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Nuclear Steam for Fuel Ethanol
from Corn
Charles W. Forsberg
Oak Ridge National Laboratory
Samuel Rosenbloom
U.S. Department of Energy
Richard Black
U.S. Department of Energy
Nuclear Steam for Fuel Ethanol from Corn
The production of fuel ethanol from corn for
cars and light trucks has increased from about 1.6 billion gallons
per year in 2000 to 5 billion gallons per year in 2006. Further
large expansions in production are predicted. Simultaneously, the
prices of natural gas and oil have dramatically increased.
However, the production of fuel ethanol requires large quantities
of fossil fuels. More than half the nonsolar-energy demand for
fuel-ethanol production from growing the corn to converting it to
fuel-grade alcohol is for low-temperature heat to distill alcohol
and dry animal-feed by-products. For a large ethanol plant
producing a 100 million gallons of fuel ethanol per year, about
120 MW(t) of steam is required, which represents a potential
market for 150-psi (~180ºC) steam from existing light-water
nuclear power plants. The value of this low-temperature steam for
electricity production is low, but it could significantly improve
ethanol economics, create an expanded market for nuclear energy,
reduce greenhouse-gas emissions, and reduce foreign-oil imports.
The idea of using nuclear power plants to
coproduce electricity and heat is not new. Canadian nuclear power
plants have been used to produce electricity and steam, with the
steam used for the isotopic separation of heavy water and other
industrial purposes. This included the use of steam for about a
decade from the Bruce Nuclear Power Station in Canada for
production of ethanol. Plants in Switzerland and Russia produce
both electricity and district heat. In the United States, a
two-unit nuclear plant was partially built at Midland, Michigan,
to produce electricity and steam for the Dow Chemical Company.
However, applications have been limited. One reason is that the
prices of fossil fuels have been low. Equally important, very few
markets exist for large quantities of steam. It is not usually
worth the effort for a nuclear power plant producing 1500 to 4500
MW of steam to modify the plant to produce a few megawatts of heat
to meet a local-industry or district-heating need.
The development of fuel-ethanol production from
corn is now creating a new potential market for large quantities
of steam from light-water reactors. The size of corn-ethanol
plants is rapidly increasing, as is the corresponding steam demand
per plant. The plants that produce ethanol from corn operate
continuously, resulting in a steady-state demand for steam. In the
production of ethanol, the primary cost is corn, followed by the
cost of energy-thus, the economic incentive to consider steam from
nuclear power plants. Finally, the steam demand is located in
rural areas where nuclear power plants already exist. There is one
economic limitation, however. The cost of corn delivered to a
fuel-ethanol plant is strongly dependent upon the cost of
transporting corn from the farm. The only nuclear reactors that
can economically provide steam for this application are in the
Corn Belt, along the Mississippi River or other waterways where
cheap barge transport is available, or where there is a demand for
the by-products of ethanol production.
Ethanol Demand and Production
Ethanol is added to gasoline for three purposes.
First, ethanol has an octane rating of 113-115 and is used as an
octane enhancer. It is replacing MBTE, a hydroscopic octane
enhancer that has caused significant groundwater contamination and
has major legal liabilities associated with its use. Second,
ethanol is used to meet the minimum oxygen-content requirements
for gasoline. Some oxygen is required in gasoline to minimize
carbon-monoxide pollution from vehicles and pollutants that
produce ozone. Last, ethanol is a fuel, both when mixed with
gasoline and when used by itself. However, the values of ethanol
as an octane enhancer and to meet minimum oxygen requirements for
the fuel are significantly higher than its fuel value.
The cost of fuel ethanol has been decreasing for
a number of reasons. The production cost of corn has gone down
because of improved production methods that have reduced the fuel,
pesticide, and fertilizer inputs per bushel of corn. The
efficiency of corn-to-ethanol plants has also significantly
increased. Finally, the government has offered multiple incentives
for ethanol production.
The production of fuel ethanol has two major
steps: growing the corn and then converting it to ethanol. More
than half the energy inputs are used in the process of converting
corn to ethanol. Corn contains carbohydrates and proteins. In the
corn-to-ethanol process, the fermentation step converts the
carbohydrates to ethanol, which uses about two-thirds of the corn
kernel. The non-fermentable components, which consist primarily of
proteins, and the other by-products of fermentation become animal
food or are converted to other useful products. Within the ethanol
plant, the primary energy input is heat to distill the ethanol
from water. Heat is also required to dry the by-products so they
can be stored and shipped without rotting and to sterilize the
mash before adding yeast to start the fermentation process.
There are lingering debates associated with
fuel-ethanol production. For instance, the energy value of the
fossil-fuel inputs to grow the corn and convert it to ethanol is
70 to 80% of the energy value of the ethanol itself. However,
liquid fuels are more valuable than natural gas or coal inputs in
the corn-to-ethanol production process, so the final product
represents a net gain. The greenhouse-gas releases from consuming
fossil fuels from growing corn through the production of ethanol
are only about 20% less than from the alternative of producing
gasoline from crude oil with an equivalent energy value.
