ETHANOL BENCHMARKING AND BEST PRACTICES

M I N N E S O T A T E C H N I C A L A S S I S T A N C E P R O G R A M


ETHANOL
BENCHMARKING AND
BEST PRACTICES
THE PRODUCTION PROCESS AND
POTENTIAL FOR IMPROVEMENT

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Ethanol Benchmarking and Best Practices (March 2008)
TABLE OF CONTENTS
ACRONYM LIST .....................................................................................................................................................................4
INTRODUCTION .................................................................................................................................................................... 5
PLANT DESCRIPTIONS ........................................................................................................................................................6
ETHANOL PROCESS DESCRIPTION ................................................................................................................................6
Table 1: Energy Consumption by Process ................................................................................................................................... 6
Figure 1: Process Thermal and Electrical Energy Use ............................................................................................................... 7
THE PRODUCTION PROCESS IS DESCRIBED AS FOLLOWS: ....................................................................................................8
Grain Handling .............................................................................................................................................................. 8
Starch Conversion .........................................................................................................................................................8
Fermentation .................................................................................................................................................................. 8
Distillation ......................................................................................................................................................................9
Dehydration ......................................................................................................................................................................9
Storage and Shipping ...................................................................................................................................................... 9
Separation ......................................................................................................................................................................10
Drying ............................................................................................................................................................................10
Plant Utilities ..................................................................................................................................................................10
Diagram 1: Proposed Water Balance for Highwater Ethanol Facility .................................................................................. 11
Diagram 2: A Schematic of a Typical Dry Mill ........................................................................................................................ 12
ENVIRONMENTAL IMPACTS ASSOCIATED WITH ETHANOL PRODUCTION ...................................................13
WATER QUALITY .................................................................................................................................................................13
AIR QUALITY .......................................................................................................................................................................14
Figure 2: Relative Criteria Pollutant Emissions ........................................................................................................................ 15
ENERGY CONSUMPTION ......................................................................................................................................................15
Thermal Energy ............................................................................................................................................................15
Electricity Use ...............................................................................................................................................................15
Table 2: Approximate Energy Costs for State of the Art 40 MGY Facility ............................................................................ 16
WATER USE .........................................................................................................................................................................16
Diagram 3: Minnesota Ethanol facilities and Corresponding Areas Where Ground Water Supplies are Lmited ............. 16
BENCHMARKS AND BEST PRACTICES .........................................................................................................................17
INTRODUCTION ..............................................................................................................................................................17
WATER QUALITY .................................................................................................................................................................18
Table 3: Examples of the Variability in TDS levels in Water Supply ...................................................................................... 18
Table 4: Trends in Monitoring Requirements based on Permit Expiration Date (5 years after issuance)* ......................... 19
Table 5: Wastewater Discharge Data ......................................................................................................................................... 20
BEST PRACTICES RELATED TO WATER QUALITY INCLUDE THE FOLLOWING: ..................................................................20
Water Resource .............................................................................................................................................................20
On-site Retention of Stormwater ....................................................................................................................................20
Segregation of Non-Contact and Process Waters ........................................................................................................21
Zero Discharge of Process Water .................................................................................................................................21
Zero Liquid Discharge Technology .............................................................................................................................21
Use of Low or No- Phosphorus Water Treatment Chemicals .....................................................................................21
AIR QUALITY .......................................................................................................................................................................21
Figure 3: VOC Emission Factor ................................................................................................................................................ 22
ENERGY ............................................................................................................................................................................... 22
Table 6: Energy Benchmarks for Dry Mill Ethanol Facilities............................................................................................... 22
Figure 4: Thermal Energy Use Index ........................................................................................................................................ 23
Figure 5: Renewable vs. Fossil Thermal Energy Use Index .................................................................................................... 23
Figure 6: Electrical Energy Use Index ...................................................................................................................................... 24
BEST PRACTICES RELATED TO ENERGY INCLUDE THE FOLLOWING: .................................................................................24
Heat Recovery from Jet Cooker and Distillation ..........................................................................................................24
Heat Recovery from TO/RTO ......................................................................................................................................24
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Ethanol Benchmarking and Best Practices (March 2008)

