A U.S. Department of Energy laboratory managed by The University of Chicago 

Analysis of the Efficiency of the U.S. Ethanol Industry 2007 

May Wu 

Center for Transportation Research 

Argonne National Laboratory 

Delivered to Renewable Fuels Association on March 27, 2008 

Summary 

In 2007, the Renewable Fuels Association (RFA) conducted a survey of US ethanol 

production plants to provide an assessment of the current US ethanol industry. The 

survey covers plant operations in both corn dry mills and wet mills. In particular, it 

includes plant type, ownership structure, capacity, feedstocks, production volumes, coproducts, process fuel and electricity usage, water consumption, and products 

transportation and distribution. The survey response was based on year 2006 data. At the 

request of RFA, Argonne National Laboratory (ANL) has performed a statistical analysis 

of the survey data, as an in-kind effort, under a non-disclosure agreement (NDA) between 

ANL and RFA. During November 2007 and January 2008, ANL processed and analyzed 

the raw data for statistics. This extended technical memo serves as an official 

documentation to summarize ANL’s analysis. 

There were 22 facilities that responded to the survey, representing 1.813 billion gallon of 

annual fuel ethanol production, which is 37% of the 2006 production (4.9 billion gallons). 

The results of the statistical analysis from this survey were compared with a Department 

of Agriculture (USDA) ethanol plant survey conducted in 2001. In comparison to those 

2001 findings, the ANL analysis found: 

• Ethanol yield per bushel of corn increased 6.4% for dry mills and 2.4% for wet 

mills. 

• Total energy use (fossil and electricity) decreased 21.8% in dry mills and 7.2% in 

wet mills from 2001 survey. 

• Another major change from 2001 survey is 15.7% decrease in grid electricity use 

in dry mills. 

• There is a shift in process fuel use from coal to natural gas in the dry mills. 

• More than one third (37%) of the dried distillers grains with solubles (DDGS), the 

feed co-product of dry mill ethanol production, was sold as wet feed which 

reduces heat demand in the plant. 

• CO2 collection and production as a co-product is on the rise that a total of 23.5% 

of the ethanol production capacities responded exported CO2. 

• Finally, water consumption in dry mills decreased 26.6% from 2001 survey. 
A U.S. Department of Energy laboratory managed by The University of Chicago 

Results 

1. General results 

There were 22 facilities that responded to the survey, representing 1.813 billion gallon of 

annual fuel ethanol production, which is 37% of the 2006 production (4.9 billion gallons). 

The majority of respondents are Limited Liability Corporations (LLC) - owned dry mills 

and investor-owned wet mills (Table 1). The data reflects rapid growth of the corn 

ethanol industry, particularly in dry mills in recent years. Among the respondents, two 

thirds of dry mill facilities were built after 2001, with a quarter of those undergoing 

expansion from 2001 to 2007. Corn is still the major feedstock, accounting for 97% of 

ethanol production. Three percent of ethanol is produced from milo (sorghum). 

Table 1. Ethanol plant ownership 

Dry mills Wet mills 

LLC 52% Investor owned 83% 

Farmer owned corp. 11% Public stocks 17% 

Investor owned 24% 

Public stocks 13% 

2. Production 

There is a considerable variation in production capacity in both dry and wet mills (Table 

2). Average scale of dry mills is 52.7 million gallons per year (MMGY) and that for wet 

mills is 145.9 MMGY (Table 2). A bushel of corn in 2006 generates 2.81 gallons of 

denatured ethanol in a dry mill and 2.74 gallons in a wet mill. The highest yields from 

those responding reach 2.96 gallons per bushel (gal/bu) in a dry mill and 2.87 gal/bu in a 

wet mill. An average dry mill facility processed 17.7 million bushels of corn a year. The 

amount of corn processed in average wet mill was 52.7 million bushels annually. 

Table 2, Ethanol production per plant (MMGY) 

Dry mills Wet mills 

Total ethanol production (MMGY)

Mean ±SD* 52.7 ± 21.6 145.9 ± 92.8 

Range 28.7 – 105.5 48.8 – 297.8 

Yield 

(gal denatured ethanol/bushel of corn) 

Mean ±SD* 2.81 ± 0.09 2.74 ± 0.13 

Range 2.62 – 2.96 2.51 – 2.87 

Corn feed^ (MM Bushel/yr) 

Mean ±SD* 17.7 ± 9.1 52.7 ± 32.7 

Range 1.7 – 37.0 16.3 – 106.5 

*SD – standard deviation 

^Ethanol produced from milo is not included. 

