TECHNICAL PAPER # 3
UNDERSTANDING ETHANOL FUEL
PRODUCTION AND USE
Cliff Bradley & Ken Runnion
C. Gene Haugh
1600 Wilson Boulevard, Suite 500
Arlington, Virginia 22209 USA
Tel: 703/276-1800 . Fax: 703/243-1865
Understanding Ethanol Fuel Production
[C]1984, Volunteers in Technical Assistance
This paper is one of a series published by Volunteers in
Assistance to provide an introduction to specific
technologies of interest to people in developing countries.
The papers are intended to be used as guidelines to help
people choose technologies that are suitable to their
They are not intended to provide construction or
details. People are
urged to contact VITA or a similar organization
for further information and technical assistance if they
find that a particular technology seems to meet their needs.
The papers in the series were written, reviewed, and
almost entirely by VITA Volunteer technical experts on a
Some 500 volunteers were involved in the production
of the first 100 titles issued, contributing approximately
5,000 hours of their time.
VITA staff included Leslie Gottschalk
as primary editor, Julie Berman handling typesetting and
and Margaret Crouch as project manager.
Cliff Bradley and Ken Runnion, co-authors of this paper,
specialize in alcohol fuel production technologies.
Bradley is a
microbiologist and Runnion a chemical engineer at Renewable
They have published several practical manuals
and booklets in the field, and are currently researching and
developing new methods of improving the starch hydrolysis
required for alcohol fuel production.
Reviewers Kenneth Brunot,
C. Gene Haugh, and Daniel Ingold are also specialists in the
area. Brunot, senior
vice president for Wright Technology, was
formerly president of Wright Energy Nevada Corporation,
specialized in studies relating to ethanol production using
geothermal energy for process energy requirements.
the Department of Agricultural Engineering at Virginia
Institute. Ingold is
a biophysicist by training and a
research engineer at Appropriate Technology Corporation.
VITA is a private, nonprofit organization that supports
working on technical problems in developing countries.
information and assistance aimed at helping individuals and
groups to select and implement technologies appropriate to
maintains an international Inquiry Service, a
specialized documentation center, and a computerized roster
volunteer technical consultants; manages long-term field
and publishes a variety of technical manuals and papers.
UNDERSTANDING ETHANOL FUEL PRODUCTION AND USE
VITA Volunteers Cliff Bradley and Ken Runnion
This paper describes the production and use of ethanol
as a liquid fuel.
The production of ethanol is a well-established
technology; however, the use of ethanol as a liquid
fuel is a complex subject.
Ethanol was one of the first fuels used in automobile
was used extensively in Germany during World War II and also
Brazil, the Philippines, and the United States.
During the postwar
period, as petroleum supplies became cheap and abundant,
gasoline largely replaced ethanol as an automotive
until the 1970s, when the supply of oil was restricted, did
ethanol re-emerge as an alternative to or extender for
liquid fuels (ethanol as an extender is added to these
fuels to increase their volume).
Today, 12 countries produce and
use a significant amount of ethanol.
In Brazil, for example, one
third of that country's automobiles uses pure ethanol as
the remaining two thirds use mixtures of gasoline and
France, the United States, Indonesia, the Philippines,
Costa Pica, Argentina, the Republic of South Africa, Kenya,
Thailand, and Sudan are other countries with government or
ethanol fuel programs.
The programs are designed to reduce a
country's dependence on costly imported fuel and to assist
creating a new domestic fuel industry.
Pure ethanol can replace gasoline in modified spark-ignition
engines, or it can be blended with gasoline at up to 20
concentration to fuel unmodified gasoline engines.
serves two purposes: (1) it extends gasoline supplies, and
as an octane enhancer, it replaces lead compounds in
Ethanol can also be used in modified diesel (compression
engines; however, this is not common.
The production and use of fuel ethanol can indirectly serve
of needs. On a
national level, ethanol can improve balance
of payments by displacing imported petroleum with
produced fuel. This
may also provide increased rural employment
and alternative markets for agricultural commodities.
On a community
or individual level, ethanol fuel production is often
viewed as a means to become independent of purchased fuels,
keep money within the local economy, and to provide an
fuel supply in the event of shortages of petroleum fuels.