Ring Dryers (vs. Rotary Dryers) ....................................................................................................................................24
Use of Renewable Energy ............................................................................................................................................25
Combined Heat and Power (CHP) ...............................................................................................................................25
Co-location with Steam Power Plants .........................................................................................................................25
Elimination of Grain Drying before Grinding .............................................................................................................25
Ship WDGS Instead of DDGS ...................................................................................................................................25
Biomethanators ............................................................................................................................................................26
Raw Starch Hydrolysis ...................................................................................................................................................26
Fractionation .................................................................................................................................................................26
High Efficiency Stillage Concentration (HESC) System ............................................................................................26
Use of Variable Frequency Drives (VFD) and High Efficiency Motors ....................................................................27
Advanced Process Contro. .............................................................................................................................................27
WATER EFFICIENCY ............................................................................................................................................................27
Figure 7: Water Efficiency ......................................................................................................................................................... 28
BEST PRACTICES RELATED TO WATER USE INCLUDE THE FOLLOWING: ...........................................................................28
Public Records of Water Use .........................................................................................................................................28
No-Contact Steam Systems vs. Direct Injection ..........................................................................................................28
Municipal Wastewater Reuse ........................................................................................................................................28
High Efficiency Dryer Technology ..............................................................................................................................29
Chemical Treatment of Cooling Tower Water ............................................................................................................29
Membrane Technology .................................................................................................................................................29
Recycling Discharge Water with Livestock Facilities .................................................................................................29
YIELD ...................................................................................................................................................................................29
Figure 8: Yield ............................................................................................................................................................................. 30
SUMMARY OF BEST PRACTICES ..........................................................................................................................................30
Table 7: Summary of Best Practices .......................................................................................................................................... 31
CONCLUSIONS .....................................................................................................................................................................32
Table 8: New Plants (2005/2006 startup) vs. Old Plants (1991 – 1999 startup) .......................................................32
RECOMMENDATIONS ........................................................................................................................................................33
REFERENCE ..........................................................................................................................................................................34

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Ethanol Benchmarking and Best Practices (March 2008)



ACRONYM LIST
BACT – Best Achievable Control Technology
PM10 – Particulate Matter less than 10 microns
BOD – Biological Oxygen Demand
RO – Reverse Osmosis
Btu – British thermal unit
RTO – Regenerative Thermal Oxidizer
CBOD5 – 5-Day Carbonaceous Biological Oxygen
SDS – State Disposal System
Demand
TO – Thermal Oxidizer
CCX – Chicago Climate Exchange
TDS – Total Dissolved Solids
CO2 – Carbon Dioxide
TSS – Total Suspended Solids
CO –Carbon Monoxide
µmhos/cm – micromhos per centimeter
CLS – Cold Lime Softening
VFD – Variable Frequency Drives
CHP – Combined Heat and Power
VOC – Volatile Organic Compounds
DDGS – Dried Distillers Grains with Solubles
WDGS – Wet Distillers Grains with Solubles
DNR – Department of Natural Resources
DOE – Department of Energy
EPAct – Energy Policy Act of 1992
EAW – Environmental Assessment worksheet

EPA – Environmental Protection Agency
F – Fahrenheit
gal – gallon
HESC – High Efficiency Stillage Concentration
HP – Horsepower
HRSG – Heat Recovery Steam Generator
IATP – Institute for Agriculture and Trade Policy
kW – Kilowatt
kWh – Kilowatt Hours
lb/hr – Pounds per Hour
LDAR – Leak Detection and Repair
MDA – Minnesota Department of Agriculture
mg/l – milligrams per liter
meq/l – milliequivalents per liter
MTBE – Methyl Tertiary Butyl Ether
MMBtu – Million British Thermal Units
MGD – Million Gallons per Day
MnTAP – Minnesota Technical Assistance Program
MPCA – Minnesota Pollution Control Agency
MGY – Million Gallons per Year
MWWTP – Municipal Wastewater Treatment Plant
NPDES – National Pollutant Discharge Elimination
System
NOx – Nitrogen Oxide
PM – Particulate Matter
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Ethanol Benchmarking and Best Practices (March 2008)
INTRODUCTION

The Ethanol Benchmarking and Best Practices study provides an overview of the ethanol production process and
some information on potential environmental issues related to the process. This study also introduces some
concepts for improvements in the use of resources including energy, water, and reducing environmental impacts.
Additionally, it is intended to educate others outside the ethanol industry of the challenges faced by facilities to
conserve resources.