If nuclear energy is used to support ethanol
production, however, the fossil-fuel inputs can be dramatically
reduced. The conversion of corn to ethanol primarily requires
low-quality, low-cost steam-something nuclear power plants are
very good at producing. If low-quality steam from nuclear power
plants is used in the corn-to-ethanol production process, it
reduces fossil inputs and resultant greenhouse-gas emissions from
growing corn and converting it to ethanol by almost half.
Fuel ethanol from corn is limited by the
availability and competing uses for corn. However, there are much
larger quantities of biomass in the form of grasses and trees,
many of which are underutilized. The potential fuel production
from these biomass sources is an order of magnitude greater than
from corn. Most of this biomass is cellulose that cannot be
directly converted to ethanol. The technology to convert these
forms of biomass into fuels is currently being taken from
laboratory- to industrial-scale applications through major
programs in the United States and elsewhere. Like ethanol from
corn, not all of the biomass can be converted to ethanol.
Unfortunately the non-fermentable components are not usable as
animal food. It is currently proposed to burn this residual
biomass to provide the heat for ethanol distillation. If steam was
available from nuclear power plants, this residual biomass could
be converted into additional liquid fuels using other biomass to
liquid fuel processes.
Nuclear Coproduction of Electricity and Steam
Since the beginning of the development of
nuclear energy, numerous studies have been conducted and multiple
reactors have been built to produce electricity and steam. The
steam has been used for district heating, production of heavy
water, and limited other uses. However, coproduced steam has never
been a major product of nuclear reactors for two reasons: (1)
there are few customers near rural nuclear-plant sites, and (2)
most of the markets for steam are so small as to not be worth the
complications of coproducing steam and electricity. The production
of fuel ethanol from corn today and the future production of fuel
ethanol from other forms of biomass change this. The need is for
large quantities of steam in rural areas-the same areas in which
nuclear power plants are built.
For ethanol production, steam would be provided
by the reactor. In the ethanol plant, the steam would be
condensed, and warm water would be returned to the nuclear power
plant. Almost all of the heat would come from condensing the
steam. Modern steam systems would allow more than a mile of
separation between the reactor and the ethanol plant. Ethanol
plants would have to be located beyond any security perimeter
because such plants require easy access by grain trucks, trains,
or barges. The separation required to avoid security concerns
would be more than that necessary to ensure safety against fires
and other accidents in the ethanol plant.
No fundamental technical or economic barriers
stand in the way of cogeneration of electricity and steam for
ethanol production. Sufficient experience exists from current and
decommissioned reactors that produced steam and electricity. If
the utility provides steam, appropriate commercial clauses must
address what to do when steam is not available. Such
considerations might result in a preference for sites with
multiple reactors or sites with nuclear and fossil units, at which
there would be a higher assurance of constant steam production.
There are also the associated issues of standards and other
components of the technical infrastructure that support commercial
enterprises. However, the potential economic, national-security
(i.e., a reduced dependence on imported oil), and environmental
benefits strongly support the commercialization of this use of
nuclear energy at existing nuclear sites in areas in which large
quantities of low-cost corn are available.
There are business risks that must be addressed,
and the appropriate business models must be developed. For a
commercial enterprise, timing is important, and thus a critical
issue is the time required in obtaining licensing amendments and
permits for the sale of steam from existing nuclear power plants.
Investing strategies and support by shareholders will ultimately
be a function of the "risk-reward" equation. There is also the
important role of government to help overcome the institutional
and other barriers for the first-of-a-kind plant that joins two
industries with very different business models and concerns.
Conclusion
The U.S. government has a national goal to
displace 30% of our gasoline by 2030, initially by using corn and
then using cellulous for the production of ethanol. That is an
extraordinary challenge that requires increasing ethanol
production by more than an order of magnitude. Biomass processing
requires massive quantities of low-temperature steam. For this
scale of operation, the total steam demand at a few hundred plants
would be tens of gigawatts. Low-temperature steam is a product
that existing and future light-water reactors are very good at
producing in combination with electricity. Because of the
potential for highly favorable economics and the potential to make
a major contribution to reducing our national dependence on
foreign oil, it is a nuclear future that the nation should explore
today. The U.S. government must be a partner with the nuclear
energy industry to meet the goals and objectives of the U.S.
Energy Policy Act. It can be a conduit that provides information
and resources to support fuel ethanol production from other
related energy and science programs such as global warming,
biomass research, 2010 and next generation nuclear plants,
renewable energy, and fuel efficiency.
Disclaimer
This manuscript has been authored by UT-Battelle,
LLC, under contract DE-AC05-00OR22725 with the U.S. Department of
Energy. The United States Government retains and the publisher, by
accepting the article for publication, acknowledges that the
United States Government retains a non-exclusive, paid-up,
irrevocable, world-wide license to publish or reproduce the
published form of this manuscript, or allow others to do so, for
United States Government purposes.
The views expressed herein are the views of the
authors and not necessarily those of Oak Ridge National Laboratory
or the U.S. Department of Energy.
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