nearby landfill) 

Corn Plus in Minnesota is adding wind turbines 

 

19 See http://www.abengoasolar.com/sites/solar/en/abengoa_solar_ist/about_us/
Energy Resources Center 

University of Illinois at Chicago

 

18

3) Corn Production Technologies 

3.1) Farm Energy

Ethanol 

Storage

Cooking

Fermentation

Distillation

Ethanol

Centrifuge

Evaporator

Dryer

Grinding

Stillage

Whole

Thin

Stillage

DDGS

WDGS

Syrup/Solubles

Corn 

Thermal 

Energy

Electric 

Energy

Farm Energy

Chemicals

Corn Traits

Farm Energy

We

Ca

t

ke Molecular Sieve

Figure 11: Farm Energy and the Ethanol Process 

Several publications by the USDA have documented the farm energy use to produce 

corn.20 These publications, adjusted for efficiency improvements form the basis for life 

cycle energy models such as the GREET model. GREET’s current default value for onfarm energy consumptions required for corn production (tractor fuel, custom hauling, 

irrigation energy, input hauling) totals 12,600 Btu/bu.21 This value reflects average 

Midwestern corn producing states. The value reflects a recent update (as of July 2008) 

where it was revised down from 22,500 Btu/bu. We believe that this value is likely 

reflective of the actual average. However, a recent survey with 29 corn growers 

delivering to the IRE ethanol plant indicates that much lower values are possible. The 

survey shows that the average grower delivering to this particular plant only utilizes 

7,800 Btu/bu during corn production. At IRE’s yield of 2.73 gal/bu the surveyed 7,800 

Btu/bu results in an energy contribution of 2,857 Btu/gal. At GREET’s assumed average 

 

20 Shapouri, H., J. A. Duffield, et al. (2004). The 2001 Net Energy Balance of Corn-Ethanol. Proceedings 

Of The Conference On Agriculture As A Producer And Consumer Of Energy, June 24-25. Arlington, VA. 

Shapouri, H., J. A. Duffield, et al. (2002). The Energy Balance of Corn Ethanol: An Update. Washington, 

DC, US Department of Agriculture. 

21 GREET Version 1.8b 
Energy Resources Center 

University of Illinois at Chicago

 

19

yield of 2.72 gal/bu the 12,600 Btu/bu results in an energy contribution of 4,632 

Btu/gal.22

Several reasons can contribute to lower on farm energy consumption: the use of no-till 

practices and advanced farm equipment technologies including tractors equipped with 

geographic positioning system (GPS) and auto-steer. 

No-till Practices: 

The results from the growers’ survey around IRE shown in Table 2 indicate that farmers 

practicing no-till reported markedly less tractor trips (4.7) across their fields than other 

growers (6.1).23 By reducing tractor trips and by inference tractor fuel consumption, notill practices also reduce global warming emissions. Furthermore, no-till practices can, 

under certain circumstances, reduce GHG emissions by increasing carbon sequestration.24

 Table 2: Tractor Trips and Tillage Practices 

 Conventional Till 

Tractor Trips 

No-Till 

Tractor Trips

Mean 6.1 4.7 

STD 1.9 1.2 

N= 8 19 

Farm Machinery Technologies Using GPS Tracking Technology with Auto-Steer: 

Purdue University in cooperation with CropLife Magazine conducts an annual “Precision 

Agricultural Services Dealership Survey.” The 2008 report states that “the biggest growth 

seen from 2007 to 2008 was in the use of GPS guidance systems with 

autocontrol/autosteer, growing from 27 percent of the dealerships in 2007 to 37% in 

2008.”25 The technology is predominantly used with tractors, combines, and selfpropelled sprayers. GPS systems and auto steer reduce the overlap along each pass across 

the field. Overlap improvements have shown to range around 4 percent.26 The resulting 

savings depend on the type of field pass. Not overlapping on tillage, for example, reduces 

fuel consumption whereas not overlapping on spraying operations reduces fuel and 

chemical product consumption.27 The newest technologies turn individual planter and 

sprayer components on and off based on their specific position in the field. According to 

John Deere, farmers are seeing an additional reduction of 5-10% in seed, fertilizer, and 

 

22 These values are stated in LHV. 

23 Mueller Steffen and Ken Copenhaver, Michelle Wander; “The Global Warming and Land Use Impact of 

Corn Ethanol Produced at the Illinois River Energy Center”; Revised 10/22/08. 