II. OPERATING PRINCIPLES
Ethanol fuel production is a combination of biological and
is produced by fermentation of sugars with
yeast. It is
concentrated to fuel grade by distillation.
is a schematic representation of the principal steps in fuel
Feedstocks, the base raw materials, are either sugar or
"Biomass Fuel Crops" (tubers and grains)
commonly include sugar beets, potatoes, corn, wheat, barley,
Jerusalem artichokes, and sweet sorghum.
Sugar crops such as
sugar cane, sugar beets, or sweet sorghum are extracted to
a sugar-containing solution that can be directly fermented
by yeast. Starch
feedstocks, however, must be carried through an
additional conversion step.
Starch is a long "chain" polymer of glucose (i.e.,
polymer units bonded in a chain).
Starches cannot be directly
fermented to ethanol.
They must first be broken down into the
simpler glucose units through a process of hydrolysis.
hydrolysis step, starch feedstocks are ground and mixed with
water to produce a mash typically containing 15 to 20
starch. The mash is
then cooked at boiling point or above and
treated in sequence with two enzyme preparations.
enzyme hydrolyzes starch molecules to short chains; the
enzyme hydrolyzes the short chains to glucose.
The mash is then
cooled to 30[degrees] C, and yeast is added.
Yeasts are microorganisms that produce ethanol.
are capable of converting sugar into alcohol by a biological
process called fermentation.
The following equation shows the
basic biological reaction in the conversion by fermentation
one kilogram of glucose to ethanol, carbon dioxide, and
Theoretically, the maximum conversion efficiency of glucose
ethanol is 51 percent on a weight basis.
However, some glucose is
used by the yeast for the production of cell mass and for
products other than ethanol.
In practice, between 40 and 48
percent of glucose is converted to ethanol.
With a 45-percent
fermentation efficiency, 1,000 kilograms of fermentable
produce about 570 liters of pure ethanol.
Conversely, about 1,800
kilograms of fermentable sugar are required to produce 1,000
liters of ethanol.
Mash typically contains between 50 and 100
grams of ethanol per liter (5 to 10 percent weight per
when fermentation is complete.
Ethanol is separated from mash by distillation--a physical
in which the components of a solution (in this case, water
and ethanol) are separated by differences in boiling point
Ethanol and water form an azeotrope, or constant boiling
of about 95 percent alcohol and five percent water.
five percent water cannot be separated by conventional
The production of pure, water-free (anhydrous) ethanol
requires a dehydration step following distillation.
a relatively complex step in ethanol fuel production, is
in one of two ways.
The first method uses a third
liquid, most commonly benzene, which is added to the
water mixture. This
changes the boiling characteristics of the
solution, allowing separation of anhydrous ethanol.
method employs molecular sieves that selectively absorb
the basis of the difference in molecular size between water
The non-fermentable solids in distilled mash (stillage)
variable amounts of fiber and protein, depending on the
The liquid may also contain soluble protein and other
The recovery of the protein and other nutrients in stillage
for use as livestock feed can be essential for economical
ethanol fuel production.
Protein content will vary with feedstock.
Some grains (e.g., corn, barley) yield a solid by-product
--distillers dried grains (DDG)--that ranges from 25 to 30
protein and makes an excellent feed for livestock.
processing equipment is constructed of stainless steel and
is carried out under well-controlled conditions, the protein
by-products can also be consumed by humans.
The production of ethanol also produces liquid effluent,
a potential pollution problem.
About 9 liters of effluent are
produced for each liter of ethanol.
In well-designed plants, some
of the effluent may be recycled.
Effluent can have a high Biological
Oxygen Demand (BOD), which is a measure of organic water
pollution potential, and it is acidic.
It requires treatment
Treatment requirements depend on feedstock and
local pollution control regulations.
Because of the acid content,
care must be taken if the effluent is spread over fields.
ETHANOL END USE
Ethanol is a high-quality, stable liquid.
Some of the chemical
and physical properties of ethanol are summarized in Table
Table 1. Summary of Ethanol
Density (20[degrees] C).......................
Boiling Point [a].............................
Heat of Combustion [b]........................
Heat of Vaporization [c]......................
Stoichiometric Air/Fuel Ratio [d].............
[a] Boiling point is
the temperature at which a liquid changes
becomes a gas; the point at which the vapor pressure
of the liquid
equals the vapor pressure of the system.
[b] Heat of
combustion is the amount of heat given off when a
unit quantity of
any hydrocarbon (e.g., ethanol) is burned
dioxide and water.