Ethanol production in Minnesota is growing at a fast pace. In 1988, ethanol was first used as an oxygenate
in gasoline to reduce carbon monoxide emissions. By 2004, many states had banned Methyl Tertiary Butyl Ether
(MTBE) as an oxygenate in fuel replacing it with ethanol. In 1980, the United States produced 175 million
gallons of ethanol; in 2007, the annual total is expected to be 7.5 billion gallons.1 First generation ethanol plants
in Minnesota were typically producing 20 million gallons per year (MGY), but the current trend is towards larger
plants. Plants permitted more recently have capacities in the range of 55-70 MGY and some approved for
construction will have capacities greater than 100 MGY.

The benchmarks and best practices presented focus primarily on dry mill facilities, since most of the
facilities in Minnesota are dry mill. Due to limited access to facilities, it was difficult to determine exactly how
many of these best practices are in place in Minnesota facilities. Even though all best practices have been
demonstrated in some facilities, they may not be practical for all facilities. Many practices may also apply to wet
mill facilities but their applicability was not reviewed during this process. Excellent resources exist that provide
guidance on energy efficiency related to the wet milling industry.2

There are three major design firms that have built most of the facilities in Minnesota and each design has
features that make them unique. Whether a facility uses a best practice listed in this report can be dependent on
the design firm used.

This study focused on the operation of the ethanol plant. There are many important issues related to
ethanol production that are not addressed in this report. They include discussions about cellulosic ethanol, climate
change, and impacts from increased corn production such as soil erosion, runoff, and water use for crop irrigation.
This report provides a comparison of newer and older facilities in Minnesota by addressing the following
questions:
• Does the data show that new facilities use fewer resources than older facilities?
• Can retrofits be made to older facilities to improve performance?
• Do the potential savings justify significant capital investment in facilities?
• Can low cost actions be taken to reduce consumption of energy, water, or reduce environmental
impact?
• What areas need support and where can the Minnesota Technical Assistance Program (MnTAP)
provide support?

Benchmarks provide a numerical standard for comparison while best practices are techniques or processes
that have demonstrated a desired result. For this study, the benchmarks and best practices focused on indicators of
reduced resource use or environmental impact. Benchmarks include volatile organic compound (VOC) emissions
in tons per million gallons of ethanol, ethanol yield in gallons per bushel of corn, energy use in British Thermal
Units (Btu) or kilowatt hours (kWh) per gallon ethanol, and water efficiency in gallons of water per gallon
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Ethanol Benchmarking and Best Practices (March 2008)

ethanol. Best practices include processes or equipment modifications that achieve reduced water use, energy use,
or create less impact on the environment.

The majority of facility information was obtained from 2006 annual data found in publicly available data
sources. For one facility, 2005 data was used because 2006 data was incomplete. Site visits were used to validate
best practices and to potentially assist facilities with energy efficiency or pollution prevention practices.
Information was shared allowing facilities to see what areas they excel at or where performance improvements
could be implemented. All private data collected on specific facilities was kept confidential and will not be shared
with others outside MnTAP.

MnTAP would like to thank all the companies that took the time to discuss their operations and provide
benchmark data. MnTAP would also like to thank Natural Resource Group for their support in promoting this
project and providing technical support.
PLANT DESCRIPTIONS
This study included 14 operating dry mill ethanol facilities in Minnesota and one in Wisconsin. The average
production rate for a facility in Minnesota for 2006 was 34 MGY. The review included site visits to all facilities
willing to participate and phone or email discussions with others. These facilities had original start up dates that
ranged from 1991 to 2006, but there was a gap from 2000 to 2004 where no new Minnesota facilities started
production. It was expected that some of the older facilities would not have the state of the art technology of the
newer facilities. As a starting point, the facilities with start up dates from 1991 to 1999 were considered “old” and
the facilities with start up dates of 2005 to 2006 were considered “new”.
ETHANOL PROCESS DESCRIPTION
The following provides a basic description of the dry mill ethanol process. Diagram 1, provided at the end of this
section, provides a schematic of the typical dry mill process. The diagram provides information on the processes
where significant energy, water, or environmental impact occurs.

