To keep a 50 MMgy cellulosic ethanol plant in operation for 300 days would require a 25-feet deep pile of corn stover covering approximately 100 acres of land. When you take into consideration the number of trucks it would take to haul the stover from the field to the plant and the equipment needed, it becomes a logistical challenge. There are also concerns about soil quality and soil nutrient levels when the crop residue is removed rather than incorporated into the soil.
 
 Stuart Birrell, an Iowa State University (ISU) associate professor of agriculture and biosystems engineering, is in the midst of a three-year study examining biomass harvesting, transportation and logistics. 
 
 At yields of 80 gallons of ethanol per ton of stover, a 50 MMgy cellulosic ethanol plant would need to collect stover from approximately a 50-mile radius if half the farmers in the area participate, Birrell says. If that stover's compacted, moving it from the field to the ethanol plant would require 320 semis per day for a three-month delivery window.
 

 The numbers from the farmer's cornfield are equally impressive. Assuming a three-ton-per-acre stover yield and that a combine can cover eight acres per hour, in 10 hours, the stover harvest would require 40 semi truckloads a day to handle uncompacted stover, or 10 truckloads if the stover is tightly compacted. Recalculate that for 1,000 acres and it would take an additional 500 semi truckloads to haul the uncompacted stover. Birrell estimates the field harvest and transportation activities would require 10 people.
 
 Birrell and ISU graduate students Dan Frohberg, Mark Dilts and Ben Schlesser considered three field systems while examining biomass harvesting. Dedicated collection equipment won't be available for 15 or 20 years so they focused on the transition phases. Farmers are quite familiar with conventional forage baling equipment and costs, so they didn't focus their attention there, Birrell says.
 
 They briefly considered a single-pass, whole plant harvester that would harvest the grain and stover together. While it would be the least expensive for field equipment, new equipment would be needed to separate the grain from the stover either on the farm if the grower wanted to sell the products separately, or at the ethanol facility if it buys the whole plant. Birrell says the grain and biomass streams can't be stored together and have to be separated relatively quickly.
 
 The research group concluded this inexpensive system of collecting the entire plant, would be problematic. "The main issue is our grain marketing system," Birrell says. "Government programs and crop insurance are based on having grain in the bin."
 
 The researchers worked on a third system-collecting the grain in the combine hopper as usual and modifying the combine for stover collection. The goal of this system is to use a single pass at speeds equal to, or at least 80 percent, of the speed to harvest the grain alone.
 
 They designed a modified row-crop header and corn reel attached to the front of the combine, and a chopper and blower attached to the back. This allows the biomass to be harvested before it touches the ground, where it can become contaminated with soil. The stover is then chopped into two-inch pieces and blown into a wagon.
 
 The prototype design worked well in field trials, and researchers estimate the cost for the attachments will be $10,000 to $15,000.
 Further research will consider ways of compacting and handling the stover efficiently. Trials are also being designed to evaluate the optimum ratio of harvested stover to residue left in the field. Crop residue benefits soil quality, providing erosion control and nutrients. Those benefits will be compared with ethanol yields and costs to determine the optimum ratios.
 
 The U.S. DOE's initial targets for cellulosic ethanol suggest a price of $35 per ton for stover delivered to a cellulosic ethanol plant. Birrell says his research indicates it may cost close to twice that. When he calculated the farmer's costs, at $35 per ton they would lose money hauling the stover any further than 10 to 15 miles. 
 

 Birrell based his calculations on conventional forage operations and hay prices. "When we looked at hay exchanges, we didn't find hay being sold at less than $60 a ton, and that's without transportation," Birrell says. ISU's biomass harvesting research has been supported by a three-year, $180,000 grant from the USDA and DOE and a two-year, $50,000 grant from John Deere of Moline, Ill. Second-year data is being analyzed now, and plans are being made for the third year of trials. Birrell hopes to secure funding to further refine their research.

Collecting Mountains of Stover

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Upcoming Events

2024 International Biomass Conference & Expo

2024 International Fuel Ethanol Workshop & Expo

Biodiesel Summit: Sustainable Aviation Fuel & Renewable Diesel

Carbon Capture & Storage Summit

North American SAF Conference & Expo

Collecting Mountains of Stover