[c] Heat of
vaporization is the heat input required to change
liquid at its
boiling point to a vapor at the same temperature
(e.g., water at
100[degrees] C to steam at 100[degrees] C).
stoichiometric air/fuel ratio is the amount of air
completely to oxidize (burn) the fuel.
Ethanol Use in Engines
Ethanol is most commonly used in transportation and
to fuel internal combustion, four-cycle, spark-ignition
It is used as a direct replacement for gasoline, or it is
with gasoline as an extender and octane booster.
The use of ethanol to replace gasoline requires
the carburetor, fuel system components, and often the
ratio. The efficient
conversion of existing gasoline engines requires
skilled, knowledgeable technicians.
Engines specifically designed and manufactured to operate on
ethanol fuel will generally be more efficient than modified
concentrations of between 80 and 95 percent
can be used as fuel, which eliminates the need for
dehydration systems and simplifies distillation.
In many cases,
the conversion of engines to operate on ethanol may be
and more cost efficient than ethanol dehydration.
of engine conversion is that vehicle travel distance is
by the available supply and distribution of ethanol.
Some "dual fuel" systems--that is, engines with a
can operate either on ethanol or on gasoline--have been
on a limited basis.
In Brazil, a significant portion of the
transportation fleet uses ethanol fuel in automobiles with
designed engines, manufactured by major international
In unmodified engines, ethanol can replace up to 20 percent
Blending ethanol with gasoline extends the gasoline
supply, and improves the quality of gasoline by increasing
octane value. As an
octane enhancer, ethanol can replace lead
compounds in gasoline.
There are advantages to using gasoline/
ethanol blends rather than pure ethanol.
Blends do not require
In this way, ethanol can be integrated
rapidly with existing gasoline supply and distribution
Replacing lead compounds with ethanol removes one of the
air pollution problems associated with gasoline.
The disadvantage of using ethanol/gasoline blends is that
ethanol must be anhydrous, requiring a dehydration step in
If non-anhydrous ethanol is mixed with gasoline, the
blends will separate into a gasoline phase and a
phase, causing erratic engine performance.
In addition to its use in gasoline-fueled automobiles and in
truck or tractor engines, ethanol can be used in other types
example, small, four-cycle gasoline engines found in
small-scale agricultural equipment (e.g., tillers, small
can often burn 80 to 95 percent ethanol as a direct
for gasoline. Such
engines fed by ethanol require
The use of ethanol in specially designed two-cycle engines
been demonstrated on a limited basis.
The problem of using ethanol
in these engines is that the ethanol does not blend well
lubricating oil. To
get around this problem, research is under
way to find lubricating oils that are not affected by
Though ethanol use in diesel-fueled engines is feasible, it
Ethanol does not ignite under compression and
does not mix well with diesel fuel.
Therefore, ethanol cannot be
used as a direct replacement for diesel fuel or blended with
diesel fuel for use in compression ignition engines.
be used as a replacement for diesel fuel only if the engine
fitted with glow plugs.
Ethanol can be used in supercharged diesel engines for up to
about 25 percent of the total fuel.
This is done by carrying the
ethanol in a separate fuel tank and injecting it into the
engine through a supercharger airstream.
Ethanol can also replace aviation fuel in aircraft engines.
Ethanol Use in Appliances
Ethanol can be used in a variety of cooking, heating, and
appliances. In some
cases, ethanol can be used in modified
appliances designed for conventional fuels.
In other cases,
appliances designed specifically for ethanol fuel are
III. PLANT DESIGN VARIATIONS
This section describes briefly the processes and equipment
for each principal step in ethanol fuel production.
provides a general discussion of the economics of ethanol
production. It is
not meant to provide specific information on
Processes and equipment vary greatly, depending on
need for starch hydrolysis, ethanol end use, available
utilities, process energy source, by-product use, and plant
Plant design studies indicate that an economy of scale
a 30,000,000 gal/year plant producing hydrated (190 proof)
and co-generating, i.e., utilizing on-site gas turbine
sets fueled with hydrated ethanol to provide associated
power needs for the plant.
The turbine exhaust gas could be used
to obtain high-pressure steam and the spent hot turbine
gas could be used in process by-product drying
to produce process by-products (distillers dried grains
(DDG), carbon dioxide, and fusel oil components should be
in the overall design in order to maximize cost
The type of feedstock chosen for ethanol fuel production has
significant impact on plant design.
Ethanol is produced from a
variety of sugar- or starch-containing crops, with
in the design of the feedstock preparation processes.
modifications are required to accommodate the physical
of the feedstock, as well as the nature of the carbohydrate
(i.e., sugar versus starch).
