Corncobs hold potential for biofuel
Think of the lowly corncob as a natural “pellet” — dense, compact, uniform, and convenient to collect and transport.
These are some of the traits that make abundant corncobs an attractive biomass energy feedstock, says Mike Reese, renewable energy director at the University of Minnesota’s West Central Research and Outreach Center in Morris.
Corncobs have a lot of advantages over other potential biomass sources, such as corn stover and native grasses, Reese says. Cobs have more consistent moisture and higher density. They can be harvested along with corn grain in a one-pass system, stored in outdoor piles without spoiling, and handled with standard wood chip equipment.
• Biomass energy is an emerging corncob market.
• Corncobs are a viable biomass source under real-world conditions.
• Implement makers are developing cob harvesting equipment.
In 2008, WCROC evaluated the feasibility of corncob collection and storage, gathering data on harvest and transportation costs, cob yields, moisture, and storage losses. The conclusion: “Corncobs can be harvested, stored and transported under real-world production conditions,” Reese says. “Cobs may be a viable and economical feedstock for biomass energy systems.”
Among the main findings:
• Collecting cobs takes more time and fuel. Grain and cobs were harvested in one pass from 3,200 acres in west-central Minnesota. Equipment included two eight-row combines with stalk-chopping heads and prototype cob harvesters from Vermeer and Ceres Residue Recovery System. The two combines averaged 7 to 8 acres per separator hour and used about 4 gallons of fuel per hour for grain and cob collection combined. Cob harvester fuel efficiency is improving, says Jay Van Roekel, Vermeer product manager.
• Cob yields averaged 1,000 pounds per acre. In hand-harvested, random samples of 28 fields across a 60-mile region, grain yields averaged 192 bushels per acre (15.5% moisture), and cob yields averaged 996 pounds per acre (dry matter basis).
• Variety affected cob yields. “Anecdotal information prior to harvest suggested that there were considerable differences between corn varieties as to the yield, moisture level and other cob characteristics,” Reese says. Limited trials in 2008 confirmed this observation, but more research is needed. Cob variety trials are under way at WCROC.
• Cobs can safely “rest in heaps.” Cobs were stored outdoors in uncovered piles and checked every two weeks. Despite average moisture levels of 39.5%, cob piles “maintained a very good condition from time of harvest through the end of July,” Reese says. Moisture levels and pile temperatures fell during the winter, rose slightly in the spring, then fell again in the summer.
• High-moisture piles should be monitored for temperature spikes. Two piles of high-moisture cobs approached 150 degrees, risking spontaneous combustion. The piles stabilized after mechanical ventilation with an 8-inch tile pipe and a grain fan, Reese says.
• Storage losses are low. Cob dry matter losses averaged 1% per month during outdoor storage, the report says.
• Cob collection could double total harvest costs. Cob harvesting expenses are not yet clear, Reese says. Preliminary estimates suggest it will cost about $50 per dry ton, or about $25 per acre.
Find the complete report at wcroc.cfans.umn.edu.
Morrison writes from Morris.
This article published in the March, 2010 edition of THE FARMER.