Figure 1 and Table 1 display the thermal and electrical energy consumption by each process in a typical
state of the art 40 MGY facility.3 These estimates are based on a computer modeling program from the
Agricultural Research Service using inputs from ethanol facilities, equipment suppliers, and engineers working in
the industry.
Table 1: Energy Consumption by Process
%
Elec,
Steam,
Nat Gas,
Elec,
Thermal
Total
Total
Process Major
Equipment
kW
lb/hr
CF
Btu/gal Btu/gal
Btu/gal
Energy
Hammermills, Conveyors, Dust
0
Grain Handling
Collectors, Fans
443 0
352
0 352
1%
Starch Conversion
Pumps, Jet Cooker, Agitators 167
23,582 0
133
5,544
5,677
16%
Fermentation
Agitators, Pumps
292
0
0
231
0
231
1%
Distillation
Reboilers, Columns
25
25,172
0
20
12,884
12,904
37%
Dehydration
Mole Sieve, Pumps
16
526
0
13
257
270
1%
Separation (Note 1)
Centrifuge, Evaporators
1,168
0
0
926
0
926
3%
Drying
Dryers 1,176
0
165,000
933
13,914
14,847
42%
Thermal Oxidizer, Cooling
Utilities (Note 2)
Tower, Air Compressor, Boiler
570
0
0
0
0
0
0%
Total
3,858
49,280
165,000
2,608
32,600
35,208

Notes:
1) Evaporator steam use is allocated to the distillation process because steam is recovered from the rectifier.
2) This process assumes a TO/HRSG combination. Natural gas use for TO is not shown because HRSG uses waste heat from TO
exhaust. Electrical energy for utilities is allocated over all processes.
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Figure 1: Process Thermal and Electric Energy Use

Process Electrical Use
Process Thermal Use
0%
11%
15%
17%
4%
Grain Handling
Grain Handling
8%
0%
Starch Conversion
Starch Conversion
1%
Fermentation
42%
Fermentation
0%
Distillation
Distillation
Dehydration
Dehydration
30%
Separation
Separation
Drying
Drying
Utilities
40%
31%
0%
1%
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Ethanol Benchmarking and Best Practices (March 2008)

The production process is described as follows:
Grain Handling
Corn kernels arrive at the plant by either truck or rail and are stored in silos. Conveyor belts move corn through
the area. There are typically two Hammermills, which have motors of approximately 250 horsepower (HP) each,
that grind the corn into flour. Baghouse fabric filters are standard particulate control equipment that have a
capture efficiency of 99% for particulate matter (PM) and PM less than 10 microns (PM10). This process is driven
by electrical power, which is approximately 11% of the electrical energy consumed by the plant. No water or
thermal energy is used in this process.
Starch Conversion
The starch conversion process includes liquefaction and saccharification. In the liquefaction process the ground
flour is mixed with process water in the slurry tank, the pH is adjusted with ammonia, and alpha-amylase enzyme
is added. Steam is injected into the mixture using a steam injection heater called a “jet cooker”; it is then heated
to about 185°F to increase viscosity and is held at that temperature for about 45 minutes. The mixture is combined
with thin stillage, which is recycled process water from the centrifuge. Steam is injected into the slurry to further
raise the temperature to about 220°F and held for about 15 minutes. The mixture is cooled through an atmospheric
or vacuum flash condenser. The waste steam recovered from the jet cooker is sent to the distillation system or
evaporators for energy recovery.

The final step of the starch conversion process is called saccharification. The pH and temperature are
adjusted and another enzyme, glucoamylase, is added. The mixture is held in tanks for about 5 hours at about
140°F to give the enzyme a chance to break down the starch into sugars. At the end of this process the mixture,
called “mash”, is pumped into the fermentation tanks.