Preparation equipment is necessary to grind, pulverizer or
the feedstock before it can be processed.
for feedstock preparation varies, depending on such
of the feedstock as moisture content, physical structure,
and fiber content.
Starch-containing feedstocks require starch hydrolysis
including tanks, heating and cooling systems, agitation
transfer pumps, and monitoring instruments.
have to be ground before hydrolysis to a particle size that
pass through a 20-mesh screen.
Steam circulated through heat exchangers is the most common
of heating the mash; therefore, starch hydrolysis heating
must be included in plant boiler capacity.
Cooling the mash from boiling to fermentation temperature
(about 30[degrees] C) generally the determining factor in
design. This is
especially true in tropical climates
where the ambient temperature of the cooling water is
The agitation systems for starch hydrolysis tanks must be
to mix viscous (thick) starch solutions efficiently.
starch is heated in water, it forms a very thick gel.
gelatinization is essential for efficient enzymatic
Thorough mixing of gelled starch mash is necessary to ensure
efficient heat exchange and enzyme activity.
Monitoring equipment for starch hydrolysis includes
to measure mash temperature and steam temperature, and
gauges to measure mash pressure if pressurized starch
systems are used.
Tests to measure the efficiency of starch hydrolysis
are also necessary.
Generally speaking, the feedstock is
the most important element in determining the economics of
production, and inefficient starch hydrolysis can have a
major economic impact on ethanol production.
Starch hydrolysis systems are of two general types: batch
and continuous systems.
Batch systems consist of tanks that are
sized in relation to fermentation tank capacity and holding
The tank is equipped with heat exchangers, usually internal
coils, that circulate steam and cooling water.
The mash is
agitated by a motor equipped with gear reduction and mixing
pumps capable of handling a high level of
solids are used to transfer the mash of fermentation
very viscous feedstocks, heat exchange and mash agitation
accomplished by pumping the mash through an external heat
and back into the tank.
Batch systems are operated by
filling the tank, carrying out the multistep process of
hydrolysis, and then pumping the entire mash volume into
Continuous starch hydrolysis systems require more
equipment, but they are usually more efficient.
generally use "jet cookers," in which mash and
mixed under pressure at temperatures of 105 to 150[degrees]
feedstock, and enzyme are fed into a premix tank at a
rate, heated, and pumped under pressure through the
jet. The mash
is kept at high pressure and high temperatures for a few
then released from the cooker to holding tanks, where it is
cooled and additional enzyme is added.
The mash is then transferred
to fermenters. The
high pressure and temperature of these
systems result in more efficient starch gelatinization and
These systems require high-pressure boilers and relatively
sophisticated systems for maintaining the mash under
Equipment is sized on the basis of plant fermenter capacity
and mash residence time in cookers.
Fermentation takes place in tanks equipped with agitation
heat exchangers to remove the heat generated by fermentation.
Tank size is based on the concentration of sugar in the
fermentation time, final ethanol concentration, and plant
Final mash ethanol concentration is a direct function of
Within the limits of feedstocks and yeast
ethanol tolerance, higher ethanol concentrations are
Maximum mash ethanol concentration is about 10 percent
concentrations higher than 10 percent, yeast are
feedstocks with high moisture content and
sugar or starch concentrations less than 20 percent can be
Feedstocks with high starch or sugar
concentrations require dilution.
The sugar will be wasted if the
concentration is in excess of the amount necessary to
maximum amount of ethanol tolerated by the yeast.
Fermentation typically requires from 12 to 72 hours
the amount of yeast used to start fermentation and mash
Plants are usually equipped with multiple fermentation
tanks run on staggered schedules to provide a continuous
supply of fermented mash for distillation.
One of the most significant problems in ethanol production,
especially in small-scale plants, is contamination of mash
utilize sugars that would otherwise be converted
to ethanol. Good
plant design and efficient fermentation
can control contamination wihout resorting to costly
Distillation systems can either be batch or continuous.
one system or the other is based on plant scale.
require heating systems, usually steam (which can be from
boilers), a distillation column, and a condenser.
Figure 2 shows schematics of these two types of systems.
Distillation column size and ethanol production rate are
the concentration of ethanol in the fermented mash,
capacity, and production schedules.
Small-scale plants--up to
about 100,000 liters annual ethanol production--can
use batch distillation systems.
