Researchers study corn stover for heat, power

By Ryan C. Christiansen
Web exclusive posted March 6, 2009, at 10:22 a.m. CST

Researchers at the University of Minnesota Department of Bioproducts and Biosystems Engineering have determined that densified corn stover, when used as a fuel for heat and power applications, produces 15 times less life cycle greenhouse gas emissions than natural gas and 25 times less than coal. The researchers suggested that ethanol plants could be tapped to produce the heat and electricity for their own operations and for general consumption on the grid, which would also lower overall emissions from those plants.

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

To determine the economic feasibility of using condensed corn stover for fuel, researchers evaluated the logistics of collecting round bales of stover from the field during fall harvest, delivering the bales to storage facilities within two miles of the field, and condensing the stover using a roll-press compactor, which increased the density of corn stover from six to 15 pounds per cubic foot. For the study, the grinding of the corn stover was completed at the University of Minnesota West Central Research and Outreach Center in Morris, Minn., and the roll compaction was completed at Bepex International LLC in Minneapolis.

After condensing the corn stover to increase the distance the stover can economically be hauled by truck, Morey said the delivered cost of the corn stover was $77 per ton. He said 30 percent of that cost is to replace the nutrients lost from harvesting the corn stover. Morey noted that replacing the nutrients accounted for 45 percent of the lifecycle carbon dioxide emissions for using corn stover as fuel.

"We were surprised by how much nutrient replacement-specifically, nitrogen, phosphorus and potassium-impacted the economic and environmental costs," Morey said. "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."

The next phase of the study will look at using the roll-press compactor to condense native grasses, straw, and alfalfa, and to look at ways to increase biomass electricity generation at ethanol plants.