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Burning Shelled Corn to Produce Heat Energy
Bill Wilcke,
Minnesota Extension Engineer
The combination of high fossil fuel prices and low corn
prices has spurred an interest in burning shelled corn to
produce heat for buildings and for drying grain. Dry shelled
corn contains a fair amount of energy and it is relatively
easy to handle. Here are some factors to consider when
making decisions about shelled corn vs. other fuels.
Fuel cost per unit of energy
Shelled corn contains about 7000 Btu (British thermal
units) per pound at 15% moisture, or about 392,000 Btu per
56-lb bushel. It is better to use dry corn as a fuel source,
because dry corn is easier to handle and store than wet
corn, and because dry corn produces more energy per unit
weight of corn. Energy content per pound of corn is
dramatically lower for high-moisture corn because more of
the weight of the corn is water, which doesn’t produce
any energy, and because more energy from the corn dry matter
is needed to evaporate water from the kernels and less is
available for heating.
In most cases, equipment used to burn corn (and other
fuels) is not 100% efficient, so it is important to use
burner efficiency in calculations for heat output. When
comparing costs for using different fuels, it is easiest to
compare cost per unit of energy produced; cost per million
Btu is a common way to compare fuel costs. Cost per unit of
fuel, energy content per unit of fuel, and burner efficiency
all need to be considered in calculating fuel costs.
Example: Calculate the cost per million Btu for
15% moisture shelled corn that costs $2.00 per bushel and
is burned in a stove that has an efficiency of 65%.
Cost per million Btu = [$2.00/bu ÷ (392,000
Btu/bu x 0.65 efficiency)] x 1,000,000
= $7.85 per million Btu
Using recent prices and typical burner efficiency
figures, the cost of fuel oil, propane, natural gas, and
electrical heat ranges from $10.00 to $23.44 per million
btu.
Keep in mind that the price for corn and for conventional
fuels will fluctuate over time and that the cheapest fuel
today might not be the cheapest fuel in the future.
Other costs for using fuel
Fuel cost per unit of energy is very important, but you
also need to consider the cost for the burner, fuel storage,
and other equipment needed to store, handle, and use the
fuel, equipment maintenance, and labor to handle the fuel
and remove ash. If you are considering new construction or
are replacing a worn out system, you can compare the annual
costs of owning and fueling conventional heating systems vs.
corn burning systems. But if you already have a conventional
system that is in good working condition and will be kept as
a back up system, then you need to compare the full cost of
owning and fueling a corn burning system to the value of
conventional fuel saved. A supplemental corn burning system
can easily cost several thousand dollars, so annual
ownership costs can be a significant addition to the cost of
the corn fuel.
Labor costs are likely to be higher for corn burning
systems than for conventional fuel systems, but may be lower
than labor costs for bulky biomass materials (like fire
wood, straw, or hay). Very little labor is required to fuel,
maintain, and clean conventional fuel systems. Corn-fueled
systems can be relatively easy to automate, but some labor
is required to periodically refill the corn hopper and to
remove the ash or clinkers that are left after corn
combustion.
Fuel handling and storage
Corn is easier to handle than some other bulky biomass
materials (wood, straw, or hay, for example) because it
flows fairly well through hoppers and augers and because
corn has a better energy to volume ratio (it takes less
space to store the same amount of energy for corn than for
bulky biomass materials). But corn is not as easy to handle
and is not as energy dense as most conventional fuels.
Corn handling and storage will be relatively easy on
farms that produce corn, but it will be more of a challenge
for nonproducers--especially for people living in urban
areas. Non-farmers will have some difficulty obtaining,
hauling, and storing the amounts of corn needed for heating
a home or other buildings. Also, the cost per bushel will
probably be somewhat higher for people who buy a few bushels
at a time.
Owners of corn burning systems who store corn inside
their home need to use tight storage containers, clean up
corn spills immediately, and avoid storing corn for long
periods of time to prevent problems with rodents and with
stored grain insects. Some species of insects that infest
stored corn could also move into food products stored in the
home.
Burner design
Designing corn burners is more challenging than designing
burners for some other biomass materials because it’s
more difficult to get enough air into the fuel pile with
shelled corn than it is for bulky biomass materials, and
because corn ash melts at a different temperature than ash
for some other biomass products. Corn ash tends to produce a
hard, glassy slag that can coat the inside of the burner,
and it can produce hard chunks (clinkers) that need to be
removed frequently (perhaps daily). It isn’t
impossible, but it would be difficult to build a homemade
burner or to modify a wood-burning stove that works well
with corn. Several companies that have tried to build
shelled corn burners have failed, so it might be best to buy
a corn-burning stove from a company that has been in
business for several years and that has a number of
satisfied customers.
Long run needs for heat energy
In the short term, it might make sense to burn corn to
produce heat energy, but it’s hard to know whether
burning corn makes sense in the long run. If our goal is to
find something that farmers can grow that will help solve
our need for heat energy, corn might not be the best answer.
It takes a lot of energy to grow, dry, and transport corn,
it takes a lot of energy to produce the fertilizers and
pesticides used to produce corn, production of corn makes
the soil more vulnerable to erosion than does production of
some other crops, and corn might be more valuable for feed,
food, and liquid fuel uses than for heat energy
production.
Other sources of information
The Ontario Ministry of Agriculture, Food and Rural Affairs
has a good web site on burning shelled corn as a heating
fuel. Keep in mind that the web site uses Canadian dollars
and a mixture of metric and English units. The web site
address is:
http://www.gov.on.ca/OMAFRA/english/crops/facts/93-023.htm
Here are some questions, adapted from the Ontario
website, that you should consider before purchasing a corn
burner:
- What is the heat output of the burner? Do you know
how much heat is needed to maintain the heated space at
the desired temperature, to dry the crop, or to meet
other needs for heat energy?
- If you are trying to heat your whole house with a
stove or space heater, does the house layout allow for
the convective movement of heat through the whole house?
Most newer houses are not built to allow convective air
movement.
- What is the size of the fuel hopper? Will it require
filling on a daily, weekly, or biweekly schedule?
- What is the seasonal heating efficiency of the corn
burner?
- Does the unit meet UL standards and safety
requirements of your insurer?
- Does the unit have hot exposed surfaces that could
cause burns to skin?
- What type of exhaust venting is required? Does it
require a chimney with a flue liner or can a combination
flue/fresh air vent pipe be used?
- Are you prepared to clean out the clinker daily and
clean the heat exchanger of ash on a weekly basis?
- Will the stove handle granular solid fuels other than
shelled corn? This is important in the event that the
economics of burning corn become unattractive or an
alternative low cost pelleted fuel becomes
available.
- Will the corn burner be a primary heat source or act
as a supplementary heat source? Stoves with small fuel
hoppers will not meet heating needs for long periods of
time, unattended.
- How and where will corn be stored?
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