Turning Field Residue Into Ethanol Feedstock

Diane Greer



DARRIN IHNEN is looking at corncobs in a new light. Once left on the fields to rot, Ihnen is now harvesting the cobs along with the corn from 4,000-acres on his farm in Hurley, South Dakota – hoping to turn the field waste into income producing feedstock for making ethanol. Typically corn is harvested by a combine that strips the ears from the corn stalks, separates the grain from the ears and then deposits the stover, consisting of both the cobs and the stalks, back on the field.

Ihnen is part of a group of farmers and equipment manufacturers assembled by Sioux Falls, South Dakota-based Poet Energy to develop and test the on-farm logistics of harvesting and storing corncobs. The cobs will be used to produce cellulosic ethanol at Poet‘‘s new $200 million biorefinery, which will be built on the site of the company‘‘s existing 50-million gallon per year (mgpy) dry mill ethanol plant in Emmetsburg, Iowa.

Slated for completion in 2011, the biorefinery will require harvesting, storing and transporting 275,000 acres of cobs, weighing between 450 and 500 tons. Once at the plant, the cobs will be combined with 300 to 350 tons of corn fiber, generated by Poet‘‘s corn fractionation process, to produce 25 mgpy of cellulosic ethanol.

Poet is targeting cobs as a biomass feedstock to produce cellulosic ethanol for several reasons. “From a scientific point of view, you want to find a biomass source that is in abundant supply, has a large potential for fermentable sugars and can be easily collected,” explains Dr. Mark Stowers, Poet Vice President for Research and Development. “Cobs score a 10 out of 10 on all three of those categories.”

From an environmental sustainability perspective, cobs comprise only six percent of the stover left on a field and are low in nutrients, such as nitrogen, phosphorous and potassium. So removing cobs from a field has minimal or no impact on soil fertility. Several landlords leasing land to Ihnen to grow corn do not permit the removal of stover due to concerns about soil fertility. “But they do not care if I remove the cobs,” says Ihnen.

Developing the best methods for harvesting and storing the cobs is presenting the research team at Poet with several challenges. Currently there is limited farm machinery available to harvest the cobs and little experience with cob storage. “We have a lot to learn about the process,” Stowers says.

The top priority is to develop methodologies to harvest the cobs that will not impede a farmer‘‘s ability to collect the grain, he adds. The goal is to collect the cobs at the same time as the grain, so that farmers do not have to go back to the field and collect cobs off the ground.

Simultaneous collection is important in South Dakota and other parts of the Corn Belt where the fall harvest window is short. Snow can come as early as the first part of November. “You do not want to go back later to pick up the cobs off a snow covered field,” Stowers says. Preventing the cobs from hitting the ground keeps dirt and other impurities out of the feedstock. “This is a critical factor when processing the cobs in the plant, because we do not want to process all that dirt,” he adds.



HARVESTING TRIAL

To address the cob harvest and storage challenge, Poet realized it had to engage farmers, original equipment manufacturers and system suppliers early in the process to meet its massive harvest goals. Equipment manufacturers collaborating with Poet on the project include Case IH, John Deere, Kinze, Claas, Vermeer, AGCO, Demco and Feterl.

Ihnen volunteered to take part in the initial field tests after hearing discussions about the Emmetsburg project during a board meeting of the farmer-owned Great Plains Ethanol plant in Chancellor, South Dakota. Poet designed, built and manages the Chancellor plant where Ihnen is the chairman of the board. “We started kicking ideas back and forth,” he says<