In batch systems, the entire mash
volume is passed, or charged, to a large vessel called a
which is then heated.
The vapors are allowed to pass into the
Though batch systems are less efficient than
continuous feed distillation systems, they are much easier
build and operate.
In continuous feed systems, fermented mash is pumped at a
rate into the distillation column, with heat introduced
at the bottom of the column.
Provision is made at the top of
the column to feed unprocessed mash back through the system.
Continuous feed columns should be used in large-scale plants
where the improved efficiency justifies the added
The intended use of the ethanol determines the need for
systems to remove the five percent water that cannot be
separated by distillation.
If ethanol is to be blended with
gasoline, dehydration is required.
The presence of water in
ethanol gasoline-blends results in phase separation in
or fuel tanks.
Dehydration is not required if ethanol is to be
used to replace gasoline.
Ethanol can be used directly in modified
engines at concentrations of between 80 and 95 percent.
Solid by-products are recovered from stillage with
This equipment can range from simple
screens to such complex equipment as centrifuges or vacuum
Soluble protein in thin stillage can be recovered by
by-products are to be stored or transported
significant distances, drying is necessary.
Stillage with high
moisture content can often be fed directly to livestock at
near the site of ethanol production with minimal separation
Production of each volume of fuel ethanol will generate
nine volumes of effluent.
A portion of the effluent can be recycled
and used to dilute high concentration feedstocks.
even if the effluent is recycled, it can still cause a
To avoid pollution of surface water or
ground water, the effluent must undergo microbiological
that is, the harmful organic matter contained in the
effluent must be broken down before the effluent is disposed
This is done anaerobically, aerobically, or by a sequential
combination of the two methods.
Effluent degradation is usually
done in a simple treatment pond, followed by a stabilization
pond, if necessary.
Alternatively, the effluent can be fed to
biogas digesters, combining energy production with waste
Ethanol production requires water, boiler fuel, and
for feedstock, ethanol, and by-products.
Electricity may be
used to run pumps, stirring motors, process controls, and
but there are many units throughout the world that
produce up to 10,000 gallons per year without
is required for mash dilution and cooling in heat exchangers
with starch hydrolysis systems, fermenters, and condensers.
Boilers used to generate process steam require a low-cost,
fuel such as natural gas, biogas, biomass, coal, residual
oil, or bagasse (bagasse is crushed sugar cane or beet
from sugar making).
High-quality liquid fuels or electricity are
uneconomical and inefficient for use as boiler fuel.
feedstock needs to be transported to the plant; and the
both ethanol and by-product animal feed, need to be
to the point of use.
The process energy requirements for ethanol fuel production
widely depending on equipment, process design, and
production of one liter of ethanol with a heating value of
Kcal/liter would typically require 800 to 1,200 Kcal for
1,300 to 1,500 Kcal for distillation, 800 to 1,000 Kcal for
dehydration, and about 300 Kcal to operate stirring motors
pumps. The drying of
by-products from the production of one
liter of ethanol might require an additional 600 to 700
production of anhydrous ethanol and dried by-products from
grain--representing the high range for process energy--would
require 2,800 to 3,800 Kcal/liter.
The production of 90 percent
ethanol from sugar feedstock without by-product
the low range for process energy--would require 1,600 to
The availability and the cost of utilities are critical
both in the scale and the economics of alcohol
factors have contributed to the failure of ethanol fuel
in developing countries:
(1) plants for the production of ethanol
fuel were so large that the support utilities were unable to
their energy needs; and (2) the plants were sited so far
feedstock that transportation was not economical.
Ethanol fuel plants range in size from a few thousand liters
more than 100 million liters of annual production.
The design and
operation of small-scale plants can be greatly simplified by
combining starch hydrolysis, fermentation, and batch
in multi-purpose process tanks.
The plants could include one or
several tanks supplying fermented mash for a single
column. Plants up to
about 100,000 liters of annual production
can be designed this way.
Even larger batch plants can be considered
if low-cost boiler fuel is available.
With good technical
assistance, small-scale batch plants can be built and
with local, community-level resources and skills.
Greater operating efficiency can be obtained in larger
separating starch hydrolysis and fermentation in specially
systems and using continuous feed distillation columns.
Generally, the greater capital cost and operating complexity
this type of plant will be returned in operating efficiency.
Large-scale alcohol plants require at least some employees
relatively sophisticated management and technical
design, equipment, and construction often require resources
the local community.