24 A recent study by the University of Illinois at Chicago showed that applying a set of published 

sequestration rates to the amount of no-till acres supplying corn to IRE (13% no-till) would reduce the life 

cycle of IRE corn ethanol from 54.8 gCO2e/MJ to 52.2 gCO2e/MJ. Subtracting the average sequestration 

numbers for encouraging 100% no-till on IRE supply acres from the life cycle of IRE corn ethanol reduces 

it to 35.9 gCO2e/MJ. 

25 Whipker, Linda and Jay Akridge:”2008 Precision Agricultural Services Dealership Survey Results”; 

Working Paper #08-09. Crop Life Magazine and Purdue University, September 2008. 

26 Prairie Agricultural Machinery Institute; ”Determining Options to Lower Mechanical Overlap in Sinuous 

Riparian Areas”; by Nathan Gregg and Patricia Lung, 2007. 27 Farm Industry News;”Autosteer Is Here”; by Wayne Wenzel, February 15, 2004. 
Energy Resources Center 

University of Illinois at Chicago

 

20

pesticides from this input control technology. 28 In summary, auto-steer will likely result 

in about 4% reduction in fuel and chemical use, whereas GPS based input control will 

result in additional 5% to 10% savings. 

 

28 Email exchange with Larry Hendrickson, John Deere. 
Energy Resources Center 

University of Illinois at Chicago

 

21

3.2) Corn Traits

Ethanol 

Storage

Cooking

Fermentation

Distillation

Ethanol

Centrifuge

Evaporator

Dryer

Grinding

Stillage

Whole

Thin

Stillage

DDGS

WDGS

Syrup/Solubles

Corn 

Thermal 

Energy

Electric 

Energy

Farm Energy

Chemicals

Corn Traits

GEO Corn

We

Ca

t

ke Molecular Sieve

Figure 12: Corn Traits and the Ethanol Process

We are not aware of a statistical assessment that summarizes how much transgenic/GEO 

corn is used for US average corn ethanol production. However, the above mentioned 

survey of growers that supply corn to the IRE ethanol plant indicates that these growers 

do utilize predominately GEO corn. The graph below shows the breakdown of 

technologies. Respondents indicated that the vast majority of delivered bushels have 

genetically enhanced organisms (GEO) traits (89%) and the vast majority of GEO corn is 

triple stack type. Figure 13 below indicates the make up of the corn trait by bushel. 

11%

11%

7%

71%

0%

Non GEO

Singe Trait

Double Stack

Triple Stack

Other

Figure 13: Corn Trait Selection of Farmers Supplying to IRE 
Energy Resources Center 

University of Illinois at Chicago

 

22

Use of GEO corn may reduce use of pesticides, herbicides thus reducing the amount of 

tractor trips across the field. Furthermore, GEO corn increases yield thus reducing the 

energy per bushel spent. 

3.3) Chemicals

Ethanol 

Storage

Cooking

Fermentation

Distillation

Ethanol

Centrifuge

Evaporator

Dryer

Grinding

Stillage

Whole

Thin

Stillage

DDGS

WDGS

Syrup/Solubles

Corn 

Thermal 

Energy

Electric 

Energy

Farm Energy

Chemicals

Corn Traits

New Fertilizer Products

We

Ca

t

ke Molecular Sieve

Figure 14: Chemicals and the Ethanol Process 

Nitrogen fertilizer and other chemicals contribute to the energy use (during application as 

well as during the manufacturing process of the chemicals) of corn agriculture. Moreover, 

nitrogen application and the resulting dinitrification and nitrous oxide production 

contribute significantly to the GWI of corn ethanol. Technologies exist that allow for the 

application of nitrogen fertilizer only where and when it is required. These technologies 

include GPS and Auto-Steer systems in farm equipment (detailed above), but also slow 

release fertilizers and nitrification inhibitors (like N-Serve produced by Dow 

Agrosciences), N-application based on soil testing and remotely sensed imagery, and Nside dressing.29 In the following a brief summary of several technologies will be 

provided. 

