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Tuesday, March 03, 2009
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Study Reveals Benefits of Corn Stover

MINNEAPOLIS - According to new research from the University of Minnesota, densified corn stover is better for the economy and the environment than previously recognised.

The research shows that, as a fuel for heat and power applications, corn stover reduces the life-cycle fossil-fuel emissions of carbon dioxide by factors of approximately 15 and 25 compared to natural gas and coal, respectively.

This means significant amounts of renewable electricity can be generated in a distributed fashion with lower overall emissions at ethanol plants and other facilities to produce heat and power.

"The new research allows us to better predict the full cost of using corn stover biomass to meet the heat and power needs of these facilities," said Vance Morey, a bioproducts and biosystems engineering professor at the U of M and a lead investigator on the study.

"This includes the environmental costs of collecting the corn stover and then transporting it to the ethanol plant."

Currently, natural gas is used for the process heating needs of ethanol plants, while coal is used to produce much of the electricity delivered by the grid to the plants.

The U of M research team evaluated a corn stover logistics system that analyzed the collection of round bales from the field during the fall harvest, as well as their delivery to storage sites within two miles of the field.

The team then evaluated the annual costs of processing at the storage sites; using mobile units, the bales were converted to bulk material by tub-grinding and roll compacting.

The roll-press compactor, a new machine that is not commercially in use at present, increases ground corn stover density from six to 15 pounds per cubic foot, thereby increasing the distance that biomass can be economically hauled.

Along with the benefits, the researchers also considered the consequences of removing corn stover from farm fields.

"We were surprised by how much nutrient replacement -- specifically, nitrogen, phosphorus and potassium-impacted the economic and environmental costs. It represented 30 percent of the total delivered cost of $77 per ton. In addition, nutrient replacement accounted for 45 percent of the carbon dioxide emissions associated with the collection and delivery of corn stover to the user," said Prof Morey.

"We thought the nutrient replacement costs would be much less. Clearly, producers need to consider nutrient replacement along with other collection costs if they decide to sell their corn stover."

As a next step, the researchers will look at ways to improve the handling characteristics of herbaceous biomass and increase biomass electricity generation at ethanol plants in the Midwest. They also plan on expanding the research to include roll compaction of native grasses, straw and alfalfa.

The coarse grinding of the corn stover was performed at the University of Minnesota's West Central Research and Outreach Center in Morris, Minnesota, while the roll compaction was done at Bepex International LLC in Minneapolis.

The University of Minnesota's Douglas Tiffany, an assistant extension professor, and Nalladurai Kaliyan, a research associate in bioproducts and biosystems engineering, also contributed to this study. Funding was provided, in part, by the Initiative for Renewable Energy and the Environment, a signature program of the University of Minnesota's Institute on the Environment.

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