It is difficult to provide general information about ethanol
economics because production costs and product value depend
plant location, feedstock, production scale, and end use.
Ethanol production includes both capital and operating
important factors in capital costs for small batch plants are
starch hydrolysis systems and boiler capacity.
In large plants,
engineering, distillation systems, and process control are
Generally, capital costs for alcohol
plants range from $.50 to $1 (U.S.) per liter of annual
capacity. Based on
figures from U.S. plants, capital
costs per liter of annual production capacity for very small
very large plants are generally greater than those for
plants--1 to 10 million liters annual production.
The greatest operating cost in ethanol production,
scale, is feedstock.
For ethanol fuel production to be profitable,
an economical supply of feedstock is essential.
plants, labor-costs may also be relatively important.
Indirect costs for engine conversion, distribution and
plant utilities, and transportation of feedstock and
also important in evaluating ethanol production costs.
Ethanol market value depends on end use.
The market value of
ethanol as a replacement fuel would generally be measured
to gasoline prices.
The market value of ethanol when blended
with gasoline may be higher than gasoline because of the
increased octane value of ethanol/gasoline blends.
By-product market value is measured against the local price
animal feed. The
value is typically determined by comparing the
protein content of feeds.
Other factors, aside from ethanol production costs and the
value of ethanol, may also be significant to the economic
Displacement of imported petroleum with domestically
renewable fuel may improve balance-of-payment deficits and
may be economically advantageous despite relatively higher
for rural employment, alternative markets
for agricultural commodities, and energy independence may
provide significant economic advantages in addition to a
accounting of plant profitability.
IV. COMPARING THE
FUELS COMPETING WITH ETHANOL
Methanol, butanol, and some types of vegetable oil are three
to ethanol. Both
methanol and butanol can be used to
replace or extend gasoline or diesel fuel.
Vegetable oils, however,
are limited to replacing only diesel fuel until further
Methanol is the most important alternative.
It is a liquid alcohol
containing one carbon atom ([CH.sub.3]OH).
Like ethanol, it is used
to replace or be blended with gasoline.
Methanol is produced by a
chemical process that uses methane as the primary feedstock.
Methanol can also be produced from coal or biomass.
worldwide scale, the methanol production industry is
large, and it uses natural gas for feedstock.
requires high temperature, high pressure, and special
This process is much more complex than ethanol production
generally economical in only very large industrial plants.
Butanol is a four-carbon alcohol.
It has two possible chemical
structures, depending on the position of the hydroxyl:
([CH.sub.3] [CH.sub.2] [CH.sub.2][CH.sub.2]OH) and 2 butanol
([CH.sub.3] [OH.sub.1] [CH.sub.2] [CH.sub.3]).
produces N butanol.
Unlike ethanol or methanol, butanol can
substitute for or be blended with diesel fuel in compression
ignition engines. It
is produced by bacterial fermentation of
starch- or sugar-containing feedstocks and purified by
The bacteria produce ethanol and acetone in addition to the
principal product, butanol.
The production of butanol has two disadvantages:
(1) the fermentation
of butanol is difficult compared with that of ethanol; and
(2) butanol fermentation produces less-useful fuel per unit
feedstock than ethanol fermentation with yeast.
Butanol has been
produced commercially under wartime conditions.
butanol is no longer produced commercially for use as fuel.
CURRENT RESEARCH AND DEVELOPMENT
Ethanol fuel production is a well-established commercial
But it is also a technology that has room to improve.
That is why research and development efforts in ethanol fuel
production are ongoing.
The research areas relating to this
technology that continue to be addressed include (1)
(2) starch hydrolysis and fermentation process design; (3)
ethanol and by-product end uses; and (4) site-specific
of ethanol production with local agricultural economics.
Feedstock is the most significant cost element in ethanol
Questions of possible competition for prime agricultural
land, and impacts of ethanol production on food supply and
are crucial to the social and economic success of this
important area of research is the identification
of starch- and/or sugar-containing crops that can be grown
poor land and that require a minimum amount of cultivation
chemical inputs (e.g., fertilizers).
Such feedstocks must be
compatible with the local climatic conditions, the water
and the soil type.
They should not disrupt the local agricultural
feedstocks under evaluation in
various parts of the world include sago palm, bamboo, sweet
potatoes, and honey locust trees.
Once potential crops are identified,
research will be directed toward increasing yields,
adapting crops to specific situations, and developing
harvest, and storage techniques.