Nitrification Inhibitors: 

Nitrification inhibitors work by retarding the formation of nitrate by nitrifying bacteria. A 

publication by Dow researchers in the Journal of Nutrient Cycling in Agroecosystems 

 

29 R. Nider, D.K. Bembi; “Carbon and Nitrogen in the Terrestrial Environment”; Springer, 2008. 
Energy Resources Center 

University of Illinois at Chicago

 

23

asserts that “greenhouse gas emissions decreased by 51%” with the application of 

nitrification inhibitors.30

Soil Testing and Remote Sensing: 

Other methods which allow a more precise application of nitrogen fertilizer include soil 

testing to determine nitrogen availability in different parts of the field and remotely 

sensed imagery which can be used in-season to apply N only where needed based on 

plant vigor. Figure 15 demonstrates a project in which near infrared (NIR) imagery was 

used to estimate nitrogen requirements for a field in east central Illinois. Corn reflectance 

from the imagery was regressed to chlorophyll meter readings (SPAD readings) taken 

throughout the field that were then converted to nitrogen requirements.31,32 This led to 

reduced nitrogen use in the field compared to a traditional application rate. 

Figure 15: Determining N-Requirements Using Remote Sensing

 

30Wolt, Jeffrey; “A meta-evaluation of nitrapyrin agronomic and environmental effectiveness with 

emphasis on corn production in the Midwestern USA”; Nutrient Cycling in Agroecosystems, 69:23-

41,2004. 

31 Spectrum Technologies, Inc.;”Using a Chlorophyll Meter to Improve N Management”; 

www.specmeters.com 

32 Image produced by Institute for Technology Development 
Energy Resources Center 

University of Illinois at Chicago

 

24

N-Side Dressing: 

This process involves direct injection of nitrogen into the soil after emergence of the 

plant. The advantage of this method is that the application is timed to coincide with the 

plant’s peak N-demand. The application system consists of a toolbar and injection 

coulters. Recent key advancements allow for applications at higher speeds (up to 12-14 

mph on fields), which is important since there is only a short time window after plant 

emergence to apply the product before the plant gets too high.33 Key manufacturers 

include John Deere, Case, and Hagie. 

Various methods exist to quantify the nitrous oxide emissions from fertilizer inputs. 

GREET employs an emissions factor model based on the Intergovernmental Panel on 

Climate Change (IPCC). Using the GREET methodology and the above referenced data 

collected for the IRE ethanol plant, the influence of precision agriculture and slow release 

fertilizers/nitrification inhibitors will be demonstrated. 

The current GREET Version 1.8b uses the following equation for N2O emissions 

estimates from fertilizer application. 

N2O from nitrogen fertilizer, and above and below ground biomass = 

(420 g/bu of N + 141.6 g/bu of N) * 0.01325 *44/28 = 11.7 g/bu 

Where: 

420 g/bu of N is the default value for N applied in fertilizer 

141.6 g/bu of N is N content of above and below ground biomass (ie corn stover 

left on the field). 

0.01325 is a factor for N in N2O as fraction of N in N fertilizer and biomass. 

GREET assumes that 1.3% (including 0.2% from leaching) of the available N is 

converted to N in N2O. 

44/28 is the mass fraction of N2O and N2 in the molecule 

At 420 g/bu or 0.93 lbs/bu the GREET default nitrogen input is slightly higher than the 

IRE surveyed N-input of 368 g/bu or 0.81 lbs/bu. Following the above equation, the 

difference in N-inputs results in different nitrous oxide production rates and subsequently 

in different contributions to the corn ethanol lifecycle: Applying 0.93 lbs/bu results in a 

contribution of 15.2, whereas applying 0.81 lbs/bu results in a contribution of 13.8 

gCO2e/MJ (assuming IRE ethanol yield). 