The motors for the pumps in the starch conversion process are relatively small. Electrical energy use is
approximately 4% of the total facility’s electric use. The steam used in the jet cooker is significant and is
estimated at 15% of the total plant process energy. This steam is not recaptured from the process, and is
equivalent to water use of approximately 45 gpm or 0.6 gallons of water per gallon of ethanol in a 40 MGY
facility.
Fermentation
Once the mash leaves the starch conversion process it is cooled to approximately 90°F and yeast is added to
convert the sugars to ethanol and carbon dioxide (CO2). The fermentation process continuously generates heat and
requires cooling to keep the solution at approximately 90° F to avoid killing the yeast. The process takes
approximately 50 to 60 hours. There are two types of fermentation: batch and continuous. In batch fermentation,
the mash ferments in a single vessel. In a continuous fermentation process the mash will flow through several
fermentation tanks until the process is complete. The product leaving the fermentation process is called beer,
which is water containing grain solids and about 10% - 15% ethanol.

The other product of the fermentation process is CO2. Each bushel of corn produces about 18 pounds of
CO 4
2 , resulting in over 130,000 tons of CO2 each year for a 40 MGY facility
2
. The CO from the fermentation
process is sent through a scrubber that removes ethanol and other water soluble VOCs before
2
the CO is emitted
to the atmosp
2
here. Additional CO is removed from the beer by heating the beer with the process streams from the
starch conversion process and passing it through a degasser drum to
2
flash off CO vapors, which then go to the
2
CO scrubber.
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Ethanol Benchmarking and Best Practices (March 2008)


The motors for the pumps in the fermentation process represent 8% of the electrical load in the facility.
The cooling water load is significant for the fermentation process and is approximately 30% of the cooling water
flow. The CO2 scrubber uses water to remove the ethanol and VOCs; the water is recovered and sent to the starch
conversion process to mix with the ground corn. The amount of VOCs released during fermentation is
approximately 20% of total plant VOC emissions, typically the second highest source.
Distillation
The distillation process removes the majority of the remaining water from the beer based on the different boiling
points of water and ethanol. The system is comprised of three columns: the beer mash tower, the rectifier, and a
side stripper. Reboilers, which provide non-contact steam for each column, are used to heat the ethanol/water
mixture to drive the process. The beer enters the beer mash tower from the fermenter and flows over trays while
the reboiler steam heats the liquid in the bottom of the tower. The solids and water, called stillage, are removed
from the bottom of the beer column and sent to the centrifuge. The vapor leaving the beer tower is 40 - 50%
ethanol and flows to the rectifier column. The rectifier takes the vapor from the beer mash tower and the
distillation process continues until it is concentrated to 95% ethanol and 5% water. The rectifier column removes
other hydrocarbons, called “fusel”, and these are mixed with the final ethanol product. Some of the ethanol
leaving the rectifier is condensed and sent back to the rectifier as reflux to draw more water out of the ethanol.
The side stripper takes the water out of the bottom of the rectifier and using steam from a reboiler, strips out any
remaining ethanol and sends it back to the rectifier.5

The energy consumed in the distillation process is primarily from the steam used by the reboilers and
represents about 70% of the steam needed by the overall process. This steam is recaptured from the process in a
closed loop system with the evaporator system where the condensate is returned to the boiler for reuse. The
electricity used in distillation is negligible compared to other processes.
Dehydration
The dehydration process consists of two molecular sieve, “mole sieve”, units that are cycled so one unit is
regenerating while the other is operating. The 95% ethanol vapor leaving the rectifier is superheated before it
enters one of the mole sieves. The vapor passes through a bed of beads where the water is adsorbed on the beads
and the ethanol vapor passes through. Just before the bed gets saturated with water, the flow is switched to the
other bed and the saturated bed is regenerated. The regeneration of the mole sieve is accomplished by passing
some of the anhydrous ethanol vapor back through the bed and applying a vacuum to pull the water out. The
recovered water is sent to the stripper column to remove any small amounts of ethanol and then used as process
water. The ethanol vapor is cooled in a condenser to convert the vapor to a liquid for storage.