3. Co-product 
A U.S. Department of Energy laboratory managed by The University of Chicago 

Dried distillers grains with solubles (DDGS) remain a dominant co-product. Increasingly, 

plants are providing wet DDGS to animal feedlots. Delivery of wet DDGS reduces 

heating costs for DDGS drying in the ethanol plant. Data shows that more than a third 

(36.7%) of DDGS is currently sold as wet feed (Table 3). Carbon dioxide (CO2) as a coproduct of ethanol production is on the rise from both dry and wet mills. Dry mills that 

collect and export CO2 represent 32% of ethanol production surveyed, which for wet mill 

is 17%. Together, they represent 23.5% of the ethanol production capacities. 

Table 3. Co-products produced from ethanol plant 

Dry mills Wet mills 

Co-products production (dry lb/gal) DDGS CGF/CGM 

Mean ±SD* 5.9 ± 0.8 6.5 ± 2.0 

Range 4.7 – 8.1 3.3 – 9.5 

Fraction sold as wet feed (%)

Mean ±SD* 36.7% ± 37.0% 41.1% ± 45.9% 

Range 0 – 100% 6 – 100% 

Share of facilities exports CO2 (as 

ethanol production percentage)^ 

31.6% 16.9% 

*SD – standard deviation 

^ Ethanol production share of CO2 producing facilities in total ethanol production 

4. Energy 

The average dry mill facility requires 31070 British thermal units (Btu), including 

electricity, to produce a gallon of fuel ethanol (as a denatured gallon) (Table 4). 

Electricity usage for dry mills averaged 0.70 kilowatt hours per gallon (kwh/gal). A 

majority of dry mill facilities (86%) generate heat to produce the steam necessary to run 

the facility using natural gas (NG), on a Btu basis. The remaining 14% are coal fired dry 

mills that supplement coal use with a range of NG (3-23%) as process fuel. 

For wet mills, 47409 Btu are required to produce a gallon of ethanol (as a denatured 

gallon). Although wet mills require large amount of electricity, most of them are 

equipped with co-generation capabilities to meet internal electricity needs and thus 

reduce net grid electricity demand. Average natural gas and coal use per gallon ethanol 

produced is presented in Table 4. More energy is needed for ethanol production if coal is 

the choice of process fuel. 

Table 4. Ethanol plant process energy use 

Dry mills Wet mills 

Total energy including electricity 

(Btu/gal1)

 

Mean ± SD2 31070 ± 7490 47409 ± 14641 

Range 17706 – 44034 28795 – 63422 

Electricity3 (kwh/gal)
A U.S. Department of Energy laboratory managed by The University of Chicago 

Mean ± SD2 0.7 ± 0.35 1.96 ± 0.67 

Range 0 – 1.57 0.75 – 2.89 

Natural gas 4,6(Btu/gal)

Mean ± SD2 27589 ± 6358 14461 ± 9586 

Range 16000 – 36883 3397 – 30830 

Coal 5,6(Btu/gal) 

Mean ± SD2 29174 ± 1708 30448 ± 21158 

Range 27966 – 30381 0 – 58553 

1. Denatured ethanol 

2. SD – standard deviation 

3. Grid electricity for dry mills. Grid and cogen electricity use for wet mills. 

4. Ethanol plant fueled with natural gas 

5. Ethanol plant fueled with coal also use 3-23% (Btu NG in total Btu use) of NG 

6. Most wet mills use both coal and NG as process fuel except one facility that uses 100% NG. 

Table 5 shows a break down of process fuel type for dry and wet mills. Natural gas holds 

79.2% share in dry mills, followed by coal (12.7%) and grid electricity (7.9%). In wet 

mills, the predominant fuel is coal (71.6%), followed by natural gas (27.1%). Biogas, tire 

combustion, residual oil, and liquefied petroleum gas (LPG) as process fuels each 

represent less than 1.2%. 

Table 5. Share of process fuels in ethanol production plants 

 Dry mills Wet mills 

Grid electricity 7.9% -1

NG 79.2% 27.1% 

LPG 0.2% 

Coal 12.7% 71.6% 

Residue oil 0.02% 0.04% 

Biogas 0.1% 

Tire 1.15% 

1. Shares of fuel type for wet mill do not include grid electricity because some of the plant data did not 

differentiate between grid and co-gen electricity. Since almost every wet mill has co-gen capability, the 

grid electricity required is likely small. 

5. Water

According to the survey responses, current dry mills use 3.45 gallons of fresh water to 

produce a gallon of ethanol (as a denatured gallon). Water use in wet mills is 3.92 gallons 

per gallon (Table 6). The lowest amount of water use from those respondents is 2.65 

gal/gal for dry mill and 1.2gal/gal for wet mill. There are significant variations in water 

use. Newly built plants tend to require less water, possibly due to improved design. On 
A U.S. Department of Energy laboratory managed by The University of Chicago 

average, dry mill requires 14.5 pounds (lbs) of steam to producing a gallon of ethanol 

(denatured). The steam required in wet mills is 29.5 lbs/gallon. 