Alternative feedstocks will require research to adapt starch
hydrolysis and fermentation equipment and procedures to the
feedstock characteristics and concentration of fermentable
research might also include the selection
of yeast strains for improved fermentation efficiency.
could include increased tolerance to high sugar and
ethanol concentrations, tolerance to high fermentation
or adaptation to particular feedstock characteristics.
Research needs in ethanol and by-product end uses could
evaluation of technology and economics for uses of ethanol
than as a motor fuel; evaluation of conversion techniques
specific types of engines; and evaluation of specific
for recovery and use of by-products.
Research on integration of ethanol fuel production with
economies could cover a broad range of topics, including
feedstock economics and cultivation, plant and equipment
to fit specific local constraints, process fuel sources,
on employment and income distribution, and effects on
balance of payments.
The successful introduction of ethanol fuel production and
developing countries requires careful planning.
must be integrated with local economic conditions, available
resources, and potential end use of both the ethanol and its
The operating efficiency of large-scale ethanol plants
may be greater than that of small-scale plants.
efficiency may be of little value if the plant is too large
the available feedstock and support utilities or if the
economics of food production and distribution are disrupted.
Ethanol plants should be scaled so that demand for feedstock
not disrupt distribution systems and markets for
utilities and transportation should be able
to support the scale of ethanol production.
One important, hidden
cost of large-scale ethanol plants is the cost of building
upgrading roads, water supply systems, pollution control
and electricity generating capacity.
The method used to finance
these support systems is an important economic question.
Distillers dried grains (DDG) are the major by-product
resulting from ethanol production.
This high protein product is
an excellent livestock feed, and feed lots could be located
the ethanol plant.
Another extremely important potential use of
this protein-rich material could be as a human food
End use of the ethanol and by-products must be on a scale
Technical resources need to be available for
engine conversions if necessary.
If ethanol is to be blended with
gasoline, marketing and distribution systems for ethanol and
ethanol/gasoline blends must be developed in parallel with
construction and operation of ethanol fuel plants.
Proper integration can enhance ethanol production economics
can be achieved with well-designed small- and medium-scale
plants can often take advantage of low value
or waste feedstocks such as food processing waste or damaged
spoiled crops. A
variety of low-cost boiler fuels such as biogas,
waste heat from other industry or power plants, or biomass
used if the plants are scaled to match the resources
within economical transport distances.
Dehydration can be eliminated
if ethanol is used in converted engines.
number of small ethanol plants can supply 80 to 95 percent
to a centralized plant for dehydration and
processing can be reduced if the plant is scaled to
supply livestock feed demand in the immediate area of the
Small-scale plants are much simpler to build and operate
large plants. With
technical support, small-scale ethanol plants
can be built and operated using locally available skills and
resources. With the
exception of such equipment as motors, boilers,
and controls, small-scale plants can be built in any
well-equipped machine shop, provided that technically sound
plans are available.
Small-scale plants can also be mounted on
flat-bed trailers so they can be moved from site to site.
Starch hydrolysis and ethanol dehydration are the two steps
requiring long-term purchase of materials outside the local
even national level.
The production of starch hydrolysis enzymes
and molecular sieves requires relatively sophisticated
Enzymes and molecular sieves are supplied by a number of
companies. As an
alternative to purchasing these materials, they
can be manufactured in centralized plants for distribution
small-scale ethanol plants.
VI. CHOOSING THE
The decision to produce and use ethanol fuel requires
both direct and indirect technical and economic
questions are important on any scale of development ranging
an individual local decision to produce on a small scale to
Direct technical and economic questions in the decision to
and use ethanol fuel include the cost and the availability
of feedstock; ethanol and by-product end uses and marketing;
and regulations; production scale; and selection of plant
and equipment options.
Factors affecting feedstock availability and cost include
storage, potential spoilage, and seasonal variations
in supply and price.
Ethanol and by-product uses are affected by product
and distribution, storage, possible spoilage of by-products,
seasonal variations in market demand or on-site use, and
the ethanol is to replace or be blended with gasoline.
is to be blended with gasoline, the costs and the systems
distribution, blending, and marketing need to be taken into
account. If ethanol
is to replace gasoline, the costs of engine
conversion and limitations to vehicle use are two important
Laws and regulations affecting ethanol fuel production will
from country to country.
Variations may also occur between legal
and political jurisdictions within countries.
Regulations must be
checked for each individual case.