The graph below shows the GWI contribution to IRE produced corn ethanol as a function 

of N-inputs. As can be seen, if growers applied N close to the theoretical minimum of 0.6 

lb/bu, these growers would contribute only 11 gCO2/MJ to the corn ethanol life cycle 

according to the GREET methodology. In contrast, growers that apply 1.6 lbs/bu would 

 

33 Allen, Carrie; “Sidedressing Nitrogen in Corn Makes Sense”; Fluid Journal, Spring 2002. 
Energy Resources Center 

University of Illinois at Chicago

 

25

Fertilizer Contribution to GWI of IRE Corn Ethanol

0.0

5.0

10.0

15.0

20.0

25.0

1.60 1.40 1.20 1.00 0.80 0.60

N Fertilizer Applied in lb/bu

gCO2e/MJ of 

Ethanol

contribute 24 gCO2//MJ. This difference of 13 gCO2//MJ (24 gCO2//MJ -11 gCO2//MJ) 

may account for 20% to 25% of the total GWI of an ethanol plant.34 Utilization of the 

above described advanced N-application technologies will result in a move further 

towards lower inputs in the graph. 

Figure 16: Relationship Between Global Warming Impact and Fertilizer Application

 

34 Remember that the IRE global warming impact totaled 54.8 g/MJ including N fertilizer contributions 

IRE

Utilization of Advanced NApplication Technologies 
Energy Resources Center 

University of Illinois at Chicago

 

26

4) Energy Summary 

Table 3 below summarizes the thermal energy and electricity requirements as well as the 

co-product balance of modern corn ethanol production systems. 

Table 3: Thermal and Electric Energy Consumption by Technology

Thermal Electric Comment 

HHV per unit anhydrous ethanol (Btu/gallon) 

Corn Agriculture 

On-Farm Energy35 8,851 (GREET, Prior to 7/08) 

4,957 (GREET, Adjusted 7/08) 

3,057 (IRE, Illinois Case Study) 

Ethanol Plant 

Base Dry Grind 

Ethanol Plant 

20,000 (boiler fuel) 

9,700 (dryer fuel) 

300 (thermal oxidizer equipment 

for emissions control) 

Total: 30,000 

0.71 Ethanol Yield: 2.73 gal/bu 

Co-Product: 5.66 lbs/gal DDGS, 

100% Drying 

Cold Cook 25,000 0.71 Ethanol Yield: 2.73 gal/bu36

Co-Product: 5.66 lbs/gal DDGS, 

100% Drying 

Corn Oil Extraction 30,000 0.71*1.1=0.78 Ethanol Yield: 2.73 gal/bu 

Co-Product: 

Corn Oil 3-4% by Volume (a 100 

mgpy ethanol plant produces an 

additional 3-4 million gallon of 

corn oil) 

Anaerobic 

Digesters37

27,290-21,000=6,290 0.71*1.03=0.73 Ethanol Yield: 2.73 gal/bu 

Co-Product: 

2.6 lbs/gal DDG 

21,000 Btu/gal of energy provided 

from digester biogas 

0.25 lbs/gal of NPK fertilizer 

 

35 Energy requirements in Btu/bu converted to Btu/gal and then to Higher Heating Value based on the 

following equations: 

22,500(Btu/bu)/2.72(gal/bu)*1.07 HHVdiesel/LLVdiesel = 8,851 Btu/gal. 

12,600/2.72*1.07=4,957 Btu/gal 

7,800/2.73*1.07=3,057 Btu/gal 

Note that the IRE farm energy value is converted based on the IRE yield, the GREET values are converted 

based on the GREET yield. 