Table 6. Water and steam use 

Dry mills Wet mills 

Water (gal/gal ethanol)1

Mean ± SD2 3.45 ± 0.59 3.92 ± 1.76 

Range 2.65 – 4.90 1.20 – 6.10 

Steam (lb/gal ethanol)1

Mean ± SD2 14.47 ±7.63 29.54 ± 14.47 

Range 0.60 – 29.60 13.40 – 45.70 

1. Denatured ethanol gallon 

2. SD – standard deviation 

6. Product transportation and distribution 

Ethanol and co-products are shipped to destinations via various transportation modes: 

truck, barge, rail, and pipelines. As indicated in Table 7, ethanol mills rely heavily on rail 

to deliver ethanol. Rail shipments are responsible for the transportation of three quarters 

(74%) of dry mill ethanol production and two-thirds (66%) of wet mill ethanol 

production. Rail and truck split DDGS delivery, while the majority (76%) of corn gluten 

feed and corn gluten meal, the co-products of wet mill ethanol production, are transported 

by truck. Most of the CO2 from dry mills is shipped via trucks (83%) and remaining by 

pipelines (17%). In wet mills, half of the CO2 is delivered through pipeline, 37% by rail, 

and a small portion (13%) by truck. 

Table 7. Average transportation mode for products and co-products 

Diesel is the major transportation fuel used for feedstock and product delivery (Table 8). 

A qualitative representation of the dry mill product distribution is shown in Figure 1. 

Data for dry mill product distribution is incomplete and therefore not presented. Ethanol 

produced from wet mills is distributed primarily in Petroleum Administration for Defense 

District (PADD) 1 (43%) and PADD2 (31%). The rest is distributed to PADD 3 (11%), 

PADD4 (4%), and PADD5 (11%). 

Truck Rail Barge Pipeline 

Dry mills 

Ethanol 26.3% 73.7% 

DDGS 43.5% 56.5% 

Wet cake 100.0% 

CO2 83.3% 16.7% 

Wet mills 

Ethanol 25.0% 66.0% 9.0% 

CGF/CGM 76.0% 1.0% 24.0% 

CO2 13.0% 37.0% 50.0% 
A U.S. Department of Energy laboratory managed by The University of Chicago 

Table 8. Transportation fuel use in dry mills* 

* Data for wet mills are not available. 

Figure 1. Dry mill ethanol 

distribution. 

7. Comparison to USDA 2001 ethanol plant survey 

Based on the survey data and statistics, a comparison was made with USDA 2001 ethanol 

plant survey for ethanol yield and energy use. Table 9 presents the results of the 

comparison based on denatured ethanol. Ethanol yield increased 6% for dry mills and 2% 

for wet mills. Total energy use (fossil and electricity) decreased 21.8% in dry mills and 

7.2% in wet mills from 2001 USDA survey. Another major change from 2001 survey is 

15.7% decrease in grid electricity use in dry mills. In addition, water consumption in dry 

mills decreased 26.6% from 2001 survey. 

Table 9. Comparison of yield and energy use in ethanol production plant 

Dry mills Wet mills 

RFA 2007 survey 

Yield (gal denatured ethanol /bu) 2.81 2.74 

Total energy use ( btu/gal denatured ethanol) 31070 47409 

Grid Electricity share in total process fuel use 7.9% NA 

Consumptive water use (gal/gal denatured 

ethanol) 

3.45 3.92 

2001 USDA survey* 

Yield (gal denatured ethanol /bu) 2.64 2.68 

Gasoline Diesel LPG E85 

% of total 

transportation fuel use 

13.0% 75.2% 9.4% 2.4% 
A U.S. Department of Energy laboratory managed by The University of Chicago 

Total energy use ( btu/gal denatured ethanol) 39719 51060 

Grid Electricity share in total process fuel use 9.4% 0% 

Consumptive water use (gal/gal denatured 

ethanol)** 

4.7 NA 

Change from 2001 survey 

Yield (gal denatured ethanol /bu) 6.4% 2.4% 

Total energy use ( btu/gal denatured ethanol) -21.8% -7.2% 

Grid Electricity share in total process fuel use -15.7% 

Consumptive water use (gal/gal denatured 

ethanol) 

-26.6% 

* Source: Shapouri, Duffield, and Wang, The energy balance of corn ethanol: An update, USDA AER/ 

814, July 2002. 

**Shapouri H., Gallagher, P., July 2005, USDA's 2002 Ethanol Cost-of-Production Survey