The principal regulations are
those that prevent the use of fuel ethanol for human
Generally, these regulations require that ethanol be
adding chemical agents to the ethanol to make it unfit for
most readily available denaturant for ethanol is
gasoline mixed at one percent per volume.
Other regulations may
govern discharges of liquid and gaseous effluents and
safety and health.
Laws dictating conformance to building
codes (e.g., electric, plumbing, and fire safety codes) may
Decisions regarding plant scale, equipment, and process
depend primarily on feedstock, the availability of markets
both ethanol and its by-products, and the availability of
of scale in ethanol fuel production are much
less important than well-planned integration of ethanol fuel
with agricultural economics, local transportation, local
utilities, and end uses.
Indirect social and economic questions are also very
the decision to produce and use ethanol fuel.
regarding ethanol production may rely more on the ability to
such objectives as increasing rural employment, achieving
independence, and providing alternative markets for crops
direct evaluation of production costs and market
decisions regarding plant scale, process design, and
may be influenced by the ability to meet such objectives as
the use of local labor and locally manufactured equipment,
creation of alternative markets for agricultural crops as
and the local use of process energy.
The emergence of ethanol as a viable alternative to gasoline
led to two major controversies that can affect decisions
ethanol fuel production.
The first controversy concerns the question of net energy
that is, whether the energy content of the ethanol is
than the energy consumed in production.
With efficient technology,
the energy content of ethanol exceeds the direct in-plant
process energy inputs by about 2 to 1.
However, one recent analysis,
which took into account the energy used to cultivate
and to transport feedstock and products, calculated that
ethanol production consumes more energy than is
technical response to this analysis is that ethanol is not a
energy source; rather, it is an energy conversion and
storage system. In
ethanol production, low-quality, diffuse primary
energy sources are upgraded to a high-quality, liquid fuel.
Solar energy in the form of plant carbohydrate and low-quality
boiler fuels is converted to a fuel suitable for use in
In simple terms, the response is that automobiles
cannot run on cassava.
When ethanol is viewed as an energy
conversion system, the net energy question is largely
Nevertheless, the question is useful because it points out
need to select those feedstocks requiring relatively little
cultivation and low inputs of fertilizer and chemicals, and
need to use low-quality boiler fuels.
The second controversy surrounds the issue of food versus
that is, whether the use of agricultural crops for ethanol
production will adversely affect the amount of land
food production and food supply, as well as affecting food
prices. This is a
complex question to which there are no absolute
answers. On the one
hand, a large-scale diversion of food crops
to ethanol production could reduce food supplies and
food prices. On the
other hand, a carefully planned and well-integrated
ethanol fuel industry does not necessarily result in
direct competition for agricultural land and food
crops grown on marginal land are often good alcohol
with poor food value.
Cultivation of low-value crops may
contribute to the economy through conversion to a high-value
rural employment may increase people's economic
access to high-quality food.
Ethanol might also be produced
from agricultural commodities that would otherwise be
Sugar cane, for example, may be worth more as a feedstock
domestic fuel production to displace imported petroleum than
an export crop. The
issue of food versus fuel emphasizes the
need for careful planning but does not mean that ethanol
production is an inappropriate technology.
The Bioenergy Council.
The Bioenergy Directory.
The Bioenergy Council.
Bernton, Hal; Kovarik, William, and Sklar, Scott.
Power Alcohol in the Twentieth Century. New
Brown, Michael H. Brown's Alcohol Motor Fuel Cookbook.
Desert Publications, 1979.
Carley, Larry W. How
To Make Your Own Alcohol Fuels. Blue
Pennsylvania: Tab Books, Inc., 1980.
Cheremisinoff, Nicholas P.
Gasohol For Energy Production.
Michigan: Ann Arbor Science Publishers,
De Rasor, Roberto.
Alcohol Distiller's Manual for Gasohol and
San Antonio, Texas:
Dona Carolina Distillers, 1980.
Development Planning and Research Associates, Inc. Gasohol:
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(1901 - March
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is available in
print from the Superintendent of
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20402, or in
microfiche from the National Technical Information
Department of Commerce, 5285 Port Royal
Springfield, VA 22161.
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U.S. Industrial Chemicals Co. Division of National
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Willkie, Herman F., and Kolachov, Paul J. Food For Thought.
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Reference inquiries on specific topics relating to ethanol
production can be referred through VITA to the staff of
Technologies, Inc., who prepared this report, or to other
volunteers with expertise in ethanol fuel.