The energy consumed for the dehydration process is mainly related to the steam used to superheat the
ethanol entering the mole sieve. This represents just 1% of the total steam used in the facility. Like distillation,
this steam is recaptured from the process. The process of condensing the ethanol vapor to a liquid is
approximately 20% of the cooling water flow.
Storage and Shipping
To make fuel grade ethanol, denatured ethanol, and 3-5% gasoline is added. The denatured ethanol is stored in
large tanks on site until it is loaded into rail cars or trucks for delivery to the customer. A loadout flare, standard
control equipment at an ethanol facility, reduces VOC emissions by 95% during the loading process. These
emissions represent approximately 10% of total plant VOC emissions. Although emissions are a concern, the
flare also protects against the explosion hazard of the fuel loading process.

No significant energy or water is used during the storage and shipping process.
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Ethanol Benchmarking and Best Practices (March 2008)

Separation
Stillage from the bottom of the beer column, containing 15% solids, is sent to centrifuges which separate the
coarse grains from the solubles. The solubles, called thin stillage, that come out of the centrifuge are sent through
evaporators where water is removed resulting in a 35% solids mixture called syrup. Biomethanators are used to
treat the removed water so it can be reused within the process. The evaporators are typically multiple-effect and
use indirect heat from reboilers. The coarse grains from the centrifuge and syrup from the evaporators are then
mixed back together to form wet distiller’s grains with solubles (WDGS), which have a moisture content of over
60%. WDGS is sold as a feedstock for cattle.

The motors for the centrifuges and vacuum pumps use approximately 30% of the total plant electrical
energy. The steam used in the evaporators is recovered from the distillation process so it does not add to the total
steam load.
Drying
The WDGS are sent to dryers to reduce the moisture content to approximately 10%. The product is now called
dried distillers grains with solubles (DDGS) and this is sold as a feedstock for cattle. Drying is needed to prevent
spoilage, reduce odors, and extend the shelf life of the grain. The typical dryer is a rotary drum dryer which has an
air heater, fired by natural gas, mixing hot air with the WDGS to evaporate the water. The VOC emissions from
the drying process, typically 30% of the total VOC emissions, are controlled with a thermal oxidizer or
regenerative thermal oxidizer (TO/RTO).

The energy used in drying is mainly from natural gas used to fire the dryer and is approximately 42% of
all thermal energy consumed in the facility. The electrical energy required is due to the size of the motors needed
to power the fans, mixers, and dryers and is approximately 30% of the electrical energy consumed. A significant
amount of water in the WDGS is evaporated in the dryer, is not recovered, and amounts to approximately 30% of
the incoming plant makeup water supply flow. There is a new technology described in the Best Practices section
of this report that is focused on trying to recover water evaporated during drying.
Plant Utilities
Plant utilities include the well water pumps, TO/RTO, boiler(s), cooling tower, chillers, air compressors, lighting,
water treatment equipment and chemicals. If a TO is used, it is combined with a heat recovery steam generator
(HRSG) to recover the waste heat from the TO exhaust to produce steam needed for the process. If a RTO is
used, the excess heat from the oxidizer is used to preheat the incoming exhaust gas instead of being ducted to a
HRSG. An RTO is combined with a package boiler fired on natural gas to produce steam needed for the
production process. Based on the level of process review, at this time, it is unclear whether one configuration is
more efficient than the other. Using a TO/HRSG versus a RTO with a package boiler is more dependent on the
design firm that built the plant.

Typical water treatment equipment may include reverse osmosis (RO) units, iron filters, cold lime
softening (CLS) units, softeners, or carbon filters. The specific equipment is dependent on the quality of the
incoming water; amount of recycling; chemical additives used; and applicable wastewater discharge limits.
Chemicals are used to protect the heat exchangers from formation of scale, rust, or microbial growth.

The electrical energy used to power the motors for plant utilities amounts to approximately 15% of the
total electrical load.

As a general approximation, water use at a dry mill ethanol facility can be broken out as 70% non-contact
utility water and 30% process water. Process water comes into contact with the corn used in the production of
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