Bill Wilcke, Extension Engineer
wilck001@umn.edu
May 28, 2001
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Bill Wilcke, 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 heating buildings and for drying grain. Dry shelled corn contains a fair amount of energy and it is relatively easy to handle, so in the short run, it can make sense to use shelled corn as a heating fuel. 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 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
Here are energy content, burner efficiencies, and costs per million Btu at average efficiency and the indicated price for several fuels:
Fuel oil, 140,000 Btu/gal, 70 to 90% efficiency (80% avg.), $1.50/gal:$13.39 per million Btu
Propane or liquefied petroleum gas (LPG), 92,000 Btu/gal, 70 to 90% efficiency (80%avg.), $1.00/gal:
$13.59 per million Btu
Natural gas, 100,000 Btu/ hundred cubic foot (ccf), 70 to 90% efficiency (80% avg.), $0.80/ccf:
$10.00 per million Btu
Electricity (resistance heat), 3413 Btu/kWh, 100% efficiency, $0.08/kWh:
$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 cost of owning and fueling a conventional heating system vs. the annual cost of owning and fueling a corn burning system. 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, although labor costs for corn systems might be lower than 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 people who don't produce corn - 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, or corn ash 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 website on burning shelled corn as a heating fuel. Keep in mind that the website uses Canadian dollars and a mixture of metric and English units. The website address is:
http://www.gov.on.ca/OMAFRA/english/engineer/facts/93-023.htm
Here are some questions, adapted from the Ontario website, that you should consider before purchasing a corn burner:
