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Biofuel Economics: Corncob Harvest Demonstration

Cole Gustafson, NDSU Biofuels Economist Cole Gustafson, NDSU Biofuels Economist
Corncobs appear to be one of the more promising sources of biomass for cellulosic biofuel.

By Cole Gustafson, Biofuels Economist

NDSU Extension Service

Last week, I had an opportunity to observe a corncob harvesting demonstration on a farm near Donnelly, Minn., sponsored by the Chipewwa Valley Ethanol plant. With the temperature and wind both equal to 30, the weather was frigid, but the event was fascinating.

Two combines were outfitted with different corncob collection systems. The first was a Ceres unit developed by two brothers in Nebraska. It consisted of a black hopper mounted on top of the combine’s original grain tank. Cobs were collected in the back of the combine and then blown to the hopper through ducts.

The second combine pulled a new Vermeer prototype corncob collection harvester. The unit was essentially a two-wheel trailer with a 100-horsepower engine and an elevator in the front that reached under the combine to collect the cobs. The elevator brought the cobs to the trailer, where a fan blew out husks and then threw them to the back of the hopper. Interestingly, the Vermeer representative indicated the company was working on wireless controls, so the only connection between the unit and the combine was a hitch pin. Both units dump the collected cobs into waiting trucks.

Collecting the cobs didn’t seem to slow the harvesting of the grain. The only time lost was dumping the cobs at the end of the field.

There were minor glitches. One unit broke down and unloading the cobs from the truck proved to be a challenge. The truck had a 3-foot-high swing gate, but the cobs were bulky and moist enough to not flow out smoothly. A front-end loader pushed the cobs into a pile for storage.

What surprised me most was how few cobs per acre there actually are. It appeared that both combines dumped cobs about three times for each time they dumped grain and the cob hoppers were not that large. A University of Minnesota study found that cobs represent about 18 percent to 20 percent of the dry matter in grain from an acre of corn.

Neither vendor has developed a price for its units or planned for distribution. While distribution through existing dealer networks is an option, they also are considering partnerships with power companies. In fact, they feel the greatest demand for the units will be to supply corn cobs for combined heat and power utilities and other power plants that are striving to produce more renewable energy.

Corn cobs appear to be one of the more promising sources of biomass for cellulosic biofuel. First, many farmers already produce corn and prototype harvesters like those at the demonstration make collecting the cobs very efficient. Farmers wouldn’t have to invest in other collection or baling equipment. Second, collecting the cobs has a negligible effect on fertility because few nutrients reside in the cob. Third, cobs are more energy dense than other stovers. This minimizes the transportation costs of hauling bulky materials. Cobs have 9,000 British thermal units per pound, while stover has 8,000 Btu per pound. Finally, cobs leave less ash when burned.

However, many questions still remain. Both machines appeared quite flexible with respect to the amount of husk contained. I was on one pile that looked like it was almost all husk and another that was essentially huskless. Moreover, one machine ground the cobs quite a bit while the other left them whole. It is unknown what premiums and/or discounts utilities or ethanol plants will have for cobs of differing composition or quality. With both machines, collecting the cobs still remains a secondary activity after the corn was harvested.

NDSU Agriculture Communication

Source:Cole Gustafson, (701) 231-7096,
Editor:Rich Mattern, (701) 231-6136,
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