Note that HHV/LLV conversions are based on diesel, recognizing that diesel is the dominant but not 

exclusive fuel share. Errors from this assumption should be small. 36Critics argue that cold cook processing may lead to starch loss. Therefore, yields may be lower, see 

Ethanol Producer Magazine article “Break it Down”, January 2006. 
Energy Resources Center 

University of Illinois at Chicago

 

27

Thermal Electric Comment 

Fractionation37 30,000*(1-.176)=24,720 1.0 Ethanol Yield: 2.64 gal/bu 

Co-Products (Common 

fractionation split): 

Approximately 2.6 lbs/gal 

HPDDG 

Approximately 3.7 lbs/gal Corn 

Gluten Feed 

Approximately 0.75 lbs/bu of corn 

oil. This equates to 3.75% corn oil 

by volume (a 100 mgpy ethanol 

plant produces 3.75 mgpy corn 

oil). 

Fractionation37

Combined With 

Anaerobic 

Digestion 

24,720 [base fractionation]-

2,710 [no stillage drying] -

21,000 [digester]=1,010 

1.03 Ethanol Yield: 2.64 gal/bu 

Co-Products: 

2.6 lbs/gal HPDDG 

Combining fractionation with 

anaerobic digestion of thin stillage 

does not enable production of corn 

gluten feed, but alternatively 0.5 

lbs/gal of bran. Bran may be used 

as a feed product. 

0.25 lbs/gal of NPK fertilizer 

Fractionation 

Combined With 

Anaerobic 

Digestion combined 

with NEMA 

Motors 

24,720 [base fractionation]-

2,710 [no stillage drying] -

21,000 [digester]-3,500 [bran] = 

-2,490 

1.03*(1-

0.053)=0.98 

Ethanol Yield: 2.64 gal/bu 

Co-Products: 

2.6 lbs/gal HPDDG 

Combining fractionation with 

anaerobic digestion of thin stillage 

does not enable production of corn 

gluten feed, but alternatively 0.5 

lbs/gal of bran. Bran may be 

combusted in a solid fuel boiler 

making the ethanol plant a net 

producer of energy, which can be 

used to absorb seasonal variations 

of digester biogas production. 

Natural gas base 

plant with 

Superboiler and 

NEMA Motors 

30,000*(1-.149)=25,530 0.71*(1-

0.053)=0.67 

Ethanol Yield: 2.73 gal/bu 

Co-Product: 5.66 lbs/gal DDGS 

 

37 The biomass in this case is credited towards reduced energy requirements since it is a co-product from 

the ethanol production process. The listed value reflects the residual natural gas requirements. 
Energy Resources Center 

University of Illinois at Chicago

 

28

Thermal Electric Comment 

Natural Gas 

Combined Heat and 

Power sized to meet 

electric load 

32,352 0.13 Ethanol Yield: 2.73 gal/bu 

Co-Product: 5.66 lbs/gal DDGS 

Natural Gas 

Combined Heat and 

Power sized to 

export power 

46,468 -2.23 kWh/gal Ethanol Yield: 2.73 gal/bu 

Co-Product: 5.66 lbs/gal DDGS 

Electric Power Export 

Biomass 

Combustion 

(Fluidized Bed 

Boiler)38

35,897 

Natural gas fuel consumption: 0 

0.85 Ethanol Yield: 2.73 gal/bu 

Co-Product: 5.66 lbs/gal DDGS 

Biomass CHP 

(Fluidized Bed 

Boiler plus Steam 

Turbine)38

39,515 

Natural gas fuel consumption: 0 

0.1 Ethanol Yield: 2.73 gal/bu 

Co-Product: 5.66 lbs/gal DDGS 

Biomass 

Gasification 

(Gasifier Retrofit to 

Natural Gas 

Boiler)38

37,500 

Natural gas fuel consumption: 0 

0.85 Ethanol Yield: 2.73 gal/bu 

Co-Product: 5.66 lbs/gal DDGS 

Other Renewable 

Energy 

Solarthermal Solar, wind Ethanol Yield: 2.73 gal/bu 

Co-Product: 5.66 lbs/gal DDGS 

 

38 Biomass is assumed to be sourced from outside suppliers. Therefore, the Btus that need to be sourced are 

stated.